Flowers in tri-trophic systems: mechanisms allowing selective exploitation by insect natural enemies for conservation biological control

Abstract

Many insects have coevolved with certain angiosperm taxa to act as pollinators. However, the nectar and pollen from such flowers is also widely fed upon by other insects, including entomophagous species. Conservation biological control seeks to maximise the impact of these natural enemies on crop pests by enhancing availability of nectar and pollen-rich plants in agroecosystems. A risk with this approach is that pests may also benefit from the food resource. We show that the flowers of some plants (viz., buckwheat, Fagopyron esculentum Moench and dill, Anethum graveolens L.), and the extrafloral nectaries of faba bean (Vicia faba L.) benefit both Copidosoma koehleri Blanchard (Hymenoptera: Encyrtidae) and its host, the potato pest, Phthorimaea operculella Zeller (Lepidoptera: Gelechiidae). In contrast, phacelia (Phacelia tanacetifolia Benth) and nasturtium (Tropaeoleum majus L.) benefited only the parasitoid. When adult moths of P. operculella were caged with flowers of phacelia or nasturtium, longevity of males and females, egg laying life, fecundity, average oviposition rate, and number of eggs in ovaries at death were no greater than in the control treatment with access to shoots without flowers plus water. All the foregoing measures were increased compared to the control when the moths were allowed access to dill, buckwheat or faba bean extrafloral nectaries. Such 'selectivity' has the potential to make the use of floral resources in conservation biological control more strategic. We present morphometric and observational evidence to illustrate how such mechanisms may operate.

Evaluation of floral resources for enhancement of fitness of Gonatocerus ashmeadi, an egg parasitoid of the glassy-winged sharpshooter, Homalodisca vitripennis

“…Hyperparasitism or predation of parasitoids may be higher at close proximity to Xoral patches and may lead to signiWcantly higher mortality of foraging adult parasitoids (Rosenheim, 1998;Stephens et al, 1998). Provisioning of Xoral resources may also enhance pest Wtness (Irvin et al, 2006b;Baggen et al, 1999), in turn masking any eVect of Xoral resources on the natural-enemy population and herbivore population (Lavandero et al, 2006). Baggen et al (1999) demonstrated that 'selective resource subsidies' can beneWt parasitoids and not the target pest.…”

“…Provisioning of Xoral resources may also enhance pest Wtness (Irvin et al, 2006b;Baggen et al, 1999), in turn masking any eVect of Xoral resources on the natural-enemy population and herbivore population (Lavandero et al, 2006). Baggen et al (1999) demonstrated that 'selective resource subsidies' can beneWt parasitoids and not the target pest. Further research is required to evaluate whether potential plant candidates for G. ashmeadi enhancement may act as potential reservoirs for H. vitripennis or X. fastidiosa.…”

Ecological restoration of farmland: progress and prospects

“…This could lead to disillusionment among agricultural and horticultural practitioners with habitat restoration methods. In order for these methods to be effective, their implementation must be guided by empirical and theoretical research, such as the initial screening of individual tussock grass (Thomas et al 1991;MacLeod et al 2004) or flower species alone (Baggen et al 1999;Lavandero et al 2006) and then in mixtures (Pontin et al 2006; i.e. a directed approach sensu Gurr et al 2004).…”

Effects of artificial diets and floral nectar on parasitization performance of Trichogramma brassicae Bezdenko, 1968 (Hymenoptera: Trichogrammatidae)

“…Parasitization performance of Trichogramma spp. (longevity, fecundity, adult emergence and female emergence) is known to be influenced by extrafloral nectar, pollen, honey, carbohydrate and protein (Ashley & Gonzalez, 1974;Hohmann et al, 1988;Baggen et al, 1999;Jervis et al, 2004;, Shearer & Atanassov, 2004Zhang et al, 2004;Wäckers, 2005;Witting-Bissinger, 2008).…”