Optimal Foraging Behavior and Efficient Biological Control Methods

Abstract

Insect parasitoids have been used for the biological control of insect pests through classical importations for the control of invasive phytophagous species, through seasonal or inundative releases for short-term suppression of indigenous or invasive pests, and through conservation of parasitoid activity by the provisioning of resource subsidies and alteration of management practices. In all cases, success in the suppression of a pest is dependent upon the behavioral decisions made by the parasitoid in searching for and parasitizing hosts. For example, in the case of classical biological control, patch choice decisions that maximize parasitoid fitness will tend to increase its regional impact, leading to greater suppression of the pest and success in biological control. In contrast, for augmentative biological control, the goal is to provide local pest suppression and behavior that maximizes fitness might, for example, lead parasitoids to abandon local patches of their hosts before the pest has been suppressed to the desired level. Thus, the behavioral ecology of insect parasitoids is central to the successful implementation of biological control programs.We explore how optimal foraging effects the suppression of global pest densities in a metapopulation context and to what extent the physiological condition and behavioral decisions of foraging parasitoids are likely to influence establishment and impact in classical biological control. In the case of inundative biological control, we discuss the trade-off between optimal foraging behavior and the level of pest suppression at a local scale and consider the use of chemical attractants and arrestants to increase parasitoid activity and patch time allocation. We also discuss the influence of host size and quality, and sex ratio (Wolbachia infection) on parasitoid mass rearing. Finally, the influence of nectar subsidies on parasitoid foraging behavior and host suppression is considered in the context of developing more efficient methods for conservation biological control.

Encapsulation rates of the parasitoid Anagyrus sp. nr. pseudococci, by three mealybug species (Hemiptera: Pseudococcidae)

“…Among natural enemies, parasitoids are the most important group for the biological control of insect pests (Mills and Wajnberg 2008). However, biological control using parasitoids can often be hampered by several factors, such as the occurrence of host immune defenses.…”

Using optimality models to improve the efficacy of parasitoids in biological control programmes

“…Although such a formal, scientific approach could lead to higher pest control efficacy than the usual trialand-error empirical method, the number of biological control programmes based on a theoretical framework remains very low. In fact, to date only a few have employed optimality models for selecting or manipulating parasitoid species (e.g., Waage, 1990;Mills & Wajnberg, 2008) but, in general, optimal models are working their way into population-management programmes. Ironically, the concept of state dependence in parasitoids was actually used to develop management decisions for some fisheries (Mangel et al, 2015).…”

“…The goal is to elucidate the roles of behaviour (in a broad sense) that enable organisms to adapt to their environment and thus to understand how animals were selected over the course of evolutionary time to maximise their long-term reproductive output (i.e., their fitness). In the case of insect parasitoids, such an approach can have a direct applied perspective as any behavioural strategy leading a parasitoid female to maximise the number of progeny produced may directly maximise the number of hosts attacked and pest control efficacy in biological control programmes (Mills & Wajnberg, 2008;Wajnberg et al, 2008). Of course, optimal behavioural strategies and biocontrol efficacy need not be congruent (see below) and here again, theoretical models can help to mitigate such differences (e.g., Roitberg, 2000).…”

Observations of parasitism and aggression by female Enoggera nassaui, an egg parasitoid of the eucalypt pest, Paropsis charybdis

“…On the other hand, time spent in aggression may increase a female's fitness (and maintain or even increase suppression of host populations) if intraspecific aggression enables the female to gain access to more hosts or prevents superparasitism. Decisions that maximise parasitoid fitness are expected to increase suppression of host populations (Mills and Wajnberg 2008), but does this prediction hold when females engage in active defence of hosts?…”