Entomologia Experimentalis et Applicata97: 347–354, 2000.© 2000Kluwer Academic Publishers. Printed in the Netherlands.

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Vacuuming tarnished plant bug on strawberry: a bench study ofoperational parameters versus insect behavior

Charles Vincent & Roger ChagnonHorticultural Research and Development Centre, Agriculture and Agri-Food Canada, 430 Gouin blvd., Saint-Jean-sur-Richelieu, Qc, Canada J3B 3E6 (Fax: (450) 346-7740; E-mail: vincentch@em.agr.ca)

Accepted: June 27, 2000

Key words:vacuum,Lygus lineolaris, strawberry, behavior, physical control method

Abstract

A vacuum apparatus was used in a test bench environment to determine the effects of two operational parameterson vacuuming efficacy for an insect pest. Nymphs and adults of tarnished plant bug,Lygus lineolarisP. de. B.(Hemiptera: Miridae), marked with fluorescent powder, were positioned on strawberry plants according to threeheight classes. Three speeds of inlet passage (i.e., 2, 4 and 6 km h−1) and two heights (passage at 2/3 and 3/3 ofthe canopy) of inlet relative to the top canopy of the plants were investigated. After vacuuming the marked insectsremaining on the plants were then found using a UV light and the class height of their position on the plant andthe substrate (i.e., soil, leaf, stem or fruit/flower) were noted. The efficacy of the vacuum was optimal when theinlet was passed at 4 km h−1 with the inlet at a height of 2/3 of the strawberry canopy. Nymphs were usuallyvacuumed more efficiently than adults. Most (64.5%) individuals that were not vacuumed did not change positionafter inlet passage. Most (85.9%) individuals that changed position after inlet passage experienced vertical, mostlydownward, movements.

Introduction

Scientific literature on the use of vacuum machines inagriculture mainly concerns two systems, i.e. the Col-orado Potato Beetle,Leptinotarsa decemlineataSay(Chrysomelidae) attacking the potato plant, andLy-gusspp. (Miridae) attacking the cultivated strawberry(Vincent & Boiteau, 2000). The differences betweenthe two systems are essentially as follows. Adult andlarval Colorado Potato Beetle cling to the plants withforces of 40, 30 and 10 nN in adults, 4th and 3rd in-stars, and 2nd instars respectively (Misener & Boiteau,1993). Furthermore, the potato plant (like celery, seeWeintraub et al., 1996) is a crop that has a rigidarchitecture (i.e. easily breakable) compared to thestrawberry plant. In field experiments, it was foundthat Colorado Potato Beetles fall to the ground, ex-hibiting a behavior known as thanathosis, probablydue to mechanical vibrations caused by the apparatusor due to ineffective removal (Boiteau et al., 1992).

In contrast, strawberry is a high value crop thatdoes not suffer structural or economic damage if thefoliage is bent: this fact offers interesting possibilitiesconcerning optimal positioning of the inlet to matchthe insect behavior. In addition, tarnished plant bugadults are highly mobile insects (Mueller & Stern,1973).

The tarnished plant bug,Lygus lineolarisP. deB. (Hemiptera:Miridae), is a key pest of strawberry(Fragaria× ananassaDuch.) fields in Eastern NorthAmerica (Schaefers, 1981; Vincent et al., 1990). Thequantitative value of a vacuum machine, the Biovacr,has been studied in field conditions to manage tar-nished plant bug populations in strawberry fields (Vin-cent & Lachance, 1993). The Biovac was passed overstrawberry plants at 7 km h−1 with the air inlets barelytouching the top of the canopy. Seven times out of15, a Biovac passage significantly reduced nymph andadult populations, while 3 times out of 15 the popula-tions were reduced but not significantly. In strawberryfields in California, Pickel et al. (1994) compared

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three machines of different types at speeds rangingfrom 4 to 8 km h−1 and air inlet speeds rangingfrom 29.6 to 55.6 km h−1. Weekly passages reducedadult and nymphalLygus hesperusKnight populationsby 74 and 43%, respectively. Pickel et al. (1994)concluded that, under their agronomic conditions, vac-uum machines did not provide adequate control forcommercial production.

