in sorghum, sorghum

PHYSIOLOGICAL RELATIONSHIPS OF GR.\IN SORGHUM, SORGHUM

^^^Q^QR (!•) TO BANKS GRASS MITE, 0LIG0NYCHU5

PRATENS S (BANKS) POPULATIONS

by

THOMAS MCADAM PERRING, B. S.

A THESIS

IN

ENTOMOLOGY

Submitted to the Graduate Faculty of Texas Tech University in

Partial Fulfillment of the Requirements for

the Degree of

MASTER OF SCIENCE

Approved

Accep ted

May, 1950

tlô^^H" ACKNOWLEDGMENTS

I am deeply indebted to my committee chairman, Dr.

Thomas L. Archer, for his patience, encouragement, and help-

ful suggestions in the direction of this research project

and preparation of this thesis. I would also like to chank

Dr. Daniel P. Bartell and Dr. Daniel R. Krieg for their

advice and assistance while serving as members of the thesis

committee. I also extend thanks to Dr. Arthur B. Onken and

Dr. Jerry W. Johnson for various contributions given through-

ou t this s tudy.

I wish to acknowledge Mrs. Chris Smith for her technical

assistance and Mr. David B. Wester for his vaiuable help in

statistical evaluation.

I am also grateful to the Texas Agricul.ure Experiment

Stations of Pecos, and Lubbock, Texas for providing the

necessary land, labor, and facilities to complete the experi-

mental parts of the thesis. Special thanks are extended to

Mr. Edsel D. Bynum for his contribution aiong these lines.

Speciai recognition is given to my family for their

support and encouragement. Finaily, to my wife Cheryi, for

her consideration and understanding in the course of my

M.S. program, I extend my deepest appreciation.

11

TABLE OF CONTENTS

ACKNOWLEDGMENTS ii

LIST OF TABLES iv

LIST OF FIGURES v

I. INTRODUCTION AND LITERATURE REVIEW 1

II. MATERIALS AND PROCEDURES 6

Test 1 7

Test 2 10

Statistical Arrangement and Analysis . iO

III. RESULTS AND DISCUSSION 12

Test 1 12

1978 Pecos and Lubbock 12

1979 Pecos 24

1979 Lubbock 29

Test 2 44

IV. SUMMARY AND CONCLUSIONS 50

LITERATURE CITED 53

APPENDIX 56

A. METHOD OF ANALYSIS FOR AMMONIUM NITROGEN. . 57

B. METHOD OF ANALYSIS FOR TOTAL NITROGEN . . . 58

C. METHOD OF ANALYSIS FOR TOTAL PHOSPHORUS . . 59

D. METHOD OF ANALYSIS FOR SUGARS 60

111

LIST OF TABLES

Table Page

1.

2.

3.

•4 .

Average number of female spider mites per plant on grain producing lines. Pecos, Texas, 1978 22

Average number of female spider mites per plant on grain producing lines. Lubbock, Texas, 1978 23

Average number of female spider mites per plant on grain producing lines. Pecos, Texas, 1979 30

Average number of female spider mites per plant on grain producing lines. Lubbock, Texas, 1979 45

IV

LIST OF FIGURES

Figure

1. Average number of female spider mites and damage rating on barren and fertile plants for all varieties taken at growth stages 4.5, 6.0, 7.0, 8.0, and 9.0. Pecos, Texas, 1978

Page

14

Average number of female spider mites, damage rating per piant, growth stages and percent of dry weight nitrogen, phosphorus , and sugar for individual varieties. Pecos, Texas, 1978 16

Average number of female spider mites and damage rating on barren and fertile plants for all varieties taken at growth stages 4 5, 6.0, 7.0, 8.0, and 9.0. Lubbock, Texas, 1978 18

Average number of female spider mites, damage rating per plant, growth stages and percent of dry weight nitrogen, phosphorus, and sugar for individual varieties. Lubbock, Texas, 1978 20

Average number of female spider mites and damage rating on barren and fertiie plants for all varieties taken at growth stages 4.5, 6.0, 7.0, 8.0, and 9.0. Pecos, Texas, 1979 26

6. Average number of female spider mites, damage rating per plant, growth stages and percent of dry weight nitrogen, phosphorus, and sugar for individual varieties. Pecos, Texas, 1979 28

7. Average number of female spider mites and damage rating on barren and fertile plants for all varieties taken at growth stages 4.5, 6.0, 7.0, 8.0, and 9.0. Lubbock, Texas , 1979 32

Average number of female spider mites, damage rating per plant, growth stages and percent of dry weight nitrogen, phos-phorus, and sugar for individual varieties. Lubbock, Texas, 1979 35

9. Linear correlation between leaf nitrogen and spider mite numbers at growth stages 7.0 and 8.0. Lubbock, Texas, 1979 37

10., Linear correlation between leaf phosphorus and spider mlte numbers at growth stages 7.0 and 8.0. Lubbock, Texas, 1979 40

11. Linear correlation between leaf sugar and spider mite numbers at growth stages 7.0 and 8.0. Lubbock, Texas, 1979 43

12. Average number of female spider mites, damage ratings, and growth stages for sorghum charac-teristic tests 47

VI

I. INTRODUCTION AND LITERATURE REVIEW

Certain species of spider mites (.Acari: Te t r any chidae)

have become of particular concern to growers of corn, Zea

mays (L.), and grain sorghum, Sorghum bicolor (L.), in the

semi-arid regions of the great plains and southwestern

United States, inciuding the Trans-Pecos and High Plains re-

gions of west Texas (Owens et al. 1976). Mites reached pest

status on corn in 1967 and on sorghum in 1968 in these Texas

areas (Ehler 1974). Pest species identified by Ehler (19 72;

1973; 1974) on corn and sorghum in west Texas are: Banks

grass mite, Oligonychus pratens is (Banks); a grass mite,

Oligonychus s tickneyi (McGregor) (corn only); two spotted

spider mite, Tetranychus uricae Koch; and carmine spider

mite, Tetranychus cinnabar inus (Boisduval) (sorghum only).

