Crop Protection 23 (2004) 801–809

ARTICLE IN PRESS

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doi:10.1016/j.cro

Laboratory bioassays and field evaluation of insecticides for thecontrol of Anthonomus rubi, Lygus rugulipennis and Chaetosiphon

fragaefolii, and effects on beneficial species, in UKstrawberry production

Jean Fitzgerald*

Horticulture Research International, East Malling, Kent ME19 6BJ, UK

Received 17 July 2003; received in revised form 7 November 2003; accepted 17 December 2003

Abstract

Abamectin, Beauveria bassiana, buprofezin, pymetrozine, tebufenpyrad, acetamiprid and the coded product 60145 were tested in

laboratory bioassays to determine their effects on the strawberry pests Anthonomus rubi, Lygus rugulipennis and Chaetosiphon

fragaefolii and on the predatory species Phytoseiulus persimilis and Chrysoperla carnea. Abamectin, acetamiprid, tebufenpyrad and

60145 were the most effective insecticides against the pests. These four compounds all had some effect on P. persimilis, but

acetamiprid was the least toxic (63% mortality after 48 h). Abamectin, tebufenpyrad and 60145 had no detectable effect on C. carnea

larvae, whereas acetamiprid caused 38% mortality after 72 h. In field experiments where acetamiprid, 60145 and abamectin were

tested against C. fragaefolii, acetamiprid was very effective at reducing numbers of the aphid. Naturally occurring beneficial

anthocorid species were reduced in number but not eliminated in the acetamiprid treatment. In field tests acetamiprid, abamectin

and thiacloprid were less effective against L. rugulipennis than the industry standard chlorpyrifos. Reductions were small but

statistically significant in the acetamiprid and thiacloprid treatments. Fruit damage was also reduced in these treatments. There was

no detectable effect of these insecticides on naturally occurring beneficial species.

r 2004 Elsevier Ltd. All rights reserved.

Keywords: Strawberry; Anthonomus rubi; Lygus rugulipennis; Chaetosiphon fragaefolii; Phytoseiulus persimilis; Chrysoperla carnea; Abamectin;

Beauveria bassiana; Buprofezin; Pymetrozine; Tebufenpyrad; Thiacloprid; Acetamiprid; 60145

1. Introduction

The European tarnished plant bug (strawberrycapsid), Lygus rugulipennis Poppius, the strawberryblossom weevil Anthonomus rubi (Herbst), and thestrawberry aphid Chaetosiphon fragaefolii (Cockerell)are major pests of strawberry in the UK. The biology ofL. rugulipennis in UK strawberry production wasdescribed by Easterbrook (1997). L. rugulipennis feedson strawberry flowers and developing fruit, causingmalformation and consequent downgrading of fruit inlate season strawberries (Easterbrook, 2000); over 50%of fruit can be downgraded as a result of L. rugulipennis

feeding on unsprayed plantations (Cross et al., 1998).

32-843833; fax: +44-1732-849067.

ss: jean.fitzgerald@hri.ac.uk (J. Fitzgerald).

front matter r 2004 Elsevier Ltd. All rights reserved.

pro.2003.12.005

A. rubi lays its eggs singly within a developingstrawberry flower bud in June-bearing strawberriesand severs the bud, so reducing yield; crop loss causedby A. rubi can be great when infestations are severe(Cross and Burgess, 1998). C. fragaefolii produceshoneydew in which sooty moulds grow, leading todowngrading of fruit. This aphid is also a vector of threeserious strawberry viruses (Shanks, 1981). Virus symp-toms are now rarely seen by growers, due to the PlantHealth Propagation Scheme, and to the currentlyeffective chemical control of aphids, but infection witha complex of aphid-transmitted viruses can reduce yield(Craig, 1957; Freeman and Mellor, 1962).Organophosphorus (OP) and carbamate insecticides,

including chlorpyrifos (Dursban) and pirimicarb(Aphox), are currently used to control a range of pestsof strawberry in the UK. The approvals for OP and

ARTICLE IN PRESSJ. Fitzgerald / Crop Protection 23 (2004) 801–809802

carbamate insecticides have recently been reviewed inthe UK, and as a result many uses on soft fruit crops willbe lost. The only currently approved alternatives to OPsare pyrethroids, e.g. bifenthrin (Talstar). The use ofpyrethroids is incompatible with IPM programmes asthey are toxic to predatory mites, including Phytoseiulus

persimilis Athias-Henriot (e.g. Hassan et al., 1987),which is used in strawberry as a biocontrol agent forTetranychus urticae (Koch), the two-spotted spider mite(Easterbrook, 1992). Predatory insects such as larvae ofChrysoperla carnea (Stephens), a green lacewing, couldplay an important part in controlling aphid numbers(Benuzzi et al., 1992; Easterbrook and Fitzgerald,unpublished results) if the insecticides used to controlother pests allow their survival. However, pyrethroidsare also toxic to this predator (Hassan et al., 1987).Other beneficial insects found naturally in strawberryplantations (Easterbrook, 1998), as well as those thatcan be artificially released (both reviewed by Cross et al.,2001), may also play a role in reducing pest numbers ifselective rather than broad-spectrum insecticides areused.This project was designed to identify insecticides that

are effective at controlling L. rugulipennis, C. fragaefolii

and A. rubi, but are not harmful to beneficialarthropods, especially P. persimilis and larvae ofC. carnea. Subject to obtaining Specific Off LabelApproval (SOLA) or on-label/full approval to permittheir use, these insecticides could be integrated into pestmanagement programmes where beneficial species areconserved and the use of biocontrol techniques ismaximised.

