Ecological Entomology

YANG, ROU‐LING; FUSHING, HSIEH; HORNG, SHWU‐BIN

doi: 10.1111/j.1365-2311.2006.00696.xpmid: N/A

Abstract 1. This study investigates how female seed beetles, Callosobruchus maculatus, distribute their eggs on various‐sized seeds when the size of seed was varied during the egg‐laying period. 2. Beetles were allowed to lay eggs on one of three arrays of 64 adzuki beans (Vigna angularis). Each array contained four size classes of seed, ranging from small (5.0–5.5 mm diameter) to large (6.5–7.0 mm), but differed in how they were distributed within the environment. In the most heterogeneous condition (the 64‐patch design), the four sizes were interspersed, while in the least heterogeneous condition (the four‐patch design) they were grouped into four separate blocks. Thus, a beetle exploring the 64‐patch design would frequently encounter all four seed sizes, whereas a beetle exploring the four‐patch design would only rarely encounter a change in bean size. 3. Beetles experiencing greater seed size heterogeneity were more likely to lay eggs on larger seeds, whereas those in the blocked condition were more likely to oviposit on small seeds. Beetle responses to seed size heterogeneity suggest that the degree of preference for large seeds depends on a female’s recent experience. 4. Female beetles exhibited size discrimination throughout their egg‐laying process; however, there was a trade‐off between seed size and egg discrimination (i.e. avoiding those seeds already containing developing eggs) in response to the change in fitness gained from either laying on larger seeds or lower egg‐load seeds during the egg‐laying process. 5. Our model provides the first evidence that evolving seed size discrimination ability is adaptive for the seed beetle with egg‐discrimination ability.

BAILEY, JOSEPH K.; WHITHAM, THOMAS G.

doi: 10.1111/j.1365-2311.2006.00774.xpmid: N/A

Abstract 1. Cottonwood (Populus spp.) are the dominant tree type in riparian forests of the western U.S.A. In these riparian forests, the beaver (Castor canadensis) is a major ecosystem engineer that commonly browses cottonwood, resulting in distinct changes to plant architecture. Here the hypothesis that beaver herbivory indirectly affects the distribution of a keystone leaf‐galling sawfly through architectural changes in cottonwood was examined. 2. It was found that: (a) beaver herbivory of cottonwood results in an increase in average shoot length over unbrowsed cottonwood; (b) sawfly galls were up to 7–14 times more abundant on browsed cottonwood than unbrowsed cottonwood; and (c) sawfly gall abundance was correlated positively with changes in shoot length after beaver herbivory. Together these data show that the individual and combined effects of cottonwood and beaver herbivory increase shoot length, positively affecting sawfly abundance. 3. Because herbivores are a ubiquitous component of most ecosystems, we argue that the indirect effects of herbivory on plant quality, and subsequently other herbivores, may be as important as environmental variation.

DARROUZET‐NARDI, ANTHONY; HOOPES, MARTHA F.; WALKER, JESSE D.; BRIGGS, CHERYL J.

doi: 10.1111/j.1365-2311.2006.00798.xpmid: N/A

Abstract 1. Host–parasitoid models often identify foraging behaviour and dispersal distance as important for system persistence. 2. Laboratory observations and field trials were used to characterise foraging behaviour and dispersal capability of Platygaster californica Ashmead (Platygasteridae), a parasitoid of the gall midge Rhopalomyia californica Felt (Cecidomyiidae). 3. Although foraging parasitoids meticulously searched plants in laboratory observations, none of the laboratory trials resulted in 100% parasitism, and the proportion of parasitism declined as midge egg density increased. 4. The field trials showed that the distribution of parasitism over distance from a central release point was hump‐shaped, as predicted by a simple diffusion model. Mean parasitoid dispersal distance was 4.5 m, considerably farther than the 1.7 m mean midge dispersal found in previous work. 5. Although the parasitoid appears to search thoroughly for midge eggs and to disperse farther than the midge, the results of this study show how this host–parasitoid system may persist due to spatially variable incomplete parasitism.