To improve the efficacy of vacuum machines, ques-tions pertaining to the design, the use and insectbehavior must be addressed. To circumvent the dif-ficulties of field work and to extend the period ofexperimentation throughout the year an apparatus wasdesigned by Khelifi et al. (1992) to study the efficacyof a vacuum machine on the Colorado Potato Beetle,Leptinotarsa decemlineata, in a test bench environ-ment. Their apparatus, fixed on a table, allowed thestudy of effects of air speed and position of insectson potato plants on efficacy of the machine and themodelling of air flows (Lacasse et al., 1994). Chagnon& Vincent (1996) designed an apparatus in a test benchenvironment that reproduced the physical attributes ofthe Biovac functioning on strawberry fields. That ap-paratus allows the precise control of speed and inletposition relative to ground or canopy level.

Little is known about the fate of insects that aremobile (and therefore may escape vacuuming) like thetarnished plant bug in the vacuuming process. In thepresent work, we hypothesized that both speed of theBiovac and inlet position relative to the canopy wouldinfluence the efficacy of vacuuming insects. Locationsof marked adults or nymphs on various substrates (i.e.,flowers, stem, leaf or soil) were noted before and afterthe passage of the Biovac inlet with the turbine on oroff. This study allowed us the determination of thesuccess of removal as a function of the location andbehavior of the tarnished plant bug.

Materials and methods

Tarnished plant bugs were reared on sprouted potatoes(Slaymaker & Tugwell, 1982) in growth chambers setat 25 ◦C, 60% r.h. and a photophase/scotophase ofL16:D8 h. Immediately before the trials, tarnishedplant bug adults or third-instar nymphs were indi-vidually marked on their dorsum. A fluorescent dye(Day Glo Color Corp., Cleveland, Ohio) was appliedas a liquid solution (dye 50%, natrosol 0.4%, water32.3%, propylene glycol 15%, by weight) with a paintbrush. This marking system had no apparent effects

Figure 1. Spatial coordinates system of the volume over the ex-perimental arena: 244 cm (=sections 1+2+3+4+5) × 45 cm(=transects A+B+C).

on behavior or mortality of insects. Marked insectswere kept individually in small vials shortly before thetrials.

The vacuum apparatus and the methodology hasbeen described in Chagnon & Vincent (1996). Briefly,a suction inlet (described in Vincent & Lachance,1993) was mounted on a dolly rolling on I-beam rails,with a bracket adjustable in height. The travel speed ofthe dolly was monitored using an optical shaft encoderconnected to a small pulley on which rode a tractioncable. The monitoring pulse signal was fed to a dataacquisition card residing in an IBM-compatible micro-computer. Data was saved as an EXCEL (MicrosoftCorporation) spreadsheet. The speed of the dolly couldbe controlled at up to 8 km h−1. The velocity pres-sure due to air speed was monitored by a Pitot tubeconnected to an ultra-low differential pressure trans-mitter. The monitoring pulse signal was fed to the dataacquisition card mentioned earlier. The suction fan,powered by a 600 V AC electric motor (13.4 Ampsor 10.9 kW) turned the fan at 2174 RPM.

Strawberry (cultivar Kent) plants were grown in agreenhouse in 45× 15× 61 cm containers. Four con-tainers were tightly aligned (total length= 244 cm)to make an experimental arena. The volume over thearena was partitioned into a spatial coordinate systemcomprised of five longitudinal sections, three lateraltransects (perpendicular to the inlet advancement axis)and three height classes (Figure 1). Because there wasvariation among plant heights, a relative system (usingthe top of the canopy as 100%) of plant height wasused. The mean plant height was 19.2 cm (± 2.69SE) (minimum= 15.0 cm, maximum= 25.5 cm).The lower height class corresponded to soil level up tothe lower third of the canopy, while the upper heightclass corresponded to the top of the canopy down tothe upper 2/3 of the canopy. The proportion of individ-uals positioned on each substrate (i.e., leaf= 29.5%,

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flowers or fruit= 45%, stem= 12.5%, crown= 4.5%,soil= 8.5%) corresponded to the observed time spentby adults and nymphs in caged plants in a strawberryfield (Rancourt et al., 2000). Immediately before eachpassage, two insects marked with a distinctive colorcode were positioned on a substrate with a paint brush.After 60 s, the position of each individual was care-fully noted with respect to section, transect, heightfrom the soil (cm) and substrate. One hundred nymphsand adults (i.e., 2 individuals per passage× 50 pas-sages) were positioned for each speed-height of inletcombinations.

