Does group feeding by toxic prey confer a defensive benefit? Aristolochic acid content,group size and survival of first‐instar pipevine swallowtail (Battus philenor L.) larvae

1. Aggregative feeding of larvae is widespread in the Lepidoptera, and many hypotheses have been proposed to explain the adaptive significance of this trait. Group feeding occurs disproportionately more in species with aposematic, chemically defended larvae compared with species with cryptic, non‐chemically defended larvae, consistent with the hypothesis that group feeding provides an enhanced aposematic signal to natural enemies. Most species characterised as having chemically defended larvae are cryptic during the first instar, when they are most highly aggregated and most vulnerable to predation. 2. The benefits of group feeding in terms of decreased predation were explored for first‐instar larvae of the pipevine swallowtail, Battus philenor, a species that sequesters aristolochic acids from its Aristolochia host plant and exhibits aposematism in later instars and as adults. We found that groups of larvae with experimentally enhanced aristolochic acid content had significantly lower survivorship due to predation both in the field and in laboratory experiments compared with groups of larvae without enhanced chemical defence. 3. A laboratory experiment found that aristolochic acid does not deter the generalist predator Hippodamia convergens. 4. No evidence was found that was consistent with the hypothesis that group feeding and increased sequestered chemical defence interact to decrease rates of larval mortality in non‐aposematic, first‐instar larvae. Future research on chemical defence, aposematism, and aggregative feeding should continue to appreciate that particular chemical defences and feeding behaviours are not universally effective against all natural enemies.     

Food selection and utilization in a danid butterfly

Summary Larvae of the danid butterfly Danaus chrysippus, fed on the milkweeds Calotropis gigantea and Asclepias curassavica grew successfully during the 9-day feeding period and pupated. In the presence of these milkweeds, the larvae preferred to feed on C. gigantea. Their preference was more pronounced during the final 2 instars than during the initial 3 instars. They consumed 605 mg, defecated 308 mg, and converted 115 mg of C. gigantea; those receiving A. curassavica consumed 563 mg, defecated 287 mg and converted 85 mg. They assimilated either food with equal efficiency (: 46%; : 50%). But they differed significantly in their efficiency in converting the assimilated food. The presence of a greater amount of latex in C. gigantea than in A. curassavica and/or the nutritional inadequacy of the latter food may perhaps be the reason(s) for the preference of C. gigantea by D. chrysippus larvae over A. curassavica.     

Instar-specific sensitivity of specialist Manduca sexta larvae to induced defences in their host plant Nicotiana attenuata

1. The time delay associated with the activation of induced defences is thought to be a liability for this type of defence because it allows herbivores to remove biomass before the defence is fully induced. When defences are costly and plants grow with competitors, however, it may be more advantageous not to induce defences too fast and motivate the herbivore to move to the neighbour when it is most voracious. 2. Such a strategy can only work when the costs for the herbivore of moving to a neighbouring plant are smaller than the costs of staying on a fully induced plant. For lepidopteran herbivores, both the sensitivity to induced defences and the costs of moving may vary considerably between instars and this variation may constrain the plant's defensive opportunities. 3. This study was designed to examine whether the cost of moving, mimicked by a starvation period of 8 h, was larger than the cost of staying on a fully induced plant for each larval instar of the specialist Manduca sexta feeding on induced and control tissues of Nicotiana attenuata. 4. For first‐ and second‐instar larvae, the costs of moving were larger than the costs of staying on a fully induced plant. In contrast, feeding on induced plant material retarded development in third‐instar larvae more than did starvation, indicating that in this instar the costs of leaving are smaller than the costs of staying on an induced plant. More than 98% of the lifetime leaf mass consumed by a M. sexta larva is consumed during the fourth and fifth instars, and during these instars larval development was not affected by either induced defences or starvation. Thus the third instar, the stage just before larvae cause the majority of damage, represents a window of sensitivity to induced defences during which larvae can be motivated to change plants. 5. These results suggest that N. attenuata plants, which commonly compete with conspecifics in nature, have the opportunity to manipulate the behaviour of the specialist herbivore M. sexta to minimise the fitness effects of inducing defences when these defences are most costly, i.e. when plants grow under intraspecific competition.     

