Host choice by Aphidius colemani: effects of plants, plant–aphid combinations and the presence of intra-guild predators

Abstract.  1. This study first measured the effect of plant (radish, pepper, and wheat), aphid–plant combination (the green peach aphid Myzus persicae on pepper and radish, and the bird cherry-oat aphid Rhopalosiphum padi on wheat) and the host on which Aphidius colemani was reared (the cotton aphid Aphis gossypii on cucumber, M. persicae on radish and pepper, and R. padi on wheat) on host choice behaviour of the parasitoid and the performance of its offspring. Then, the effect of predator presence ( Coccinella undecimpunctata larvae) on host preference of the wasps was tested.
2. When reared on M. persicae on either radish or pepper , wasps preferred the aphid–plant combination from which they had emerged. Wasps reared on A. gossypii (naïve to all hosts offered) and R. padi preferred to parasitise M. persicae on radish and M. persicae on either radish or pepper, respectively. Rhopalosiphum padi on wheat was the least preferred and also the least suitable host, as determined by offspring body size.
3. Contrary to expectations, the presence of predators did not influence the host choice of A. colemani , even when predator-free plants were offered nearby. Results indicate that wasps are more likely to remain in some host systems but not in others, even when facing risk of predation.
4. Results are discussed in respect to field data and the relative importance of risk of predation and host preference to wasp fitness.     

The effect of previous host plant on the fecundity of Myzus persicae and its ability to transmit beet yellows virus

Myzus persicae transferred to rape produced offspring with higher survival, larger weight and faster development than aphids transferred to beet, irrespective of whether they had been reared on rape or beet. Aphids transferred from rape to beet produced fewer offspring than those reared continuously on rape. On beet, rape-reared adults produced progeny with lower survival, slower development, smaller adult size and lower fecundity than the progeny of beet-reared individuals, but there were no differences in these characteristics associated with host plant after one generation. Aphids from rape were less than half as efficient in transmitting beet yellows virus as aphids reared continuously on beet but after one subsequent generation on beet this difference had disappeared completely. These results are discussed in relation to field conditions.     

Cryptic maternal effects in Hippodamia convergens vary with maternal age and body size

Maternal effects can mold progeny phenotypes in various ways and may constitute ecological adaptations. By examining the effect of oviposition sequence on progeny produced by different size classes of female ladybird beetles (produced by controlling larval access to food), we show that maternal signals can change through adult life and alter the developmental programs of progeny, ostensibly to synchronize their life histories with predictable resource dynamics, thus maximizing maternal fitness. We also show that female body size, as determined by larval food supply, interacts with female age to influence progeny fitness. When fed ad libitum as adults, small females reared with limited food access laid fewer, smaller eggs than large females reared with ad libitum food access. Maternal body size interacted with oviposition sequence to influence progeny development, but the latter had greater impact. Eggs laid later by medium and large females hatched faster than those laid earlier, larvae fed longer in the fourth instar, their pupation period was shorter, total developmental time was reduced, and adults emerged with greater mass, most notably daughters. Oviposition sequence effects on progeny from small mothers were non‐significant for total developmental time and progeny mass. Only large mothers increased egg size over time and egg mass was not consistently correlated with developmental parameters, indicating that progeny phenotype was impacted by other, more cryptic, maternal signals. Such signals appear costly, as food limitation during development constrained not only fecundity and egg size but also maternal ability to manipulate progeny phenotype. The production of faster‐developing offspring that mature to larger sizes late in the oviposition cycle may be adaptive for exploitation of ephemeral aphid outbreaks with predictable dynamics of prey abundance and competition.     

Transgenic Bt maize and Rhopalosiphum padi (Hom., Aphididae) performance

Abstract.  1. The population abundance and age structure of Rhopalosiphum padi , one of the most common maize aphid species, on transgenic Bt (expressing the Cry1Ab protein) and non-Bt isogenic maize was studied in commercial plots during three crop seasons.
2. A higher density of aphids, particularly alates and young nymphs, occurred in Bt plots at very young maize development stages, corresponding to the settlement period, in the 3 years studied. Possible causes are discussed. After this period, there were no differences between Bt and non-Bt maize.
3. Mortality, development, and reproduction of the offspring of alate forms of R. padi and the offspring of different generations of apterous forms fed with Bt maize were evaluated in the laboratory under controlled conditions.
4. The developmental and pre-reproductive times of the offspring of the first generation of alatae were shorter and the intrinsic rate of natural increase ( r _m ) higher when aphids fed on Bt maize. The opposite occurs with the offspring of the first generation of apterous mothers, which have lower nymphal and adult mortality, shorter developmental and pre-reproductive times, a higher effective fecundity rate, and greater r _m , when fed on non-Bt maize. The differences in aphid development on the two cultivars may be linked to changes in host-plant quality due to pleiotropic effects of the genetic modification.
5. No differences on aphid mortality, developmental and pre-reproductive times, fecundity, and r _m were found between the offspring of apterous aphids maintained on Bt or non-Bt maize for several generations.     