The Biovac inlet was passed at 2 (± 0.03 s.d.), 4 (±0.03 s.d.), and 6 (± 0.04 s.d.) km h−1. In one series,the inlet barely touched the top of the canopy, hereafterdenoted as height= 3/3. In a second series, the inletwas passed at two-thirds of the canopy height relativeto soil level (height= 2/3). Control passes (i.e., passesof inlet with the turbine off) were done at 2, 4 and6 km h−1 with the inlet barely touching the top canopyof the plants or at 2/3 of the canopy height.

Immediately after the inlet passage, the lights wereturned off and marked individuals were searched for5 min utilizing a UV light to facilitate their detection.In blind tests, that method allowed the recovery ofca. 87% of marked individuals (Chagnon & Vincent,1996). During tests in which the operator knew wherethe insects were before the inlet passage, 97 and 99%of individuals (n = 937 nymphs or adults) were re-covered within 100 and 200 s of search, respectively.Upon recovery the insect’s position on the substrateand the spatial coordinates were noted. Individualsthat were not found after 5 min were considered vac-uumed. Tested individuals were removed from theexperimental setup and new individuals were taken forsubsequent testing. In very few cases marked adultsthat were overlooked after a 300 s search and foundsubsequently in the experimental area were positivelyidentified thanks to the color code on their elytra. Inthese cases the relevant data were deleted and a newindividual was tested.

G-tests (log-likelihood ratio for contingency ta-bles) were used to compare the proportions of individ-uals found on either different substrate type or spatialcoordinates (Sokal & Rohlf, 1995).

Results and discussion

The pattern of percent removal was consistent in allcases: the higher on the plant canopy the insect oc-

curred before inlet passage, the higher the percentageof insect removal (Table 1). In all cases, the per-cent removal of either nymphs or adults was signif-icantly lower when individuals were located in thelower height class of the plant before the inlet passage(Table 1).

When the inlet was passed at 2/3 of canopy height,the percent removal of both adults and nymphs wasconsistently higher than that observed at 3/3 of thecanopy. This effect was more pronounced when indi-viduals were located in the lower height class beforeinlet passage. For example, 26 and 3% of nymphs thatwere in the lower height class were removed after inletpassage at 2/3 and 3/3 of the canopy respectively.

For a given speed of inlet passage, there was adefinitive benefit from passing the inlet at 2/3 of thecanopy. Efficacy of removal of individuals located inthe upper third of the canopy was marginally improvedby lowering the inlet at 2/3 of the canopy (Table 1).Even after numerous passages, there was no apparentdamage caused to the plants by the passage of inlets at2/3 of the canopy. While strawberry plants allow suchan approach, other plant species that have a more rigidarchitecture (e.g., potatoes, raspberries, celery) cannotbe treated similarly without harming the plants.

At speeds of 2, 4 and 6 km h−1, nymphs were re-moved significantly more often at 2/3 than at 3/3 of thecanopy (Table 2). This could be important informationbecause it is the nymphs that are mostly targeted byinsecticidal treatments in commercial fields (Mailloux& Bostanian, 1988). A significant difference betweenproportions of adults removed at 2/3 versus 3/3 of thecanopy was observed at 6 km h−1. In strawberry fields,the optimal combination should therefore be a passageat 4 km h−1 with the inlet positioned at 2/3 of thecanopy.

In order to explain the failures of collecting tar-nished plant bugs the data were first compiled (alldolly speed pooled) into three hierachical groups (Ta-ble 3). The first group summarized the frequency ofindividuals vacuumed (n=504) versus non-vacuumed(n=718) when the turbine was on. Then, within non-vacuumed individuals, the second group involved in-dividuals that exhibited changes in spatial coordinates(n=255) or in substrate (n= 284). Thirdly, for individ-uals that exhibited change in spatial coordinates, thefrequency of individuals that moved laterally acrosstransects (n=58), longitudinally (n=77) and vertically(n=219) are presented. No lateral movements thatcould be interpreted as an escape behavior were ob-served. Therefore, an optimal design of inlets should

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Table 1. Effect of position of individuals before inlet passage (at two heights) on percentage of removal of tarnishedplant bug (all dolly speed pooled, turbine on)