2. Materials and methods

2.1. Insecticides

The insecticides used in these experiments wereselected by focusing on classes of compounds withdifferent modes of action. The insecticides chosen forlaboratory bioassays were: abamectin (Dynamec,19 g a.i. l�1 EC, Syngenta Bioline) at 0.25ml of for-mulated compound per litre; Beauveria bassiana (Bota-niGard, 22% a.i. w/w WP, Emerald BioAgriculture) at1.25 g l�1; buprofezin (Applaud, 250 g a.i. l�1 SC,Syngenta) at 0.3ml l�1; pymetrozine (Plenum, 25% a.i.w/w WP, Syngenta) at 0.8 g l�1; tebufenpyrad (Masai,20% a.i. w/w WP, BASF) at 0.5 g l�1; the coded product60145 (200 g a.i. l�1 SC, BASF) at 0.12ml l�1 andacetamiprid (20% a.i. w/w SP, Certis) at 0.25 g l�1.Industry standards used in the assays were chlorpyrifos(Dursban, 480 g a.i. l�1 EC, Dow) at 1.5ml l�1 forA. rubi and L. rugulipennis, and pirimicarb (Aphox,50% a.i. w/w, WG, Syngenta) at 0.56 g l�1 forC. fragaefolii.

2.2. Laboratory bioassays of pest species

2.2.1. A. rubi

Weevils were collected from infested strawberryplantations at HRI East Malling using a petrol-enginedportable garden sweeper/vacuum, modified as describedby Macleod et al. (1994), and sorted in the laboratory.The inner sides of Petri dishes (9 cm diameter) were

painted with Fluon (a PTFE suspension with a lowcoefficient of friction), and allowed to dry; this materialprevented weevils from climbing out of the dishes. Forall except the pymetrozine treatment, five weevils wereplaced in a Petri dish and sprayed with insecticidesunder a Burkard Precision Sprayer (Burkard Manufac-turing Co., Ltd., Rickmansworth, UK), linked to acomputer. At the settings used the sprayer delivered avolume of 2 ml cm�2 and gave a deposit pattern similarto that of high volume field sprayers. Distilled water wasused as the non-toxic control and chlorpyrifos as theindustry standard. Ten individuals were sprayed pertreatment, and the experiment was repeated five times.After spraying, weevils were transferred immediately to5.5 cm diameter Petri dishes containing damp filterpaper and petals were removed from untreated straw-berry flowers. One weevil was placed in each dish. Thefilter paper was kept moist throughout the experiment.For the pymetrozine (feeding inhibitor) treatment,

strawberry flowers were sprayed in the Burkard sprayer,as described above. Once dry, each flower stem wasplaced in water in a small lidded pot (diameter 4.5 cm),through a hole drilled in the lid, and placed in a plasticbox (7� 7� 7.5 cm3). A weevil was added to each box.A water control was set up in the same way. Ten flowerswere sprayed per treatment, and the experiment wasrepeated five times.All treated insects were kept in a constant tempera-

ture room at 20�C with an 18L:6D photoperiod. Forboth experiments, mortality of weevils was recorded 24and 48 h after treatment. In the pymetrozine assayrecords were also taken 96, 120, 144 and 168 h aftertreatment.

2.2.2. L. rugulipennis

Adult and immature L. rugulipennis were collected bysweep net sampling on various weed species, and by tapand suction sampling on strawberry plots at HRI EastMalling.Adult L. rugulipennis were dipped in insecticides. The

dipping pots consisted of plastic open-ended tubes(2� 7.5 cm2) with fine nylon gauze covering one end,and a plastic cap with several fine holes drilled throughit covering the other. The gauze covered end of the potwas dipped into the insecticide until all the insects wereimmersed. Excess insecticide was then drained off andthe tube and contents blotted on filter paper. Distilledwater was used as the non-toxic control and chlorpyrifos

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as the industry standard. Ten individuals were dippedper treatment replicate, and the experiment was repeatedfive times. Individuals were removed from the tubes andconfined individually on flowers of scentless mayweed(Tripleurospermum inodorum) standing in water asdescribed above for strawberry flowers.The effect of buprofezin (an IGR) was tested only on

nymphal L. rugulipennis, with water and industrystandard (chlorpyrifos) controls. Treatmenttechniques were as for adults, except the nymphalstadium was noted before treatment. Ten individualswere dipped per treatment, and the experiment wasrepeated twice.All treated insects were kept in a constant tempera-

ture room at 20�C with an 18L:6D photoperiod. Adultmortality was recorded 24 and 48 h after treatment. Forthe nymphal bioassay, evidence of successful moultingwas recorded, and recording continued every 24 h untilthe nymph became adult or died.

2.2.3. C. fragaefolii

C. fragaefolii, collected from infested strawberryplants at HRI East Malling, were reared on strawberryplants in a gauzehouse at ambient temperature. Aphidswere removed from these culture plants for thebioassays.Capillary matting was cut to fit inside 9 cm diameter

Petri dishes. The matting was kept wet, and leaf discs(2.7 cm diameter) from the youngest, fully expandedstrawberry leaves taken from potted plants in an insect-proof glasshouse, were placed on the matting, ventralsurface up. Ten first or second instar aphids were placedon each leaf disc 24 h before spraying, to enable them tosettle and start feeding. Each leaf disc was checkedimmediately prior to spraying to record numbers ofaphids remaining on the leaf. Leaf discs were removedfrom the capillary matting, placed in Petri dishes, andsprayed with insecticides under the Burkhard sprayer.Distilled water was used as the non-toxic control andpirimicarb as the industry standard. After spraying, thediscs were returned to the original Petri dishes. Eachtreatment was replicated five times, and the experimentwas repeated four times.All treated insects were kept in a constant tempera-

ture room at 20�C with an 18L:6D photoperiod. At 24and 48 h after treatment the numbers of live and deadaphids on each leaf disc were recorded. Except in the B.

bassiana treatment, all dead aphids were removed fromthe leaf after each record. In the B. bassiana treatmentmortality was also assessed 72 h after treatment.In a separate experiment, 60 aphids were sprayed with

B. bassiana as above, and 25 with water as the controltreatment. Eight days after treatment (DAT), deadaphids were removed from the leaf and kept on moistfilter paper to determine if they were infected with thefungus.

