S U P P L . T 2 SOUTHWESTERN ENTOMOLOGIST F E B . 1 9 B 9

PHYSIOLOGICAL RELATIONSHIP BETWEEN BRACONID ENDOPARASITES ANDTI{EIR HOST'S : TIIE MICROPLITIS CROCEIPESY-TIELIOTHIS SPP.Z SYSTEMY

S. B. Vinson9 and D. L. DahlmanJ

ABSTRACT

The suitability of Heliothis sBp. larvae as a host for the solitary endoparasitoidMicroplitis croceipes (Cresson) is reviewed from the point of view of the physiologicalinterrelationship. The constraint that a host represents is discussed, but it is the regulationof the host by the parasitoid which is emphasized. The sources of potential M. croceipesregulatory factors are described and compared to other parasitoids. Of the sources, thecalyx fluid (containing polydnaviruses) and the effects calyx fluid have on threephysiological systems are discussed in more detail. The thrce systems emphasized are theendocrine system, the host's immune system, and titer of nutrients in the hemolymph.

INTRODUCTION

The physiological interrelationships between parasitoids and their hosts havereceived relatively little attention over the years. The work prior to the 1950's wasgenerally with parasitoids of grain insects that could be easily reared all year, or withspecies available in large numbers from the field. This early work has been reviewed byDoutt (1963), Fisher (1971) and Matrhews (1974). In general, the physiology andbehavior of parasitoid species that attack phytophagous insects have not been studied eventhough such species were known to be important in the control of these pests. Thisdeficiency was mainly due to the cost, both in time and funds, to consistently maintainsufficient numbers of the host, its food and the parasitoid.

The development of artificial diets in the 1940's for certain species of herbivores(Bottger 1942, Beck et al. 1949) improved the ability to rear lilge numbers of host insectsin or on which egg and larval parasitoids could be reared. Nevertheless, rearing stillremains costly. Expense might be further reduced if parasitoids could be rearedindependent of their host. However, progress in in vitro rearing has been slow (seeGreany et al., this issue, Thompson 1986), largely due to the lack of knowledgeconceming the basic physiology of the relationship.

Subsequent research on the parasitoid-host relationship has opened up newopportunities to utilize insect parasitoids to a greater advantage (Greany et al. 1984, Vinson1986). However, additional information on the basic physiological and biochemicalparameters of the parasitoid-host interaction is critical to the realization of this relationship.In this regard, Microplitis croceipes (Cresson), a braconid endoparasiroid of kpidoptera ofthe genus Heliothis, has been targeted as an example of a potentially useful biological

l/ Hymenoptera: Braconidae./ lrpidoptera: Noctuidae.f,/ Approved as TA 22835 by the Director, Texas Agricultural Experiment Station, CollegeStation, TX77843. Supported in pan by USDA competitive grants 85-CRCR-I-1764 and86-CRCR-2087, Tex. Agric. Exp. Sta. expanded research funds and Texas AdvancedTechnology Research program.4/Departrnent of Entomology, Texas A&M University, College Station, Texas77843.l/ Depanment of Entomology, University of Kentucky, Lexington, Kentucky 40546.

1 1

control agent._ Natural parasitism of Heliothis spp. croceipes is often high; M.tory., and there is potential ro

control agent. Narural parasitism of Heliofhrs spp.by M. croceipes is often high;crocplpqs can be relativeJy easily reared on hosls in the laboratory, and rhere is potenti,manipulate .the behavior_ gr

-Mlcrsplilis in the field. Alihough the sriperfamily

Ichneumonoidae, to which Iv[. crogeipe,i belongs, has probably been stidied more intenselythan all the other raxa of parasitoid- comb-ined, ielatively littte is known about the

probably been studied more intensely:elatively little is known about the

physiology of the Braconidae within the superfamily. Funhei, M. croceioes is a relativelysmall genus within the Microgasterinae, on6 of 20 sobfa-ilies o-f Brac6i]-dae. This reviewwill focus 91 !!* croceipel but wilt include information on other genera of theIchneumonoidea for comparative purposes.

Information regarding the physiology of either the immarure or free living adulttoid. stage is. sparse. The suitability of the host or the physiological relatilonship]n the parasitoid and its host, that begins at the time of oviposition, has been rG

parasltold. stage ls. sparse. - The suitability of the host or the physiological relationshipbetween the parasitoid and its host, that begins at the rime of oviposit-i,on, has been th'esubjectofmostinvestigationsandwil lbecoisideredhere. AlthougiSalt( i938)usedtheterm host suitability to include the suitability of the host as an ovipdsition sire, we will usethe term in a more restricted sense as descritied by Vinson and Iwantisch (1980a).

HOST SUITABILITY

- lost suitability can be divided into two subcomponents: host constraints and hostlegulation (I awrence 1986a, Vinson and Barbosa 1987). These two subcomponents areboth intenelated but they are also opposing conditions that determine the overail suitabiliryof a particular host as a resource for the developing parasitoid. In effect, the host is acontainer with a finite amount ofresources available to the developing parasiroid. Theparasitoid egg, when placed in or on the container, must either confoimiothe amount andform of the resource or try to alter the amount and form (vinson and Barbosa 1987).. . For a parasitoid attacking a nonfeeding host stage (eggs or pupae) or aparalyzedlarval stage, alrering the amouni of resources may not b; a poisibiliiylFig. 1A,'B). Suchhosts are rel'erred to as "conformers" by Lawrence (1986a). For others, however, theability.to alter or control not only the form and biochemical pathways but also the amountof available resources may be imponant @ig. lC). such manipulation of the host has beenreterred to as hosr regulation (Vinson 1975). This is particularly significant forendoparasitoids that attack a host before it contains resources sufficient for thJparasitoid tocomplete development. For such species the ability to manipulate the host would be ofadvanmge.. Funher, the parasitoid must not kill the host too early for it may becomeevolutionarily associated with only young and small hosts or restricted to a shon period ofavailable hosts.

Askew and Shaw (1986) have referred to parasitoids that benefit from the continuedlife of their host as koinobionts, a tenn they modified from Halselbarth (1979) who dividedparasitoids on the basis of whether or not they permit their host to grow and developbeyond the stage attacked. Askew and Shaw (1986) conclude that the categorization oTparasitoids into koinobionts or idiobionts (host consumed at the location and in the state irwas when attacked) is superior to the terms endo-ecto-parasitism as a correlate of hostrange.. The idiobionts are often being facultative secondary parasitoids, while thekoinobionts appear to require a prolonged contract with a host, in evolutionary time, torncolporate a new host (Shaw 1983). The idiobionts function more as conformers, and thekoinobionts as regulators. However, the idiobionts may regulate aspects of their host froma physiological point of view (Strand er al. 1986).