Contrasting diel activity and feeding patterns of four instars of Rhyacophila dorsalis (Trichoptera)

1. Ontogenetic shifts in prey choice and predator behaviour can affect food‐web structure. Therefore, it is important to establish if the diet and feeding activity differ between life‐stages of the same species. This hypothesis was tested for second, third, fourth and fifth larval instars of Rhyacophila dorsalis by comparing their diel activity and feeding patterns. Second to fifth instars collected from two streams were used either for gut analyses or for observations of their activity and feeding patterns in three stream tanks. Food was provided in excess; being organisms living in bryophytes on top of a large stone in each tank, augmented by different‐sized larvae of Ephemeroptera, Simuliidae and Chironomidae. As few first instars for gut analyses were found in the field, the diet of first instars reared in the laboratory was also studied. 2. Larvae for gut analyses were taken 1 h before dusk or dawn (n = 50 larvae per instar for each day or night sample). First and second instars fed on the smaller food items with no significant day‐night differences in diet. Gut contents indicated a progressive trend from feeding chiefly at night in third instars to almost exclusively at night in fifth instars. Fourth and fifth instars fed on the larger food items, whilst the diet of the third instar larvae overlapped with that of both the earlier and later instars. 3. Diel activity patterns of single larvae differed between instars but not within each instar (n = 20 larvae per instar). Second instars were active throughout the 24 h, with peaks at dusk, around midnight, dawn and around midday. A similar pattern was shown by third instars but the peak of activity at midday was less than the other three peaks. Prey were captured only during these peaks for both instars. Fourth and fifth instars were most active, and fed only, at night. They used an ambush strategy to capture more active prey at dusk and dawn (e.g. Baetis, Gammarus), and a searching strategy to capture more sedentary prey during the night (e.g. chironomids, simuliids). These experiments provided support for the hypothesis under test. If competition and/or interference occur between instars, then it could be reduced between earlier and later instars because of differences in their diet and diel pattern of feeding activity.     

Female beetles facilitate leaf feeding for males on toxic plants

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Ontogenetic shifts in the functional response and interference interactions of Rhyacophila dorsalis larvae (Trichoptera)

1. Ontogenetic shifts in predator behaviour can affect the assessment of food‐web structure and the development of predator–prey models. Therefore, it is important to establish if the functional response and interference interactions differ between life‐stages. These hypotheses were tested by (i) comparing the functional response of second, third, fourth and fifth larval instars of Rhyacophila dorsalis, using three stream tanks with one Rhyacophila larva per tank and one of 10 prey densities between 20 and 200 larvae of Chironomus sp.; (ii) using other experiments to assess interference within instars (two to five larvae of the same instar per tank), and between pairs of different instars (one, two or three larvae per instar; total predator densities of two, four or six larvae per tank). 2. The first hypothesis was supported. The number of prey eaten by each instar increased with prey density, the relationship being described by a type II model. The curvilinear response was stronger for fourth and fifth instars than for second and third instars. Mean handling time did not change significantly with prey density, and increased with decreasing instar number from 169 s for fifth instars to 200 s for second instars. Attack rate decreased progressively with decreasing instar number. Handling time varied considerably for each predator–prey encounter, but was normally distributed for each predator instar. Variations in attack rate and handling time were related to differences in activity between instars, fourth and fifth instars being more active and aggressive than second and third instars, and having a higher food intake. 3. The second hypothesis was partially supported. In the interference experiments between larvae of the same instar or different instars, mean handling time did not change significantly with increasing predator density, and attack rate did not change for second and third instars but decreased curvilinearly for fourth and fifth instars. Interference between some instars could not be studied because insufficient second instars were available at the same time as fourth and fifth instars, and most third instars were eaten by fourth and fifth instars in the experiments. Prey capture always decreased with decreasing attack rate. Therefore, interference reduced prey consumption in fourth and fifth instars, but not in second and third instars. The varying feeding responses of different instars should be taken into account when assessing their role in predator–prey relationships in the field.     

