Effect of host plant on parasitism ofHelicoverpa armigera (Lep.: Noctuidae) byMicroplitis demolitor (Hym.: Braconidae)

Abstract

Microplitis demolitorWilkinson is an important larval parasitoid of Helicoverpa armigera (Hiibner) and H. punctigera (Wallengren) in Australia. The effect of host plant on parasitism of second instar H. armigera by M. demolitor was investigated in a glasshouse experiment. Parasitism was low (0 %) on chickpea. Moderate to high levels of parasitism (22.4 % to 75.4 %) were recorded on sorghum, sunflower, maize, cotton and soybean. The results suggest that releases of larval parasitoids into chickpea are unlikely to enhance parasitismlevels during the first spring generation of Helicoverpa spp. KEY-WORDS : Host plant effect, larval parasitoids, biocontrol.Microplitis demolitor Wilkinson is a native larval parasitoid of two important crop pests, Helicoverpa armigera (Htibner) and H. punctigera (Wallengren), in Australia. It has been reported from a range of different host plants of Helicoverpa spp. where it sometimes achieves high levels of parasitism (Shepard et aL, 1983 ;Broadley, 1984 ;Zalucki et al., '1986).During favourable seasons, large populations of Helicoverpa spp. develop during winter in inland non-cropping regions and subsequently migrate to eastern cropping regions (Gregg et al., in press). Chickpea have become an important alternative to winter cereals in eastern Australian cropping regions since the mid 1980s, and in southern Queensland, chickpea flowering in spring (September-November) can be an important host for the first spring generation of Helicoverpa spp. Thus chickpea may allow early season population increases which could subsequently threaten traditional summer crops such as cotton, sorghum, soybean, maize and sunflower. In springtime surveys of field crops on the Darling Downs, Queensland, during 1985-87, parasitism of third and fourth instar Helicoverpa spp. by M. demolitor on chickpea was relatively low (0-4.4 %) (I. J. Titmarsh, Unpublished). It was not known whether low parasitism levels were the result of poor performance by the parasitoid on chickpea, as was reported for Cotesia kazak Telenga (Jalali et al., 1988), or simply low seasonal activity immediately following winter. A glasshouse trial was carried out to study the effect of host plant on the level of parasitism of H. armigera larvae by M. demolitor. The implications of these results for Helicoverpa spp. management in southern Queensland are discussed.

Host plant derived feeding deterrence towards ants in the turnip sawfly Athalia rosae

“…Effects of host plant species on the impact of predators and parasitoids on herbivores have been shown in different multitrophic systems (Murray & Rynne, 1994;Dicke, 2000;Trigo, 2000). In this study we demonstrate an influence of host chemistry on a generalist predator of a herbivorous Hymenopteran species.…”

A comparison of naïve and conditioned responses of three generalist endoparasitoids of lepidopteran larvae to host-induced plant odours

“…Nevertheless, it could be considered more of a specialist than the other two, which could explain a more specific use of host location cues (Vet and Dicke, 1992;Steidle and van Loon, 2003). However, more specialized species of the same genus have been shown to be very good learners (Drost et al, 1986;Hérard et al, 1988;Lewis et al, 1991;Murray and Rynne, 1994).…”

“…From previous studies we know that naïve females of M. rufiventris are also highly attracted to induced maize odours (Hoballah and Turlings, 2005;Tamò, 2006), but the effect of experience on this behaviour is unclear (Hoballah and Turlings, 2005). The behaviour of some other Microplitis species has been studied more extensively and indicates a keen ability of each species to learn to respond to host cues by association (Drost et al, 1986;Hérard et al, 1988;Murray and Rynne, 1994). It is unlikely, however, that the recorded behaviour of a particular species can be extrapolated to other species belonging to the same genus.…”

Spatio-Temporal Variation in Landscape Composition May Speed Resistance Evolution of Pests to Bt Crops

“…armigera and H . punctigera in Australian cotton [53, 54] and show increasing parasitism with host density at the scale of fields [55]. Similarly, viral and fungal pathogens often show density-dependent spread through fields [56].…”