Variation in host plant has no effect on the performance and fitness‐related traits of the specialist herbivore Pareuchaetes insulata

The effect of host plant dissimilarity on insect preference and performance was tested using two morphological forms of Chromolaena odorata (L.) King & Robinson (Asteraceae) (one from Florida, USA, another from South Africa), and a specialist herbivore, Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae: Arctiinae) from Florida, USA, that was introduced as a biological control agent in South Africa. Although this insect did establish at one site, of some 21 sites at which over 800 000 individuals were released, its population level in the field has remained low after an initial outbreak in 2006. To explain the poor performance of P. insulata, we hypothesised that P. insulata larvae prefer Floridian C. odorata to the southern African C. odorata, which is morphologically and probably genetically distinct, and that larvae reared on Floridian C. odorata should have higher fitness and performance. We tested this by comparing insect performance metrics on each of the two plant forms in laboratory experiments. Apart from pupal mass, which was significantly greater on southern African C. odorata, P. insulata performance metrics were similar on both plant forms; there were no significant differences in total leaf area consumed, egg and larval development, immature survival rates, feeding index, host suitability index, growth index, and fecundity between the Floridian and southern African C. odorata plants. In sum, we could not demonstrate that differences in plant forms in C. odorata are responsible for the poor performance of P. insulata in South Africa.     

The nutritional landscape of host plants for a specialist insect herbivore

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Effects of the ant Formica fusca on the transmission of microsporidia infecting gypsy moth larvae

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The inhibitory effects of rose powdery mildew infection on the oviposition behaviour and performance of beet armyworms

In this study, we investigated whether the oviposition behaviour and performance of the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), on the rose cultivar Rosa chinensis Jacq. (Rosaceae) were affected when the plants were infected by rose powdery mildew, Podosphaera pannosa (Wallr.: Fr.) de Bary (Erysiphales). The bioassays revealed that the moths significantly avoided ovipositing on mildew‐infected rose leaves when compared to healthy leaves. Pupal weights, emergence rates, and fecundity decreased when the caterpillars were fed mildewed rose leaves. Further laboratory bioassays aimed to elucidate the effects of two volatile headspace extracts (separately collected from healthy and mildewed rose plants) on the oviposition behaviour and performance of the moths. The moths clearly preferred to oviposit on healthy rose leaves that were not sprayed with additional volatiles rather than on healthy leaves sprayed with the volatile extracts from mildewed plants. The mean number of eggs laid on the former leaves was more than six times higher than that laid on the latter leaves. Olfactory bioassays demonstrated that ovipositing moths were significantly more attracted to volatiles emitted by healthy rose leaves than to those emitted by mildew‐infected leaves. Similar results were obtained when comparisons were made between the volatile extracts collected from healthy and mildewed rose plants. Thus, volatiles from mildew‐infected roses have a strong inhibitory effect against the moths. These results indicated that rose volatiles play a role in the oviposition behaviour of the moths, and that the volatiles induced by powdery mildew might be used for insect control.     

The roles of foraging environment,host species,and host diet for a generalist pupal parasitoid

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Effects of quantitative and qualitative differences in volatiles from host‐ and non‐host‐infested maize on the attraction of the larval parasitoid Cotesia kariyai

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The selection of a host of high nutritional quality is of great importance to the development of offspring of larvipositing aphids, as is the avoidance of natural enemies. Little is known, however, about their ability to select host plants based on these factors. This article tests the preference of aphids Sitobion avenae (Fabricius) and Rhopalosiphum padi (L.) (both Hemiptera: Aphididae) for different winter wheat cultivars, Triticum aestivum (L.) (Poaceae), and their ability to detect and avoid predators in sacrifice of their most preferred host. In both species a preference was observed for nutritionally superior hosts. The preference of both species then exhibited a change towards a nutritionally inferior host after infestations of the harlequin ladybird, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), that had been consuming conspecific aphids. This investigation opens the door to the interesting prospect of the ability of aphids to make complex decisions regarding a compromise between high‐quality nutrition and avoidance of predation.     

The interaction between host and host plant influences the oviposition and performance of a generalist ectoparasitoid

The successful development of parasitoids of herbivores depends on the quality of their host, which is often affected by the host plant. Therefore, a parasitoid’s oviposition decisions will directly depend on the host, but also on plant quality. Here, we investigated the direct effects of host species and the indirect effects of the host’s food plant on the oviposition decisions and performance of the gregarious ectoparasitoid Euplectrus platyhypenae Howard (Hymenoptera: Eulophidae). With a series of no‐choice experiments, we determined the oviposition and performance of the parasitoid on: (1) two caterpillar species, fall armyworm, Spodoptera frugiperda JE Smith (Lepidoptera: Noctuidae), and velvet armyworm, Spodoptera latifascia Walker, reared on maize (Zea mays L., Poaceae), (2) the same caterpillars reared on maize, bean (Phaseolus vulgaris L., Fabaceae), or squash (Cucurbita pepo L., Cucurbitaceae) leaves, and (3) S. latifascia caterpillars reared on leaves of wild and cultivated lima bean, Phaseolus lunatus L. All these insects and plants originate from Mesoamerica where they have coexisted for thousands of years in the traditional agricultural system known as Milpa in which maize, beans, and squash are planted together. We found that the preferred and best combination of host and host plant for parasitoid performance was S. frugiperda on maize. Parasitoids laid larger clutches, had higher survival, and more females and larger adults emerged from S. frugiperda reared on maize. However, when both caterpillar species were reared on squash, S. latifascia was the better host. Contrary to the literature, S. frugiperda was not able to develop on bean plants. Results from the lima bean experiment showed that parasitoid performance was best when S. latifascia was reared on leaves of cultivated compared to wild lima bean. These findings are discussed in the context of mixed cropping in which the ability of generalist parasitoids to switch among hosts and host plant species could be advantageous for pest management.     

The influence of landscape configuration and environment on population genetic structure in a sedentary passerine: insights from loci located in different genomic regions

The study of the factors structuring genetic variation can help to infer the neutral and adaptive processes shaping the demographic and evolutionary trajectories of natural populations. Here, we analyse the role of isolation by distance (IBD), isolation by resistance (IBR, defined by landscape composition) and isolation by environment (IBE, estimated as habitat and elevation dissimilarity) in structuring genetic variation in 25 blue tit (Cyanistes caeruleus) populations. We typed 1385 individuals at 26 microsatellite loci classified into two groups by considering whether they are located into genomic regions that are actively (TL; 12 loci) or not (NTL; 14 loci) transcribed to RNA. Population genetic differentiation was mostly detected using the panel of NTL. Landscape genetic analyses showed a pattern of IBD for all loci and the panel of NTL, but genetic differentiation estimated at TL was only explained by IBR models considering high resistance for natural vegetation and low resistance for agricultural lands. Finally, the absence for IBE suggests a lack of divergent selection pressures associated with differences in habitat and elevation. Overall, our study shows that markers located in different genomic regions can yield contrasting inferences on landscape‐level patterns of realized gene flow in natural populations.     

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