Some observations on the food of larvae of Procladius bellus (Diptera: Chironomidae)

Analysis of the gut contents of Procladius bellus (Loew) larvae collected in field samples indicated that it was a detrivitore‐omnivore. The observed dietary change from first and second instars (detritivore‐herbivores) to third and fourth instars (omnivores) did not suggest a change in feeding behaviour from detritivore to predator, but rather that the animal material was consumed along with larger detrital material. Small detrital material (1–15 μm) was an important dietary component and detritus in general contributed 50–70% of the overall diet. Diatoms and green algae contributed 15–20%, while blue‐green algae contributed about 10%. Animal material contributed about 5% to second and third instar larvae and 20% to fourth instar larvae.     

It’s the first bites that count: Survival of first‐instar monarchs on milkweeds

Mortality of first instars is generally very high, but variable, and is caused by many factors, including physical and chemical plant characters, weather and natural enemies. Here, a summary of detailed field‐based studies of the early‐stage survival of a specialist lepidopteran herbivore is presented. First‐instar larvae of the monarch butterfly, Danaus plexippus, a milkweed specialist, generally grew faster and survived better on leaves when latex flow was reduced by partial severance of the leaf petiole. The outcome depended on milkweed species, and was related to the amount of latex produced, as well as other plant characters, such as leaf hairs, microclimate and concentration of secondary metabolites. Even for a so‐called ‘milkweed specialist’, larval performance and survival appears to be related to the concentration of cardenolides produced by the plants (a potential chemical defence against herbivory). This case study of monarchs and milkweeds highlights the need for field‐based experiments to assess the effect of plant characters on the usually poor survival of early instar phytophagous insects. Few similar studies concerning the performance and survival of first‐instar, eucalypt‐specific herbivores have been conducted, but this type of study is considered essential based on the findings obtained using D. plexippus.     

Onshore–offshore variations of copepod community in northern South China Sea

Previous studies which have tested the feeding preferences of shredders for fungal species and the food quality of fungi used detritus uniformly colonized by a fungus, which is not the case for decaying leaves in streams. It is not known whether shredders in different development stages exhibit variations in feeding preference and larval performance. This study examined the feeding preferences and the growth of the third and the fifth instars of Pycnopsyche gentilis larvae using fungal-colonized patches and whole leaves, respectively, having different fungal species compositions (Alatospora acuminata, Anguillospora filiformis, Articulospora tetracladia, Tetrachaetum elegans, and all species combined). The aquatic hyphomycetes used were co-dominant on leaves in the stream inhabited by the caddisfly. During 14 d of feeding, the larvae of both instars did not show significant differences in feeding preferences for the patches growing on oak leaves, although the third instar larvae were slightly more selective than the fifth instar larvae. When fed with maple leaves for 18 d, larval growth rates, gross growth efficiencies, and survivorship were not significantly different among the fungal treatments. However, the larval growth of both instars fed with fungal-colonized leaves was always significantly greater than the growth of larvae fed with diets of uncolonized leaves. The third instar larvae grew faster than the fifth instar larvae, but the growth efficiencies of the two instars were similar. These results suggest that P. gentilis larvae exhibit less selectivity in their feeding than other caddisfly shredders that have been examined and that the dominant fungi colonizing leaves in their habitat are similar in palatability and food quality for this shredder. Handling editor: B. Oertli     

Is the effect of priming plants,and a functional JAR1, negligible on the foraging behaviour and development of a generalist lepidopteran,Helicoverpa armigera?

Theory and recent literature suggest strong effects of induced plant defences in some plant herbivore systems. Few have studied behavioural effects on intact plants. Differences in foraging behaviour as well as weight gain were determined for first instar Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on Arabidopsis thaliana (L.) Heynh. (Brassicaceae) mutant and wild type plants, non‐primed, or primed by herbivore feeding or methyl jasmonate. The differences in feeding were primarily in the length of feeding time as opposed to the area fed on, feeding location, or frequency. More larvae dispersed from plants after priming by mite feeding than dispersed after caterpillar feeding. Other behavioural activities such as resting were not significantly affected. Early instars gained less weight feeding on ein2 (ethylene insensitive) mutant, but there was no difference in weight gain between larvae feeding on induced and non‐induced plants of the same type. We concluded that there are fitness consequences for neonates of the generalist H. armigera after feeding on induced plant tissues in some cases, and that distinct changes in behaviour are recognisable both at the fine scale and at grosser levels (dispersal). However, these changes are more subtle than might be expected.     