Banks grass mite was the most frequently collecced species

(Ehier 1973). In the present study, 0_^ pra t ensis was the

only species noted. Chandler (1978) reviewed Banks grass

mite history, distribution, bioiogy and host plants.

Mite damage on grain sorghum first appears as disco-

loration of the leaves. Infestations develop on the under-

side of the lower ieaves and move up the plant as numbers

increase. Severe infestation prior to soft dough plant

stage has caused yieid loss due to shrunken seeds and exten-

sive head webbing (Jeppson et ai. 1975). Mite stress reduces

the natural resistance of the piant, making it susceptible to

1

disease (Ward et al. 1972) and lodging (Teetes 1975).

Tetranychid control techniques have given sporadic re-

sults and are often ineffective. Past insecticide and

acaracide usage has resulted in mite resistance, while reduc-

ing competitive organisms (Huffaker et al. 1969; Archer and

Bynum 1978) . Ehler (1974) noted that predators exhibited a

delayed response to mite increases and were unable to reduce

mite densities before economic damage had occurred. Cultural

practices (i.e. irrigation, fertilizers) influence spider

mite populations (Chandler et ai. 1979; E.D. Bynum, per-

sonal communication), yet have limited use in a pest manage-

ment program.

As with several other pest species, recent research

concerning Tetranychids deals with arthropod-plant relation-

s h i p s . _0_ pr at ens is population densities were shown to be

low in early grain sorghum developmental stages, increasin

with plant maturity (Pate and Neeb 1971; Ehler 1974; Feese

and Wilde 1977; Kattes and Teetes 1978). Criticai densities

of mites noted by these authors occurred at bioom (Pate and

Neeb 1971), hard dough (Ehler 1974) and prior to senescence

(Kattes and Teetes 1978). These discrepancies may be the

result of variations in abiotic factors associated with the

study areas or different methodoiogy of each study. Al-

though the variations existed, they indicated a relationship

between mite population increases and plant maturitv.

The movement of plant constituents into and throughout

maturing sorghum plants is well defined. Vanderlip (1972)

reviewed the uptake and translocation of nitrogen and phos-

phorus as they relate to specific growth stages. By bloom,

60% of the phosphorus and 70% of the nitrogen are taken into

the plant. As grain develops, large quantities of nitrogen

and phosphorus move from other plant parts to the grain.

Carbohydrates produced during earlier growth stages are

translocated to maturing grain (D.R. Krieg, personal communi-

cation). Because mite numbers increase as the piant matures,

these plant constituents may be significant in the mite-

plant interaction.

Several authors have studied the relationships of ni-

trogen and phosphorus to Tetranychid populations. Suski and

Badowska (1975) summarized many of these studies and stated

that T. ur t icae numbers are not dependent upon any particu-

lar chemical, but upon concentration ratios of the consti-

tuents involved, and to the metabolic activity of the plant

as affected by these chemicals.

The reiationship of plant sugars to spider mites also

has been studied. Rodriguez et ai. (1960) and Hennberry

(1962) observed positive correlations between total sugars

and T_ ur t ic ae numbers. Opposing results showed mite de-

creases with increases of totai sugars (Hennberrv 1963).

Teetes (1975) and Foster et al. (1977) supported this view

in their observations that sorghum lines exhibiting resistmce

t o 0_ prat ensis were relatively high in sugar content.

In addition to these works, relationships of other

chemical and physical characteristics of sorghum to insects

and mites have been observed. Webster et ai. (1948) stated

that varieties of sorghum susceptible to chinch bugs were

much lower in tannins than non-susceptible varieties. More

recently, Chan and Waiss (1978) have suggested tannins as

possible deterrents to insect damage. Little research of

tannin relationships to spider mites has been reported.

Major physical plant characteristics that influence

arthropods include maturity, senescence (i.e. dying), and

leaf bloom. Screening by Foster et al. (1977) indicated

that Banks grass mite resistant sorghums were non-senescing

types. Leaf bloom has been shown to have adverse effects

upon populations of the greenbug, Schizaphus graminum

(Rodani) (Weibel and Starks 1977).

Although past research has provided useful information,

it fails to explain relationships between mite densities

and physioiogical changes of a maturing piant. This study

was designed to describe several basic factors controiiing

these relationships . This information will be useful, not

only in understanding mite-host relationships, but also as

a basis for helping to understand other arthropod-plant

systems. Understanding these relationships may aid plant

breeders in choosing characteristics for breeding mite re-

sistant varieties.

The objectives were (1) to determine the relationshÍDs

among grain sorghum growth changes in leaf nitrogen, phos-

phorus, and sugar concentrations and spider mite densities,

and (2) to determine the relationships among several physio-

logical and morphoiogical characteristics of sorghum (i.e.

tannin, maturity, senescence, leaf bloom, and midrib

character) and mite numbers.

II. MATERIALS AND PROCEDURES

Experimental sites at Pecos (Reeves Co.) and Lubbock

(Lubbock Co.), Texas were chosen for study in the sumraers

of 1978 and 1979. The two locations provided different

climatic and agricultural regions. Standard agronomic prac-

tices of each area were followed with the exception of

several mite enhancing techniques. Four rows of corn were

strip planted around and through the sorghum fields to serve

as a primary host for mites moving out of overwintering

grasses bordering the field. This movement took place prior

to germination of the sorghum. Upon corn maturity, mites

moved into the established sorghum. To aid overwintering

mites, triticale, X Triticosecale Whittmack, was planted

adjacent to the test plots in Pecos following the summer of

1978. In Lubbock, artificial infestations were necessary in

both years to obtain a mite population. This was done by

placing naturally infested corn leaves near the base of

every third plant. Ethyl parathion was applied to the Lub-

bock test in both years, at the rate of 1.1 kg Al/ha, to

reduce competitors as well as enhance mite numbers (Kattes

and Teetes 1978). One application per year was effective

and no further treatments were necessary.

