Oviposition-site shift in phytophagous mites reflects a trade-off between predator avoidance and rainstorm resistance

Abstract

Predators can reduce prey population densities by driving them to undertake costly defences. Here, we report on a remarkable example of induced antipredator defence in spider mites that enhances the risk to rainstorms. Spider mites live on the undersides of host plant leaves and usually oviposit on the leaf undersurface. When they are threatened by predatory mites, they oviposit on three-dimensional webs to avoid egg predation, although the cost of ovipositing on webs has not yet been clearly determined. We prepared bean plants harbouring spider mite ( Tetranychus kanzawai ) eggs on either leaf surfaces or webs and exposed them to rainstorms outdoors. We found that fewer eggs remained on webs than on leaf surfaces. We then examined the synergistic effect of wind and rain by simulating both in the laboratory. We conclude that ovipositing on webs comes at a cost, as eggs are washed off the host plants by wind and rain. This may explain why spider mite populations decrease drastically in the rainy season, although they inhibit leaf undersides where they are not directly exposed to rainfall.

Predator‐ and killed prey‐induced fears bear significant cost to an invasive spider mite: Implications in pest management

“…However, in the presence of predation risk, T. kanzawai females shift their oviposition from leaf surface to webs, resulting in higher egg mortality due to wind and rain. 43 This could increase offspring mortality further in T. ludeni, which is worth testing in the future. We suggest that the nonconsumptive effects reported in this study may play a critical role in biological control using predators and should be considered for the evaluation of total T. ludeni population suppression by P. persimilis.…”

“…34,42 Furthermore, shift of oviposition from leaf surface to webs in response to predation risk results in higher egg mortality due to wind and rain. 43 Application of predatory mites for biological control is a wellestablished method against spider mite pests around the world, with Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) being the most used predator for the control of the serious invasive pest, Tetranychus urticae Koch (Acari: Tetranychidae). [44][45][46][47][48] These reports mainly evaluated the effectiveness of biological control based on the relationship between the release of P. persimilis and population size changes of T. urticae, assuming that the spider mite population decline is caused by direct predation.…”

Cooperative Behaviors in Group-Living Spider Mites

“…females usually do not deposit eggs on webs away from the leaf surface, which points at fitness costs of oviposition on webs. Costs may include delayed and/or more complicated access to the leaf surface by hatching offspring and/or eggs on webs away from the leaf surface being more strongly exposed to abiotic hazards such as rain and wind (Okada and Yano, 2021).…”

Avoidance of ant chemical traces by spider mites and its interpretation

“…Predators reduce prey population densities through consumption and by driving prey to adopt defenses (Werner and Peacor 2003 ; Preisser et al 2005 ) that are costly due to reduced foraging (Morrison 1999 ; Downes 2001 ), enhanced predation risk (Losey and Denno 1998 ; Sih et al 1998 ; Otsuki and Yano 2014a ) or exposure to abiotic stressors (Hirayama and Kasuya 2014 ; Okada and Yano 2021 ). The non-consumptive effects of predators on prey are sometimes comparable in strength to the effects of direct consumption (Lima 1998 ; Morrison 1999 ; Bolker et al 2003 ; Creel and Christianson 2008 ; Okada and Yano 2021 ).…”

“…Predators reduce prey population densities through consumption and by driving prey to adopt defenses (Werner and Peacor 2003 ; Preisser et al 2005 ) that are costly due to reduced foraging (Morrison 1999 ; Downes 2001 ), enhanced predation risk (Losey and Denno 1998 ; Sih et al 1998 ; Otsuki and Yano 2014a ) or exposure to abiotic stressors (Hirayama and Kasuya 2014 ; Okada and Yano 2021 ). The non-consumptive effects of predators on prey are sometimes comparable in strength to the effects of direct consumption (Lima 1998 ; Morrison 1999 ; Bolker et al 2003 ; Creel and Christianson 2008 ; Okada and Yano 2021 ). Considering the vast abundance of ants in nature (Hölldobler and Wilson 1994 ) and that their repellent traces do not immediately decline, prey arthropods that avoid ant traces may have far less flexibility in colonizing and moving onto their host plants than previously expected.…”