Interspecific variation in the escape responses of aphids: effect on risk of predation from foliar-foraging and ground-foraging predators

Abstract

A series of laboratory experiments was conducted to determine the effect of interspecific differences on prey defensive behavior on the susceptibility of two aphid species (Acyrthosiphon pisum and A. kondoi) to a ground-foraging predator, Harpalus pennsylvanicus, and a foliar-foraging predator, Coccinella septempunctata. These organisms are representative of a biologically and economically important predator/prey system in alfalfa. The primary defensive behavior of both aphid species toward C. septempunctata was to "drop" from the plant. Both aphid species were significantly more likely to drop from the plant in the presence of C. septempunctata. However, when C. septempunctata was present, a significantly lower proportion of A. kondoi individuals dropped (0.42 ± 0.07) compared to A. pisum (0.73 ± 0.08). As a result of their lower propensity to drop from the plant A. kondoi individuals are significantly more likely to be consumed by C. septempunctata. Conversely, the higher propensity of A. pisum individuals to drop increased their susceptibility to ground-foraging predators. When A. pisum was the prey species, ground-foraging predators made a significant contribution to overall aphid suppression and there was a significant synergistic interaction between ground and foliar-foraging predators. When A. kondoi was the prey there was no interaction between the predator species. As either a cause or consequence of its higher propensity to drop, A. pisum seems to be more adapted for survival and dispersal off the plant. In comparison to A. kondoi individuals, A. pisum individuals relocate plants more quickly (63 ± 41 s vs. 164 ± 39 s), disperse farther (18 ± 1.7 cm vs. 13 ± 0.66 cm), and survive longer (37 ± 2.0 h vs. 25 ± 2.0) off the plant. This study demonstrates the importance of prey defensive behavior in determining the susceptibility of a prey species to a multiple-predator complex.

Host Location by Apterous Aphids After Escape Dropping from the Plant

“…From an evolutionary perspective, the choice between defensive tactics, should be based on risk assessment and the tradeoff between cost and benefit (Dill et al, 1990). Among the behavioral tactics, dropping provides the greatest advantage, immediately eliminating the danger of predation on the plant, although it exposes the aphid to the risks of desiccation, starvation and ground predation (Dill et al, 1990;Losey and Denno, 1998a).…”

“…Dropping can be triggered by tactile stimulation, sensing the chemical, visual and vibrational cues produced by enemies, detecting the alarm pheromone produced by conspecifics, and combinations of the above (Clegg and Barlow, 1982;Dill et al, 1990;Stadler et al, 1994;Losey and Denno, 1998a). Various factors may influence dropping behavior, including genotypic variation, temperature, humidity, host plant quality, alarm pheromone quality and quantity, age, disease infection, parasitism, and enemy-specific traits (e.g., McAllister and Roitberg, 1987;Dill et al, 1990;Losey and Denno, 1998a;Braendle and Weisser, 2001). The frequent dropping in some species, despite the inherent risks, indicates that aphids should be able to efficiently locate a host after dropping.…”

Biodiversity and Resilience of Ecosystem Functions

“…Reactive 61 management might be too slow to avert consequent deficits in function, with impacts for 62 societal well-being [9]. An analogy of this situation is the difference between monitoring 63 whether a bridge is either standing (i.e. providing its function) or collapsed, prompting need 64 for a re-build, as opposed to monitoring and repairing damage to prevent the collapse from 65 ever happening.…”

Intersection between biodiversity conservation, agroecology, and ecosystem services

“…For example, ladybird beetles forage on vegetation thereby disrupting prey who then fall on the ground and are preyed upon by ground foraging predators (Losey and Denno 1998). Many pollination studies suggest that pollinators complement one another, but evidence for facilitation is more limited.…”