For any particular parasitoid-host relationship, the parasitoid must either conform !othe constraints that a host reDresents or alter the constraints throueh the manioulation

f:c-l!g:]^gllh,"-l-::l-lr-!ri?bql: "L.lyi.ry".,(1?8,6u1'.f9ned. tg.-narasitoids is either

parasitoid stage is sparse.

conformers" or "regulators"; the conformers adjust or confonn to the constraints of thelost while the regulators alter or regulate their host to some degree. However. thesehost while the regu alter or regulate their host to some degree. However, these

categories exist as a continuum with some parasitoids possessing more characteristics ofconformers while others possess more characteristics of regulaaors. The problem is todetermine the limits of these two approaches to the parasit6ids habit, the

^physiological

aspects of the relationship open to regulation, and the methds by which regulation isaccomplished.

1 8

$l,ii&

-$r;l

!ri,r ,gltili

:r''"T o'"'ii* :* &

&.,,F'

FIG. 1 A. Telenomis heliothidis Ashmead, a scelionid, attacks a finite.resource and has

i"J"J io ilrurrv serEt an a-aequate resource. B. eglolacggs grandii (.B.urkes)' attacks a

wide ranse of hosi sizes. s".uui" it paralyzes its h-ost there is no additional nutritional

i;;"i, ;;"d i. g',ffi-ionrorms to thi sizti of its resource. c. cardioc=hile! nigrigeoi

Vi";rk,-; tui6iiluactr u.attge oi host sizes but regulates the size of the host which

may continue to feed and add resource.

Host Constraints. As a container, the hostprovides both the nutrition for the developmentof the Darasitoid and the enuironment in wliich it lives. It may allq contain chemicals and

;;;iffi;,#;;;;ff*i ttti oeuetopnlent of the parasitoid' .Host consraints can be

;;?ifi;rh;]me irfovlposition for a species that at-tacks a restricted resource such as an

i1;;A* igg.-rai, Hoiuewr, at the time of oviposition it is not.possible to describe the

iiort .oti.?i,inis for'a parasitoid such as gardipchiles nigficeps (Vierick) that may attack a

first instar Heliothis spp. larva (Fig. 1C). The host, when attacked, lacks tne resource

ir..!J-ilyi;i?"irp =t"te'deueiopni"ni

of the parasitoid and continues to- grow and develop,

ffi;ffi! 6oirii,o,itiionil-resorlrces as weu irs other factors that may affect the developingparasitoid.

T 9

In studies of Biosteres lonsicaudatus (Ashmead), a braconid endoparasitoid ofAnastrepha susoensa (Loew), Lawrence (1986b) has found evidence thar rhb srowrh anddevelopment of the parasitoid is controlled by the endocrine system of the host.

-From such

results Lawrence (1986a) proposed the idea that some parasitoids respond to th€ conditionsof thelr host. i.e. they conform. Lawrence (1986a) discussed this concept from the aspectof the endocrine system. However, for a particular parasitoid in or on a host, the conceprof whether it is a conformer or a regulator can be extended to other systems. some speciisconform to the constraints provided by the host by adjusting their size (Fig. lB), number,sex, or,adultfecundity (vinson and Barbosa 1987). others adjust the size-of the host; andregardless of initial host size (Fig. lC), the resulting parasitoid adults are of similar size,sex ratio, numtler, and adult fecundity. However, there are limits to these adjustments, andpaftsitglds may be responders under certain conditions and regulators under bthers.

_. I-lost Regulation. The concept ofhost regulation (Vinson 1975) developed from arealization that a parasitoid egg was notjust deposited in a host and left to respond to theenvironment per se in which the egg and subsequent larvae found themselves. Instead, itwas shown that female parasitoids inject substances along with their eggs that alter thebiochemistry and physiology of the [ost. Further, the ddveloping par;;ibid larva andassociated cells (teratocytes) may continue to release substances that affect the host.

The concept of host regulation has met with some controversy (Thompson 1983,Jones et al. 1986). One problem has been the failure of some critics to recognize thedifference between a parasite and a parasitoid. These critics have discussed thJ benefit-harm concept of the parasite-host relationship and have suggested that the host may sustainvarying degrees of harm. Such a concept does not apply to parasitoids as the host is notonly harmed but is genetically dead. For some parasitoids such as Telenomus heliothidisAshmead (Strand et al. 1986) which attacks an egg, or Bracon mellitor Say, whichparalyzes its boll weevil larval host (Vinson, personal observation), the host is a containerof preserved tissue. A major difference between B. mellitor or T. heliothidis and regulatorssuch as C. nigriceos is that the host of the laner parasitoid is not killed prior to theparasitoid's lawal development. In fact, the host continues to grow and develop. This isaccomplished by a parasitoids' alteration of only certain biochemical pathways whileallowing other pathways to proceed as in healthy hosts.

Sources of Host Regulatory Factors. The evolution of the "sting" in Hymenopteramay have had a major impact on the subsequent evolution of sociality (Starr 1985) as wellas on the evolution of the parasitoid habit. When a female hymenopterous parasitoidattacks a host, she first penetrates the host integument (there are exceptions) and then laysan egg either in, on, or nearby. The cuticular penetration provides the wasp theopportunity to inject substances into a host, Sources of such prducts vary among theparasitoid families. For example, T. heliothidis only has one accessory gland (Strand andVinson 1983a), but sources of accessory substances that may be injected along with an egginclude the Dufour's gland (Guillot and Vinson 1972a, Weseloh 1976), poison gland(Beard 1978, Shaw 1981), calyx epithelium (Salt 1968, Norton et al. 1975), commonoviduct epithelium (Strand and Vinson 1983a), and follicular cells @avies et al. 1987a, b).Of the possible sources of compounds, only the Dufour's gland, poison gland and thecalyx have been reported in M. croceioes.

The Dufour's gland is well-developed in both M. croceioes and C. nigriceps andcontains on oily secretion which has been reported to function in host marking (Guillot andVinson 1972a, Vinson and Guillot 1972). Hydrocarbons were reported as rhe responsibleDufour's gland components in C. nigriceps (Cuillot er al. 1,974) and the role ofhydrocarbons has been confirmed in the ichneumonid Venturia (llemedd$ canescens(Gravenhorst) (Mudd et at. 1982). Vinson (1979) suggested that Dufour's gland has somesex pheromone function in C. niericeos. Weseloh (1976) reported the same thing inanother braconid, Cotesia (= Apanteles) melanoscelus (Ratzeburg). However, in a relatedApanteles species, Tagawa (1977) found a gland located at the base of the 2nd valvifer tobe responsible. Weseloh (1980) reevaluated his earlier work with Qmelanoscelus anddiscovered glands on the 9th tergite. Tagawa (1983), working with several Apantelesspecies, confirmed the presence of epithelial secretory cells on the 9th tergite in both sexeswhile only females had a pair of secretory glands on the 2nd valvifer. Thus, the source ofthe sex pheromone and the role of Dufours gland, if any, in sexual communication

20

remains unclear (see Elzen and Powell 1988). It is likely that Dufour's gland in M.croceipes contains hydrocarbons which, along with other compounds, function in hostmarking and may be involved in close range sexual behavior.