2.3. Laboratory bioassays of beneficials

2.3.1. P. persimilis

Mites were purchased from Biological Crop Protec-tion, Wye, UK. Adult female mites were placed dorsalside down onto double-sided sticky tape on microscopeslides, using a fine paintbrush. Ten mites were placed oneach slide. Four replicates of 10 mites were used for eachtreatment. Treatments were 60145, acetamiprid, aba-mectin, tebufenpyrad, a water control, and chlorpyrifosas the industry standard. Slides were dipped for 30 s andwere allowed to dry. Slides from each treatment wereplaced into a separate plastic box containing dampabsorbent paper to maintain humidity. The boxes wereplaced into a constant temperature room at 20�C withan 18L:6D photoperiod.Mortality was assessed at 17, 24 and 48 h after

treatment by inspection under a stereo microscope.Mites were classified as alive if their mouthparts wereseen to move when the mite was touched with a finepaint brush.

2.3.2. C. carnea larvae

Chrysopid larvae (second instar) were purchased fromBiological Crop Protection, Wye, UK. Larvae wereplaced individually in small Petri dishes (5 cm diameter),and sprayed under the Burkard sprayer. Treatmentswere as for P. persimilis. Twenty-seven larvae were usedper treatment, and were sprayed in batches of nineindividuals. After spraying, the larvae were placed intospecimen tubes (7.5� 2 cm2), and provided with the peaaphid Acyrthosiphon pisum (Harris) as prey. The tubeswere placed into a constant temperature room at 20�Cwith an 18L:6D photoperiod.Mortality was assessed at 24, 48 and 72 h after

treatment. Larvae were classified as ‘moribund’ if theywere alive, but not moving or feeding normally.

2.4. Field experiment on June-bearing strawberries

This experiment was undertaken on variety EM791,grown in double rows through polythene mulch onraised beds at HRI East Malling. Plants were 0.4mapart within and between rows. The beds were plantedat 1.8m centres. The experiment was designed todetermine the effects of insecticides on C. fragaefolii

and naturally occurring beneficial species. There werefive treatments, and five replicates per treatment,arranged in a randomised complete blocks design. Eachtreatment plot consisted of two beds of 2� 17 plants,with plots separated by 2� 5 guard plants. Thetreatments were abamectin, 60145, acetamiprid, pirimi-carb and an untreated control. Insecticides were appliedusing a Hardi Mini tractor-driven sprayer, at a rate of1000 l ha�1 on 1 June. Concentrations of insecticides in

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100 l water were: abamectin 25ml; 60145 12ml; acet-amiprid 25 g; pirimicarb 56 g.Samples for aphids consisted of 20 trifoliate leaves per

plot. One leaf was taken from each of 20 plants, 1 daypre-treatment, and 3 and 11 DAT. Leaves wereexamined in the laboratory and numbers of aphidscounted under a stereomicroscope.Suction samples for beneficial arthropods were taken

on 20 plants per plot, 3 and 11 DAT. Different plantswere sampled on each occasion to ensure that anydepletion of any less-mobile beneficials from plants inthe first sample did not affect the second sample.Samples were examined under a stereo-microscope inthe laboratory and numbers of beneficial species wererecorded.

2.5. Field experiments on everbearer strawberries

This experiment was undertaken on cv Bolero, grownin double rows through polythene mulch on raised beds,at HRI East Malling. The experiment was designed todetermine the effects of insecticides on L. rugulipennis

and naturally occurring beneficial species. There werefive treatments and five replicates per treatment in arandomised complete blocks design. Each treatmentplot consisted of two rows of 20 plants, planted 0.5mapart in the row. The rows were 0.4m apart on the bedsand the beds were planted at 6m centres. Each plot wasseparated from neighbouring plots by a 5m gap withinthe bed. The treatments were acetamiprid, abamectin,thiacloprid (Calypso, 480 g a.i. l�1 SC, Bayer), chlorpyr-ifos, and an untreated control. Concentrations ofinsecticides in 100 l water were: abamectin 25ml;acetamiprid 25 g; thiacloprid 25ml; chlorpyrifos100ml. Insecticides were applied using a Hardi Minitractor-driven sprayer, at a rate of 1000 l ha�2 on 31July.Pre-treatment assessment of L. rugulipennis was done

by tap sampling 10 plants per plot. Dislodged insectswere caught in a bowl, counted and returned to theplants. The first post-treatment sample at 3 DAT forboth L. rugulipennis and beneficial insects was also doneby tap sampling, and the arthropods were returned tothe plants so that numbers were not depleted early in theexperiment. Other samples (at 7 and 17 DAT) weretaken using a suction sampler on 10 plants per plot.Arthropods were taken to the laboratory, sorted andcounted under a binocular microscope.On the day of spraying a sample of 20 recently opened

flowers was tagged to enable timing of fruit developmentto be followed post-treatment. Thirty ripe fruits werepicked from each plot 24 DAT and 50 ripe fruits at 30and 38 DAT. These fruits were graded into damagecategories as described by Easterbrook (2000). Many ofthe flowers tagged at the time of spraying had developedto ripe fruit by 24 DAT and the remainder by 30 DAT.