Mites were counted weekly at Lubbock (1978,1979) and at

growth stages 4.5, 6.0, 7.0, and 8.0 (Vanderlip 1972) at

Pecos in 1978. In 1979, counts in Pecos were made biweekly.

Counts of female spider mites, which provided an estimate

of total numbers (Ehler 1974), were made on sorghum leaves

three, four, and five from the bottom, when leaf number one

was the lowest leaf that was at least 1/3 green. Mite num-

bers on these leaves are representative of the density of

the entire plant (E.D. Bynum, personal communication).

Counts were taken on eight randomiy selected plants within

each treatment. Damage ratings were taken on the eight

plants as well as a row average, using a scale published by

Chandler et al.(1979). Plant growth stages were recorded at

each count. Beneficial arthropods were counted on the three

leaves to determine their influence on the mite population.

Test 1

Two tests were conducted at each experimental site.

Test 1 was a study of the influence of growth changes asso-

ciated with plant development upon mite populations. In

order to study a range of plant material, five sorghum varie

ties varying in maturity rates and degree of mite resistance

were used. These varieties and their characteristics were:

BTx 378 (Redlan) BTx 618 BTx 3197 (Kafir 60)

BTx 623 SC 599-6 (9188)

- late maturity, susceptible - early maturity, susceptible - medium maturity, possibie resis-

tance in crosses with other var iet ies

- late maturity, resistance unknown - early maturity, most resistant of

varieties tested.

Each variety had an A-line and a B-line. A-line piants

.re male sterile iines and B-line plants are "sterility

w^- 1 rm

8

restorer" lines. B-lines are not oniy capable of self-

fertilization but also can poliinate or "restore" A-lines.

A and B iines are near isogenic except for this trait. Heads

were bagged following exertion and prior to pollination to

prevent seed set in the A-line plants. This created a range

of chemical concentrations in the leaves of barren and fer-

tile plants of the various varieties, and mite numbers on

the ieaves were correlated with these chemicals. The

technique of creating barren plants to alter chemical compo-

sition was adapted from Moss (1962).

Each plot contained A and B iines planted in separate

rows on 1 meter centers. The plot arrangements for the two

years varied slightly. In 1978, plots were 4.2 meters lon § ,

u u

and the lines were planted in the following fashion: B.\ABAAB.

A-line (sterile) piants were used entirely for mite count

rows. All A-line piants were bagged for 21 days, half of

them just prior to fiowering, preventing pollination and seed

formation. The other two A-line rows were bagged after flower-

ing, allowing them to be pollinated by the B-lines.

In 1979, plots were 7.6 meters long, which provided more

plants for sampling, and the arrangement was changed to:

SAASBBS. This arrangement allowed ali plants within a variety

to be simultaneously bagged, increasing the efficiency of

bagging and pollination over the i9"8 test. S-rows vere bor-

ders of variety TX 7000, a highly mite susceptibie sorghum.

Remembering that A and B lines were near isogenics, no plant

variables aside from those introduced by bagging should have

been present (Jerry Johnson, personal communication). There-

fore, although mites on only A-line plants were counted in

1978 and mites on both A and B lines were counted in 1979,

the tests were similar. Also in 1979, bags were left on the

heads until termination of the experiment to reduce bird

predation on the seeds, which could have influenced the

plant physiology by reducing sink size (D.R. Krieg, per-

sonal communication).

Biochemical ranges associated with poliinated (fertile)

and non-pollinated (sterile) plants were measured by analy-

sis of leaves three, four and five. These three leaves

correspond to those on which mite counts were taken. Leaves

were collected as closely as possible to growth stages 4.5

and 7.0 in 1978 and at additional stages 6.0 and 8.0 in

1979. Leaf samples were taken from the row opposite the

count row, washed, dried, and ground with a Wiley^^ labora-

tory mill. Total nitrogen was determined using the Kjeldahl

procedure while phosphorus concentration was determined using

the official micro-method (Anon. 1950). In 1978, Kjeldahl

nitrogen was determined colorimetrically. In 1979 this deter-

mination was slightly altered using comparable ammonium elec-

trode analysis (Shau 1979). Alcohol soluble sugars vere deter-

mined using the anthrone procedure (Sunderwirth et al. 1964),

with the addition of decoiorizing carbon to remove chloro-

phyll (Murphy 1958). These techniques are summarized in

10

the Appendix.

Test 2

Test 2 was a study to observe mite relationships with

several physiological and morphological characteristics of

sorghum. Lines and their characteristics of interest as

they were compared are:

SC 423 SC 423

BTx 615 BMR

SC 103-12 SC 326-6

SC 599 TX 09

SC 239 SC 239

CK 60 CK 60

low leaf tannin higher ieaf tannin

low leaf tannin very low leaf tannin

early maturity, senescing late maturity, non-senescing

nonsenes cing s enesc ing

j uicy midrib dry midrib

"bloomless" "bloom"

Each plot contained two sorghum lines that had opposite

characteristics . Each line was planted in double rows 4.2

meters (1978) and 7.6 meters (1979) long on 1 meter centers.

Variety TX 7000 was planted as a border separating the lines

from each other and the adjacent plots.

Mite counts, beneficiai arthropods, damage ratings, and

growth stages were recorded foliowing previousiy mentioned

me thods.

Statistical Arrangement and Analysis

.\il plots in both tests were arranged in a randomized

11

block design with four replicates to reduce variation in mite

numbers due to irrigation patterns (Kattes and Teetes 1978).

Statistical analysis inciuded tvo-way analysis of variance

to explain mite differences on varieties tested. Student's

t-test was used to determine differences in mite counts, da-

mage ratings, and chemical concentrations which occurred on

physiologically and morphologically different plants. Linear

regression was used to describe plant biochemical relation-

ships with mite densities.

III. RESULTS AND DISCUSSION

Identification of spider mites collected in all experi-

ments revealed £. pratensís as the only species present.

The identifications were made by E.D. Bynum and the author

with the use of reference specimens.

Beneficial arthropods were similar to those found by

Chandler et al. (1979). Low beneficial numbers were observed

in each study throughout the season and had little influence

upon mite populations.