Effects of host plant on life‐history traits in the polyphagous spider mite Tetranychus urticae

Studying antagonistic coevolution between host plants and herbivores is particularly relevant for polyphagous species that can experience a great diversity of host plants with a large range of defenses. Here, we performed experimental evolution with the polyphagous spider mite Tetranychus urticae to detect how mites can exploit host plants. We thus compared on a same host the performance of replicated populations from an ancestral one reared for hundreds of generations on cucumber plants that were shifted to either tomato or cucumber plants. We controlled for maternal effects by rearing females from all replicated populations on either tomato or cucumber leaves, crossing this factor with the host plant in a factorial design. About 24 generations after the host shift and for all individual mites, we measured the following fitness components on tomato leaf fragments: survival at all stages, acceptance of the host plant by juvenile and adult mites, longevity, and female fecundity. The host plant on which mite populations had evolved did not affect the performance of the mites, but only affected their sex ratio. Females that lived on tomato plants for circa 24 generations produced a higher proportion of daughters than did females that lived on cucumber plants. In contrast, maternal effects influenced juvenile survival, acceptance of the host plant by adult mites and female fecundity. Independently of the host plant species on which their population had evolved, females reared on the tomato maternal environment produced offspring that survived better on tomato as juveniles, but accepted less this host plant as adults and had a lower fecundity than did females reared on the cucumber maternal environment. We also found that temporal blocks affected mite dispersal and both female longevity and fecundity. Taken together, our results show that the host plant species can affect critical parameters of population dynamics, and most importantly that maternal and environmental conditions can facilitate colonization and exploitation of a novel host in the polyphagous T. urticae, by affecting dispersal behavior (host acceptance) and female fecundity.     

Limited scope for maternal effects in aphid defence against parasitoids

Abstract.  1. A mother's environment frequently affects her offspring's phenotype. Such maternal effects may be adaptive, in particular with respect to pathogens or parasites, for example if maternal exposure increases offspring resistance.
2. In aphids, maternal effects are likely to occur as a result of their telescoping generations. This study investigated whether maternal effects influence the susceptibility of the peach-potato aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), to its parasitoid Diaeretiella rapae (M'Intosh) (Hymenoptera: Braconidae: Aphidiinae).
3. In a first experiment, susceptibility was compared among offspring of aphid mothers that had either no contact to parasitoids, had contact but were not attacked, or were attacked but not mummified. Mothers from the last group had successfully resisted the parasitoid.
4. In a second experiment using two different clones, maternal and progeny environment were manipulated by rearing each generation either on a benign (radish) or a more stressful host plant (silver beet) before progeny exposure to parasitoids.
5. The first experiment revealed no significant effect of the maternal treatment on offspring susceptibility to parasitoids and thus no evidence for trans-generational defence. In the second experiment, maternal environment effects were also weak, yet with a trend towards less susceptible offspring of aphid mothers reared on the more stressful plant. However, there was a significant difference among clones and a strong clone × progeny host plant interaction, illustrating that the outcome of a parasitoid attack may be determined by a complex interplay of genetic and environmental factors.
6. Overall, the results suggest that there is limited scope for maternal effects in aphid defence against parasitoids.     