2.6. Statistical analysis

For the A. rubi and L. rugulipennis bioassays, datawere analysed using a basic binomial generalised linearmodel, which examined proportions killed directlywithout transformation of the data. The means werecompared using a simple test of the normal approxima-tion to the binomial distribution. The time to death forthose L. rugulipennis larvae reaching the adult stagefollowing treatment with buprofezin was subjected toANOVA. In the C. fragaefolii bioassays, where manyaphids left the leaf during the experiment, an analysis ofdeviance was performed for the proportion of aphidsmissing and dead at 24 and 48 h after treatment. Thenumbers missing after 24 h were calculated from thenumbers remaining on the leaf at 24 h compared withthe number before spraying. The number dead after 24 hwas recorded as a proportion of those remaining on theleaf. The same was done for the 48 h record. For thebioassays of P. persimilis and C. carnea larvae, datawere also subjected to an analysis of deviance.In the field experiments counts of pest and beneficial

species were transformed log10 and transformed anduntransformed data for each species/taxon were sub-jected to ANOVA to determine if there were anytreatment effects. The nature of the differences betweentreatments was such that transformation did not changethe interpretation of the data, and untransformed meansare given in the tables. For analysis of percentage fruit ineach damage category resulting from feeding by L.

rugulipennis, data were arc sine transformed beforeANOVA.

3. Results

3.1. Laboratory bioassays of pests

3.1.1. A. rubi

Chlorpyrifos caused 100% mortality within 24 h, butthe acetamiprid and tebufenpyrad treatments were nomore effective than the water control (Table 1). Theeffects of 60145 and abamectin were intermediate andwere significantly different from each other and from thewater and industry standard controls. At 48 h aftertreatment, mortality in the 60145 treatment hadincreased to 84%. Acetamiprid and tebufenpyrad werestill not significantly different to the water control.Mortality in the pymetrozine treatment varied greatly

between assays (e.g. at 120 h post-treatment from 0 to80% between the five assays) and the data were notsuitable for formal statistical analysis. It is possible thatthis variability was the result of differences in feedingstatus of weevils collected from the field at differenttimes for the assays. Weevils that had previously fedwould be able to withstand a longer period without

ARTICLE IN PRESSJ. Fitzgerald / Crop Protection 23 (2004) 801–809 805

feeding in the feeding inhibitor treatment. The meanpercentage mortality was around 50% 120 h aftertreatment, compared with 10% for the water controls.From this result it would appear that any effects ofpymetrozine are likely to be too slow acting to preventblossom damage by A. rubi, unless other behaviouraleffects, not tested in this assay, also prevent them fromegg laying.

3.1.2. L. rugulipennis

With the exceptions of the water control andtebufenpyrad treatments, all the other insecticides killedalmost all L. rugulipennis adults, although the speed ofkill was different (Table 2). At 24 h after treatment,60145 and chlorpyrifos gave 100%, and acetamiprid98% mortality. Effectiveness of the other treatmentsdeclined in the order abamectin, tebufenpyrad and watercontrol. Mortalities in these treatments were signifi-cantly different from each other and from the three mosteffective treatments, using a simple test of the normalapproximation to the binomial distribution. By 48 hafter treatment abamectin also gave 96% mortality,indicating a slower mode of action for this insecticide.Chlorpyrifos killed all L. rugulipennis nymphs within

24 h. There was no difference in the numbers of nymphsthat reached the adult stage in the water control and thebuprofezin treatments. There was no significant effect oftreatment on time to death. The mean time to death indays (SE in parentheses) in the control and buprofezintreatments in assay one were 10.63 (4.14) and 7.62(2.97), and in assay two were 10.00 (3.51) and 12.00(5.44).

Table 1

Proportion of Anthonomus rubi dead 24 and 48 h after treatment with

insecticides in laboratory bioassays (n ¼ 50)

Treatment 24 h (SE) 48 h (SE)

Water 0.04 (0.03) 0.06 (0.03)

60145 0.56 (0.06) 0.84 (0.05)

Abamectin 0.28 (0.06) 0.32 (0.06)

Acetamiprid 0.10 (0.04) 0.16 (0.05)

Tebufenpyrad 0.10 (0.04) 0.16 (0.05)

Chlorpyrifos 1.00 —

Table 2

Proportion of Lygus rugulipennis adults dead 24 and 48 h after

treatment with insecticides in laboratory bioassays (n ¼ 50)

Treatment 24 h (SE) 48 h (SE)

Water 0.06 (0.03) 0.12 (0.05)

60145 1.00 —

Abamectin 0.66 (0.07) 0.96 (0.03)

Acetamiprid 0.98 (0.02) 0.98 (0.02)

Tebufenpyrad 0.22 (0.06) 0.30 (0.06)