LIU, SHU‐SHENG; LIU, TONG‐XIAN

doi: 10.1111/j.1365-2311.2006.00777.xpmid: N/A

Abstract 1. In holometabolous insects, learning has been demonstrated in both larval and adult stages. Whether learning can be retained through metamorphosis from larva via pupa to adult has long been a subject of debate. The present study is designed to distinguish between preimaginal and imaginal conditioning in the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae) using oviposition preference tests on females exposed to various types of learning experiences during immature and adult stages. 2. Cohorts of test insects were reared from egg to pupa on an artificial diet, or on one of two host plants, Chinese cabbage, Brassica campestris L. ssp. pekinensis, and common cabbage, Brassica oleracea L. var. capitata. The ensuing females reared on the three kinds of food showed similar oviposition preference between the two plants. A brief experience of the less preferred host, common cabbage, by adults slightly increased their preference for this plant. 3. Cohorts of test insects were reared from egg to pupa on an artificial diet with or without the addition of a neem‐based oviposition deterrent (Neemix® 4.5). Larval feeding experience did not alter oviposition response to the deterrent. However, emergence conditioning and early adult learning, achieved through experience of a residue of the deterrent carried over from the larval food on pupal cuticle and cocoons, altered oviposition preference significantly. 4. The combined results revealed no evidence of preimaginal conditioning in this insect but a strong effect of emergence conditioning and early adult learning on oviposition preference.

MOCZEK, ARMIN P.; COCHRANE, JEFFREY

doi: 10.1111/j.1365-2311.2006.00773.xpmid: N/A

Abstract 1. Brood parasitism occurs when individuals parasitise each others’ investment into parental care, and has been documented primarily as an interspecific interaction. Intraspecific brood parasitism, in contrast, is often difficult to detect and quantify, and evidence for it is comparatively scarce. The present study documents the occurrence of intraspecific brood parasitism by females of the tunnelling dung beetle Onthophagus taurus, and investigates the contributions of two variables to the propensity of female brood parasitism: female body size and dung desiccation rate. 2. Female O. taurus were found to routinely utilise brood balls made by conspecific females as food provisions for their own offspring. 3. Contrary to expectations, large and small females did not differ in the likelihood of engaging in brood‐parasitic behaviour. 4. Dung desiccation rate appeared to influence likelihood of brood parasitism. Females that were given access to rapidly drying dung were significantly more likely to detect and utilise brood balls produced by conspecific females. 5. While interspecific brood parasitism has been documented in dung beetles before, the present study is among the first to present evidence for intraspecific brood parasitism as an alternative reproductive tactic of female dung beetles. Results are discussed in the context of the evolutionary ecology of onthophagine beetles.

KYNEB, ANN; TOFT, SØREN

doi: 10.1111/j.1365-2311.2006.00775.xpmid: N/A

Abstract 1. The reproductive output of an individual is known to be influenced by diet quality, but the quality of the parent's diet can also influence the performance of the offspring. Dietary maternal effects may interact with the effects of the offspring's diet to produce a variety of response patterns. 2. Maternal effects were investigated in a polyphagous predator, the rove beetle Tachyporus hypnorum, using three single‐species diets: two low‐quality diets consisting of the aphids Sitobion avenae and Rhopalosiphum padi, and the high‐quality control Drosophila melanogaster diet. Offspring of females fed these diets were raised on the same monotypic diets and allowed to reproduce. Several fitness parameters were measured to indicate possible maternal effects in both F1 and F2 generations. 3. Maternal diet effects in F1 were found in egg size, hatching success, time to hatching, larval development time, larval survival, and sex ratio. Both aphid diets resulted in smaller eggs. A diet of R. padi resulted in reduced hatching success, longer time spent in the egg stage, and a female‐biased sex ratio. A maternal diet of R. padi also prolonged larval development on S. avenae diet, while a maternal diet of S. avenae decreased survival on the R. padi diet. These effects were independent of egg size. 4. A maternal diet of R. padi enhanced the survival of F1 larvae raised on the same diet. Developmental selection operating through a high egg mortality may be the explanation for this seemingly positive effect. 5. Sitobion avenae alone caused a significant reduction in the hatching success of F2 eggs, thus revealing grandmaternal effects. 6. The prediction that polyphagous predators are less likely to evolve adaptive maternal effects is supported by the fact that none of the documented maternal effects could be interpreted as adaptive.