Test 1

1978 Pecos and Lubbock

During 1978, statistical differences (p<0.05) were not

present in mite numbers or damage between barren and grain

producing lines, in Pecos (Figure 1,2) or Lubbock (Figure 3,

4) according to t-statistics. Because of these similarities,

correlations between mite numbers and chemical constituents

were useless.

Environmental conditions (high temperature and low humi-

dity) in Pecos were ideal for mites, and numbers rapidly in-

creased causing premature plant death. This increase prior

to grain filling contradicted earlier reports, that mites

increased as grain filling stages were reached. As a result

of early plant death, mites were no longer present at plant

maturity (9.0).

12

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21

T-tests of leaf samples (Figures 2, 4) showed no sta-

tistical differences (p<0.05) in phosphorus or nitrogen

(except Figure 2, variety BTx 378) concentrations between

barren and producing plants. Sugars were influenced aore

by bagging than phosphorus or nitrogen with several signi-

ficant differences seen between lines (Figure 2, varieties

BTx 378, BTx 623, and SC 599-6 and Figure 4, variety SC

599-6). In variety BTx 378, the higher sugars were in the

barren plants but the reverse occurred in varieties 3Tx 623

and SC 599-6. These discrepancies were due to problems with

bagging and pollination. Recalling that only niale sterile

plants (A-lines) were used as count rows, and "sterility

restorer" (B-lines) were used as pollinators, plants not

bagged prior to flowering were pollinated. Thus, even though

an effort was attempted to keep half of the A-lines sterile,

some became fertilized. Those A-lines which were supposed

to become fertilized were poorly pollinated causing irregu-

lar seed se t.

Varietal influence on mite densities for each counting

date are shown in Table 1 (Pecos) and Table 2 (Lubbock).

These values were obtained from grain producing plants. Two-

way analysis of variance showed no significant differences

(p<0.05) among the varieties for any date at Pecos (Table 1).

Mite numbers for each variety on all counting dates at

Lubbock (Table 2) were statistically different only on August

15 and 22. On August 15, densities on varieties BTx 378 and

22

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SC 599-6 were statistically higher than on varieties BTx 3197

and BTx 623. On August 22, as populations began to decrease,

SC 599-6 still showed higher mite numbers, with BTx 378 very

close behind. Recalling the characteristics of these varie-

ties (BTx 378-late maturing, mite susceptible; SC 599-6-early

maturing, most resistant of varieties tested) explanations

for the similarity in mite counts between the two are the

bagging and pollination problems, causing sporadic seed set

in the fertile lines.

1979 Pecos

Rainfall and its attendant phenomena, which Ehler (1972)

and Chandler et al. (1979) noted to cause a reduction of mite

nurabers, prevailed over much of the early growing season in

Pecos during 1979. Therefore, population levels were low in

all varieties until late in the growing season (Figures 5, 6)

at which time no differences occurred in mite numbers or da-

mage between sterile and fertile lines. Because of these si-

milarities, chemical to mite correlations were not made.

Changing the plot arrangement from BAABAAB in 1978 to

SAASBBS in 1979 increased the effectiveness of the bagging

technique. This was evident when chemical constituents were

reviewed (Figure 6). Although few statistical differences

were shown in chemical concentrations between barren and

fertile lines, the data indicated several important trends.

For most varieties, nitrogen levels remained higher in the

leaves of barren plants. Varieties BTx 623 and SC 599-6

25

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29

showed significant differences (p<0.05) in phosphorus levels

between barren and fertile lines. However, higher numbers

on the barren line of BTx 623 and on the fertile line of

SC 599-6, indicated that a varietal response of phosphorus

to seed production may have taken place. Sugar concentra-

tions were generaily higher in barren plants with a statisti-

cal difference in SC 599-6. This variety also exhibited the

only observable difference between mite counts on barren and

fertile lines, in a negative relationship with sugar levels.

These trends indicated movement of nitrogen and sugar

from the leaves to the filling grain in fertile plants,

while preventing seed set obviously interfered with this move-

ment. Phosphorus seemed less influenced by grain production

physiology, and appeared to be more influenced by varietal

dif ferences.

Varietal comparisons (Table 3) showed no significant

difference (p<0.05) between seed producing plants of each

variety according to two-way analysis of variance. This can

be accounted for by the low mite numbers of this test.

1979 Lubbock

Statistical comparison (Student's t-test) of mite

numbers and damage ratings between barren and fertile lines

(Figure 7) showed differences (p<0.05) at plant growth

stages 8.0 and 9.0 in Lubbock during 1979. The separation

beginning at growth stage 7.0 indicated a relationship

between mite dynamics and grain filling physiology of the

30

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33

plant. To further support this, statisticai differences

existed between barren and fertile lines in mite numbers,

damage ratings, and chemical constituents of several varie-

ties (Figure 8).

Tan and Ward (1977) indicated that Oj_ pratens is egg to

adult deveiopmental time was from 6 to 9 days. Considering

this information, correlations were made between leaf consti-

tuents and adult female mite counts taken oae week after leaf

samples were collected. This provided time for the influence

of plant chemicals on mite reproduction and inmature stages

to become apparent.

Linear regression analyses of total nitrogea concentra-

tion with mite numbers are given in Figure 9. Correlations

were not made at growth stages 4.5 or 6.0 due to low mite

numbers at this time. Also, physiological differences be-

tween sterile and fertile lines (near isogenics) should not

have been present, because grain filling had not yet com-

me nced. At the early grain filling stage (7.0), a low r

value (0.262) indicated little relationship between nitrogen

and mites. Reviewing Figure 8 at growth stage 7.0, varieties

BTx 378, BTx 618, and SC 599-6 had higher nitrogen levels in

the fertile lines, statistically higher in variety BTx 618,

correlating to higher numbers of mites on these lines. Va-

r 1 ieties BTx 3197 and BTx 623 represent slight negative rela-

tionships between nitrogen and mite numbers. The overall

effect was a nonsignificant positive relationship (r=0.262).

