Host selection in phytophagous insects: a new explanation for learning in adults

Abstract

Insect learning can change the preferences an egg laying female displays towards different host plant species. Current hypotheses propose that learning may be advantageous in adult host selection behaviour through improved recognition, accuracy or selectivity in foraging. In this paper, we present a hypothesis for when learning can be advantageous without such improvements in adult host foraging. Specifically, that learning can be an advantageous strategy for egg laying females when larvae must feed on more than one plant in order to complete development, if the fitness of larvae is reduced when they switch to a different host species. Here, larvae benefit from developing on the most abundant host species, which is the most likely choice of host for an adult insect which increases its preference for a host species through learning. The hypothesis is formalised with a mathematical model and we provide evidence from studies on the behavioural ecology of a number of insect species which demonstrate that the assumptions of this hypothesis may frequently be fulfilled in nature. We discuss how multiple mechanisms may convey advantages in insect learning and that benefits to larval development, which have so far been overlooked, should be considered in explanations for the widespread occurrence of learning.

Quantitative genetics of preference and performance on chickpeas in the noctuid moth, Helicoverpa armigera

“…Previous studies have suggested that adult host preference is strongly influenced by factors such as plant abundance and experience with a particular host (Papaj and Rausher, 1987;Cunningham et al, 1998Cunningham et al, , 1999Cunningham and West, 2001). Whether the lack of preference for either genotype of chickpea found here is due to the inability to discriminate between the two or due to a lack of experience with either host, it seems likely that females encountering a large patch of host plants, as would occur in an agricultural situation, would oviposit regardless of the genotype present.…”

Invasive Spiraea tomentosa: a new host for monophagous Earias clorana?

“…Spiraea tomentosa is a widespread species in some areas of Central Europe. Even without direct improvements in adult foraging efficiency, evolution in the host selection behaviour of ovipositing insects can be advantageous because costs caused by switching hosts may be minimised in larvae that develop on a more abundant species (Cunningham et al 2001). Increased foraging efficiency on a particular, more abundant host species can outweigh the disadvantages of ignoring higher quality, but less abundant, host species.…”

“…An insect's choice of host plant depends on the insect's food preferences and its ability to change the host, which depends on the structure and chemistry of the new host plant, as well as the availability and abundance of the host species in the insect's habitat (Cunningham et al 2001;Harvey et al 2010). As insects are strongly dependent on their preferred food (Ehrlich and Raven 1964;Coley et al 2006), feeding on the optimal host plant allows them to obtain a larger body size (Haukioja and Neuvonen 1985;Ohmart et al 1985;Awmack and Leather 2002).…”

“…Conversely, another hypothesis, the "bad motherhood" hypothesis, suggests alternate scenarios in which a female could sometimes make "bad" (not the best) oviposition choices (Mayhew 2001), resulting in detrimental conditions for the growth and development of progeny (Digweed 2006;Gripenberg et al 2007). As the search for an alternative food source is a gradual process and is reversible upon encountering other host species, insects are most likely to utilise the most abundant host species (Cunningham et al 2001). This appears to favour the colonisation of invasive species, characterised by mass occurrence .…”

Oviposition behavior in wild Anastrepha obliqua (Macquart, 1835) (Diptera: Tephritidae): Initial study of associative learning related to a protein source.

“…In this way, on a subsequent encounter, the response that was previously elicited only by the meaningful stimulus is then elicited by the conditioned stimulus as well (Bernays, 1995). In insects, learning may change the preference for oviposition sites by females that are exposed to different host plants (Cunningham & West, 2001). Gravid females of Pieris rapae (Linnaeus, 1758) (Lepidoptera), for instance, associate a favorable chemical stimulus of oviposition with the appearance of the acceptable site, which facilitates host selection from a distance (Traynier, 1984).…”