The effect of fungus infection ofMetopolophium dirhodum [Hom.: Aphididae] on the oviposition behaviour of the aphid parasitoidAphidius rhopalosiphi [Hym.: Aphidiidae]

Abstract

The oviposition behaviour of the hymenopterous parasitoid Aphidius rhopalosiphi on Metopolophium dirhodum nymphs at successive stages of infection with the aphid-pathogenic fungus Erynia neoaphidis was compared with that on uninfected nymphs. The frequency with which the parasitoid attempted to oviposit diminished in aphids inoculated with the fungus 3 days previously, that is within only 24 h of dying of the infection, but not in those infected only 1 or 2 days previously. The parasitoid did not attempt to oviposit in aphids killed by the fungus. KEY-WORDS : Cereal aphids, parasitoid behaviour, Aphidiidae, Entomophthorales, fungus-parasitoid interactions.The rose grain aphid, Metopolophium dirhodum (Walker), is an occasional pest of cereals in Great Britain and Europe, responsible in some years, most recently 1979, for large yield losses (Prew et al., 1983). The numbers of this aphid are normally controlled by a complex of natural enemies including hymenopterous parasitoids and fungi of the order Entomophthorales. The importance of these organisms in controlling the aphid is partly affected by their interactions.Previous work on the parasitoid Aphidius rhopalosiphi de Stefani Perez and the fungus Erynia neoaphidis Remaudi6re & Hennebert as representatives Of these groups of organisms attacking M. dirhodum showed that the development of the parasitoid larva was almost entirely prevented if the fungus infected an aphid parasitized up to 3 days earlier but that infection thereafter had progressively less effect on parasitoid development (Powell et al., 1986). This was explained simply on the grounds that the development time of the parasitoid is longer (8-9 days at 20 *C) than the incubation period of the fungus, from host inoculation to death (3-4 days), giving the fungus a competitive advantage. Similar results were obtained for other aphid/parasitoid/fungus systems (Milner et al., 1984).If parasitoid development is prevented even when the aphid is infected after parasitisation then clearly the parasitoid will be unable to complete development in an already infected aphid. The effect of fungus infection on the oviposition behaviour of a parasitoid has not been investigated. However, some parasitoids avoid intraspecific super-parasitism and sometimes even interspecific super-parasitism by recognizing and not ovipositing in (*) To whom requests for reprints should be addressed.

Influence of plant resistance at the third trophic level: interactions between parasitoids and entomopathogenic fungi of cereal aphids

“…Dispersal or transmission of the fungi by the parasitoid into a new experimental environment free of infective conidia did not occur. Since the parasitoid does not attempt to oviposit in sporulating aphids (Brobyn et al 1988), it is unlikely that an infective conidium would reach the parasitoid, to be dispersed and subsequently infect other aphids. In addition, grooming behaviour is characteristic of many parasitoids and may further reduce their potential as eective fungal vectors.…”

“…In the ®eld, negative correlations between parasitoid and fungal abundance suggest potential antagonistic or competitive interactions between them during the growing season (Powell et al 1986). In laboratory studies it was shown that the parasitoid only reached the adult stage if oviposition had occurred at least 4 days before fungal infection (Powell et al 1986), and that parasitoids continued to oviposit in infected aphids until one day prior to fungus-induced death (Brobyn et al 1988). Although competition of this type has never been tested experimentally in the ®eld, cereal aphid populations¯uctuate from low levels to pest status within and between growing seasons (Carter 1994) and, under circumstances of low aphid density and high parasitoid and/or fungus densities, aphids are likely to become a limiting resource such that competition between A. rhopalosiphi and E. neoaphidis could become important.…”

BIZARRE INTERACTIONS AND ENDGAMES: Entomopathogenic Fungi and Their Arthropod Hosts

“…Regardless of direct susceptibility, some parasitoids detect and avoid infected hosts (27,61) and some decrease the susceptibility of their host to subsequent fungal attack, an example of the parasitoid hijacking its host's physiology to avoid competition (23,28). In contrast, there are also examples in which parasitoids do not alter their attack behavior until the host is close to death (11). Aphidius ervi, although not directly susceptible, competes for aphid hosts with the fungal pathogen P. neoaphidis.…”

Compatibility among entomopathogenic hyphocreales and two beneficial insects used to control Trialeurodes vaporariorum (Hemiptera: Aleurodidae) in Mediterranean greenhouses

“…Depending on the protagonists, their interactions may be detrimental, inconsequential or even mutually beneficial (Brooks, 1993). Some aspects of fungusparasitoid interactions have been studied, mainly in aphid hosts (Milner et al, 1984;Powell et al, 1986;Brobyn et al, 1988;Poprawskti et al, 1992;Mesquita et al, 1997;Mesquita and Lacey, 2001) and, to a lesser extent, in whitefly hosts (Fransen and van Lenteren, 1994). Despite these studies, there is a relative lack of data on the susceptibility of parasitoids and predators to entomopathogenic fungi used as mycoinsecticides under laboratory and field conditions.…”