Influence of adult nutrition on the relationship between body size and reproductive parameters in a parasitoid wasp

Abstract.  1. An important constraint upon life-history evolution in parasitoids is the limit imposed by body size on allocation of limited metabolic resources to different fitness-related physiological functions such as reproduction and survival.
2. The influence of adult nutrition on reproductive and maintenance variables was studied in the synovigenic ectoparasitoid Mastrus ridibundus , and it was determined whether resource allocation to these different functions depends on body size.
3. Over the course of adult life there was a positive relationship between body size and the number of mature eggs in adult females both in the presence and absence of food. However, only in the presence of food did egg maturation rates increase significantly with body size. Starved wasps produced significantly smaller eggs than fed ones, which has not been documented before. Moreover, starved wasps produced fewer offspring than fed wasps, and attacked fewer hosts.
4. The availability of food had a major effect on longevity, with fed females living about 10 times longer than starved ones. There was also a positive relationship between body size and longevity. In starved wasps, this relationship was the same both in the presence and absence of hosts, but in fed wasps there was a positive relationship between body size and longevity in the absence of hosts only. Allocation to initial eggs relative to lifetime progeny production did not decline with body size.
5. The data reveal that in M. ridibundus the trade-off between maintenance and reproduction varies with life expectancy.     

Competition and dispersal in the pea aphid: clonal variation and correlations across traits

Abstract.  1. The presence of an across-species trade-off between dispersal ability and competitive ability has been proposed as a mechanism that facilitates coexistence. It is not clear if a similar trade-off exists within species. Such a trade-off would constrain the evolution of either trait and, given appropriate selection pressures, promote local adaptation in these traits.
2. This study found substantial levels of heritable variation in competitive ability of the pea aphid, Acyrthosiphon pisum Harris (Homoptera: Aphididae), measured in terms of relative survival when reared with a single clone of the vetch aphid, Megoura viciae Buckton (Homoptera: Aphididae).
3. Pea aphids can move to new patches by either flying (longer distance dispersal) or walking (local dispersal) from plant to plant. There was considerable clonal variation in dispersal ability, measured in terms of the proportion of winged offspring produced, and ability to survive away from their host plant.
4. Winged individuals showed longer off-plant survival times than wingless forms of the same pea aphid clone.
5. There was no evidence of a relationship between clonal competitive ability and either measure of dispersal ability, although the power of the test is limited by the number of pea aphid clones used in the trial.
6. However, there was a positive correlation between clonal fecundity and the proportion of winged offspring produced. Although speculative, it is suggested that clones that are more likely to either overwhelm their host plant or attract higher numbers of natural enemies as a result of having higher fecundity are more likely to produce winged morphs.     

Preference and performance of the hyperparasitoid Syrphophagus aphidivorus (Hymenoptera: Encyrtidae): fitness consequences of selecting hosts in live aphids or aphid mummies

Abstract.  1. Theoretical models predict that ovipositional decisions of parasitoid females should lead to the selection of the most profitable host for parasitoid development. Most parasitoid species have evolved specific adaptations to exploit a single host stage. However, females of the aphid hyperparasitoid Syrphophagous aphidivorus (Mayr) (Hymenoptera: Encyrtidae) display a unique and atypical oviposition behaviour by attacking either primary parasitoid larvae in live aphids, or parasitoid pupae in dead, mummified aphids.
2. In the laboratory, the correlation between host suitability and host preference of S. aphidivorus on the host Aphidius nigripes Ashmead parasitising the aphid Macrosiphum euphorbiae (Thomas) was investigated.
3. The relative suitability of the two host stages was determined by measuring hyperparasitoid fitness parameters (survival, development time, fecundity, sex ratio, and adult size of progeny), and calculating the intrinsic rate of population increase ( r _m). Host preference by S. aphidivorus females and the influence of aphid defence behaviour on host selection was also examined.
4. Hyperparasitoid offspring performance was highest when developing from hosts in aphid mummies and females consistently preferred this host to hosts in parasitised aphids. Although aphid defensive behaviour may influence host selection, it was not a determining factor. Ecological and evolutionary processes that might have led to dual oviposition behaviour in S. aphidivorus are discussed.     

Age-related fecundity and sex ratio variation in Apanteles galleriae (Hym., Braconidae) and host effect on fecundity and sex ratio of its hyperparasitoid Dibrachys boarmiae (Hym., Pteromalidae)

Abstract:  Age-related progeny production and sex ratio of Apanteles galleriae Wilkinson, a koinobiont, solitary, larval endoparasitoid of two lepidopteran species, Galleria mellonella (L.) and Achoria grisella Fabr., were studied at 25± 1°C, 60 ± 5% relative humidity, and a photoperiod of 12 : 12 h (L : D). The effect of host type on fecundity and sex ratio of the hyperparasitoid Dibrachys boarmiae (Walker), an idiobiont, gregarious pre-pupae or pupae ectoparasitoid on A. galleriae was also investigated. Total progeny produced by A. galleriae showed very little host-dependent variation. The mean total number of offspring produced by a female was 232.6 and 239.7 on G. mellonella and A. grisella , respectively. Progeny production and proportion of females per host by A. galleriae decreased directly with parental age. Fecundity of D. boarmiae on A. galleriae pupae reared on G. mellonella and A. grisella was 3.3 and 2.9 respectively. Host type had no significant influence on progeny production and sex ratio of D. boarmiae .     