Height class of Inlet passed at 2/3 of canopy Inlet passed at 3/3 of canopy

individual before % removal na Gh (P)b % removal n Gh (P)

inlet passage

(A) Nymphs

Upper 68ac 90 61a 127

1.34 (0.25>P>0.1) 19.6 (<0.001)

Median 60a 141 33b 122

23.3 (<0.001) 27.8 (<0.001)

Lower 26b 73 3c 67

(B) Adults

Upper 74a 44 51a 145

12.4 (<0.001) 12.0 (<0.001)

Median 46b 145 28b 80

22.6 (<0.001) 17.6 (<0.001)

Lower 18c 113 4c 75

aNumber of individuals tested.bProbability calculated for the G-statistic.cFor either adults or nymphs, % removal values with same letters are not significantly different (G-test at P=0.05)between relative heights of inlet passage.

Table 2. Effect of speed and relative height of inlet on tarnished plant bug removal (turbine on)

Speed Relative Nymphs Adults

of inlet height of % removal na Gh(P)b % removal na Gh (P)

(km h−1) inlet in canopy

2 2/3 60ac 100 39a 102

11.7 (<0.001) 0.22 (0.75<P<0.5)

2 3/3 37b 112 36a 100

4 2/3 59a 102 34a 100

7.9 (0.005<P<0.001) 0.02 (0.9<P<0.75)

4 3/3 39b 102 35a 100

6 2/3 44a 102 47a 100

1.0 (0.05<P<0.025) 7.8 (0.01<P<0.005)

6 3/3 37b 102 28b 100

aNumber of individuals tested.bProbability calculated for the G- statistic.cFor either adults or nymphs, % removal values with same letters are not significantly different (G-test at P=0.05) between relativeheights of inlet passage.

be to maximize vertical air flow and not to preventlateral escape of individuals.

The frequency of horizontal movements, either lat-eral or longitudinal, ranged from 11 (adults, inlet at2/3) to 23 (nymphs, inlet at both 2/3 and 3/3). The fre-quency of vertical movements (range= 42 to 69) wasconsistently more than double that of the maximumfrequency of horizontal movements.

From the non-vacuumed individuals (n = 718),463 did not change their spatial coordinates and 255

changed coordinates (Table 3). We examined the latterdata to determine if the insects had a consistent es-cape scheme. An analysis was also done of the spatialand substrate distribution of insects (all speeds pooled)before and after the inlet passage. In terms of spatialre-distribution as a result of inlet passage when theturbine was on, the results were consistent for bothadults and nymphs at 2/3 and 3/3 inlet height (Table 4).For example, of adults that were in upper and medianheight classes before the passages and moved then,

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Table 3. Fate of tarnished plant bug adults and nymphs when Biovac inlet was passed at2/3 and 3/3 (i.e., barely touching) of strawberry canopy height (all dolly speed pooled,turbine on)

Adults Nymphs Total

2/3 3/3 2/3 3/3 number

Number vacuumed 121 99 165 119 504

Number non-vacuumed 181 201 139 197 718

(A) Change in space

No 128 148 66 121 463

Yes 53 53 73 76 255

Transect∗ 11 19 14 14 58

Section∗ 17 14 23 23 77

Height 44 42 64 69 219

(B) Change in substrate

No 111 145 63 115 434

Yes 70 56 76 82 284

Total No. of individuals 302 300 304 316 1222

∗Could be a change in one or two transects or in one or more sections (see Figure 1).

Table 4. Percent of tarnished plant bug adults and nymphsthat changed spatial coordinates after inlet passage at twoheights (all dolly speeds pooled, turbine on)

Height class before passage Height class after passageLower Median Upper

(A) Adults, Inlet 2/3 (n=44)Upper 0.0 0.0 0.0Median 0.0 0.0 5.0Lower 0.0 80.0 16.0

(B) Adults, Inlet 3/3 (n=42)Upper 0.0 2.4 0.0Median 2.4 0.0 14.3Lower 0.0 47.6 33.3

(C) Nymphs, Inlet 2/3 (n=64)Upper 0.0 0.0 0.0Median 0.0 0.0 2.0Lower 0.0 66.0 33.0

(D) Nymphs, Inlet 3/3 (n=69)Upper 0.0 2.9 0.0Median 2.9 0.0 4.3Lower 0.0 56.5 33.3