34

4< II .1»

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n 1 o fti

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35

O N i l » » 1 0 » « » 0

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, o

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II * o n s \ S P W 0 M 4 S 0 H 4 \ N l O O l i l M ^ i N T ^ 4 S l l l " t OM

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pr Figure 9. Linear correlation between leaf nitrogen l't and spider mite numbers at growth stages 7.0 and 8.0. {> Lubbock, Texas, 1979. Significant r (p < 0.05) based on

»|IIMI.-

•c ll«*ll

r-•ni

c

t-statistics (Steel and Torrie 1960) are indicated by the * .

37

hm

O

mi

a. \

(/)

Ui

H

800

700

600

500

400

300

200

100

••

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1.6 1.8 2.0 22 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8

% N I T R O G E N

38

At growth stage 8.0, BTx 378 was omitted from the regression

analysis because mite counts were not taken the veek follow-

ing leaf collection. The other four varieties show negative

correlations, with higher nitrogen in the barren lines,

statistically higher in variety BTx 623, correlatiag with

lower mites on that line. This resulted in a significant

negative relationship (r=-0.435)(Figure 9). Analysis across

both growth stages indicated little seasonal relationship

(r=0.006) between nitrogen and mite numbers.

Regression analysis of phosphorus and spider mites

(Figure 10) showed a positive relationship with a signifi-

cant (p<0.05) r value (0.436) at growth stage 7.0 (soft

dough). Opposingly, at the 8.0 (hard dough) growth stage a

negative relationship occurred, although the r value (-0.223)

was not significant. At soft dough (Figure 8), varieties

BTx 378 and BTx 3197 had a strong positive reiationshi? be-

tween phosphorus and mite numbers, while varieties BTx 618,

BTx 623, and SC 599-6 exhibited weak negative relationships.

The overall effect was that of a significant positive rela-

tionship (r=0.436). At hard dough, variety BTx 378 was again

left out of the regression. With no difference between

sterile and fertile phosphorus levels in this variety, its

contribution to the overall regression should have been :nini-

mal. Variety BTx 623 increased the degree of its negative

relationship from growth stage 7.0 to 8.0, and all other

varieties remained relatively the same. This caused the

• : n Cî

b n B 10 . \

39

4 | l M

«

ri

\ • l

>

•c

Figure 10. Linear correlation between leaf phos-phorus and spider mite numbers at growth stages 7.0 and 8.0. Lubbock, Texas, 1979. Significant r (p < 0.05) based on t-statistics (Steel and Torrie 1960) are indicated by the * .

Irs !!S2

40

I I 1 r I I r

IM

300

700

600

500

400

300

•

*

8.0

.16 .18 .20 .22 .24 .26 .28 .30 P H O S P H O R U S

41

relationship between phosphorus and mite numbers to change

from significantly positive (r=0.436) at grovth stage 7.0 to

slightly negative (r=-0.223) at growth stage 3.0. Throughout

the growing season, head bagging caused sporadic results in

phosphorus levels between A and B lines, with a low correla-

tion noted (r=0.163). Comparing these results with Pecos

(1979) data further indicated that a varietal response to

bagging may have been an influencing factor in the phos-

phorus-mite relationship.

Linear regression analysis of alcohol soiuble sugars

and spider mite numbers (Figure 11) indicated a strong nega-

tive relationship with a significant (p<0.05) r value

(-0.587) at early grain filling. During the later stage,

the negative relationship was still present, although the r

value was not significant (-0.211). Unlike nitrogea and

phosphorus, sugars in the barren plants of all varieties at

growth stage 7.0 (Figure 8) were higher than in fertile

plants, with statistical differences in three of the five va-

rieties ( BTx 618, BTx 623, SC 599-6). This indicated a

movement of sugars from the leaves to the developiag grain

in fertile plants, while the lack of this sink (graia) re-

sulted in higher sugar levels in the leaves of barren plants

(Loomis 1935; Sayer et al. 1931). Moss (1962) and Allison

and Weinraann (1970) reported similar results when fruitiag

was prevented in Z_^ mays . The decline ia sugar levels o:

sterile plants at growth stage S.O, was probabiy due to

9U

Figure 11. Linear correlation between leaf sugar and spider mite numbers at growth stages 7.0 and 8.0. Lubbock, Texas, 1979. Significant r (p < 0.05) based on t-statistics (Steel and Torrie 1960) are indicated by the * .

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16

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44

axillary growth (i.e., tillering) at this later stage, and

movement of sugars to these growing structures. This would

also explain the reduction in r values from -0.587 at growth

stage 7.0 to -0.211 at growth stage 8.0. Although this de-

cline in r values existed, indications were that a negative

relationship between leaf sugar concentration and mite dyna-

mics was still present at the later stage. Regression ana-

lysis of combined growth stages further supports this negative

relationship with a significant (p<0.05) r value (-0.431).

These results are similar to those obtained by Teetes (1975)

and Foster et al. (1977), as they indicated 0_ pratensis

numbers were lower on plants with high sugar concentrations.

Analysis of variance (Table 4) for varietal compari-

sons showed major differences at later counting dates. In

contrast to 1978 Lubbock, the higher numbers occurred on the

more mite susceptible varieties, BTx 378, BTx 618, and

BTx 3197.

Test 2

Characteristic comparisons that were studied included:

tannins, maturity, senescence, midrib juiciness, and leaf

"bloom." Mite counts, damage ratings and growth stages for

all comparisons at Pecos (1978) and Lubbock (1978 and 1979)

are shown in Figure 12. Data were not taken at Pecos in

1979 due to low mite numbers, resulting from inclement wea-

ther conditions (cool temperatures, high humidity, rain) .

Statistical differences (p<0.05) were not found in mite

45

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Figure 12. Average number of female spider mites ...li, (line graph) , damage ratings (bar graph) , and growth nn stages for sorghum characteristic tests. Characteristics

were: low (solid line and bar) and high tannin (I), very low (solid) and higher tannin (II); early (solid) and late maturing (III); nonsenescent (solid) and senescent

irx (IV); juicy (solid) and dry midrib (V); and bloomless •C^ (solid) and bloom (VI). When growth stage differences '"* existed between the two lines, these differences are f shown. NC = no count. Significant differences (p < 0.05) ^ according to Student's t-test are indicated by the * .

