Foraging Behaviour

In this chapter, we consider practical aspects of the foraging behaviour of insect natural enemies in its widest sense (so wide that we even include a few examples concerning non-insect arthopods, such as mites). Initially, most insect natural enemies must locate the habitat where potential victims may be found. Within that habitat, the victims themselves must be discovered. Once a patch of potential targets is identified, the predator or female parasitoid must choose its victim. Furthermore, in judging host quality, a female parasitoid must decide whether to feed from the host, to oviposit, or to do both. If she does decide to oviposit, then there are questions of sex allocation and offspring number that need to be addressed. All of these activities fall under the aegis of ‘foraging behaviour’. Studies of the foraging behaviour of insect natural enemies lie at the heart of much of modern ecology. These studies have taken two broadly defined pathways, where the emphasis is determined by the interest of the researcher (see below). Irrespective of the motivation of the researcher, it is clear that any attempt to understand the foraging behaviour of a predator or a parasitoid will greatly benefit from knowledge gleaned from both approaches. This crossfertilisation of ideas is something we try to emphasise in this chapter. In addition, we provide a review of the foraging behaviour of insect natural enemies. This is meant to be illustrative, with stress placed on the experiments used to study the behaviour itself. For greater detail on the behaviour of parasitoids one should refer to Godfray (1994), Quicke (1997) and Wajnberg et al. (2008) and, for a shorter overview, to Hardy and Godfray (2023). The literature on insect predators is much more diffuse, but New (1991) provides a good introduction to the behaviour of predators in general, while Dixon (2000) reviews the behaviour of ladybird beetles (Coccinellidae), and Davies et al. (2012) provide an excellent introduction to many aspects of animal behaviour in general. Where possible, we deal with insect predators and parasitoids together, although there are some sections (e.g., sex allocation, Sect. 1.11) where the examples come exclusively from the parasitoid literature, and other sections (e.g., superparasitism/cannibalism, Sect. 1.9) where both are dealt with, but separately. Nevertheless, many of the approaches to studying foraging behaviour, and the theory underpinning it, are similar for both predators and parasitoids. In this chapter, we first describe the methodological approaches that underpin studies of the foraging behaviour of insect natural enemies. Second, we discuss how the predators and parasitoids find the habitat patches where potential prey or hosts may be encountered. Third, we reflect on what occurs after the prey or host is found, dealing with issues such as clutch size and sex allocation decisions, and patch defence behaviour. We also deal with considerations such as the cost of reproduction to natural enemies and the resistance of their hosts or prey to being exploited. Finally, we touch briefly upon some of the wider population and ecological consequences of insect natural enemy foraging behaviour.

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