33.3 and 47.6%, respectively, were found in the lowerheight class after the passages (Table 4). Consistentlya large (from 48 to 80%) proportion of individuals(nymphs or adults) located in the median height classbefore the inlet passage were also relocated at a lowerstratum after passage. Rarely, individuals were relo-cated in a higher stratum after inlet passage, i.e. three

Table 5. Percent of tarnished plant bug adults andnymphs that changed substrates after inlet passageat two heights (all speeds pooled, turbine on)

Substrate before passage Substrate after passageSoil Stem Fruit Leaf

(A) Adults, Inlet 2/3 (n=70)Soil 0.0 10.0 18.6 47.1Stem 1.4 0.0 10.0 8.6Fruit 0.0 0.0 0.0 0.0Leaf 0.0 4.3 0.0 0.0

(B) Adults, Inlet 3/3 (n=56)Soil 0.0 16.1 7.1 21.4Stem 5.4 0.0 1.8 26.8Fruit 0.0 1.8 0.0 0.0Leaf 1.8 5.4 12.5 0.0

(C) Nymphs, Inlet 2/3 (n=76)Soil 0.0 6.6 1.3 65.8Stem 3.9 0.0 2.6 14.5Fruit 0.0 0.0 0.0 0.0Leaf 0.0 3.9 1.3 0.0

(D) Nymphs, Inlet 3/3 (n=82)Soil 0.0 18.3 6.1 40.2Stem 2.4 0.0 2.4 18.3Fruit 0.0 0.0 0.0 1.2Leaf 0.0 4.9 6.1 0.0

cases ranging from 2.4 (Table 4) to 2.9% (Table 4: twocases).

The re-distribution of insects in terms of substrateshowed a less clear pattern. From 21.4 to 65.8% of

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Table 6. Percent of tarnished plant bug adults and nymphs thatchanged spatial coordinates after inlet passage at two heights (allspeeds pooled, turbine off)

Height class before inlet passage Height class after passage

Lower Median Upper

(A) Adults, Inlet 2/3 (n=53)

Upper 0.0 1.5 0.0

Median 10.0 0.0 20.6

Lower 0.0 17.9 39.7

(B) Adults, Inlet 3/3 (n=24)

Upper 0.0 8.6 0.0

Median 10.0 0.0 8.3

Lower 0.0 8.6 8.3

(C) Nymphs, Inlet 2/3 (n=54)

Upper 0.0 1.5 0.0

Median 3.3 0.0 15.4

Lower 0.0 19.1 59.6

(D) Nymphs, Inlet 3/3 (n=23)

Upper 0.0 1.5 0.0

Median 0.0 0.0 3.2

Lower 0.0 10.3 20.6

the insects that were on leaves before the inlet passagewere found on the soil after passage (Table 5). Lesserproportions of insects that were on flower/fruit (rang-ing from 1 to 19%) or stem (ranging from 7 to 18%)were relocated on the soil after passage.

Of the 718 non-vacuumed individuals, most(n=434) stayed on the same substrate (i.e. leaves,fruit/flower, stem and soil) (Table 3). Some individualsthat might have moved within the same substrate class(i.e., from one leaf to another) were not taken into ac-count in Table 5. When the Biovac was passed with theturbine on, there was a clear tendency among individ-uals that changed substrate (n = 284) for movementsfrom the upper (i.e., flowers and leaves) to lower (i.e.,stem or soil) substrates (Table 5). This observationconfirms the typical downward movements describedearlier.

The question arises as to whether the vertical re-location of nymphs or adults in lower levels of thecanopy after Biovac passage is a consequence of apassive or an active behavior exhibited by the in-sects. For instance, Boiteau et al. (1992) found that13 and 23% of adults and large Colorado Potato Bee-tle larvae, respectively, fell to the ground during onepassage of a vacuum machine, a behavior known

Table 7. Percent of tarnished plant bug adults and nymphs thatchanged substrates after inlet passage at two heights (all speedpooled, turbine off)

Substrate before passage Substrate after passage

Soil Stem Fruit Leaf

(A) Adults, Inlet 2/3 (n=144)

Soil 0.0 0.0 12.5 12.1

Stem 14.3 0.0 8.9 8.8

Fruit 0.0 0.0 0.0 2.2

Leaf 0.0 17.4 8.0 0.0

(B) Adults, Inlet 3/3 (n=138)