Experimental comparison of laboratory reared vs. wild-typeTrichogramma confusum [Hym.: Trichogrammatidae] I. Fertility,fecundity and longevity

A comparative study was made of the fertility, fecundity and longevity ofTrichogramma confusum Vigg. reared in the laboratory on eggs ofCorcyra cephalonica St., vs. a wild type population of the same species. Laboratory reared females showed a significantly higher degree of sterility than wild-type females while sterility amongst males did not differ significantly. Under laboratory conditions, laboratory reared females lived longer than wild-type females but produced fewer progeny as indicated by life-table data suggesting that their “effective” life is shorter. The high precentage of sterility amongst laboratory reared females should be taken into account when making inundative field releases. As size of the host may influence the fecundity and behaviour of laboratory rearedTrichogramma, the use of a suitable host which produces larger eggs would have to be considered in any mass-breeding programme.     

Sex-specific transgenerational effects of early developmental conditions in a passerine

Most studies dealing with the trade-off between offspring number and quality have overlooked the long-term consequences for the progeny. High investment in offspring number usually results in an increased competition among nest mates. The deterioration of the early developmental conditions, due to this increased competition, can impair individual quality over the long term, and subsequently affect survival and lifetime fecundity. Moreover, the consequences of the allocation rule to offspring number vs. quality can extend across generations and give raise to grandparental effects. These transgenerational trade-offs have been explored rarely. In the present study, we manipulated the breeding effort of captive zebra finches ( Taeniopygia guttata ) by offering them enlarged or reduced broods. Offspring reared under these conditions were allowed to breed freely in an outdoor aviary, during their entire lifespan. Second-generation fledglings whose mother was raised in enlarged broods were in lower body condition than offspring whose mother was raised in reduced broods. However, second-generation fledglings were not affected by the brood size experienced by the father. These results show that the solution of parental dilemma, whether producing a small number of high quality offspring or a large number of poor quality descendants, must take into account the long-term transgenerational effects acting on grandchildren.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 469–474.     

Sex ratio regulation in Coccygomimus turionella Linnaeus (Hymenoptera: Ichneumonidae) and its ecological implications

Abstract. 1. Sex regulation and its relevance to the ecology of a k-selected pupal parasitoid was investigated in Coccygomimus turionellae.
2. The ratio varied with host size, females predominating in large hosts.
3. Egg transfer experiments and comparative mortality rates among the progeny of virgin and inseminated females demonstrated that the phenomenon was due to parental behaviour.
4. The study of the mechanism confirmed Aubert's hypothesis of host size estimation with the addition that the host had to be exposed from the poles and had to contain the proper host kairomones.
5. Host size was highly correlated to parasitoid fecundity via influences on size and longevity but not the number of ovarioles per female or daily egg production.
6. Host encounters are more limiting than egg production and host size had no effect on host acceptance.
7. Sex regulation allows a maximal host encounter rate at the same time that it maximizes the reproductive potential of female progeny.
8. Low host density increased the production of female progeny resulting in more offspring searching for the limited resource. Concealed hosts and a high host density resulted in a shift towards a Fisher 1:1 sex ratio.     

