The chemical ecology of herbivory on willows

Phenolic secondary compounds and trichomes are instrumental in the regulation of herbivory on Salicaceae. The roles of phenolics in willows as toxins or deterrents, as phagostimulants or ovipository signals, and as precursors in insect chemical defence are briefly reviewed. The interactions between salicaceous plants, herbivores and their predators are discussed in the context of theories on the evolution of interactions among three trophic level

Genetic (RAPD) Diversity between Oleria onega agarista and Oleria onega ssp. ( Ithomiinae , Nymphalidae, Lepidoptera) in North-Eastern Peru

Oleria onega agarista Felder and Felder and Oleria onega ssp. nov. are two Ithomiinae subspecies from north-eastern Peru, that differ for some morphological and behavioural traits. Two contact zones are known near the town of Tarapoto: Ahuashiyacu, where both subspecies cohabit but do not seem to hybridise, and Estero (near the village of Shapaja), where they apparently hybridise. Genetic differences between the two subspecies and between populations were investigated with random amplified polymorphic DNA (RAPD) markers. Both Cluster and Principal Coordinates Analyses (CCoA and PCoA) performed using these data, provided a clear but weak discrimination between the two subspecies. Genetic diversity is much higher within the populations than between them. Moreover, the geographically more distant populations are grouped together by the genetic data. Morphological traits on the wing patterns of the hybrids are intermediary between the two butterflies subspecies, while RAPDs data place them closer to O. onega agarista than to O. onega ssp. The individuals of the Ahuashiyacu population are clearly separated into two groups, those of O. onega ssp. and O. onega agarista, by both morphology and RAPDs data. Moreover, none of those individuals show RAPD similarity with the hybrids, suggesting that hybridisation has not occurred in this populatio

y-free space for eggs contribute to a leaf beetle's oviposition preference for a nutritionally inferior host plant?

Summary 1. Natural enemies are likely to influence the interactions between herbivorous insects and their host plants. In particular, selection exerted by natural enemies could favour host-plant switches and cause, or maintain, oviposition preference for a host species that is nutritionally inferior to another acceptable host. 2. In a previous study, it was shown that larvae of the leaf beetle Oreina elongata perform better on Adenostyles alliariae (Asteraceae) than on Cirsium spinosissimum (Asteraceae). Moreover, A. alliariae provides larval and adult beetles with sequestrable chemical defences. However, in the field, egg densities are much higher on C. spinosissimum than on adjacent A. alliariae . 3. In this study, it was investigated whether this oviposition pattern could be maintained by C. spinosissimum , providing the eggs of O. elongata with better protection from natural enemies. In a field experiment, the survival of eggs was quantified on plants of each of the two species, with and without enemy exclusion. 4. Egg survival was equal for both host species when enemies were excluded from the plants, but it was higher on C. spinosissimum than on A. alliariae when enemies were allowed to the plants. It was also experimentally tested whether the higher egg densities observed in the field on C. spinosissimum are actually due to oviposition preference by the beetle. In a no-choice test, females laid more eggs on C. spinosissimum than on A. alliariae . 5. It can thus be confirmed that C. spinosissimum is really preferred for oviposition and it is concluded that this preference is likely to be maintained, at least partly, by a higher egg survival on C. spinosissimum due to enemy-free space provided by this host plant