Detrimental effects of latex and cardiac glycosides on survival and growth of first-instar monarch butterfly larvae Danaus plexippus feeding on the sandhill milkweed Asclepias humistrata

1. A novel experimental method was developed to study negative physical and chemical effects of latex and cardiac glycosides on first‐instar monarch butterfly larvae in their natural environment in north central Florida. Forceps were used to nibble through the petioles of leaves of the sandhill milkweed Asclepias humistrata, mimicking the behaviour of mature monarch larvae. This notching cut off the supply of latex to the leaves without significantly reducing either their cardiac glycoside concentration or water content. 2. The mean cardiac glycoside concentration in larvae that fed on intact leaves was nearly two and a half times greater than in larvae that fed on notched leaves. This was probably because more latex is present in the gut of the larvae that fed on the intact leaves. Supporting this is the fact that the mean concentration of cardiac glycosides in the latex was 34–47 times that in the leaves. 3. Wet weights, dry weights, and growth rates of first‐instar larvae that fed on intact leaves over a 72‐h period were less than half those of larvae that fed on notched leaves. 4. Mortality due to miring in the latex was 27% on the intact leaves compared with 2% on the notched leaves. 5. Latex, cardiac glycosides, and other as yet undetermined plant factors all have a negative effect on first‐instar larval survival. 6. Video‐analyses indicated that ingestion of latex caused the larvae to become cataleptic and increased their chances of being mired on the leaf by the setting latex glue. Dysfunction resulting from latex ingestion may lead to the larvae falling off the plant and being killed by invertebrate predators. 7. The difficulty of neonate monarch larvae surviving on A. humistrata – one of the principal milkweed species fed on each spring as monarchs remigrate from Mexico into the southern U.S.A. – is evidence that a co‐evolutionary arms race is operating in this plant–herbivore system.     

Maintenance of narrow diet breadth in the monarch butterfly caterpillar: response to various plant species and chemicals

In order to better understand the maintenance of a fairly narrow diet breadth in monarch butterfly larvae, Danaus plexippus L. (Lepidoptera: Nymphalidae: Danainae), we measured feeding preference and survival on host and non-host plant species, and sensitivity to host and non-host plant chemicals. For the plant species tested, a hierarchy of feeding preferences was observed; only plants from the Asclepiadaceae were more or equally preferred to Asclepias curassavica, the common control. The feeding preferences among plant species within the Asclepiadaceae are similar to published mean cardenolide concentrations. However, since cardenolide data were not collected from individual plants tested, definitive conclusions regarding cardenolide concentrations and plant acceptability cannot be made. Although several non-Asclepiadaceae were eaten in small quantities, all were less preferred to A. curassavica. Additionally, these non-Asclepiadaceae do not support continued feeding, development, and survival of first and fifth-instar larvae. Preference for a host versus a non-host (A. curassavica versus Vinca rosea) increased for A. curassavica reared larvae as compared to diet-reared larvae suggesting plasticity in larval food preferences. Furthermore, host species were significantly preferred over non-host plant species in bioassays using a host plant or sucrose as a common control. Larval responses to pure chemicals were examined in order to determine if host and non-host chemicals stimulate or deter feeding in monarch larvae. We found that larvae were stimulated to feed by some ubiquitous plant chemicals, such as sucrose, inositol, and rutin. In contrast, several non-host plant chemicals deterred feeding: caffeine, apocynin, gossypol, tomatine, atropine, quercitrin, and sinigrin. Additionally the cardenolides digitoxin and ouabain, which are not in milkweed plants, were neutral in their influence on feeding. Another non-milkweed cardenolide, cymarin, significantly deterred feeding. Extracts of A. curassavica leaves were tested in bioassays to determine which components of the leaf stimulate feeding. Both an ethanol extract of whole leaves and a hexane leaf-surface extract are phagostimulatory, suggesting the involvement of both polar and non-polar plant compounds. These data suggest that the host range of D. plexippus larvae is maintained by both feeding stimulatory and deterrent chemicals in host and non-host plants.     