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48

numbers or damage between juicy and dry midrib plants

(Figure 12, V) or between "bloom" and "bloomless" plants

(Figure 12, VI).

Fenny (1968) and Chan and Waiss (1978) noted tannins

provided plants with resistance to some arthropods. In the

present study, indications of this relationship were not

present. Differences between low and high tannins (rigure

12, I and II) were present, only during early developmenta1

stages at Lubbock in 1979. Statistically higher damage

occurred on the higher tannia plants (Figure 12, II) although

mite numbers between the two lines were similar. Observa-

tion of the growth stages of the lines indicated a maturity

rate difference between them. The results are similar to

those which occurred in the maturity rate comparison (Figure

12, III), and therefore, indicate that they are due to

maturity differences rather than tannin differences.

In the maturity test, plants with maturity rate dif-

ferences had similar mite numbers throughout the season, re-

gardless of growth stage differences. This aaturity response

contradicted observations by Pate and Neeb (1971), Ehler

(1974), and Kattes and Teetes (1978), who indicated that

maturity differences would affect niite numbers. Damage vas

significantly higher on early maturing lines which indicated

that later maturing lines were able to tolerate mite feediag

better than early maturing lines.

In the senescence test (Figure 12, IV), significantl;

49

higher mite numbers and damage ratings occurred on the

senescent plants (Pecos 1978 and Lubbock 1979). Similar

trends were noted in Lubbock 1978 although they were not

significant. Foster et al. (1977) observed 0_ pratensls

tolerant sorghums were nonsenescing varieties, which supports

the present findings. Reviewing the expected physiological

differences between these two lines may help explain this

relationship. In a senescent plant, nutrients translocate

from the leaves to the maturing grain, putting stress on

the leaves and causing higher mite numbers and damage. Non-

senescent plants retain enough life supporting material in

the leaves to enable them to be functional, and mite num-

bers and damage on these were lower.

IV. SUMMARY AND CONCLUSIONS

In physiological studies during 1978, technical pro-

blems with bagging techniques and pollination resulted in

nonsignificant differences between the physiological changes

of barren and grain producing plants. Because of the simi-

larity, no differences were found in mite numbers or damage

ratings between the two lines. These problems were dealt

with when designing 1979 tests, and improved techniques

were used.

Inclement weather resulted in low mite numbers at Pecos

in 1979. Because of these low numbers, significant dif-

ferences in numbers or damage between barren and fertile

plants were not detected. Using male sterile (barren) and

"sterility restorer" (fertile) lines as sampling plants in

the bagging process, resulted in several notable treads in

chemical constituents. For most varieties tested, nitrogen

and sugar were translocated from the leaves of fertile plants

to the maturing grain. This movement did not occur in sterile

plants. No general patterns were noted concerning phosphorus

levels, as inconsistent varietal differences occurred. During

the same year in Lubbock, significant differences in nite

numbers and damage between barren and fertile lines vere ?re-

sent. Chemical differences in nitrogen and sugar also

were found between lines, with generally higher concentra-

tions of both constitueats in sterile plants. Phosphorus

50

f ;?í

51

concentrations again were influenced more by plant variety.

Linear regression analysis between mite numbers and

chemical constituents showed that sugar concentration was

more highly correlated to numbers than nitrogen or phospho-

rus. Sugar exhibited a negative relationship with mite

densities, not only at particular growth stages but through-

out the entire grain filling period. Seasonal correlations

among mites and nitrogen and phosphorus concentrations showed

no influence of these chemicals upon numbers. However, a

negative correiation between nitrogen and mites was present

during late grain filling, and a positive relationship was

present between mites and phosphorus during early grain

filling. Suski and Badowska (1975) suggested that mites

responded not to the amount of any particular element, but

rather to the metabolic activity of the plant as affected

by these chemicals. A similar relationship may be involved

in the present study causing the phosphorus influence on

mites to be greater during eariy grain filling and nitrogen

influences to be greater during late grain filling.

Plant characteristic comparisons showed no affect of

tannin, leaf bloom, or midrib juiciness upon mite numbers

or damage. Plants with maturity rate differences had simi-

lar mite numbers throughout the season which contradicts

the general belief that mite increases are concomitant

with plant growth stage. Damage was higher on early matur-

ing lines indicating a higher tolerance to mite feeding in

52

later maturing lines. In senescence tests, higher mite

numbers and damages occurred on senescent lines than on

nonsenescent lines.

Combining data presented in test 1 and test 2 serves

to summarize these studies. Similarities in mite numbers

between early and late maturing lines, coupled with early

mite increase prior to grain filling at Pecos in 1978, in-

dicated that mites are not as closely tied to plant maturity

as previous authors had indicated. The relationship seems

to depend on the physiological condition of the leaves upon

which mites feed. Examination of physiologica1 differences

between the leaves of barren and fertile lines indicated

relationships similar to what would be expected between

senescing and non-senescing lines. Baggiag sterile plants

created a non-senescing type situation in the leaves bv

preventing the formation of a grain filling sink, resulting

in lower mites and damage. In the grain filling lines,

nutrients were transported to the maturing grain creating a

senescing type situation by putting stress on the leaves.

Consequent ly, mite numbers and damage on these plants were

higher .

The results of these studies indicate the existence of

relationships among mites and several host plant factors.

In an effort to completely understand spider mite dvaaniics,

future research concerning the mite-plant complex should

continue.

1«

I, ii

1

LITERATURE CITED

Allison, J.C.S. and H. Weinmann. 1970. Effect of absence of developing grain on carbohydrate content and senescence on maize leaves. Plant Physiol. 46: 435-6.

Anonymous. 1950. Official methods of analysis of the Asso-ciation of Official Agricultural Chemists, 7th Edition George Banta Publishing Company, Menasha, Wisconsin. 910 pp.