Chlorpyrifos 1.00 —

3.1.3. Chaetosiphon fragaefolii

The B. bassiana treatment was excluded from theanalysis because the method of recording was differentfor this insecticide, primarily because of its expectedslow mode of action.At 24 h after treatment there was a significant effect of

treatment on the number of aphids missing from theleaves (Po0:01) (Table 3). This was mostly as a result ofthe pymetrozine treatment, where more than 50% of theaphids were lost from the leaves. When this treatmentwas excluded from the analysis there was still asignificant effect of treatment (Po0:05), because of60145. This analysis shows that pymetrozine and 60145were repellent to the aphids, causing them to stopfeeding and disperse from the leaf. At 24 h aftertreatment there was also a significant effect on mortalityof those aphids remaining on the leaf (Po0:01).Tebufenpyrad, acetamiprid and pirimicarb killed 96%,86% and 88% of remaining aphids respectively.After 48 h there was still a significant effect of

treatment on both numbers missing and mortality ofaphids remaining on the leaf (Po0:05). In the pyme-trozine treatment 32% of the aphids present at 24 h haddispersed from the leaves, indicating that repellency hadpersisted. Thirty percent of aphids in the abamectintreatment were also lost from the leaves. Mortality ofremaining aphids was high in the acetamiprid, abamec-tin and pirimicarb treatments (100%, 82% and 100%mortality, respectively). Buprofezin had little effect onaphid numbers at either 24 or 48 h after treatment.In the experiment to determine if B. bassiana would

infect aphids under the conditions of the assay, after 8days 14 out of 25 aphids had died in the water control,and 33 out of 60 in the B. bassiana treatment. Of these,one and 28 aphids were found to be infected with thefungus respectively.There was no evidence that the B. bassiana treatment

had any repellent effect on C. fragaefolii, with amaximum of three aphids lost in a 24 h period in anyof the B. bassiana assays and two in the controls. Theaverage mortality over 72 h in three bioassays was 10%in the control treatment and 45% in the B. bassiana

treatment.These results indicate that under the conditions of the

experiment B. bassiana was not as effective as acetami-prid, tebufenpyrad or abamectin at reducing C. fragae-

folii numbers. It seems likely that in the drier conditionsexperienced in field plantings this fungus would be evenless effective.

3.2. Laboratory bioassays of beneficials

3.2.1. Phytoseiulus persimilis

Mortality of P. persimilis in the water control was34% after 48 h, indicating that the assay system usedwas stressful for this species. All mites treated with

ARTICLE IN PRESS

Table 5

Mean numbers of Chaetosiphon fragaefolii per 20 leaves in insecticide

treated and untreated June-bearing strawberry plots

Treatment Mean numbers of aphids per 20 leaves

Pre-treatment 3 DAT 11 DAT

60145 213 150 35

Acetamiprid 249 2 0.4

Abamectin 216 107 27

Pirimicarb 288 1 0.4

Untreated 297 194 42

LSD 117.6 69.7 14.7

Po0:001; 16 d.f.

J. Fitzgerald / Crop Protection 23 (2004) 801–809806

tebufenpyrad and chlorpyrifos were dead within 17 h oftreatment. An analysis of deviance showed thatthere was a significant difference (Po0:05) betweenthe 60145 treatment and the water control 24 h aftertreatment (Table 4). By 48 h after treatment there wasno difference between the 60145 and abamectin treat-ments, with over 90% mortality in both. Acetamipridwas least toxic to P. persimilis, with 63% mortality after48 h.

3.2.2. C. carnea larvae

Chrysopid larvae were relatively tolerant to theinsecticides tested; there was no effect of 60145,abamectin or tebufenpyrad on mortality. At 24 h aftertreatment with chlorpyrifos 56% of larvae weremoribund and 40% were dead; in the acetamipridtreatment 35% were moribund, but none were dead. At48 h after treatment in the chlorpyrifos treatment 44%were moribund and 52% dead, and in the acetamipridtreatment 4% were moribund and 15% dead. By 72 hafter treatment all moribund individuals had died (Table4). Although time to death was quite long in thechlorpyrifos assay, many individuals were moribundand not feeding within 24 h of treatment, and so wouldnot be of practical use as biocontrol agents. Acetamipridwas moderately toxic to chrysopid larvae, with 38%mortality 72 h after treatment.

Table 3

Proportions of Chaetosiphon fragaefolii missing and dead 24 and 48 h afte

138–153)

Treatment 24 h after treatment (SE)

Proportion missing Proportion d

Water 0.07 (0.05) 0.00

60145 0.45 (0.09) 0.51 (0.09)

Abamectin 0.21 (0.07) 0.68 (0.07)

Acetamiprid 0.15 (0.06) 0.86 (0.05)

Tebufenpyrad 0.13 (0.06) 0.96 (0.02)

Pymetrozine 0.55 (0.09) 0.37 (0.09)

Buprofezin 0.17 (0.07) 0.23 (0.06)

Pirimicarb 0.12 (0.06) 0.88 (0.04)

Table 4

Proportions of Phytoseiulus persimilis adults and Chrysoperla carnea larvae d

P. persimilis and n ¼ 27 for C. carnea)

Treatment Phytoseiulus persimilis

24 h (SE)

Water 0.12 (0.05)

60145 0.64 (0.07)

Abamectin 0.49 (0.08)

Acetamiprid 0.42 (0.08)

Tebufenpyrad 1.0

Chlorpyrifos 1.0

3.3. Field experiment on June-bearing strawberries

3.3.1. Chaetosiphon fragaefolii

Acetamiprid and pirimicarb were effective at reducingaphid numbers, with over 99% reductions 3 DATcompared with numbers in the controls (Table 5). Thenumbers remained low on these treatments 11 DAT.60145 and abamectin had no detectable effect on aphidnumbers when compared with the control on eithersample date. Aphid numbers were decreasing on allplots during this experiment, with an 86% reductionafter 12 days in the untreated plots.

