Lying down with protective setae as an alternative antipredator defence in a non-webbing spider mite

Shuichi Yano,Kanako Shirotsuka

doi:10.1186/2193-1801-2-637

Abstract

An antipredator defence in the citrus red mite Panonychus citri, which does not produce protective webs, was examined experimentally. P. citri adult females lie down on citrus leaf surfaces with their dorsal setae (hair) directed in all upper directions. They seldom move in response to physical stimuli. Compared to normal lying females, both manipulated non-lying females and hair-removed females suffered higher predation by predatory mites. A predator approaching the body surface of a lying female inevitably created elasticity with a confronting seta, which eventually repelled the predator away from the female. These observations indicated that lying down with protective setae functions as an antipredator defence in P. citri females. This inflexible defence could also explain why the mite rarely runs away, even when it is consumed together with host plant leaves (via coincidental intraguild predation) by gigantic swallowtail caterpillars, against which protective setae are totally ineffective.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-2-637) contains supplementary material, which is available to authorized users.

Highlights

The life-dinner principle (Dawkins and Krebs 1979) predicts that antipredator behaviour should evolve faster than prey capture behaviour because successful defence means life to the prey, but only a lost meal to the predator
One can clearly see that setae forms and lying postures were different between the species: long setae of P. citri extend in independent directions, whereas short setae of T. kanzawai point in the same direction, and gaps between the mite body and the leaf surface were minimal in P. citri but variable in T. kanazawai (Figure 2)
Lying P. citri females did not move in response to external physical stimuli as a rule, except when they were stimulated at the tail end

Summary

Introduction

The life-dinner principle (Dawkins and Krebs 1979) predicts that antipredator behaviour should evolve faster than prey capture behaviour because successful defence means life to the prey, but only a lost meal to the predator. Spider mite and predatory mite systems offer one of the best examples of such predator–prey interactions: many spider mite species have developed co-operative defences against predators using three-dimensional protective webs (Saito 1986a; 1986b; Mori et al 1999; Yano 2012), the webs are ineffective against some predatory mites that specialize in preying on web-spinning spider mites (McMurtry et al 1970; Sabelis and Bakker 1992; Shimoda et al 2009) Spider mites such as the citrus red mite [Panonychus citri (McGregor)] that do not produce protective webs (Saito 1983) thrive under the same ecological conditions as mites producing protective webs. We hypothesised that by not moving in response to external stimuli, mites should realise a considerable benefit that overwhelms the cost of intraguild predation

Methods

Results

Conclusion