Impact of transgenic cotton plants on a non-target pest, Aphis gossypii Glover

Abstract.  1. Transgenic crops have shown great promise for the control of target pest insects, but in some cases they can also influence non-target species. This study investigated the impact of Bt and Bt+CpTI transgenic cottons on the non-target cotton aphid, Aphis gossypii Glover, by comparing life-table parameters, feeding behaviour, and the fluctuating asymmetry of morphological traits of aphids reared on transgenic cotton and those on untransformed control plants.
2. Aphids on the Bt+CpTI cotton showed a shorter reproductive duration and maximum lifespan, lower survival rates and potential maximum fecundity, and an earlier occurrence of peak daily mortality in the first or second generation. However, the aphid population soon developed fitness and overcame the negative effect in the second or third generation. The aphids on the Bt cotton had significantly longer reproductive durations in the first generation, higher survival rates in the third generation, and apparently larger potential maximum fecundity in all three generations.
3. The percentages of accumulated duration of feeding waveforms E1 and E2 were significantly lower in aphids on the Bt+CpTI cotton than in those on the Bt or control cotton, whereas the frequencies of moving and finding feeding sites, and probe behaviour were significantly higher.
4. Fluctuating asymmetry in three morphological characters of aphids reared on transgenic and control cotton was detected. The fluctuating asymmetry value of the third segment of antenna in aphids on Bt+CpTI cotton was significantly higher than that of aphids on Bt or control cotton. Based on the fluctuating asymmetry value, the stress of cotton on the aphids could be ranked as Bt+CpTI cotton > Bt cotton > control cotton.     

Effects of host-plant shift on immune and other key life-history traits of an eruptive Geometrid, Epirrita autumnata (Borkhausen)

Abstract.  1. Population density of Epirrita autumnata (Lepidoptera: Geometridae) reaches outbreak densities regularly in northernmost Scandinavia. During these outbreak years, the most abundant host species, the mountain birch ( Betula pubescens ssp. czerepanovii ), is regularly exhausted, although larvae may rescue themselves from starvation by using alternative host species.
2. In this paper, the effects of the shift of host species on the immune defence and other life-history traits of E. autumnata were investigated, and possible consequences for population dynamics were briefly discussed. Moth larvae were reared on the leaves of the main host, mountain birch, until larvae reached their third instar. After this, larvae were allocated randomly to five treatments: larvae were either allowed to finish larval stage on the mountain birch or were shifted onto four alternative host species that are typical species for the area.
3. As expected, the host species had a major effect on fitness traits: body weight, development, and survival rate of the moths. The pupal weight was lower and development rates slower on the three alternative host species, Salix myrsinifolia Salisb., Vaccinium uliginosum L., and Betula nana L., than on the main host, mountain birch.
4. The immunity was, however, the same or better on the alternative hosts than on the main host. The immunity and pupal weights were negatively related, suggesting a trade-off between body size and immunocompetence.
5. The decreased body size and fecundity of E. autumnata during outbreak years may be partly due to the shift to alternative host species whereas the host-plant species probably does not affect markedly the rate of parasitism.     

A comparison of maternal effects and current environment on vital rates of Aphis nerii, the milkweed–oleander aphid

Abstract.  1. Non-Mendelian maternal effects, the effects of maternal phenotype or environment on offspring phenotype, have been documented in numerous taxa. By affecting offspring vital rates (birth, death, and movement), maternal effects have the potential to influence population dynamics. However, relatively few studies have directly linked maternal phenotype or environment to offspring vital rates. Additionally, even fewer studies have compared the magnitude of across-generation effects (i.e. maternal effects) to within-generation effects.
2. Because of their telescoping generations, aphids can be strongly influenced by maternal effects. The effects of maternal density and maternal host-plant species on offspring survival, fecundity, and alate formation were investigated experimentally in Aphis nerii , the milkweed–oleander aphid.
3. Additionally, the relative strength of maternal effects were compared with those operating within a generation. Therefore, in another set of experiments, the effects of current density and host-plant species (within-generation effects) on aphid vital rates were examined.
4. While maternal effects were present, within-generation effects were much stronger and more strongly influenced aphid vital rates. Within a generation, aphids exhibited density-dependent survival, fecundity, and alate formation and these effects varied among host-plant species.
5. These results indicate that while maternal effects have the potential to affect population dynamics, this potential is not always met. Additionally, the current environment, not the environment of previous generations, more strongly impacts population dynamics.     