Life‐history traits in a parasitoid dipteran species with free‐living and obligate parasitic immature stages

The robber fly Mallophora ruficauda Weidemann (Diptera: Asilidae) is an important pest of apiculture in the Pampas of Argentina. As adults, they prey on honey bees and other insects, whereas the larvae are ectoparasitoids of Scarabaeidae grubs. Females of M. ruficauda lay eggs in grassland where the larvae drop to the ground after being wind‐dispersed and burrow underground searching for their hosts. A temporal asynchrony exists between the appearance of the parasitoid larvae and the host, with the parasitoid appearing earlier than the host. The present study investigates whether a strategy of synchronization with the host exists in M. ruficauda and determines which of the larval instars are responsible for it. Survival patterns and duration of the immature stages of the parasitoid are investigated to determine whether there is a modulation in the development at any time that could reduce the asynchrony. Experiments are carried out to determine the survival and duration of free‐living larval stadia in the absence of cues associated with the host. It is established that the first instar is capable of moulting to the second instar without feeding and in the absence of any cues related to the host, a unique event for parasitoids. Also, the first instar of M. ruficauda moults to the second stage within a narrow temporal window, and the second instar never moults in the absence of the host. After parasitizing a host, the second instar has the longest lifespan and is the most variable with respect to survival compared with the rest of the instars. All larval instars, except for those in the last (fifth) stadium, have a similar rate of mortality to that of second‐instar larvae. Additionally, it is established that the host is killed during the fourth (parasitoid) stadium and that the first‐ and fifth‐larval instars develop independently of the host. Finally, possible mechanisms that could aid in compensating for the asynchrony between the parasitoid and the host, promoting the host–parasitoid encounter, are discussed.     

Feeding behaviour of Helicoverpa armigera larvae on insect-resistant transgenic cotton and non-transgenic cotton

Abstract: Feeding behaviour of Helicoverpa armigera Hübner (Lep.; Noctuidae) larvae on non‐transgenic Bacillus thuringiensis (Bt) cotton (Gossypium hirsutum L.), Zhong 30, and transgenic cowpea trypsin inhibitor (CpTI)‐Bt cotton, SGK 321, and non‐transgenic cotton, Shiyuan 321, was investigated in both choice tests and no‐choice tests. The results of choice tests suggested that neonates have the ability to detect and avoid transgenic cotton. In the choice tests of neonates with both transgenic and non‐transgenic cotton leaves, a significantly greater proportion of larvae and higher consumption were observed on non‐transgenic cotton than on the transgenic Bt or CpTI‐Bt cotton. In the choice tests with leaves of two transgenic cotton lines, the proportion of neonates on leaf discs of the two lines was not significantly different, but there was significantly higher consumption on CpTI‐Bt transgenic cotton than that on Bt transgenic cotton. In addition, significantly more neonates were found away from the leaf discs, lower consumption and higher mortality were achieved in the choice test with two transgenic cotton leaves than in the choice tests containing non‐transgenic cotton leaves. Leaves and buds were examined in choice tests of fourth instars. It appeared that fourth instars were found in equal numbers on transgenic and non‐transgenic cotton, except when larvae were exposed to leaves for 3 h. However, the total consumption on transgenic cotton was lower than that of the non‐transgenic cotton, so fourth instars may still have the capacity to detect transgenic cotton and reduce feeding on it, although they showed no preference on either transgenic or non‐transgenic cotton. More larvae were found off diet in the treatments with leaves than that of buds, and the number of injured leaf discs by per fourth instar was significantly higher than that of buds in choice tests, suggesting that leaf is a less preferred organ for H. armigera larvae, elicited more larval movements. Similarly, in no‐choice tests of fifth instars, significantly fewer feeding time and more moving time occurred on leaf than that of bud, boll and petal. When cotton line was considered, compared with non‐transgenic cotton, significantly lower feeding time and higher resting time occurred on the two transgenic cottons. Overall, H. armigera larvae have the ability to detect the transgenic Bt and CpTI‐Bt cottons or the less preferred organs and selectively feed more on the non‐transgenic cotton or the preferred organs, especially the neonates, which have a high capacity for avoiding transgenic cotton.     