BILU, EINAT; HOPPER, KEITH R.; COLL, MOSHE

doi: 10.1111/j.1365-2311.2006.00786.xpmid: N/A

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.

CIZEK, LUKAS; FRIC, ZDENEK; KONVICKA, MARTIN

doi: 10.1111/j.1365-2311.2006.00783.xpmid: N/A

Abstract 1. With respect to seasonal availability for herbivores, plants defended by synthesising qualitative compounds differ from those protected by accumulation of quantitative macromolecules, leaf toughness, and low water and/or nutrient content. While the palatability of the former plants remains relatively constant during the season, the palatability of the latter group decreases with leaf age. 2. It was hypothesised that in seasonal temperate environments, quantitative plant defences should restrict the annual numbers of insect generations. To test this hypothesis, European butterflies were used as a model, both non‐corrected regressions and tests controlling for phylogeny were carried out, and potentially confounding factors such as body size or occurrence in short‐season environments were treated as covariables. 3. Non‐phylogenetically controlled regressions corroborated that butterflies feeding on quantitatively protected hosts (woody plants + grasses) form fewer generations than species feeding on qualitatively protected forbs. Plant defences fitted voltinism better than butterfly size, and remained significant even after controlling for short seasons. Using independent contrasts, feeding on woody plants plus grasses, and feeding on woody plants only, predicted fewer generations. These patterns, however, applied exclusively for foliage‐feeding species. 4. The association between plant defences and voltinism represents a hitherto overlooked pattern in the ecology of temperate herbivores. It may explain why large insects tend to form fewer generations and feed on structurally complex hosts, and why some species remain monovoltine although they are not restricted by short season.

SCHILE, LISA; MOPPER, SUSAN

doi: 10.1111/j.1365-2311.2006.00799.xpmid: N/A

Abstract 1. Salinity is an important cause of abiotic stress in wetland communities yet little is known about its consequences for freshwater plants and their insect herbivores. The goal of this study was to test the effect of salinity on a leafmining insect, Cerodontha iridiphora, and its herbaceous host plant, Iris hexagona. 2. Leafminer performance was evaluated on irises grown in control and saline treatments, and the effects of salinity and herbivory on leaf quality and mortality was measured. 3. Leafminer density and size were significantly lower on irises grown in saline water compared with freshwater. 4. Both salinity and herbivory accelerated leaf senescence and mortality, and their combined effects increased tissue loss by an order of magnitude compared with controls. 5. Leafminers acted as nutrient sinks. The undamaged regions of mined leaves contained 40% less nitrogen than unmined leaves, providing a mechanism for the premature leaf mortality. 6. Salinity was detrimental to the performance and survival of both the iris leafminer and its host plant. We propose that glycophytic host plants and their insect herbivores will suffer more than halophytic communities from environmental salinity because they lack the adaptive mechanisms to tolerate this potent physiological stress.

ALCOCK, JOHN; SIMMONS, LEIGH W; BEVERIDGE, MAXINE

doi: 10.1111/j.1365-2311.2006.00791.xpmid: N/A

Abstract 1. Females of Dawson’s burrowing bees vary in body weight over a twofold range. Despite the potential for differences in body weight to affect several aspects of the competition among nesting females, no clear advantages were documented for larger females. 2. Nesting females were not consistently larger than emerging females, nor was there a consistent relationship between body size and the weight of pollen and nectar carried to the nest on provisioning trips. At one nesting location, larger females did not produce larger pre‐pupal offspring nor did they produce offspring at a faster rate than their smaller nesting companions. 3. In addition, large body size was not associated with greater success in nest defence despite the fact that nesting females regularly encountered intruders in their burrows. Residency, not body size, determined the outcome of almost all contests for control of a nest burrow. The absence of a large body size effect here appears to stem from an intruder strategy designed to enable nest‐searching females to acquire burrows that had been abandoned through death or dispersal of their original owners rather than securing existing nests through an aggressive takeover strategy. 4. Thus, although large body size conveys significant fitness advantages to males, this attribute does not promote female success in either provisioning or defending their nests.