The function of the poison gland for M. crocieoes, like the gland in many braconids,is even less clear than Dufour's gland. Stoltz (1986) commented that "venom glandsclearly secrete substances capable of exerting a significant effect on host physiology".Funher, a wide range of activities has been ascribed to the poison glands-of parasiticHymenoptera, including induction of paralysis (Beard 1978), alteration of developrnent(Straw t$St), reducrionif immune sysiem capability through hemocyte destruction (Rizki

and Rizki t98+), or overwhelming ihe recognition system (osman 1978a, b). Some ofthese functions'.having been desdilbed in iamilies other than the Braconidae. In theBraconidae the venom glands seems to either result in tempolaly or long_tenn P{!t1^sjs(Beard 1978), or the venom has little or no effect by itself (Guillot and Vinson 1972b'Ables and Vinson 1982). Those species having a paralyzing venom are_^gen€rallyectoparasitoids and have a thick-wa[6d poison (or type I) gland.@dson et al. 1982). For

species of braconids having thin walled type II ilands, of which IV! qrgceipgs is an

eiample, the function of the gland is unkno*n. Jones and Lewis (1971) injected poisonglandi macerated in saline int6 H. zea and reported no effects on growth. In similar studiesiuith C. niericeos injections of the venom gfinds had no effect on HelioJhi$ virescell (F.)

alone-buTi?ifi--synergistically with calyx fluid to reduce_host growth (Cuillot and Vinson

lg72b). In more rec;nt years the poison gland material of several speclel of braconids

having the type II poison lland has been reported to synergize the effectsjlf the calyx fluid.

Ables"and Viirson itggZ) indicated that the poison gland and calyx fluid ghqlorus insulariS

Cresson were syneigistic in regard to their effects on host gowlh. In other braconids bothpoison gland and calyx fluid afpear to be necessary in affecting the immune. system (Kitano

i986, S"tottr and Gu2o 1986, Tanaka 1987). This synergistic effect should receive more

afien;ion in the species of braconids having both viral calyx fluid and type II poison glands.

The third iource of materials in fei-rale M. croceioes for innoduction into a host is

the calyx fluid. The calyx of the ichnuemonid V. canescans was recognized by Salt ( 1968'

1970) ind Rotheram (1967,1973a, b) to be secretory, producing proteinaceous particles

whicir had an effect on the host immune system. An effect of caylx fluid, on the hostimmune system was also found in the braionid c. nielicePs (vinson 1972); however,Vinson and Scott (1975) found that the particles appeared to be similar to viruses and tests

for DNA were posirive. Viral-like partiales were also seen in the ichneumonid eA!0@]9!issonorensis (Cameron), an ichneumonid (Norton et al. 1974). It is now known that thesepat#t ia-"i*ses are ;ssembled in the calyx epithelium or the distal regions of the lateralbviducts of certain genera of endoparasitic ichn-eumonids and braconids. T\9f -are releasedinto the lateral ovid-uct lumina wh^ere they form a thick paste referred to as "calyx fluid" in

which mature ova are often embedded. When a host is attacked both an egg and the viral

calyx fluid are injected into the host, and the virus then invades vadous host tissues (Stoltz

and Vinson 1979b).The parasitoid viruses resemble the baculoviruses (Stoltz and Vinson, 1979a)' and

based on mbrphology they can be presently divided into two genera within the virus family

Polydnaviridie (Stditz et-at. 1984). The Pblydnavir-us genus is characterized by a fusiformnucieocapsid surrounded by 2 unit-membran-e envelops and have. been observed only.in theichnuembnids. The second unnamed genera of Polyndaviridae are observed in thebraconids and consist of cylindrical nucleocapsids of variable length surroun{ed by-a singleunit envelope. The genomes of both generi1.of viruses consist of a^gloup of polydisperye'single-strarided circilar DNA molecu-les (Krell and Stoltz 1979, 1980, Stoltz et d. 1981,Xrjtt et al. 1982). While the polydnavirus appears to be replicated only in_the femalecalyx, viral DNA.is present in bottrthe male and female tissues (Stoltz et al. 1986, Flemingand summers 1986), suggesting vertical transmission. The virus does not aPp-ear t9replicate in host tissue (ffr'eilmann and Summers 1986) but is expressed (Blissard et al.1986a, b).

While progress on the characterization of the polydnavirus is being made, the role ofthe virus is^coirplex and much of what is knbwn concerns ichneumonids. Theichneumonid virui has been implicated in reduction of host growth (Vinson-et al. 1979)'

abrogation of the host immune iesponse (Edson et d. 1981, Davies et al. 1987a, b, Stoltz

2 I

and Guzo 1986), inhibition of the host endocrine systqm (Dgver et al. 1-987), alteration ofhemolymph tte'halose levels @ahlman and-Vinson 1976), induction ofnew lgpply-pltproteiis (book et al. 1984), and inhibition of phenoloxidases (Stoltz and Cook 1983); in allca$es without the aid of other secretory substances.

EFFECTS OF BRACONIDS ON SELECT HOST SYSTEMS.

Summarizing the literature we have chosen to examine three host systems which M.croceipes and relaied genera have been implicated in regulating: effect on nutrient flow,immunity, and growttiand development. Species, such as M. croceioes, lack a paralyticvenom, and such venoms (Beard 1978) .ue not considered here.

A. Effect of Parasitoidism on Nutrient Flow. Parasitoids have been reported tocause changes in thahemolymph level of proteins, amino acids, caftohydrates and lipids oftheir hosts (Vinson and Iwantisch 1980b). In some species nutrients in the hosthemolymph may increase while in other species nutrients may decrease.

The rehalose level in the hemolymph of H. virescens significantly increases oneday after parasirism by M. croceipes @ahlman and Vinson 1975). The insrease could beduplicated by the injection of calyx fluid but did not occur with saline, Dufouls, or poisongland injections @ahlman and Vinson 1977). T\e glycogen content of one-day parasitizedH. virescens larvae was signiflcandy lower than both 0- and l- day controls @ahlman andVinson 1980) and remained lower through 8 days (Table 1). This decrease in fat bodyglycogen was similar to that observed for other species (Sluss 1968, Vinson and Barras1970, Iwantisch and Smilowitz 1976). However, the glycogen concentration offat bodywas equal to or greater than controls for the first several days, a result similar to thatreported by Fiihrer (1972) in studies of another braconid attacking a lepidopterous larva.These results suggest that ttre calyx fluid reduces the glycogen content of tissues other thanthe fat body resulting in the conversion of enough glycogen to

TABLE l. The Glycogen Content of Unparasitized Conrols, Parasitized Heliothisvirescens and the oarasitoid Microolitis croceiDes when the Host was Parasitized as aPremolt 3rd Instar.

Post-Oviposition (me/larva) (ms/larva) (ue/arva)

I 0.8010.132 2.16!0.223 1.8010.424 5.04XO.235 6.41+0.596 7.43+1.217 5.32+0.468 5.22tO.46

0.3410.060.88r0.090.8510.110.9110.17r.60fl.zsd2.46fl.46dt.44fl.48il0.2810.04d

r.st o.s5.0+ 1.2

r23.2X38.6358.4+32.3376.8X32.8

3y' Parasite removed form host before determination of total glycogen.

