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The studies of the long-term effects of insect infestations on plant anti-herbivore defences tend to focus on feeding-induced damage. Infestations by an entire insect generation, including egg depositions as well as the feeding insects, are often neglected. Whilst there is increasing evidence that the presence of insect eggs can intensify plants’ anti-herbivore defences against hatching larvae in the short term, little is known about how insect infestations, including insect egg depositions, affect plant defences in the long term. We addressed this knowledge gap by investigating long-term effects of insect infestation on elm’s (Ulmus minor Mill. cv. ‘Dahlem’) defences against subsequent infestation. In greenhouse experiments, elms were exposed to elm leaf beetle (ELB, Xanthogaleruca luteola) infestation (adults, eggs and larvae). Thereafter, the trees cast their leaves under simulated winter conditions and were re-infested with ELB after the regrowth of their leaves under simulated summer conditions. Elm leaf beetles performed moderately worse on previously infested elms with respect to several developmental parameters. The concentrations of the phenylpropanoids kaempferol and quercetin, which are involved in egg-mediated, short-term effects on elm defences, were slightly higher in the ELB-challenged leaves of previously infested trees than in the challenged leaves of naïve trees. The expression of several genes involved in the phenylpropanoid pathway, jasmonic acid signalling, and DNA and histone modifications appeared to be affected by ELB infestation; however, prior infestation did not alter the expression intensities of these genes. The concentrations of several phytohormones were similarly affected in the currently challenged leaves of previously infested trees and naïve trees. Our study shows that prior infestation of elms by a specialised insect leads to moderately improved defences against subsequent infestation in the following growing season. Prior infestation adds a long-term effect to the short-term enhancer effect that plants show in response to egg depositions when defending against hatching larvae.

While traits of plant resistance to herbivory often change during ontogeny, it is unknown whether the primability of this resistance depends on the plant’s developmental stage. Resistance in non-flowering Arabidopsis thaliana against Pieris brassicae larvae is known to be primable by prior egg deposition on leaves. We investigated whether this priming effect is maintained in plants at the flowering stage. Larval performance assays revealed that flowering plants’ resistance to herbivory was not primable by egg deposition. Accordingly, transcriptomes of flowering plants showed almost no response to eggs. In contrast, egg deposition on non-flowering plants enhanced the expression of genes induced by subsequent larval feeding. Strikingly, flowering plants showed constitutively high expression levels of these genes. Larvae performed generally worse on flowering than on non-flowering plants, indicating that flowering plants constitutively resist herbivory. Furthermore, we determined the seed weight in regrown plants that had been exposed to eggs and larvae during the non-flowering or flowering stage. Non-flowering plants benefitted from egg priming with a smaller loss in seed yield. The seed yield of flowering plants was unaffected by the treatments, indicating tolerance towards the larvae. Our results show that the primability of anti-herbivore defences in Arabidopsis depends on the plant’s developmental stage.

Aims We aimed to elucidate whether the DNA extraction kit and bacteria therein affect the characterization of bacterial communities associated with butterfly samples harbouring different bacterial abundancies. Methods and Results We analysed bacteria associated with eggs of Pieris brassicae and with adults of this butterfly, which were either untreated or treated with antibiotics (ABs). Three DNA extraction kits were used. Regardless of the extraction kit used, PCR amplification of the bacterial 16S rRNA gene detected very low bacterial presence in eggs and AB-treated butterflies. In untreated butterflies, bacterial signal intensity varied according to the kit and primers used. Sequencing (MiSeq) of the bacterial communities in untreated and AB-treated butterflies revealed a low alpha diversity in untreated butterflies because of the dominance of few bacteria genera, which were detectable regardless of the kit. However, a significantly greater alpha diversity was found in AB-treated butterflies, evidencing a true bias of the results due to bacterial contaminants in the kit. Conclusions The so-called ‘kitome’ can impact the profiling of Lepidoptera-associated bacteria in samples with low bacterial biomass. Significance and Impact of the Study Our study highlights the necessity of method testing and analysis of negative controls when investigating Lepidoptera-associated bacterial communities.

Insects live in a highly complex odorant world. Within a variety of odor blends, they need to locate potential food sources, mates, and oviposition sites to gain reproductive success. In nature, volatile cues leading to a resource are always present with numerous other volatiles—here referred to as background odor—which may affect the parasitoid's response to resource-indicating cues. Three different types of background odor are discussed in this article: (a) irrelevant background odor, (b) background odor that may mask the resource-indicating signals, and (c) background odorants that may “sharpen the view” for resource-indicating odor and enhance the response to these. Odor orientation to resources especially in herbivorous and parasitic insects are addressed.

Selection pressure by natural enemies on phytophagous insect larvae is intense and has frequently triggered the evolution of chemical defence as an effective counterstrategy. In the chrysomelid subfamily Galerucinae, glandular structures and defensive fluids have been described for the tribe Sermylini Wilcox, 1965. Previous morphological and ultrastructural studies raised doubts that these defensive devices in Sermylini can be traced back to a common origin. The taxonomy of the Galerucinae cannot clear these doubts because the phylogeny of this taxon is a matter of current debate. We therefore investigated the phylogeny of the Galerucinae based on approximately 1740 bp of the mitochondrial 12S and 16S rRNA and the nuclear elongation factor 1 alpha genes. Our data support the hypothesized close relationship between the subfamilies Galerucinae and Alticinae, yet, by contrast to other recent analyses, the two groups are mostly resolved as monophyletic sister groups or, in some analyses, with the Galerucinae nested paraphyletically within the Alticinae. Within the subfamily Galerucinae, only the tribe Galerucini formed a monophyletic taxon, except for one species, Cerochroa brachialis Stal, 1858. In none of our analyses were the Sermylini recovered as a monophyletic tribe. However, our data support monophyly of each of the three groups within the Sermylini that have morphologically distinguishable larval defensive openings. We conclude that the defensive structures in larvae of Sermylini have no common origin, but evolved independently. Our data suggest that the tremendous selection pressure by natural enemies led to the recurrent evolution of similar chemical defensive devices in Sermylini larvae. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 93, 165–175.