Dytiscus latissimus and D. circumcinctus (Coleoptera,Dytiscidae) larvae as predators on three case-making caddis larvae

The predacious behaviour of Dytiscus circumcinctus and D. latissimus larvae was studied experimentally. When offered different prey simultaneously, D. latissimus larvae preferred cased caddis larvae relative to mayfly nymphs and isopods, whereas in D. circumcinctus the preference order was reversed. Notonectid nymphs and tadpoles were consumed in higher numbers by D. circumcinctus than by D. latissimus larvae. D. circumcinctus larvae and instar III larvae of D. latissimus most frequently captured caddis larvae through the case wall, whereas the instar I and II larvae of D. latissimus normally attacked the thorax of the exposed larva from above the front opening of the case. Limnephilus borealis, L. nigriceps and L. rhombicus caddis larvae differed in case structure, and they were all successfully captured by D. latissimus and D. circumcinctus instar II and III larvae. Neither capture success nor ingestion efficiency varied significantly between the two Dytiscus species or between different prey species. Instar II and III D. circumcinctus larvae had shorter reaction times than those of D. latissimus. The larger L. borealis and L. rhombicus larvae were preferred by the two last Dytiscus larval instars, and the handling time of these two prey was longer than that of L. nigriceps larvae.     

Cyanide as a feeding stimulant for the southern army worm, Spodoptera eridania

ABSTRACT.

• 1 All instars of Spodoptera eridania larvae grow as well or better when cyanide is present in their diet as when it is absent. Concentrations up to 0.05% stimulate feeding in first to fourth instar larvae. Concentrations from 0.1% to 1.0% stimulate feeding in fifth and sixth instar larvae.
• 2 Three-day-old sixth instar larvae pre-exposed to cyanide are completely resistant to its acutely toxic effects, but previously unexposed larvae suffer reversible symptoms of poisoning when feeding on a diet containing 1.0% KCN.
• 3 A 1.0% dietary KCN exposure during the sixth instar reduces ecdysis to 17% adult emergence and completely inhibits oviposition.
• 4 Cyanide concentrations from 0.5% to 1.0% in the diet, although effecting increased growth rates, induce necrotic lesions in larval mid-gut epithelial cells.
• 5 Thiocyanate, one of the in vivo cyanide metabolites, at 0.5% in the diet reduces pupation to 23%, delays and reduces adult emergence to 20% and inhibits oviposition.
• 6 The preferred host plant of S.eridania is the lima bean, Phaseolus lunatus, probably due to its content of the cyanogenic glycoside linamarin. Dietary valine has no effect on the southern armyworm feeding and growth behaviour (Long & Brattsten, 1982) but dietary cyanide does. The lima bean is known to contain up to 31 ppm cyanide in some varieties.

     

Biology and performance of two indigenous larval parasitoids on Tuta absoluta (Lepidoptera: Gelechiidae) in Sudan

Tuta absoluta is an alien invasive pest in Sudan. Since it was detected in the country, the pest continues to cause major tomato losses. Alarmed by its devastating nature and the speed of spread, tomato growers resorted to the indiscriminate use of broad-spectrum insecticides. Promising indigenous parasitoid(s) may contribute to suppression of this pest. The biology and performance of the native parasitoids, Bracon nigricans Szépligeti (Braconidae) and Dolichogenidea appellator (Telenga) (Braconidae), was therefore evaluated against different immature stages of T. absoluta under laboratory conditions. A significantly higher number of fourth instar larvae was accepted for oviposition by B. nigricans. Similarly, fourth instar larvae yielded a considerably higher number of parasitoid offspring compared to third instar larvae. The male ratio of B. nigricans offspring which emerged from both larval instars was high, 0.96 and 0.66 for third and fourth instar larvae of T. absoluta, respectively. There was, however, no significant difference in the number of males and females that emerged from fourth instar larvae. Conversely, the number of hosts killed by stinging behaviour or host feeding was significantly higher on third instar larvae. B. nigricans potential fecundity varied with the age of the wasp with the lowest fecundity on the day of eclosion. The performance of D. appellator in terms of the total number of offspring produced and female progeny was similar for second and third instar larvae of T. absoluta. The preimaginal developmental time for both parasitoid species did not vary with either host stage or sex of the parasitoid. B. nigricans adult longevity was similar for both sexes, while that of D. appellator significantly varied with females living longer than males. Prospects for conservative biological control of T. absoluta are discussed in the light of the results of this study.     