TABLE 2. Total and Active in Whole Body Extacts ofand

ug Pilmg prcteOviposition Control Parasitized Contr,ol Parasitized

12l 8

18.91 1.723.5+ 3.1

15.3+ 2.7 ns 51.6t,3-7 68.816.2*23.51 6.1 ns 41.8+4.2 61.618.6 *

24 41.5+ 5.6 37.5t 4.7 ns 45.1+2.7 60.Oj3.7'**72 t9.&. 4.1 27.?.1. 3.1ns 4E.8+3.6 65.114.2 *

3/ ns = non significant, * and ** significantly and highly significantly different fromcontrols, respectively,

2 2

trehalose to elevate trehalose levels. The explanation for this increase in Eehalose isunknown, but recent research has shown that the percent active glycogen phosphorylasesignificantly increases within 12 hr post-parasitization (Table 2) while the amount of totalglycogen phosphorylase (active plus inactive) did not (Dahlman unpublished). Thissuggeits that some mechanism associated with parasitization activates the release of glucosewhich in tum appears as rehalose in the hemolymph.

All of ttie earlier work of Dahlman and Vinson on the effects of parasitization onhemolymph trehalose titer had been conducted using premolt 3rd instar 4 v,irescens larvaeas hosis fbr M. croceioes. This work has recently been expanded to include premolt 2ndand 4th instar larvae a1 hosts. An attempt was made to correlate the larvae sampled withrhe stages described by webb and Dahlman (1985). Gr_oups were.sampled at dailyintervali after parasitizafon, and the results, reported by Dalrlma1 and Vinson (1975), wereconfirmed w6en hosts initially parasitized as premolt 3rd instars were reexamined.However, when premolt 2nd instan were used as hosts, the parasitoids elnerged from theirhosts at a stage earlier in the host's development, and it was difficult to correlate theparasitized lariae with conrols. Nevertheless-, Dahlman and Moore (unpublished data) didnot observe any significant increase in host hemolymph trehalose titer over.that of same-aged control t:#va-e. tn contrast, when initial parasiaization was done with premolt 4thiristar hosts, the hemolymph titers of trehalose were significantly elev_ated within 2 daysand continued increasing in concentration right up to the time the parasitoid emerged fromits host. These final coicenffations were nearly double those observed when the host wasparasitized as a premolt 3rd instar (Dahlman and Mo-ore,- unpublished)- .One possible

bxplanation for these observations is that the amount of body fat in the 5th instar is muchgr6ater than in either of the preceding instars @ahlman and Vinson 1980), and the capacity6f the host to prduce trehalbse in reiponse to the stimulus lrom ttre pafasitoid.was geatq.

The el6vation of trehalose in'the hemolymph of H. virescens parasitized by M.

croceipes may be significant. Micropliti$ croceiogg is a hemolymph feeder and does not

attffi"d directly cdnsume host tissue (Vinson a;d tfwis 1973), thus the developing larvamust obtain nutrition from the hemolymph. How a developing larva is able to compete-with the growing host tissues for nutrients in the hemolymph is important. In the case ofM. crocei-pes thJpresent evidence suggests that both calylfluid and teratocytes may affectttte hostlila *ay-favorable to the developing parasitoid. Further, the larva has evolved aneverted hind gut referred to as an anal vesicle which takes advantage of changes inhemolymph nuEient levels

ihi newly eclosed lst instar M. g9!p9g larva is mandibulate, and these mandiblesare used in defense (Greany 1986I but sinCe vital tissues are not attacked (Vinson andLewis 19?3), their role in fi:eding is likely minimal. In fact, ligation of the head did notprevent the absorption of nutrients (Edsonand Vinson 1977) although the consumption of'host

hemolymph proteins, likely orally, is very imponant to laflal grorylh^(Qrgaly 1986).The lnai vesicle is common in endoparasitic braconids (Thorpe 1932), being present

from ecolsion through eglession from the host in M. croceipes (Lgwfs 1970a). In otherspecies the anal vesicle is only well-developed during the lst and-2nd.instars, and as thelarvae begins the physical consumption of select host tissue, the anal vesicle inverts to formthe hind-gut (Thoipe 1932, Lewis and Vinson 1968). The an.al vesicle has beenhypothesiied to function in locomotion, respiration, excretion, and absorption (Edson andViirson 1976, Fisher 1971). Thorpe (1932) presented evidence suggesting an active role inrespiration for the anal vesiclet-however, this is not the function of the organ in M.croceipes @dson and Vinson 1976). In fact, aerobic respiration may-not_be.as imponant aslnffi tiuing forms (Fisher 1971). The larvae of M. crogeipes are facultatively anaerobic(Edson and-Vinson 1976) and are thus able to sustain themselves during periods of lowoxygen tension. This is probably important to an insect living in an aquatic_environmentwiilia low oxygen partial presssure. The reduced respiratory qcJivity of Helialhis zea(Boddie) larvie-par6sitized by M. croceioes (Jones and Lewis 1971) may furtherreducehemolymph oxygen titer making facultative anaerobic metabolism an advantage, assuggested for some other species by Salt (1966).--

In M. croceipes the anal veslcle, while not involved in respiration, was found to beimportant in Eicred'on @dson and Vinson 1976), thus supporting.the ideas proposed earlierby'Weissenberg (1909) and Tower (1915). Ultrastructural studies (Edson etal. 1977) of

2 3

the anal vesicle of M. croceipes revealed epithelial cells containing many cellular infoldings,an abundance of active mi-tochondria, and extensive rough endoPlasmic reticulum, allindicative of an active transport function. The anal vesicle was also found to be importantin the absorption of both amino acids and sugars @dson and Vinson 1977), particularlydisaccharides. The absorption of both amino acids and disaccharides by the anal vesiclemay be important in the larval competition for these substances with host tissues which alsodraw on the hemolymph for nutrition.

The effects of calyx fluid in elevating trehalose levels in the hemolymph may furtherimprove the larval parasitoid's advantage in competition with host tissue. How a parasitoidobtains the amino acids and proteins necessary for growth and development is not clear.Although larvae must consume proteins for maximum growth (Greany 1986) theabsorption of the simpler biochemicals, which are often under hemostatic control, mayprovide an advantage to a parasitoid over host tissues that respond to these controls.Barras et al. (1969) found that the titer of various amino acids in the hemolymph of Itvirescens parasitized by C. niericeps decreased. Some of these amino acids wereconcentrated in the developing parasitoid while others appeared to be used for energy.Their research also indicated an increase in the titer of peptides in the hemolymph ofparasitized larvae. What these changes mean to the developing parasitoid and whethercertain amino acids are elevated in the hemolymph of M. croceipes parasitized host areunknown.