Survival and reproduction when food is scarce: implications for a lekking Hawaiian Drosophila

Abstract.  1. In insects, larval diet can have a major impact on development, survival, and reproductive success. However, resource availability at the adult phase of the life cycle is also likely to have strong effects in species where there is an extended period of sexual maturation following adult eclosion.
2. The effect of diet on the survival and reproductive success of the lekking Hawaiian fruit fly, Drosophila grimshawi , was explored. Two generations of emerging adults were exposed to one of two feeding regimes: 'constant' and 'varied' (corresponding to food 'each day' or 'every other day' respectively). The impact of resource availability on survival and reproductive success in each generation was then investigated.
3. The probability of survival to 5 weeks old was higher for individuals fed a constant diet than individuals fed a varied diet, but was comparable for males and females.
4. There was a significant maternal effect on offspring survival. Offspring whose mothers were reared on a constant feeding regime had higher survival than offspring whose mothers were reared on a varied diet.
5. There was no relationship between feeding regime and the quantity of pheromones deposited by males (a measure of male reproductive investment); however F₂ sons were more likely to deposit pheromones and deposited a larger quantity of pheromone than their F₁ sires. The number and sex ratio of offspring (a measure of female reproductive effort) emerging from the F₁ generation was unrelated to maternal or paternal feeding regime.
6. The implications of variation in the foraging environment for mate choice in D. grimshawi are discussed.     

Host age and fitness-related traits in a koinobiont aphid parasitoid

Abstract.  1. Trade-offs play a key role in species evolution and should be found in host–parasitoid interactions where the host quality may differ between host age categories.
2. The braconid wasp, Aphidius ervi , is a solitary endoparasitoid that allows its aphid hosts to continue to feed and grow after parasitisation. The hypotheses that host age influences their quality and that female parasitoids exploit their hosts based on that quality were tested under laboratory conditions using no-choice tests.
3.  Aphidius ervi females accepted the aphid Myzus persicae for oviposition and their progeny developed successfully in all host ages. The fitness-related traits of parasitoids did not increase linearly with the host age in which they developed. Host quality was found to be optimal at intermediate host ages and the females preferred to parasitise these hosts. The shortest progeny development time and a more female-biased sex ratio were observed in hosts of intermediate age.
4. This study suggests the existence of multiple interactive trade-offs occurring during host–parasitoid interactions according to host age related quality.     

Female size and fitness in the leaf-cutter bee Megachile apicalis

1. The effects of female size on fitness of the leaf-cutter bee Megachile apicalis Spinola (Hymenoptera: Megachilidae) were examined using artificial nesting sites in the field.
2. Although female size had no significant effect on female longevity or sex ratio of progeny, it did have a significant effect on fecundity; larger females attained greater realized fecundity than did smaller females.
3. This significant effect of female size on fecundity occurred because larger females produced cells faster than did smaller females.
4. Female size also had a significant effect on egg size; larger females laid larger eggs than did smaller females.
5. Female size had a significant effect on the size of investment in each progeny. The size of investment estimated by brood cell weight was greater for larger females than for smaller females. This pattern was largely absent, however, when the size of investment was estimated by adult progeny weight.
6. Female size had a significant effect on nest usurpation behaviour; larger females had a higher capacity to usurp nests than did smaller females.     

The effect of host plant species on performance and movement behaviour of the cabbage looper Trichoplusia ni and their potential influences on infection by Autographa californica multiple nucleopolyhedrovirus

• 1 Cabbage loopers Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae) are serious pests in greenhouses growing tomatoes, cucumbers and bell peppers. A potential microbial control, now in development, is the broad host‐range virus Autographa californica multiple nucleopolyhedrovirus (AcMNPV).
• 2 The relationships between the three host plants and the feeding behaviour, larval movement and performance of cabbage looper larvae that might relate to their interaction with AcMNPV applications were investigated.
• 3 Larvae reared on cucumber plants consumed approximately ten‐fold more leaf area than larvae reared on pepper plants and almost five‐fold more than larvae reared on tomato plants. This could influence the amount of AcMNPV consumed if it were used as a microbial spray because increased consumption can be associated with increased probability of infection. Survival from neonate to pupa also varied, with the greatest being on cucumber, followed by tomato and pepper plants. Larvae fed cucumber were approximately four‐fold heavier than larvae fed tomato and over 15‐fold heavier than larvae fed pepper plants.
• 4 The distribution of larvae on plants in commercial greenhouses where a single crop was being grown also varied with food plant with 73% being found on the bottom and middle portions of tomato plants and 87% occurring in the top portions of pepper plants. Larvae tended to be distributed on the middle portion of cucumber plants, the lower portion of tomato plants and the top portion of pepper plants. Larval movement did not vary between AcMNPV‐infected and uninfected controls.
• 5 It is predicted that the higher leaf area consumption and location of larvae in the middle portion of cucumber plants may make them more susceptible to viral sprays. Furthermore, given their greater survival than larvae fed tomato and pepper, there may be a greater need for virus applications.