r treatment with insecticides in laboratory bioassays (n ranged from

48h after treatment (SE)

ead Proportion missing Proportion dead

0.03 (0.02) 0.05 (0.03)

0.28 (0.10) 0.61 (0.13)

0.30 (0.10) 0.82 (0.11)

0.23 (0.12) 1.00

0.00 0.21 (0.24)

0.32 (0.09) 0.72 (0.12)

0.12 (0.04) 0.25 (0.06)

0.28 (0.13) 1.00

ead after treatment with insecticides in laboratory bioassays (n ¼ 40 for

Chrysoperla carnea larvae

48 h (SE) 72 h (SE)

0.34 (0.07) 0.00

1.0 (0.02) 0.04 (0.04)

0.90 (0.05) 0.05 (0.04)

0.63 (0.07) 0.38 (0.10)

— 0.09 (0.06)

— 0.92 (0.05)

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3.3.2. Beneficials

The mean numbers of the most abundant beneficialarthropods collected from plants in each treatment areshown in Table 6. ANOVA showed significantly fewerparasitoids in the 60145 and acetamiprid treatments 3DAT (Po0:001), and in these two treatments plus thepirimicarb treatment 11 DAT (Po0:001); by this timethis result may be due to lack of hosts. Anthocoridnumbers (nymphs plus adults) were significantly lowerin the acetamiprid treatment compared with the control3 DAT (Po0:05); nymphal numbers were also lower inthe acetamiprid treatment 11 DAT, but the differencewas not quite significant (P ¼ 0:051). There were nosignificant differences in numbers of any other bene-ficials in any of the treatments.

3.4. Field experiment on everbearer strawberries

3.4.1. L. rugulipennis

Chlorpyrifos had eliminated L. rugulipennis nymphsfrom the treated plots 3 DAT (Table 7). The numbers ofboth nymphs and adults remained very low throughoutthe experiment in this treatment. There was a small butsignificant reduction of L. rugulipennis nymphs in the

Table 6

Mean numbers of the most abundant beneficial arthropods collected in su

treatment with different insecticides

Treatment Spiders Parasitoids Coccin

3 11 3 11 3

60145 8.2 8.2 12.6 12.4 7.2

Acetamiprid 10.8 8.2 23.8 27.2 6.4

Abamectin 6.6 6.2 58.2 51.8 6.6

Pirimicarb 8.4 7.4 64.6 25.4 3.2

Untreated 8.2 7.8 76.2 45.2 6.8

LSD 4.6 3.7 21.3 17.6 3.5

Po0:05; 16 d.f.

Coccinellid numbers for 3 DAT are larvae only and for 11 DAT are larvae

Table 7

Mean numbers of Lygus rugulipennis nymphs and adults recorded from inse

Treatment Mean number per 10 plants

pre-trt 3 DAT

ny ny+

Acetamiprid 43.0 24.0

Abamectin 37.0 35.8

Thiacloprid 39.4 25.4

Chlorpyrifos 44.4 0

Untreated 43.2 36.6

LSD 18.1 10.1

Po0:05; 16 df or +12 df

Samples were collected pre-treatment and 3 DAT by tap sampling and 7 an

acetamiprid treatment 3 and 7 DAT (Po0:05), and asmall but significant effect of thiacloprid on nymphs at 3DAT. Abamectin had no effect on L. rugulipennis

nymphs. Other than chlorpyrifos, none of the insecti-cides reduced numbers of L. rugulipennis adults on anysample date.

3.4.2. Beneficials

Beneficials recorded in the plots (with range of meannumbers per 10 plants 17 DAT in parentheses) werespiders (19–28), nabids (1–2), anthocorids (5–18),chrysopid larvae (1–2) and anystid mites (1–3). Withthe exception of chrysopid larvae, which had beeneliminated from the chlorpyrifos treatment 7 DAT,there were no significant differences in beneficialarthropod numbers in any treatment compared withthe control.

3.4.3. Fruit damage

Fruit damage was significantly lower in the chlorpyr-ifos, acetamiprid and thiacloprid treatments comparedwith the control in samples taken 24 DAT (Table 8). Inthe two later samples damage was significantly loweronly in the chlorpyrifos treatment.

ction samples on June-bearing strawberry plots 3 and 11 days after

ellids Anthocorid ny Anthocorid ads

11 3 11 3 11

5.2 9.0 6.6 1.4 2.4

3.4 1.8 3.6 0.6 2.2

2.0 6.4 9.2 1.4 4.4

2.2 10.8 10.6 6.4 2.2

3.2 10.2 17.0 2.8 4.4

3.1 8.9 8.8 2.1 3.5

plus adults.

cticide treated and untreated everbearer strawberry plots

7 DAT 17 DAT

ny+ ad+ ny ad

26.4 2.2 27.8 7.0

49.2 5.6 28.2 14.6

34.2 2.8 26.4 9.2

0.4 0 9.6 1.4

49.2 6.4 28.6 11.0

16.9 12.0 5.4

d 17 DAT by suction sampling.