Host-age discrimination during host location byCotesia glomerata, a larval parasitoid ofPieris brassicae

Some parasitoids are restricted with respect to the host stage that they attack and even to a certain age within a stage. In this paper we investigate whether the parasitoidCotesia glomerata can discriminate between old and young caterpillar instars of its host,Pieris brassicae, before contacting these hosts, since contacts with older instars are very risky with a chance of being killed, due to the aggressive defensive behaviour of the caterpillars. Flight chamber dual choice tests showed that volatile chemicals emitted by Brussels sprouts plants (Brassica oleracea var. gemmifera) after feeding damage by 1st and 5th larval instars are equally attractive to the wasps. Simulated herbivore damage by 2nd and 5th larval instars, obtained by treating mechanically damaged leaves with carterpillar regurgitant, was also equally attractive, even when the wasps were exposed to repeated experience on different larval instars to increase their discriminatory ability. In contrast, single choice contact bioassays showed that the time spent searching on a leaf with feeding damage of 1st instar larvae was significantly longer than the time spent on 5th instar feeding damage or on mechanically damaged leaves. Both flight and contact bioassays did not show any effect of egg-related infochemicals. The results demonstrate thatC. glomerata can discriminate between young and old larval instars ofP. brassicae, without contacting the caterpillars. This is not done through volatile herbivore-induced synomones but through cues that are contacted after arrival at a caterpillar-infested leaf.     

Mines over matter: Effects of foliar particulate matter on the herbivorous insect,Helicoverpa armigera

Coalmines, which are major contributors of particulate matter in the form of coal dust, are expanding globally into rural environments. However, ecological effects on organisms interacting with coal‐dusted foliage in mining landscapes are unknown. We tested how the behaviour, development and survival of a polyphageous insect herbivore, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is affected by consuming tomato leaves Lycopersicon esculentum laden with coal dust. We tested (a) feeding site establishment preference of neonates, (b) feeding behaviour and leaf consumption of late‐instar larvae, (c) survival of neonates and (d) survival and development of late‐instar larvae. We found that coal dust consumption increased the mortality of late‐instar larvae but did not influence their development. Despite long‐term implications for survival, late‐instar larvae did not adjust their feeding behaviour or the amount of leaf material consumed in response to foliar coal dust. Contrastingly, when neonate H. armigera were given a choice, they avoided establishing themselves on the coal‐dusted adaxial surface of leaves. Neonate mortality was 99% within 7 days, with no effect of coal dust. Our study provides the first data on the impact of coal dust on an insect herbivore. This has implications for ecological interactions in landscapes adjoining coalmines.     

Biology of Microplitis kewleyi (Hymenoptera: Braconidae): A parasite of Agrotis ipsilon (Lepidoptera: Noctuidae) larvae

Microplitis kewleyi Muesebeck is a gregarious internal parasite of larvae of the black cutworm Agrotis ipsilon (Hufnagel). Studies of the biology of the parasite revealed that there was an inverse relationship between host instar and parasite preference. Duration of development from egg to pupa ranged from 18 days at 27°C to 68.7 days at 16°C. Development from egg to pupa took 13.5–21.6 days when fourth and first instar host larvae, respectively, were parasitized. A larger number of parasites emerged from hosts parasitized in the fourth instar (22.4) than the first instar (11.5). Parasite pupation occurred when the host was in the fifth/sixth instar, depending on the instar parasitized. Thirty‐nine per cent of host larvae exposed as first instars to parasites died before parasite emergence. This decreased to 0% for host larvae exposed as fourth instars. The sex ratio was 1:1.2 (M:F). Thirty‐seven per cent of hosts exposed diurnally were stung, compared to 24% exposed nocturnally. Mean daily progeny was highest (12) on the first day, decreasing to zero after 20 days. Percent host parasitism was also highest on the first day (35%) decreasing to nearly 0% after 18 days. There appear to be three parasite larval instars. Host larvae often remained alive after parasite emergence.