Pea aphid dropping behavior diminishes foraging efficiency of a predatory ladybeetle

Abstract

Antipredator defensive behaviors are a well‐studied and often crucial part of prey life histories, but little has been done to quantify how such behaviors affect natural enemies, their foraging, and their effectiveness as biological control agents. We explored how the generalist predatory coccinellid Harmonia axyridis Pallas (Coleoptera: Coccinellidae) affects the dropping behavior of the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), and in turn, how that defensive behavior affects the foraging efficiency of the predator. Experimental arenas that allowed or prevented pea aphid dropping were compared to determine how dropping influences the foraging of multiple life stages of H. axyridis: second instars, fourth instars, and adults. Dropping reduced predation on aphids by all ladybeetle life stages. Despite older predators inducing more dropping, aphid dropping reduced predation by approximately 40% across all ladybeetle life stages. Aphid dropping and predator consumption of aphids were both correlated with how much the predator moved, which also increased with predator life stage. We suggest that the high rates of dropping induced by H. axyridis and the subsequent decrease in H. axyridis foraging efficiency may partially explain why H. axyridis is less effective at controlling pea aphids than it is at controlling other aphid species that do not drop.

Food Relationships

“…Predation by Har. axyridis on A. pisum was reduced by approximately 40% by aphids dropping (Francke et al 2008 ). The ratio between aphid dropping and aphid consumption is correlated with the predator ' s stage of development and its rate of movement.…”

Personality variation in a clonal insect: The pea aphid,Acyrthosiphon pisum

“…5 days are a substantial part of an aphid's adult life: previous studies have measured an average of 6-10 days reproductive activity and adult longevity for pea aphids (Morgan, Walters, & Aegerter, 2001;Lu & Kuo, 2008) kept under similar temperature regimes as reported here. An individual's response to a predator threat can have substantial fitness consequences: the costs of staying on a plant can be high since dropping significantly reduces the risk of being predated by a coccinellid predator (Niku, 1976;Francke et al, 2008). At the same time, dropping off a plant entails costs as well (e.g., risk of desiccation, loss of foraging opportunity, risk of ground-predation; Roitberg & Myers, 1978;Dill et al, 1990;Losey & Denno, 1998b;Nelson, 2007).…”

“…However, in previous studies individual aphids were kept in groups (but see Braendle & Weisser, 2001) and conspecifics' reaction to predation risk has been shown to influence peer behavior in aphids (Montgomery & Nault, 1978;Dill, Fraser, & Roitberg, 1990). Secondly, most of those previous studies released predators at the host plant for a certain time period without controlling for predator activity (which influences escape behavior of aphids: Francke, Harmon, Harvey, & Ives, 2008) and without ensuring contact between the predator and prey. Finally, most studies assessed escape responses of individuals of just one to four clones.…”

Symbiont infection affects aphid defensive behaviours

“…Pea aphids also present a large repertoire of defensive strategies, including morphological, social, chemical and behavioural defences [4]. Most prevalent, however, are defensive behaviours like aggressiveness towards the enemy, or escape reactions [5].…”