Abstract
Predator searching efficiency increases in response to a variety of environmental cues associated with its prey. The sugary excretion of aphids (honeydew) has been found to act as a prey-associated cue for many aphid natural enemies. In the present study, the honeydew excreted by Acyrthosiphon pisum (Harris) was identified as an arrestant and a contact kairomone for young larvae and adults of a common predatory hoverfly, Episyrphus balteatus (De Geer) (Diptera: Syrphidae). First and second instar larvae increased their foraging behaviour in the honeydew-treated area. When plants were sprayed with crude honeydew, the speed of movement of female E. balteatus was significantly higher than in controls, resulting in a longer period of time spent on treated plants and laying eggs. We conclude that the honeydew excreted by A. pisum induces searching behaviour and acts as and arrestant not only for adults but also for young E. balteatus larvae.
Highlights
Homopteran insects, including aphids, excrete copious amounts of honeydew comprised of substances derived from both the host plant and the insect itself (Heidari & Copland, 1993; Leroy et al, 2011)
The honeydew excreted by Acyrthosiphon pisum (Harris) was identified as an arrestant and a contact kairomone for young larvae and adults of a common predatory hoverfly, Episyrphus balteatus (De Geer) (Diptera: Syrphidae)
Our behavioural observations showed that 80% of the first instar larvae tested immediately after hatching orientated themselves to the zone containing honeydew: a significant difference was observed between the two zones (x21 = 5.72; P = 0.017)
Summary
Homopteran insects, including aphids, excrete copious amounts of honeydew comprised of substances derived from both the host plant and the insect itself (i.e. specific sugars and amino acids) (Heidari & Copland, 1993; Leroy et al, 2011). Many studies have shown that this excretory product acts as an attractant for the adult stage of predators and parasitoids, such as Chrysopidae (McEwen et al, 1993; Petersen & Hunter, 2002), Coccinellidae (Evans & Dixon, 1986; Evans & Richard, 1997), Syrphidae (Budenberg & Powell, 1992; Shonouda, 1996; Bargen et al, 1998; Shonouda et al, 1998a, b; Sutherland et al, 2001) or Aphidiidae (Budenberg, 1990; Budenberg et al, 1992; Du et al, 1997) These studies demonstrated that aphid honeydew induces oviposition and increases localisation of hosts or prey. Gries (1986) noted that newly emerged syrphid larvae stretch their papillae for better perception of prey-associated odours which induce a search behaviour: after fixing its anal end to the surface, the larva raises the rest of its body: it touches the surface with its mouthparts before choosing a new direction (Bhatia, 1939)
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