Principles of Ecology

388 hal,;ill,;21 c

Predatory hoverflies increase oviposition in response to colour stimuli offering no reward: implications for biological control

There are increasing efforts worldwide to engineer agroecosystems to enhance ecosystem services such as carbon storage, minimisation of erosion, and biological control of pests. A key group of insect biological control agents is the hoverflies (Diptera: Syrphidae). While adult Syrphidae are pollen and nectar feeders, the larvae of many species are aphidophagous, thus demonstrating life-history omnivory and their potentially important role in the biological control of aphids and other pests. Several experiments have been conducted to assess whether the presence of flowers in or near crops has an effect on oviposition by syrphids, but the results have often been inconclusive. This paper describes a large-scale field experiment carried out over two years, in which standardised model flowers were placed in field margins and oviposition rates monitored near them. Statistically significantly more eggs were laid on broad bean (Vicia faba) infested with the pea aphid, Acyrthosipon pisum, near yellow model flowers with and without pollen and honey resources than at positions with no model flowers nearby. These results suggest strongly that the presence of model flowers increases hoverfly oviposition and that colour may be more important than food resources in enhancing this behaviour. This work indicates that biological control of pests by hoverflies can be enhanced by simple, non-floral agroecological intervention

Increasing floral diversity for selective enhancement of biological control agents: A double-edged sward?

Lavandero, B. Instituto de Biologia Vegetal y Biotecnología,Universidad de Talca,2 Norte 685,Casilla 747,Talca,Chile.Floral resource subsidies can have differential effects on insect herbivores compared with the herbivores’ natural enemies. While the nectar of many plant species enhances parasitoid fitness, it may also increase damage by herbivores. This may occur as a result of enhanced herbivore fitness or by enhancing fourth-trophic-level processes, possibly disrupting a trophic cascade as a result. The responses of different arthropod guilds to different floral resource subsidies were compared using Plutella xylostella (Hyponomeutidae), its parasitoid Diadegma semiclausum (Ichneumonidae) and data from two other published herbivore–parasitoid systems. These were Dolichogenidea tasmanica (Braconidae) and its host Epiphyas postvittana, and Copidosoma koehleri (Encyrtidae) and its host Phthorimaea operculella. The parasitoids and hosts in the three systems exhibited differential responses to the nectar sources. The differential response was not explained by morphology, demonstrating that physical access to nectaries alone does not determine the potential of flowers as a food source. For some flowering plants, enhancement of herbivore and parasitoid fitness occurred. Other flowering plants, such as buckwheat and phacelia, conferred a selective enhancement on parasitoids by increasing only their fitness. More effective conservation biocontrol may be achieved by the provision of selective floral resources. Attempts to ‘engineer’ agroecosystems to enhance biological control require an extensive knowledge of the ecology of the herbivore, its enemies and their interactions with potential resource subsidies

Effects of ivermectin on pastureland ecology - reply

This editorial discusses the effects of ivermectin on pastureland ecology