From Plants to Birds: Higher Avian Predation Rates in Trees Responding to Insect Herbivory

BACKGROUND: An understanding of the evolution of potential signals from plants to the predators of their herbivores may provide exciting examples of co-evolution among multiple trophic levels. Understanding the mechanism behind the attraction of predators to plants is crucial to conclusions about co-evolution. For example, insectivorous birds are attracted to herbivore-damaged trees without seeing the herbivores or the defoliated parts, but it is not known whether birds use cues from herbivore-damaged plants with a specific adaptation of plants for this purpose. METHODOLOGY: We examined whether signals from damaged trees attract avian predators in the wild and whether birds could use volatile organic compound (VOC) emissions or net photosynthesis of leaves as cues to detect herbivore-rich trees. We conducted a field experiment with mountain birches (Betula pubescens ssp. czerepanovii), their main herbivore (Epirrita autumnata) and insectivorous birds. Half of the trees had herbivore larvae defoliating trees hidden inside branch bags and half had empty bags as controls. We measured predation rate of birds towards artificial larvae on tree branches, and VOC emissions and net photosynthesis of leaves. PRINCIPAL FINDINGS AND SIGNIFICANCE: The predation rate was higher in the herbivore trees than in the control trees. This confirms that birds use cues from trees to locate insect-rich trees in the wild. The herbivore trees had decreased photosynthesis and elevated emissions of many VOCs, which suggests that birds could use either one, or both, as cues. There was, however, large variation in how the VOC emission correlated with predation rate. Emissions of (E)-DMNT [(E)-4,8-dimethyl-1,3,7-nonatriene], beta-ocimene and linalool were positively correlated with predation rate, while those of highly inducible green leaf volatiles were not. These three VOCs are also involved in the attraction of insect parasitoids and predatory mites to herbivore-damaged plants, which suggests that plants may not have specific adaptations to signal only to birds

Aphids and parasitolds on willows and poplars in southeastern Europe (Hornoptera : Aphidoidea; Hymenoptera : Braconidae, Aphidiinae)

Aphid and aphid parasitoid associations on willows (Salix spp.) and poplars (Populus spp.) in southeastern Europe are reviewed. In total 13 aphid parasitoid species were reared from aphids on these plants. The specific parasitoid complex of Acyrthosiphon cf. malvae (Mosley) on Salix retusa and the aphids and parasitoids composition on willows and poplars are discussed. The most frequently sampled and the most abundant parasitoid species in poplar aphid-aphid parasitoid associations was Adialytus salicaphis Fitch. Furthermore, Lysiphlebus confusus Tremblay & Eady was the most abundant species collected on willow-feeding aphids, whereas A. salicaphis, Euaphidius cingulatus (Ruthe) and Binodoxys heraclei (Haliday) were the most frequently sampled parasitoid species on willows. Trophic connections between aphids and parasitoids associated with willow agroecosystems are also discussed. A key for the identification of aphid parasitoids associated with aphids on willows and poplars in southeastern Europe is provided

Multiple host use by a sap-sucking membracid: population consequences of nymphal development on primary and secondary host plant species

Aconophora compressa is a gregarious, sap-sucking insect that uses multiple host plant species. Nymphal host plant species (and variety) significantly affected nymphal survival, nymphal development rate and the subsequent size and fecundity of adults, with fiddlewood (Citharexylum spinosum) being significantly best in all respects. Nymphs that developed on a relatively poor host (Duranta erecta var "geisha girl") and which were moved to fiddlewood as adults laid significantly fewer eggs (mean ± SE = 836 ± 130) than those that developed solely on fiddlewood (1,329 ± 105). Adults on geisha girl, regardless of having been reared as nymphs on fiddlewood or geisha girl, laid significantly fewer eggs (342 ± 83 and 317 ± 74, respectively) than adults on fiddlewood. A simple model that incorporates host plant related survival, development rate and fecundity suggests that the population dynamics of A. compressa are governed mainly by fiddlewood, the primary host. The results have general implications for understanding the population dynamics of herbivores that use multiple host plant species, and also for the way in which weed biological control host testing methods should be conducted