Archer, T.L. and E.D- Bynum. 1978. Pesticide resistance by arthropod pests on feed grains. Southwest. Sntomol. 3: 251-9.

Chan, B.G. and A.C. Waiss, Jr. 1978. Condensed tannin, an antibiotic chemical from Gossypium hirsutum (L.). J. Insect Physiol. 24: 113-8. \n

Chandler, L.D. 1978. Effects of irrigation practices on spider mite populations in field corn and development of a technique for estimating mite densities. Master of Science Thesis, Entomology Department, Texas Tech University, Lubbock, Texas. 53 pp.

Chandler, L.D., T.L. Archer, C.R. Ward, and W.M. Lyle. 19"? Influences of irrigation practices on spider mite densities on field corn. Environ. Entomol. 8: 196-201.

Ehler, L.E. 1972. Preliminary studies of spider mites on corn and sorghum in west Texas. 5th Ann. Tex Conf. on Insects, Plant Diseases and Weed and Brush Control. 8 pp.

1973. Spider mites associated with grain sorghum and corn in Texas. J. Econ. Entomol. 66: 1220.

1974. A review of the spider mite problem on grain sorghum and corn in west Texas. Tex. Agr. Exp. Stn. Bull. #1149. 15 pp.

Feeny, P.P. 1968. Effect of oak leaf tannins on larval growth of the winter moth, Operophtera brumata. J. Insect. Physiol. 14: 804-17.

Feese, H. and G. Wilde. 1977. Factors affecting survival and reproduction of the Banks grass mite, 01igonychus pratensis. Environ. Entomol. 6: 53-6.

•1

M

53

54

Foster, D.G., G.L. Teetes, J.W. Johnson, D.T. Rosenow, and C.R. Ward. 1977. Field evaluation of resistance in sorghums to Banks grass mite. Crop Sci. 17: 821-3.

Hennberry, T.J. 1962. The effect of host plant nitrogen supply and age of leaf tissue on the fecundity of the two-spotted spider mite. J. Econ. Entomol. 55: 799-800

1963. Effect of host plant condition and fertilization on two-spotted spider mite fecundity. J. Econ. Entomol 56: 503-5.

Huffaker, C.B., M. van de Vrie, and J.A. McMurtry. 1969. Ecology of Tetranychids and their natural enemies: A review II. Tetranychid populations and their possi-ble control by predators: An evaluation. Hilgardia. 40: 391-458.

Jeppson, L.R., H.H. Keifer, and E.W. Baker. 1975. Mites injurious to economic plants. University of California Press. Berkeley, Calif. 614 pp.

Kattes, D.H. and G.L. Teetes. 1978. Selected factors in-fluencing the abundance of Banks grass mite in sor-ghums. Tex. Agr. Exp. Sta. Bull. #1186. 7 pp.

Loomis, W.E. 1935. The translocation of carbohydrates in maize. lowa St. Coll. J. Sci. 9: 509-20.

m

Moss, D.H. 1962. Photosynthesis and barrenness. Crop Sci. 2: 366-7.

Murphy, R.P. 1958. A method for the extraction of plant samples and the determination of total soluble carbo-hydrates. J. Sci. Food Ag. 7: 714-7.

Owens, J.C, C.R. Ward, and G.L. Teetes. 1976. Current status of spider mites in corn and sorghum. Proc. 31st Ann. Corn and Sorg. Res. Conf. pp. 38-64.

Pate, T.L. and C.W. Neeb. 1971. The Banks grass mite problem in the Trans-Pecos area of Texas. Tex. Agr. Exp. Stn. Prog. Rep. #2871. pp. 23-5.

Rodriguez, J.G., D.E. Maynard, and W.T. Smith, Jr. 1960. Effects of soil insecticides and absorbents on plant sugars and resulting effect on mite nutrition. J. Econ. Entomol. 53: 491-5.

Sayer, J.D., V.H. Morris, and F.D. Richey. 1931- The effect of preventing fruiting and of reducing the leaf area on the accumulation of sugars in the corn stem. J. Am. Soc. Agron. 23: 751-3.

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Shau, S.H. 1979. Nitrogen assimilation in sorghum geno-types. Master of Science Thesis, Departraent of Plant and Soil Sciences, Texas Tech University, Lubbock, Texas. 50 pp.

Steel, R.G.D. and J.H. Torrie. 1960. Principles and proce-dures of statistics. McGraw-Hill Book Company Inc. New York, N.Y. 481 pp.

Sunderwirth, S.G., G.G. Olson, and G. Johnson. 1964. Paper chromatography-anthrone determination of sugars. J. Chromatog. 16: 176-80.

Suski, Z.W. and T. Badowska. 1975. Effect of the host plant nutrition on the population of the two-spotted spider inite, Tetranychus urticae Koch (Acarina, Te t rany chidae) . Ekol. pol. 23: 185-209.

Tan, F.M. and C.R. Ward. 1977. Laboratory studies on the biology of the Banks grass mite. Ann. Entomol. Soc. Am. 70: 534-6. th

Teetes, G.L. 1975. Insect resistance and breeding strategies in sorghum. Proc. 30th Ann. Corn and Sorg. Res. Conf. pp. 32-48.

Vanderlip, R.L. 1972. How a sorghum plant develops. Contri-bution #1203. Agron. Dept., Kan. Agr. Exp. Stn. 19 pp.

Ward, C.R., E.W. Huddleston, J.C. Owens, T.M. Hills, L.G. Richardson, and D. Ashdown. 1972. Control of the Banks grass mite attacking grain sorghum and corn in west Texas . J. Econ. Entomol. 65: 523-9.

' *

Webster, J.E., J.B. Sieglinger, and F. Davies. 1948. Chemi cal composition of sorghum plants at various stages of growth and relation of composition to chinch bug inju-ry. Okla. Ag. and Mech. Coll. Tech. Bull. T-30. 32 pp.

Weibel, D.E. and K.J. Starks. 1977. Greenbug counts on bloom and bloomless sorghums. Sorg. News. 20: 110-1.

