Role of excreta in predator avoidance by the Kanzawa spider mite, Tetranychus kanzawai (Acari: Tetranychidae)

Keiko Oku

doi:10.14411/eje.2008.083

Abstract

The Kanzawa spider mite, Tetranychus kanzawai (Acari: Tetranychidae) constructs webs over leaf surfaces and usually lives under these webs. T. kanzawai produces two types of excreta, black and yellow pellets, and uses its webs as a place for excretion. T. kanzawai also uses its webs as a refuge when the predatory mite, Neoseiulus womersleyi (Acari: Phytoseiidae) is present. To clarify what factors deter N. womersleyi from foraging on T. kanzawai webs, I experimentally examined the effects of T. kanzawai excreta on its own fitness (fecundity) and the foraging behaviour of N. womersleyi. When the excreta of T. kanzawai was put on leaf surfaces, the fecundity of T. kanzawai adult females was reduced by the black but not the yellow faecal pellets. On the other hand, predation by N. womersleyi was reduced by the yellow but not the black pellets. Although this effect of the yellow pellets on N. womersleyi did not last on leaf surfaces, it deterred N. womersleyi from staying on the web regardless of its freshness. These results suggest that T. kanzawai deposits black pellets on webs to avoid its negative effect on their own fitness, and yellow pellets are deposited on webs to reduce the risk of predation.

Highlights

Many herbivorous arthropods use refuges on plants to avoid the risk of predation
Adult females of T. kanzawai excreted more pellets on webs than on leaf surfaces, with 83.3 ± 0.08 % of the black pellets and 65.4 ± 0.04 % of yellow pellets excreted on webs
Fresh yellow pellets of T. kanzawai negatively affected the number of T. kanzawai eggs consumed by N. womersleyi compared with clean leaves (d = 2.253, D = 0.05, P = 0.043; Fig. 4), but the presence of old yellow pellets on leaf surfaces did not affect the consumption of eggs by N. womersleyi (P = 0.861)

Summary

Introduction

Many herbivorous arthropods use refuges on plants to avoid the risk of predation. Herbivores select parts of host plants that are less likely to be searched by predators/parasitoids (e.g., Damman, 1987; Hopkins & Dixon, 1997). Absolute enemy free space seldom or never exists (Jeffries & Lawton, 1984), places where physical factors, such as plant structures, deter predators/parasitoids from foraging provide refuges for prey (e.g., Gross & Price, 1988; Venzon et al, 2000; Kasai et al, 2005). In the presence of the predatory mite, Neoseiulus womersleyi (Acari: Phytoseiidae), T. kanzawai uses its webs as a refuge (Oku et al, 2003, 2004). N. womersleyi can invade and move around on the webs of T. kanzawai (Ehara & Amano, 1993), it prefers to forage on the surfaces of leaves (Oku et al, 2006). This may explain why T. kanzawai webs function as a refuge for T. kanzawai, it is unknown what factors deter N. womersleyi from foraging on T. kanzawai webs

Methods

Results

Conclusion