This study investigated the physiologically adaptive significance of elytral coloring and other thermal adaptations to different climes of Central and Northern Europe in a leaf beetle. Adults of Chrysomela lapponica L. differ in the coloring pattern of their red and black elytra when comparing populations from Finnish Lapland (Northern Europe) and from the Czech Republic (Central Europe). While the elytra of adults of the Czech population were bright red in color with a proportion of 51% of black marks, the relative size of the black marks of the Finnish beetle’s elytra was significantly higher (68%). When exposed to light, the dark morphs from Finland increased their body temperature within a shorter time and reached higher mean body temperatures than the lighter morphs from the Czech Republic. The walking speeds of the two different morphs did not differ at temperatures of 20, 15, and 10°C. However, at 5°C, the walking speed of the melanic beetles from Finland was significantly higher. The specific metabolic rate during overwintering of the adults was significantly higher in the Finnish morph at a temperature of 5°C compared with the Czech morph. The average and maximum temperatures during overwintering in the leaf litter layer in the Czech Republic were more variable and on average higher than under the snow cover in Finland. These results on the thermoregulation in C. lapponica are discussed with special respect to melanic elytral coloring as adaptation toward lower ambient temperatures.

Host-foraging behavior of the tachinid parasitoid, Drino inconspicua Meigen (Diptera: Tachinidae), was studied by laboratory bioassays to elucidate the role of physical and chemical factors for host finding and recognition. Larvae of the European spruce sawfly, Gilpinia hercyniae Hartig (Hymenoptera: Diprionidae), were used as hosts. While volatiles of spruce twigs with feeding sawfly larvae did not attract the parasitoid, movements of host larvae and of dummies of the host significantly elicited a positive response at short range. Females of D. inconspicua showed a direct walking behavior to a moving object at distances of 9-10 cm. The maximum distance at which the parasitoids were attracted by movement was 16 cm. At short range, parasitoid females preferred to contact a moving larval dummy made of filter paper rather than an unmoved dummy or an unmoved freshly killed larva of C hercyniae. The tachinid females which were reared from G. hercyniae larvae showed no preference for this host species when compared with larvae of Diprion pini L. (Hymenoptera: Diprionidae) and the unnatural host species Galleria mellonella L. (Lepidoptera: Pyralidae). Furthermore, D. inconspicua did not prefer certain instars of G. hercyniae for oviposition. The role of cuticular chemicals of C. hercyniae larvae for host acceptance was tested by offering host larvae washed with solvents of different polarities and unwashed larvae, Each tested parasitoid female readily accepted both treated and untreated larvae for oviposition. When a hexane extract of the cuticle of host larvae was applied to a dummy, ovipositing D. inconspicua did not significantly distinguish between a treated dummy and a control dummy. Whereas the parasitoid's response to dummies offered as oviposition sites did not depend on the presence of cuticular extracts of hosts, the softness of the dummies was crucial. The parasitoid females significantly preferred soft dummies (hardiness unit [HU]:0.05± 0.01 Nmm -2 ) to hard ones (HU: 207.72± 6.16 Nmm -2 ) for oviposition. Thus, physical factors like movement of the host and its softness clearly play a major role in host foraging of D. inconspicua rather than chemical signals of the host or its host plant.

Host foraging of parasitic wasps attacking insects living in stored food may be guided by volatile cues emanating from these postharvest products. However, little knowledge is available as to how habitat odor released from noninfested stored food affects the parasitoid's response to host-specific chemicals. In this study, we investigated the impact of wheat grist odor on the olfactory host search by the ectoparasitoid Holepyris sylvanidis This parasitoid attacks larvae of the confused flour beetle Tribolium confusum, a common pest of grain products. Olfactometer bioassays showed that female H. sylvanidis were attracted by volatiles released from host larval feces, whereas odor of noninfested wheat grist was neither attractive nor did it mask the host-indicating cues. We analyzed the odor of host larval feces and wheat grist by coupled gaschromatography-mass spectrometry and recorded the parasitoid's electroantennographic (EAG) responses to the detected volatiles. Two specifically host-associated components of the fecal odor, (E)-2-nonenal and 1-pentadecene, elicited strong EAG responses. Both components were attractive when tested individually, but less than larval feces. Attraction of parasitoids to these host-specific key compounds was enhanced by addition of (i) noninfested habitat substrate odor or (ii) a blend of 3 EAG-active (but not behaviorally active) volatiles that had been identified in odor of noninfested grist (benzaldehyde, 1-tetradecene, 1-hexadecene), but were also detected in the host fecal odor. The impact of these volatiles ubiquitously released in a food store by noninfested habitat substrate on the parasitoid's orientation to host-specific volatile cues is discussed.