Soil 0.0 0.0 3.4 0.9

Stem 9.1 0.0 0.9 1.8

Fruit 0.0 8.0 0.0 0.9

Leaf 9.1 4.0 8.5 0.0

(C) Nymphs, Inlet 2/3 (n=138)

Soil 0.0 13.0 6.5 26.7

Stem 9.1 0.0 4.6 2.2

Fruit 0.0 4.3 0.0 3.3

Leaf 9.1 4.3 5.6 0.0

(D) Nymphs, Inlet 3/3 (n=130)

Soil 0.0 5.3 5.0 7.0

Stem 12.5 0.0 1.0 3.1

Fruit 0.0 0.0 0.0 0.0

Leaf 0.0 5.3 2.0 0.0

in many coleopteran species as ‘thanatosis’ (Racetteet al., 1990).

Vertical relocation when the turbine was off couldbe the consequence of at least two mechanisms. First,it is likely that individuals present in the upper heightclass were knocked off the plant by the inlet passage(at 2/3 of the canopy) and fell to a lower height class(Tables 6A and 6C). This is reflected in the percent-ages of individuals that were repositioned from anypart of the plant to the soil after inlet passage withthe turbine off (Tables 7A and 7C). Secondly, whenthe inlet was passed with the turbine off, a larger pro-portion of individuals relocated in the upper stratumthan when the turbine was on. For example, 10% ofadults relocated from a lower to a medium height classafter inlet passage at either 2/3 or 3/3 with the turbineoff (Tables 6A and 6B). The same movements wereobserved in nymphs, but to a lesser extent, i.e., 3.3%(Table 6C). In a similar fashion, both adults (1.5%, Ta-ble 6A: 8.6%, Table 6B) and nymphs (1.5%, Table 6C)relocated from median to upper height class after inletpassage with the turbine off. Individuals present in the

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lower height class that relocated in the median heightclass probably actively relocated themselves, suggest-ing an active behavior that occurred following the inletpassage. Adults, which are typically more mobile thannymphs, relocated in larger proportions than nymphs.

When the turbine is on, another mechanism maycome into effect. Lacasse et al. (1994, 2000) proposedthe concept of insect capture efficiency (i.e., the ratioof the number of individuals collected by the machineto the total number of individuals initially present onthe plant) as the result of (1) the insect dislodging effi-cacy (i.e., % of individuals removed from the plantsunder the effect of air flow) and (2) the insect col-lection ratio (i.e., % of individuals picked up by anycollecting device installed on the machine). While thefirst parameter is valid for our system, the latter doesnot apply because many parts of strawberry plants lieclose to the soil and collecting devices would harmthe plants or the fruit. Although this reasoning mightbe valid for Colorado Potato Beetle larvae or adultsfeeding on potato plants, we argue that dislodgingtarnished plant bugs from strawberry plants (withoutcollecting them out) would have marginal effect onnymph and adult tarnished plant bug mortality: dis-lodged individuals would easily climb or fly back tothe plants. Furthermore, it should be noted that inmany strawberry cultivars a large proportion of fruitlies on the ground. Individuals dislodged from theplant and fallen on the ground would have feeding oroviposition resources nearby.

In conclusion, our vacuum apparatus removed ca.60% of the nymphs and 47% of adults from strawberryplants in a test bench environment. The optimal set-upwas a passage at 4 km h−1 with the inlet set at 2/3 ofthe canopy and it is likely that these results will be thesame in field conditions. Further engineering refine-ments or a better timing (in reference to the presenceof insects on the plants) of passage in the field shouldincrease the efficiency of the method.

Acknowledgements

We acknowledge B. Rancourt, S. Bellerose, N.Prud’homme, R. Lamontagne, B. Lacasse and P.-M. Roy for technical help. S. Côté helped inanalyzing the data. Drs. B. Panneton (Agricul-ture and Agri-food Canada, Saint-Jean-sur-Richelieu,Québec, Canada), C. Laguë (Laval University, Ste-Foy, Québec, Canada) and S. Hellqvist (Sweden)

commented on an early version of the manuscript. Pre-mier Tech Inc. (Rivières-du-Loup, Québec, Canada)provided a Biovac inlet and metal tubing. This iscontribution No 335/2000.07.01R of the Agricultureand Agri-Food Canada Horticultural Research andDevelopment Centre at Saint-Jean-sur-Richelieu.

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