ARTICLE IN PRESS

Table 8

Percentage and arc sine transformed data for fruit, cv Bolero, in moderate plus severe damage categories from insecticide treated and untreated plots

Treatment 24 DAT 30 DAT 38 DAT

% Trans % Trans % Trans

Acetamiprid 1.3 0.013 6.8 0.068 2.8 0.056

Abamectin 16.0 0.162 12.0 0.121 6.6 0.133

Thiacloprid 4.0 0.040 6.8 0.068 4.4 0.088

Chlorpyrifos 0.7 0.007 0.4 0.004 1.6 0.032

Untreated 14.0 0.141 10.0 0.100 4.4 0.088

LSD 0.094 0.081 0.043

P (16 df) o0.01 0.07 o0.01

J. Fitzgerald / Crop Protection 23 (2004) 801–809808

4. Discussion

The laboratory bioassays assessed short-term acutetoxicity. The insects were covered with the test chemical,so if they survived a particular insecticide in thelaboratory they are unlikely to be directly affected byit in a field application. Laboratory bioassays arequicker and less labour intensive than field experiments,and are thus a useful way of screening a range ofinsecticides to determine which should be taken forwardto full field evaluation. However, any effects onfecundity, etc. will not be detected in short-termlaboratory bioassays. Also, insecticides that are toxicin laboratory bioassays may be less effective in the field,where insects may not experience the same degree ofdirect exposure as in laboratory bioassays, and may alsobe able to avoid residues on the plant.In laboratory bioassays abamectin, tebufenpyrad, the

coded product 60145 and acetamiprid all reducednumbers of A. rubi, L. rugulipennis and C. fragaefolii,and 60145, abamectin and tebufenpyrad showed noacute toxicity to chrysopid larvae. Abamectin has beenreported to be of low toxicity to other chrysopid species(Ribeiro et al., 1988; Tzeng and Kao, 1996). 60145 hasbeen reported to have different effects on C. carnea

larvae depending on test method; toxicity was classed ashigh in residual tests (Toda and Kashio, 1997).Abamectin, 60145 and acetamiprid were damaging toP. persimilis, but acetamiprid was the least toxic with63% mortality 48 h after treatment. Tebufenpyrad wasas toxic as the industry standard with 100% mortalityafter 24 h. There are few reports of the effects of theseinsecticides on P. persimilis. Zhang and Sanderson(1990) reported that abamectin was of low toxicity,but that reproduction was reduced, whereas Stolz (1994)categorised abamectin as toxic to P. persimilis in residuetests. Tebufenpyrad and 60145 are reported to be highlytoxic to other species of phytoseiid mites (CostaComelles et al., 1997; Grout et al., 1997).In the field experiments, only pirimicarb and acet-

amiprid effectively reduced numbers of C. fragaefolii.

The numbers of aphids were decreasing throughout theexperiment in the other treatment plots, including thecontrol. This decline in aphid populations has beenobserved in other field experiments (Fitzgerald, unpub-lished results), and may be due to the effects of naturalenemies, entomopathogens, or to the physiologicalcondition of the plants.Of the naturally occurring beneficial species assessed,

the numbers of parasitoids were significantly lower inthe 60145, acetamiprid and pirimicarb treated plotswhen compared with the untreated plots. In theacetamiprid and pirimicarb treated plots this wasprobably because aphid numbers had been reduced bythe insecticide applications. Anthocorid numbers werealso significantly lower, but not eliminated, in theacetamiprid treatment when compared with the un-treated plots, which again may be a response to preydensity.Chlorpyrifos, the industry standard, eliminated L.

rugulipennis from the treated plots 3 DAT, and numbersremained very low throughout the experiment. Therewere also small but significant reductions of L.

rugulipennis in the thiacloprid (31%) and acetamiprid(34%) treatments 3 DAT. By 7 DAT there was nodifference between the thiacloprid treatment and thecontrol. By 17 DAT the only significant difference fromthe control was in the chlorpyrifos treatment. In thelaboratory bioassays acetamiprid and abamectingave over 90% mortality of L. rugulipennis adults. Thecontrasting poor control by these compounds in the fieldexperiments may be due to lack of effect of theinsecticides on nymphs or eggs, or to low persistenceenabling nymphs that hatched successfully to survive.When fruit that had been susceptible to feeding

damage by L. rugulipennis was assessed, fruit damagein the moderate plus severe categories (Easterbrook,2000) was significantly lower in the chlorpyrifos,thiacloprid and acetamiprid treatments compared withthe untreated control 24 DAT; the reduction in damagewas less in the acetamiprid and thiacloprid treatmentthan in the chlorpyrifos treatment. By 38 DAT, with the

ARTICLE IN PRESSJ. Fitzgerald / Crop Protection 23 (2004) 801–809 809

exception of the chlorpyrifos treatment, there were nodifferences in these damage categories among thetreatments. This finding is in line with the L. rugulipennis

numbers found in the different treatments at the firstpost-treatment sample, at the time when this damagewould have been caused.Apart from a reduction in chrysopid numbers in the

chlorpyrifos treatment, there appeared to be no detri-mental effect of any treatment on naturally occurringbeneficial species. In the experiment on everbearerstrawberries there was no evidence of the short-termreduction in anthocorid numbers seen in the June-bearerexperiment.These field experiments showed that acetamiprid was

effective at controlling C. fragaefolii, and any effect onnaturally occurring beneficials was short-lived. Thiscompound was also the least toxic of those testedagainst P. persimilis and showed no detectable effect onC. carnea larvae. None of the other insecticides reducedC. fragaefolii numbers. The only insecticide thateliminated L. rugulipennis was the industry standard.There was a small but significant reduction of L.

rugulipennis in both the thiacloprid and acetamipridtreatments. Fruit damage was also reduced in thesetreatments and there was no detectable effect onnaturally occurring beneficials.Thus, of the insecticides tested, acetamiprid showed

promise as a replacement for OPs for control of C.

fragaefolii and L. rugulipennis. Thiacloprid also showedsome promise for the control of L. rugulipennis. Repeatapplications may be needed to target nymphs thatemerge from any eggs that survived the first spray, oradults that migrate into the field after the insecticideapplication.