In addition to elevated trehalose titen, amino acid changes, and changes in lipids(Barras et al. 1970), parasitization is known to cause major changes in the quantity andquality of host hemolymph proteins (Brewer et al. 1973). Changes in hemolymph proteinshave been described for M. croceioes (Banas et al. 1972), but the significance of thesechanges is unknown. In the hemolymph of the host for M. croceipes and several other

FIG. 2. Proteins of healthy and Microplitis croceipes-parasitized Hgbbis virescens larvaewhich has been separated on a Cl8 reverse phase HPLC column.

zo

o

o

E

24

Darasitoids, maior "new" proteins are thought to be produced by the host in response to theinvasion oi th6 parasitoi'd or in responstto factors introduced into the host during_ theovioosition proclss (Vinson and Iwintisch 1980b). Examples have been reported in hostparlsitized 6y ichneumonids (Cook eJ al. 1984). S,eparation of lI. vire,scerlf hemolymphiiotAnr on a'Cl8 reverse phase HPLC column resolved three major peaks.^ When the total

i-iii" f* "*h peak was ietermined and the values from.the same stag:,of parasiliTd andirnparasitized larvae were compared, it was apparent that the presence of M.:qrocpiDesitt!..d tftr protein compositioir of its host. iire frst two peaks from parasitized larv;;;h;!""'"d in size (Fig. 2). The.frst peak contained phenoloxidlsj which was initt!..4 tftr protein compositioir of its host. iire frst two peaks fr91n Parasitized larvae are;;h;fi;J in size (Fig. 2). The frst peak contained phenoloxidale which was in muchmuch reduced in size @g. 2). The frst peak contained phenoloxrdase whrch was ln mucn

ttiehir.on""ntrations'in-thc hemolymph of unparasitized larvae. Kinetic studies on the.#i.l.rridase from the two sourcel Show that-the Vmax is about the same, whereas thephlnoloxidase from the two sources that-the Vpa;6 is about the same, whereas the

k6 is much greater for phenoloxidase from parasitized larvae (Thomas and Dahlman,

unDublished d;ta). The reason for the difference is not clear at this time.-.-'--F;;igvi.h'and Dillard (1986) determined that there was no uptake _of radiolabeled

trost tremolymph proteins by '[

ciopeipgs !BBs. - These results suggest.gglgJo proteinsvnrhesis fioni si'mple precur-sori abffibed-by the egg. Yet Greany (1986) providedeuidence that the presenie of proteins in an anificial leqlng r-neq3 promoted M' crocelppsess and larval iowth. Griany (1986) suggested that the disparate results may.be['&""if"Alf ttte-parasitoid's egls depend no-t-on host hemolymph pr.gpins as nutritionsource but on faciors transpo;A by'such proteins. Another possibility is that a high

oiorcin iont"ntration, which does noi greatly increase the osmotic pressl're' can be slowlyiiil"d;" -"intuin ttt" amino acid levEls in ihe media at a favorable level for absorption.--"-

er tfr" fu*u" of IV!. croceioes hatch, a number of cells are released into the hosthemolvmph from the "*-t affi-ic membrane which begin to growand develop^in-theiiem;iil;il.-i-rt"i"i"tti have ieceived numerous names (Vinson and Iwanlsch 1980b)'i,"'iii?.i.[v"r isurt isitl will be used here. These cells are commo,nly found in theinaoou*ritoiO senera of b;aconids and have been reported several times from Scelionidae.tlffh.* beeti ui.riU"O to have various roles, raniing from providing food to serving aDrotective function (Vinson and Iwantisch 1980b). In IVt croceipef about /,)U teratocytes-'';ifi;r;r-"c"

lO.s'prn l" diameter, are released. lhey rgacfr 140 pm. in diameter in 8-9davs. at whiih time'the parasitoid larva egresses from the host leaving the teratocytesUiiriirO-tVi"i"n and Lewis 1973). Becluse the number of teratocytes. released isi"ui"*U)V constant, the presence of tSOO teratocytes shows that two eggs had hatched'1250;;ii( Joggeittift.e"'eggs had hatched, etc. even though only a single larva can befound.- -

The functions of teratocytes in general are little known. When the teratocytes ^fromg. niEiceps are injected into ion-parisitized hosts,_they conti.nue to.grorv (Vinson 1970)'ilOiffit-ocytes from a scelionid iultured in vito (Sm;d et d. 1985). While these resultsshow that teratocyte growth does not require the presence of a parasitoid larva, the resultsirAi""t" ttr" t.*ais pisence may place sbme conirol over teratocyte development. On theother hand, teratocytes may be i-ponunt to the gl-owthand development of the parasitoidfarvie. Strand et if. <f S'S8), wdrking with dheliothidi!, found that the presence ofteratocvtes in an in vitro cultuii media alffected the media and improved larval growth' The;ltri;;ircrat.-yles from Telenomus revealed several e^nzymes important.in cytolysis;,iiil .ppgal 616 i-portaniT-me nectosis of host tissue follbwing eclosion (Strand et al.1t86i.

'li similar secretory function has beersuggesle4 for teratocytesofJhe braconids

(Slujs and Leutenegger i968, vinson ano Scoti t9z+;. Greany (1986).referred toirnpuUfitn"O informliion that indicated teratocytes were important to the in vitrodevelopment of IV!, croceiPes.-- ---if'"

u"uifaUf-"li6ffiiion suggests that teratocytes may have_a trophic funcdon, butthis funciion mlgtrt aiffer from earliJr concepts-which suggest that they absorbed nutrientsand grew rapidly thus serving directly as fo& for the dev-e-io_!'ing parasitoid (Jackson 1928,i;;6i"yl,i6ol The teratocytes may secrere enzymes that digest host tissues (Strand et al.iS8?ii;i.fi*r'host tissuJs iausing ihe releasl-oi nurients to the hemolymph (Sluss andLeutenegserlg66).Thistypeoffu-nctioncouldbefavorabletothgdevelopingparasitoidil;;;iafi! incre'ase6 nutrition without having to physically consume nutrient-laden hostii"rlii, . pti"ess which destroy the life-maintaining iunction of these tissues' However,

2 5

teratocytes have been reported to have other functions (Vinson and Iwantisch 1980b), andthey may have several different functions even within the same host system.

B. Insect Immunitv. There is very little research on the immune response of hoststo braconid endoparasitoids. There is some evidence that the egg of some braconids maybe passively protected by a fibrous layer (Davies and Vinson 1986). However, this layerappears to be temporary (Vinson 1974a) and other factors may be involved. Thephenoloxidase-tyrosine system is currently believed to play an important role in insectimmunity (Soderhall 1982, Ratcliffe et al. 1984). Earlier work demonstrated that theinhibition of phenoloxidase resulted in decreased encapsulation of C. nigriceps eggs in ahost (Brewer and Vinson 1971). Thus, a logical conclusion from the finding that calyxfluid also inhibited phenoloxidase (Stolu and Cook 1983) was that the ability of calyx fluidto inhibit the immune system (Edson et al. 1981) was by interferring with thephenoloxidase system. However, Sroka and Vinson (1978) and Kitano (1986) found noevidence that either braconids or one species of ichneumonid inhibited the hostphenoloxidase system.