APPENDIX

A. Method of analysis for ammonium nitrogen-Kjeldahl, (used in 1978)

B. Method of analysis for total nitrogen - micro Kjeldahl, (used in 1979)

C. Method of analysis for total phosphorus

D. Method of analysis for alcohol soluble sugars

56

57

APPENDIX A: METHOD OF ANALYSIS FOR AMMONIUM NITROGEN -KJELDAHL (USED IN 1978)

1. Into 500 ml Kjeldahl flasks, place 0.5 g dry plant

material. Add 1 g sodium sulfate (Na^SO^), 7-10 Hengar

granules, 1 g copper sulfate (CuSO^), and 30 ml concen-

trated sulfuric acid (H^SO^).

2. On a standard Kjeldahl apparatus, slowly heat until

solution turns to a green color. Increase heat to form

a condensation ring on the neck of the flask, 1" from

the bulb. Heat until solution turns clear.

3. Remove from heat and let cool for 30 minutes. After

this time, add 100 ml tap water.

4. Just prior to distillation, slowly add 150 ml concen-

trated sodium hydroxide (NaOH). Add 2-3 gm boiling

chips and distill with low flame into 50 ml boric acid

(H^BOo) until 150 ml of distillate are produced.

5. Read optical density (O.D.) at 620 nm.

Standards: 1000 ppm ammonia (stock) Ammonium chloride (NH^Cl) 3.15 g Distilled water 1.0 liter

Prepare dilutions from .15 ppm to 15 ppm for calibration.

•^ Concentration of ammonium nitrogen was calculated from optical density readings from a Technicon® CSM 6 auto-analyzer. Sample was mixed with potassium sodium tartrate, alkaline phenol, and sodium hypochlorite before reading.

58

APPENDIX B: METHOD OF ANALYSIS FOR TOTAL NITROGEN - MICRO KJELDAHL (USED IN 1979)

1. Into a 75 ml heating tube, add 150 mg of dried plant

material, 0.8 to 1 gm of catalyst (ratio of 1:10

copper sulfate (CUSO^) to potassium sulfate (K^SO^), and

5 ml concentrated sulfuric acid ( H ^ S O A ) .

2. Heat —^ at 380*C for 4 hrs or until samples become

clear in color.

3. Allow to cool and bring to approximately 75 ml volume

with deionized H^O.

4. Adjust to pH 4.0 with potassium hydroxide (KOH) and bring

to 100 ml volume with deionized H^O. Allow to cool.

5. Adding several drops of concentrated KOH (resulting in

a blue color) changes pH to 10. Measure the concen-

2 / tration of ammonia with a specific ion electrode.-^ •

Standards: 10,000 ppm ammonia (stock) y Ammonium chloride 38.2 gm | Deionized water 1000 ml '

1000 ppm - 100 ml stock solution 50 ml H2SO4 8 gm to 10 gm catalyst (see above) 125 ml conc. KOH - adjust to pH 4.0 Bring to 1 liter

100 ppm - 10 ml stock same as above

10 ppm - 1 ml stock same as above

-^ The Technicon^-^ BD-40 heating unit was used to digest samples.

-^ The Orion^^—' research model 601 digital ionanalyzer equipped with an ammonium electrode was used to measure NH~ concentration.

59

APPENDIX C: METHOD OF ANALYSIS FOR TOTAL PHOSPHORUS

1. To a #230 Coors crucible add 0.5 g dry plant material.

2. Moisten sample with 1 ml of 50% anhydrous magnesium

nitrate (MgCNO^)^ • ^H^O). Evaporate to dryness.

3. Place samples into a cold muffle furnace and set

temperature as follows: (muffle door open) 204*0 until

'total combustion completed; (close door) 316'C for 30

minutes; 371^*0 for 30 minutes; 566**C for 2 h hours.

Allow to cool.

4. Moisten ash with deionized H^O and then add 2 ml of 1:1 h

hydrochloric acid (HCl). On a steam bath, under hood, I

evaporate to near dryness.

5. With 3-4 washings of distilled water, quantitatively

transfer contents left in crucible and filter through

#2 Whatman filter paper. During filtration add 10 ml 1

of 1 N H c i . :

6. Bring filtrate to 100 ml volume and read optical density

at 660 nm.

Standards: 400 ppm phosphorus (stock) Anhydrous potassium dihydrogen phosphate 0.143 g Distilled water 1 liter

Prepare dilutions from 2.5 ppm to 25 ppm for calibration.

Phosphorus concentration was calculated from optical density readings at 660 nm on Technicon CSM® 6 autoanaly-zer. Ammonium molybdate and chlorostannous reductant were added to sample before reading.

60

APPENDIX D: METHOD OF ANALYSIS FOR ALCOHOL SOLUBLE SUGARS

1. Into 125 ml erlenmeyer flask, add 1 gm dry plant ma-

terial, 50 ml of 80% ethanol and 1 gm of decolorizing

carbon . Shake for 2 hours (200 shakes/minute).

2. Filter through #2 Whatman filter. Use 1 ml of filtrate

for analysis.

U

3. To 1 ml of filtrate, add 10 ml of anthrone reagent

Shake well and heat-^for 30 minutes at 100''C. Cool

rapidly in ice bath.

4. Read optical density at 620 nm. Blank consists of 1 ml

H^O and anthrone reagent.

Standards: Prepare standard solutions ranging from 0.1 - 1.0

mg glucose per ml.

U Removed chlorophyll and approximately 10% of the sugars, which were added to final calculations.

•^ Anthrone reagent. j4„^,-ii^^ Add 666 ml of concentrated H2SO4 to 280 ml of distilled H9O. Do not allow temperature of solution to rise above 110-C. Dissolve 10 gm of thiourea into solution. After cooling to less than 90*C add 0.5 g of anthrone. Solution will remain stable for 4 weeks when stored at 4 C.

iV The Tecam Dry B l o c k ® heat block was used for heating samples.

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in sorghum, sorghum

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