Within‐patch oviposition site shifts by spider mites in response to prior predation risks decrease predator patch exploitation

Abstract

In egg‐laying animals with no post‐oviposition parental care, between‐ or within‐patch oviposition site selection can determine offspring survival. However, despite the accumulation of evidence supporting the substantial impact predators have on oviposition site selection, few studies have examined whether oviposition site shift within patches (“micro‐oviposition shift”) reduces predation risk to offspring. The benefits of prey micro‐oviposition shift are underestimated in environments where predators cannot disperse from prey patches. In this study, we examined micro‐oviposition shift by the herbivorous mite Tetranychus kanzawai in response to the predatory mite, Neoseiulus womersleyi, by testing its effects on predator patch exploitation in situations where predatory mites were free to disperse from prey patches. Adult T. kanzawai females construct three‐dimensional webs on leaf surfaces and usually lay eggs under the webs; however, females that have experienced predation risks, shift oviposition sites onto the webs even in the absence of current predation risks. We compared the predation of eggs on webs deposited by predator‐experienced females with those on leaf surfaces. Predatory mites left prey patches with more eggs unpredated when higher proportions of prey eggs were located on webs, and egg survival on webs was much higher than that on leaf surfaces. These results indicate that a micro‐oviposition shift by predator‐experienced T. kanzawai protects offspring from predation, suggesting adaptive learning and subsociality in this species. Conversely, fecundity and longevity of predator‐experienced T. kanzawai females were not reduced compared to those of predator‐naïve females; we could not detect any costs associated with the learned micro‐oviposition shift. Moreover, the previously experienced predation risks did not promote between‐patch dispersal of T. kanzawai females against subsequently encountered predators. Based on these results, the relationships of between‐patch oviposition site selection and micro‐oviposition shift are discussed.

Behavioural flexibility in spider mites: oviposition site shifts based on past and present stimuli from conspecifics and predators

“…Offspring laid on the leaf surface can feed right after hatching, whereas those on webs first need to move onto the leaf surface before feeding. Thus, although oviposition on the web is beneficial in terms of predation avoidance [ 13 , 14 ], it may bring costs for nymph growth. We suggest that T. kanzawai females choose oviposition site corresponding to the current presence of conspecific eggs, and that their choice may promote effective predation avoidance.…”

“…This suggests that threat-experienced mites indeed perceived no predator on the new leaf. As mentioned above, the web is a safer site than the leaf surface for eggs [ 13 , 14 ], and in fact eggs laid on the web are less frequently predated in an open environment where the predatory mite N. womersleyi can disperse easily [ 14 ]. These results suggest that T. kanzawai females appear to change oviposition site in a new situation based on threat experience, functionally preparing against future egg predation.…”

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

“…However, predatory mites that specialise on spider mites will invade the webs [14] and feed preferentially on spider mite eggs [15,16]. In response to these attacks, adult female spider mites disperse from the invaded patches [4,17,18] or oviposit on the webs instead [19][20][21][22], an action we refer to as an oviposition site shift. These eggs are attached to complicated and irregular silk threads [23].…”

The stealthiness of predatory mites as spider mite biological control agents

“…Moreover, adult female spider mites that are aware of predatory mites can reduce predation by shifting their oviposition site onto the webs Yano, 2007, Lemos et al, 2010) where eggs are predated less than those on leaf surfaces (Otsuki and Yano, 2017). Therefore, whether predatory mites are detected by spider mites should largely determine the success of biological control of spider mites using predatory mites.…”

“…We also measured the proportions of spider mite eggs laid on webs in response to predatory mite eggs. We used T. kanzawai as the prey species, as this species has been reported to disperse (Oku et al, 2004, Bowler et al, 2013 or shift oviposition sites onto webs Yano, 2007, Otsuki andYano, 2017) in response to predatory mites. As predatory mites, we examined two commercialized biological control agents used against spider mites of the genus Tetranychus: Phytoseiulus persimilis (Hussey and Bravenboer, 1971) and Neosiulus californicus (Cooping, 2001).…”