In conEast, there has been progress in understanding the antibacterial response ofsomeLepidoptera. Bomanetal.(1974,1978)andBomanandSteiner(1981)isolatedandidentified two groups of bactericidal proteins that play a major role in the antibacterialactivity of insect hemolymph (Dunn 1986). Since parasitism has an effect on the insectimmune system, interference with such a system could have serious consequences. If thehost dies before the parasitoid can develop and emerge, the parasitoid will also die. Rossand Dunn (1986), in a study of the effects of Cotesia congregata (Say) on the antibacterialresponse of Manduca sexta, (L.) found that the ability of a parasitized insect to mount adefense against the bacteria decreased relative to unparasitized controls. The results ofinvestigation of the bactericidin and lysozyme hemolymph levels indicated that, whileparasitized insects were still able to respond and produce the antibacterial factors, themodulation response was impaired; and the altered hemolymph environment was unable tokeep the bacteria in check (Ross and Dunn 1986).

There is increasing evidence that the calyx fluid in ichneumonids causes a decrease inthe number of circulating cells, particularly those thought to be involved in capsuleformation, and it alters the ability ofthe cells to attach and spread (Stoltz and Guzo 1986,Davies et al. 1987a). There is evidence that the ichneumonid female iniects a virus thatdecreases the host's immune response (Stoltz and Guzo 1986, Davies er al. l987a,b).Similar effects are associated with the venom gland in chalcids (Rizki and Rizki 1984). butthe siruation in braconids is less clear.

In a recent review of the effects of Apanteles glomeratus (L.) on the host immunesystem Kitano (1986) presented evidence that the venom apparatus was involved. Thisauthor suggested that the venom may react in some way with the egg sudace to provideprotection. When the venom apparatus was removed and the females were allowed todeposit calyx fluid and other substances into the hemocoel, encapsulation still occurred(Kitano and Nakatsuji 1978). However, their conclusion that the poison appartus was themajor factor inhibiting the immune response may have been premature. Although Kitano(1982) showed that injections of calyx fluid along with venom gland contents wereeffective in reducing encapsulation, later studies (Kitano 1986) provided evidence thatvenom injected alone into hosts also reduced encapsulation of parasitoid eggs. However,the data (Kitano 1986) show that over 50Vo of the eggs encapsulated in three of sixreplications of the venom injected larvae. In contrast, injections of both venom and calyxfluid resulted in six to seven replications where the encapsulation was 5O7o or less. Calyxfluid alone was not effective (Kitano 1986).

In contrast, Vinson (1972) examined the effect of M. croceipes on the immunesystem of H. zea by determining the ability of M. croceioes to inhibit the immune responseof H. zea to the eggs of C. nigriceps which are habitually encapsulated in !! 4. Theresults indicated that calyx fluid of M. croceioes protected the eggs of C. nigniceos fromencapsulation. However, these effects were restricted to the egg; larvae that hatched wereencapsulated (Vinson 1972). Could it be that venom and calyx would be more effective?Such a suggestion may be reasonable in view that host weight-gain when parasitized bybraconids is reduced, and the effect is effectively duplicated only by the injection of bothcalyx fluid and poison gland contents (Ables and Vinson 1982, Guillot and Vinson 1972b).

2 6

lQ. Host Growth and Development. There is abundant information on the effects of

parasitization on the growth and development of the host. Most of this is of a descriptivenature and, with respect to physiology and biochemistry, it is only of secondary value.However, such observations provide suggestions and clues about specific changes in thephysiological and biochemical relationships between a p:uasitoid and its host. Insectgrowth and development are controlled by the dynamic interaction between severalhormones, and it is through changes in the titers or the timing of the release of thesehormones that parasitoids may exercise control over the development of their hosts. Ofcourse, there are many secondary effects which result from the alteration of these hormonaltiters, some of which have already been mentioned and in some species may provide thesignals necessary for host synchronization.

The endocrinological interactions between endoparasitic insects and their hosts hasrecently been reviewed (Beckage 1985). The remarkable developmental synchronybetween parasitoids and their hosts provides strong secondary evidence for simultaneousendocrinological control of both species. However, in many cases, as the parasitoidcompletes its development, the development of the host is altered in the process. Examplesfrom Braconidae include prolongation of the final instar and suppression of pupation byApanteles congregatus (now Cotesia congregata) in M. sexta (Beckage and Riddiford1978, 1982a), induction of supernumerary larval instars by A. congregatus in M. sexta(Beckage and Riddiford 1978) and Apanteles bignellii Marshall in Euph),dryas aurinia(Porter 1983), juvenilization of morphological features by Aohidus platensis Brethes inAphis craccivora Koch (Johnson 1959), precocious metamorphosis in both Lepidopteraand Diptera by several different genera (Alston 1920, Bradley and Arbuthnot 1938,Zinovjeva 1974, Rechav and Orion 1975, Jones et al. 1981, Shaw 1981), interference withegg maturation (Weiss and Williams 1980), and prevention or premature cessation of hostdiapause (Holdaway and Evans 1930, Varley and Butler 1933).

A detailed study on the endocrinological aspects of a parasitoid-host interactions ofA. congregatus and M. sexta indicated the parasitoid larvae always ecdyse to their 2ndinstar 2-3 days after the host ecdyses to its terminal stage (Beckage and Riddiford 1983a).However, this stage of the host may be either the 3rd, 4th, 5th, or even as a supemumerary6th instar, depending upon the parasitoid load (Beckage and Riddiford 1978). Ifthis hostis parasitized as a 5th instar, the parasitoid is able to delay the host's development longenough for the parasitoid to complete its development without any additional lawal-larvalecdysis by the host (Beckage and Riddiford 1978, 1983a). Thus, the timing of theparasitoid's molt is regulated by the rate of growth and development of the host larva.

Metamorphosis of M. sexta parasitized by A. congreeatus is suppressed. Normallythejuvenile hormone (JH) titer decreases after ecdysis to the 5th instar but, in parasitizedlarvae it increased to a maximum on the 3rd day of the 5th instar (Beckage and Riddiford1982a). The titer then gradually declined; but since detectable levels remained eventhroughout the post-emergence period, host metamorphosis seems impossible.

In M. sexta parasitized by A. congregatus the level of JH esterase activity dropped tozero during the 5th instar instead of increasing the normal l0Gfold (Beckage and Riddiford1982a). In vitro assays of the corpora allata (CA) activity in parasitized larvae showed thatthey maintain a high level of JH synthesis during the period when CA activity normallydeclined in the 5th instar (Beckage and Riddiford 1982a). Thus, there is both enhancedsynthesis and decreased degradation of JH in parasitized larvae. In contrast, ecdysteroidtiters showed normal peaks at the prewandering level during emergence of the parasitoids.Titers declined rapidly within 2 days post-emergence (Beckage and zuddiford 1982a).However, the second release of ecdysteroid is only expressed as a slight and delayed peakwhich is not sufficient to trigger metamorphosis. Injection or infusion of ecdysone into thehost accelerated parasitoid emergence while neck ligation prior to ecdysone releaseprevented parasitoid emergence (Beckage and Riddiford 1982a). At the time of parasitoidemergence, the enzyme which converts ecdysone to 20-hydroxyecdysone, 20-monooxgenase (20-MO), is relatively inactive in the tissues of M. sexta parasitized by {congregatus. HPLC analysis confirmed that the hemolymph of parasitized larvae containsprimarily ecdysone, rather than 20-OH ecdysone (Beckage and Templeton 1986).Application of IH to the host prevented emergence of the parasitoid (Beckage and

2 7

Riddiford 1982b). Thus, the host's developmental urest seems to be due to multipleeffects of parasitism on the host's endocrine physiology.