Acknowledgements

This project was funded by the Horticultural Devel-opment Council. Acetamiprid and the coded product60145 were provided by Certis. Thanks to John Fenlonfor statistical analyses, and to Mike Easterbrook,Jennifer Butcher, Matthew Dilling, Gael Perlet andTom Pope for technical assistance.

References

Benuzzi, M., Manzaroli, G., Nicoli, G., 1992. Biological control

in protected strawberry in northern Italy. IOBC/WPRS Bull. 22,

445–448.

Costa Comelles, J., Bosch, D., Botargues, A., Cabiscol, P., Moreno,

A., Portillo, J., Avilla, J., 1997. Action of some acaricides on

phytoseiids and the red mite Panonychus ulmi (Koch) in apple

orchards. Bol. Sanid. Vegetal. 23, 93–103.

Craig, D.L., 1957. A two-year comparison of virus-free and common

stock strawberry plants. Plant Dis. Rep. 41, 79–82.

Cross, J.V., Burgess, C.M., 1998. Strawberry fruit yield and quality

responses to flower bud removal: a simulation of damage by

strawberry blossom weevil (Anthonomus rubi). J. Hortic. Sci.

Biotechnol. 73, 676–680.

Cross, J.V., Jay, C.N., Easterbrook, M.A., Innocenzi, P., Hall, D.,

Burgess, C.M., 1998. Management of pests of strawberry without

broad-spectrum insecticides. Proceedings of the ADAS/HRI/

EMRA Soft Fruit Conference, 24–25 November 1998, Ashford,

Kent, UK, pp. 29–39.

Cross, J.V., Easterbrook, M.A., Crook, A.M., Crook, D., Fitzgerald,

J.D., Innocenzi, P.J., Jay, C.N., Solomon, M.G., 2001. Review:

natural enemies and biocontrol of pests of strawberry in northern

and central Europe. Biocontrol. Sci. Tech. 11, 165–216.

Easterbrook, M.A., 1992. The possibilities for control of two spotted

spider mite Tetranychus urticae on field grown strawberries in the

UK by predatory mites. Biocontrol. Sci. Tech. 2, 235–245.

Easterbrook, M.A., 1997. The phenology of Lygus rugulipennis, the

European tarnished plant bug, on late-season strawberries, and

control with insecticides. Ann. Appl. Biol. 131, 1–10.

Easterbrook, M.A., 1998. The beneficial fauna of strawberry fields in

the south-east of England. J. Hortic. Sci. Biotechnol. 73, 137–144.

Easterbrook, M.A., 2000. Relationships between the occurrence of

misshapen fruit on late-season strawberry in the United Kingdom

and infestation by insects, particularly the European tarnished

plant bug. Lygus rugulipennis. Entomol. Exp. Appl. 96, 59–67.

Freeman, J.A., Mellor, F.C., 1962. Influence of latent virus on vigour,

yield and quality of British Sovereign strawberries. Can. J. Plant

Sci. 42, 602–610.

Grout, T.G., Richards, G.I., Stephen, P.R., 1997. Further non-target

effects of citrus pesticides on Euseius addoensis and Euseius citri

(Acari: Phytoseiidae). Exp. Appl. Acarol. 21, 171–177.

Hassan, S.A., Albert, R., Bigler, F., Blaisinger, P., Bogensch .utz, H.,

Boller, E., Brun, J., Chiverton, P., Edwards, P., Englert, W.D.,

Huang, P., Inglesfield, C., Naton, E., Oomen, P.A., Overmeer,

W.P.J., Rieckmann, W., Sams^e-Petersen, L., St.aubli, A., Tuset,

J.J., Viggiani, G., Vanwetswinkel, G., 1987. Results of the third

joint pesticide testing programme by the IOBC/WPRS working

group ‘‘Pesticides and Beneficial Organisms’’. J. Appl. Entomol.

103, 92–107.

Macleod, A., Wratten, S.D., Harwood, R.W.J., 1994. The efficiency of

a new lightweight suction sampler for sampling aphids and their

predators in arable land. Ann. Appl. Biol. 124, 11–17.

Ribeiro, M.J., Matioli, J.C., Carvalho, C.F., 1988. Effect of

avermectin-B1 (MK-936) on the larval development of Chrysoperla

externa (Hagen) (Neuroptera: Chrysopidae). Pesqui. Agropecu.

Bras. 23, 1189–1196.

Shanks, C., 1981. Strawberry aphids and strawberry viruses, EB 1012.

Bulletin of Cooperative Extension, College of Agriculture,

Washington State University, 2pp.

Stolz, M., 1994. Efficacy of different concentrations of seven pesticides

on Phytoseiulus persimilis A.-H. (Acarina: Phytoseiidae) and on

Tetranychus urticae K. (Acarina: Tetranychidae) in laboratory and

semifield test. IOBC/WPRS Bull. 17 (10), 49–54.

Toda, S., Kashio, T., 1997. Toxic effect of pesticides on the larvae of

Chrysoperla carnea. Proc. Assoc. Plant Prot. Kyushu 43, 101–105.

Tzeng, C.C., Kao, S.S., 1996. Evaluation on the safety of pesticides to

green lacewing, Mallada basalis larvae. Plant Prot. Bull. Taipei 38,

203–213.

Zhang, Z.Q., Sanderson, J.P., 1990. Relative toxicity of abamectin to

the predatory mite Phytoseiulus persimilis (Acari: Phytoseiidae) and

two spotted spider mite (Acari: Tetranychidae). J. Econ. Entomol.

83, 1783–1790.