Dropping to escape: a review of an under‐appreciated antipredator defence

Abstract

Dropping is a common antipredator defence that enables rapid escape from a perceived threat. However, despite its immediate effectiveness in predator–prey encounters (and against other dangers such as a parasitoid or an aggressive conspecific), it remains an under‐appreciated defence strategy in the scientific literature. Dropping has been recorded in a wide range of taxa, from primates to lizards, but has been studied most commonly in insects. Insects have been found to utilise dropping in response to both biotic and abiotic stimuli, sometimes dependent on mechanical or chemical cues. Whatever the trigger for dropping, the decision to drop by prey will present a range of inter‐related costs and benefits to the individual and so there will be subtle complexities in the trade‐offs surrounding this defensive behaviour. In predatory encounters, dropping by prey will also impose varying costs and benefits on the predator – or predators – involved in the system. There may be important trade‐offs involved in the decision made by predators regarding whether to pursue prey or not, but the predator perspective on dropping has been less explored at present. Beyond its function as an escape tactic, dropping has also been suggested to be an important precursor to flight in insects and further study could greatly improve understanding of its evolutionary importance. Dropping in insects could also prove of significant practical importance if an improved understanding can be applied to integrated pest‐management strategies. Currently the non‐consumptive effects of predators on their prey are under‐appreciated in biological control and it may be that the dropping behaviour of many pest species could be exploited via management practices to improve crop protection. Overall, this review aims to provide a comprehensive synthesis of the current literature on dropping and to raise awareness of this fascinating and widespread behaviour. It also seeks to offer some novel hypotheses and highlight key avenues for future research.

Ontogenetic differences in the chemical defence of flea beetles influence their predation risk

“…Insects evolved numerous strategies to escape predation including behavioural, structural and chemical defences (Gross, 1993;Humphreys & Ruxton, 2019;Pasteels, Grégoire, & Rowell-Rahier, 1983;Rettenmeyer, 1970). Which defence strategies an insect uses depends on the community of natural enemies it encounters, and this can change across insect ontogeny depending on the respective life style and habitat (Boege, Agrawal, & Thaler, 2019;Lindstedt, Murphy, & Mappes, 2019;Pasteels et al, 1983).…”

Bugs scaring bugs: enemy‐risk effects in biological control systems

“…Pest fitness may be affected by decreased foraging time due to refuge use or consistent foraging on lower quality resources. Some pests, particularly aphids, will drop off a plant in response to enemy risk (Humphreys and Ruxton, 2019). This behaviour incurs significant costs, as dropping reduces feeding time (Nelson and Rosenheim, 2006; Nelson, 2007).…”

Predators as drivers of insect defenses

“…This behavior helps them escape from spider predation (Miyatake et al 2004). Dropping is frequently used in combination with death feigning (Humphreys & Ruxton 2019). Phytophagous insects can escape from predators by dropping from host plants (Sugiura & Yamazaki 2006;Matsubara & Sugiura 2018).…”