At this time the studies with H. y!1esgg!$ and M. croceipes are not as detailed nor ascomplete as those with !! gg and A. congregatus. Some significant progress has beenmade in defining specific stages in the development of H. virescens that can be used tocoordinate specific points in the development of parasitized larvae. Webb and Dahlman(1985) used characters such as size, shape, behavior, chronological age, and a number ofmorphological markers to describe these stages. The key markers are those associated withthat period of time when the unDarasitized larva beeins formine a cell in which it ouoatesthat period of time when the unparasitized larva begins forming a cell in which it pupatesthree days later. Parasitized larvae cease development at this point (or at least thethree days later. Parasitized larvae cease development at this point (or at least thedevelopment is markedly slowed). At the beginning of this stage (Cell Formation, Day Idevelopment is markedly slowed). At the beginning of this stage (Cell Formation, Day Ior CF-l) the distinct white-pigmented band covering the ocelli has decreased in prominencebut is still plainly visible. One day later (CF-2) this band has faded, and the pigment of theocelli has begun to diffuse and move posterially in relation to the ocelli lense. By thesubsequent dav. the larva is a Dharate DuDae and the larval head capsule has slippedsubsequent day, pharate pupae and the larval head capsule has slippedforward, the lenses of the ocelli are clear, and the diffuse ocellar pigment is located somedistance posterior to the ocellar lenses.

Radioimmune assay determination of ecdysteroid titers in parasitized andunparasitized H. virescens ilearly show a reduced peak of ecdysteroid during the premoltperiod of the 4th instar (when parasitized in the premolt 3rd instar). However, the titerobviously is adequate to promote the molt to the 5th instar. Titers in parasitized larvae aresomewhat elevated as compared to controls during the early portion of the 5th instar(Dahlman et al. in press). Finally, a very rapid increase in ecdysteroid titer occurs inunparasitized larvae between CF-l and CF-2. This elevation is only about 1/5th as large inparasitized hosts (Webb and Dahlman 1986) and is not sufficient to promotemetamorphosis. Ecdysteroid titer reduction and dovelopmental arrest were also observ€dby Dover et al. (1987) in H. virescens injected with calyx fluid from the ichneumonid, esonorensis.

While it is certain that ecdysteroid titers in parasitized H. virescens are low, thespecific cause is not certain. The reduced titer is not explained by insufficient sterolprecursors because sufficient levels have been observed in parasitized insects (Coar 1986).This contrasts with the observation of very low levels of steroids in the hemolymph of M.$gE heavily parasitized by A. congregatus (Dahlman and Greene 1981). Secondly,preliminary examination suggests that the activity of 20-MO appears to be similar inparasitized and nonparasitizel,luyae (Coar 1986), in contrast to that observed in M. sexta(Beckage and Templeton 1986). Injections of polydnavirus from the ichneumoid Qsonorensis into 5th instar H. virescens caused the host prothoracic gland to atrophy within3 days (Dover et aI.1988).

The tissues of parasitized H. virescens :ue responsive to injected doses of bothecdysone and 20-OH ecdysone. The response was mor€ pronounced when the larvae wererefied at 32o than at 25o C. Tissue response was defined as tanning of the cuticle, ocellarpigment migration or head capsule slippage. None of these occur in pamsitized lawae. Adose of 2.5 pg per larvae produced one or more types of tissue rcsponse in 757o of thelarvae reared at32o C and injected at CF-I. The response was abott 65Vo in larvae injectedone day earlier, In contrast, pamsitoid larvae did not emerge from hosts showing a tissueresponse (Webb andDahlman 1986). It would seem that the parasitoid uses the increase inecdysteroid titer as a signal to exit from its host under normal conditions. However, if thetiter is too high, the parasitoid must wait until the titer falls again, and appalently under theexperimental conditions, death of the parasioid occurs first. At lower temperatures andunder experimental conditions where larvae were neck ligated at earlier stages, theparasitoids successfully emerged from their host and spun cocoons (Webb 1983, WebbandDahknan 1986).

We have begun to appreciate the degree of variability of ecdysteroid titers whichoccur even between larvae that have been carefully staged. The initiation of the ecdysteroidpeak between CF- I and CF-2 occurs so rapidly that if groups of insects are pooled at 12 hrintervals, the amount of variation results in nonsignificant differences. However, ifsamples are taken from individual insects, it becomes apparent that variability is caused byour present inability to precisely stage the lanae (Dahlman et al. in press).

2 8

Topical applications of JH, JH analogues, or a JH esrerase inhibitor have beenstudied in a preliminary manner using the H. virescens and M. croceipes system. If JH wasadministered l-2 days prior to CF-I, the host fed longer and often did not enter the CFphase. They usually stopped feeding at about the time of parasite egression, which may beseveral days later than normal. Applications of JH or methoprene (a JH analogue)subsequent ofCF-l had little affect on the egression ofthe parasitoid from the host (Webb1983). Nevertheless, there was some reduction in the number of adult wasps eclosingfrom cocoons resulting from these treatments and some of the wasps had shortened anddeformed wings (Webb 1983). The cocoons of those parasitoids which had not emerg€dwithin 30 days were dissected. The majority of the cocoons from the control containeddiapausing larvae while the cocoons from the methoprene-treated larvae held adultpamsitoids, many of which had incompletely sclerotized abdomens. Vinson (1974b)reported that application of methoprene reduced the egression of C. nigriceps larvae fromtheir host when applied to the host late in the relationship. Methoprene treatment of eitherneck- or thorax-ligated M. croceioes parasitized larvae resulted in a decreased emergence ofparasitoid larvae, with the effect being slightly more pronounced if the host was ligatedprior to the CF-l stage (Webb 1983). This indicates that the JH effect was not mediatedthrough the head or the thorax because the removal of these endocrine centers did notprevent the expression of the JH effect.

The JH esterase inhibitor (Ro 13-5223) had no effect on the emergence orsclerotization of parasitoid larvae, indicating that it was the presence of JH and not theprevention of JH degradation that was responsible for the observed effects of JHapplications (Webb 1983). Braconids such as M. croceioes appear to not only influencethe endocrine system of their host but also to respond to changes that are a result of theinteraction.

