Abstract
Abstract For herbivorous insects, dropping from the host plant is a commonly-observed antipredator defence. The use of dropping compared to other behaviours and its timing in relation to contact with a predator was explored in both pea aphids (Acyrthosiphon pisum) and potato aphids (Macrosiphum euphorbiae). Pea aphids dropped more frequently in response to ladybird adults (Adalia bipunctata) than lacewing larvae (Chrysoperla carnea). Potato aphids mainly walked away or backed-up in response to both predator types; but they dropped more frequently relative to other non-walking defences when faced with ladybird adults. Contact with a predator was an important influencer of dropping for both species, and most drops occurred from adjacent to the predator. Dropping appears to be a defence adaptively deployed only when the risk of imminent predation is high; factors that increase dropping likelihood include presence of faster-foraging predators such as adult ladybirds, predator proximity, and contact between aphid and predator.
Highlights
The threat of predation is a major selective force for prey species, driving the evolution of morphological, physiological and behavioural antipredator adaptations that increase the likelihood of survival (Edmunds, 1974; Caro, 2005; Ruxton et al, 2018)
Where aphid dropping occurs in relation to a foraging predator is not often recorded, even though this would be expected to affect the sense of imminent threat experienced by the prey. This current study explored a range of defensive behaviours exhibited by pea aphids and potato aphids (Macrosiphum euphorbiae) in response to two predator types with different foraging styles: two-spot ladybird (Adalia bipunctata) adults and lacewing (Chrysoperla carnea) larvae
We considered the propensity of pea aphids to use different defences in response to the two predator types
Summary
The threat of predation is a major selective force for prey species, driving the evolution of morphological, physiological and behavioural antipredator adaptations that increase the likelihood of survival (Edmunds, 1974; Caro, 2005; Ruxton et al, 2018). The obvious benefit of such a defence is immediate and rapid escape from the perceived threat (Losey & Denno, 1998a; Humphreys & Ruxton, 2019), but this behaviour can carry shortand long-term fitness costs to the dropped individual such as: exposure to new predators (Losey & Denno, 1998a), exposure to harsher environmental conditions (Ruth et al, 1975; Roitberg & Myers, 1979), reduced feeding time (Roitberg et al, 1979; Johnson et al, 2007), increased development time (Agabiti et al, 2016), and reduced lifetime fecundity (Nelson et al, 2004; Nelson & Rosenheim, 2006; Nelson, 2007; Agabiti et al, 2016). Dropping has been studied most commonly in aphids (order Hemiptera), a group in which post-dropping tonic immobility is exhibited (Bilska et al, 2018), and several abiotic and biotic factors have already been demonstrated to influence the trade-offs associated with the decision to drop (see Dill et al, 1990; Losey & Denno, 1998a, b; and Braendle & Weisser, 2001 for examples)
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