SUMMARY

Microplitis croceioes, as observed by Lewis (1970b), appears to control thedevelopment of its host. When older larvae are attacked, the growth and development ofthe parasitized host is stopped while parasitized younger larvae continue to grow anddevelop. But does the pamsitoid just allow the parasitized larvae to continue to grow anddevelop only until the host contains the food reserves that the parasitoid progeny require, ordoes the parasitoid actively regulate the development of the host? Evidence from certainbraconids and ichneumonids indicates that viruses and other chemicals injected into theirhosts redirect select biochemical pathways and affect select tissues. Further, the viruses, inconcert with other injected and parasitoid progeny released factors, many have a certaineffect one day after parasitism and different effects 3 or 8 days later. For example, theeffect of elevating trehalose titer is immediate (Dahlman and Vinson 1975), whereas theprevention of increased ecdysteroid is delayed (Webb and Dahlman 1986). In addition, thedeveloping egg and subsequent larva and associated teratocytes also appear to releasesubstances into the host that may not only influence the biochemical pathways of the hostbut also may affect the action of other factors that have been or are being released. A hostis not only affected by these various secretions and viruses, but the effects may differ in ahost attacked as a lst or 2nd instar in comparison to a host attacked as a 4th or 5th instar.For example, when !L gtqgeilgs is attacked as a premolt 2nd instar the hemolymphnehalose level is not affected but when a premolt 4th instar host is attacked the hemolymphtrehalose titer is elevated @ahlman and Moore, unpublished).

Many complex interactions can occur between the developing pamsitoid and thephysiology of the host, but they are limited by both the evolutionary and historicalconstraints that a particular host represents. While there is good evidence that M. croceipesis a regulator, the developing parasitoid must also respond to the conditions of a changinghost. There is increasing evidence that some parasitoids such as T. heliothidis orTrichogramma oretiosum Riley (Snand and Vinson 1985, Strand et al. 1988, Xie et al.1986) develop abnormally large sizes when provided sufficient nutrition. Normally f.heliothidis will only attack a specific size of host that represents the correct amount ofnutrition (Strand and Vinson 1983a, b) while T. preliglgm adjusts the number of eggs

z9

deposited, depending on the size of the resource (Schmidt and Smith 1987). In both casesthe parasitoid pupates when the host is consumed.

For a species such a !!. glggglpgl which is a hemolymph feeder and does notconsume all the tissue, the response to egress and pupate must be figgered by otherfactors. One way is to respond to changing host conditions or signals produced by the hostas described for { congregatus by Beckage and Riddiford (1978, 1983a, b). The complexrelationships between M. croceioes and its host ale just beginning to be defined and it willbe particularly interesting !o comparc VL gl@lpel to other parasitoids. Comparisons withQ nigriceos, a species in a closely related genus that attacks some of the same hosts butdirectly consumes host tissue later in its development (Vinson and Barras 1970), and C.sonorensis, an ichneumonid that attacks the same host but does not release teratocytes intoits host, will provide insight into what host physiological systems are amenable tomanipulation by parasitoids.

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Askew, R. R., and M. R. Shaw. 1986. Parasitoid communities: their size, structure anddevelopment, pp. 225-264. In: J. Waage and D. Greathood (Eds.) InsectParasitoids. Academic Press.

Barras, D. S.f G. Wiygul, and S. B. Vinson. 1969. Amino acids in the hemolymph ofthe tobacco budworm, Heliothis virescens (F.) as affected by its habitual parasite.Comp. Biochem. Physiol. 3l: 7O7 -7 14.

Barras, D. J., R. L. Joiner, and S. B. Vinson. 1970. Neutral lipid composition of thetobacco budworm, Heliothis virescens (F.), as affected by its habitual parasite,Cardiochiles ni griceps Viereck. Comp. Biochem. Physiol. 36: 77 5-7 83.

Barras, D. J., R. L. Kisner, W. J. Lewis and R. L. Jones. 1972. Effects of theparasitoid, Microolitis glecelpg! on the haemolymph proteins of the corn earwonn,Heliothis zea. Comp. Biochem. Physiol. 138:941-947.

Beard, R. L. 1978. Venoms of Braconidae, Vol. 48, pp. 773-800 (Arthropod Venoms).In: S. Bettini, @d.),

"Handbuch der Experimentellen Pharmakologie," SpringerBerlin.

Beck, S. D., J. N. Lilly, and J. F. Stauffer. 1949. Nutrition of the European corn borer,Pvausta nubilalis (Hbn.). Ann. Entomol. Soc. Am. 42:483-496.

Beckage, N. E. 1985. Endocrine interactions between endoparasitic insects and theirhosts. Ann. Rev. Entomol. 30:371-413.

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Beckage, N. E., and L. M. Riddiford. 1982a. Effects of parasitism by Apantelescongregarus on the endocrine physiology of the tobacco homworm Manduca gg4.Gen. Comp. Endocrinol. 47 : 308-322.

Beckage, N, E., and L. M. Riddiford. 1982b. Effects of methoprene and juvenilehormone on larval ecdysis, emergence, and metamorphosis of the endoparasiticwasp, Apanteles congregatus. J. Insect Physiol. 28:329-334.

Beckage, N. E., and L. M. Riddiford. 1983a. Growth and development of theendoparasitic wasp Apanteles congregatus: dependence of host nutritional statusand parasite load. Physiol. Entomol. 8:231-241.

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Beckage, N. E., and T. J. Templeton. 1986. Physiological effects of parasitism byAoanteles congregatus in terminal-stage tobacco hornworm larvae. J. InsectPhysiol. 32:299-314.

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Blissard, G. W., J. G. W. Fleming, S. B. Vinson, and M. D. Summers. 1986a.Campoletis sonorensis virus: expression in Heliothis virescens and identification ofexpressed sequences. J. Insect Physiol. 32:351-359.

Blissard, G. W., S. B. Vinson, and M. D. Summers. 1986b. Identification, mapping,and in vitro translation of Camooletis sonorensis virus in RNA's from parasitizedHeliothis vircscens larvae. J. Virol. 57: 318-327.

Boman, H. G., and H. Steiner. 1981. Humoral immunity in cecropia pupae, pp. 75-91.In: W. Henle, P. H. Hofschneider, J. Koprowski, O. Maaloe, F. Melchers et al.(Eds.) Current Topics in Microbiology and Immunology, vol. 94D5. Springer-Verlag, Berlin.

Boman, H. G., I. Nelsson-Faze, K. Paul, and T. Rasmuson. 1974. Insect immunitv. I.Characteristics of an inducible cell-free antibacterial reaction in hemolymph ofSamia c]'nthis pupae. Infect. Immun. l0: 136-145.

Eoman, H. G., I. Faye, A. Pye, and T. Rasmuson. 1978. The inducible immunitysjstem of.giant silk moths, pp. 145-165. In: L. A. Bulla and T. C. Cheng (Eds.),Comparative Pathobiology, Vol. 4. Invertebrate Models of Biomedical Research.Plenum Press, N. Y.

Eottger, G.T. 1942. Development of synthetic food media for use in nutrition studies ofthe European corn borer. J. Agric. Res. 65: 493-500.

Eradley, W. G., and K. D. Arbuthnot. 1938. The relation of host physiology to thedevelopment of the braconid parasite, Chelonus annulioes Wesmael. Ann.Entomol. Soc. Am. 31: 359-365.

Brewer, F. A., and S. B. Vinson. 1971. Chemicals affecting the encapsulation of foreignmaterial in an insect. J. lnvert. Pathol. 18: 287-289.

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