長 泰行

Recently, we reported brood parasitism in the tiny predatory mite Neoseiulus californicus (Acari: Phytoseiidae); adult females of this species prefer to add their eggs to a cluster of eggs of another predatory mite species, Gynaeseius liturivorus (Acari: Phytoseiidae), which guards its own eggs against egg predators. Here, we investigated the cues used by the blind N. californicus to detect eggs of G. liturivorus. We show that N. californicus locates oviposition sites of G. liturivorus using volatiles emanating from eggs of the latter species. Adult female G. liturivorus spent more time guarding oviposition sites that contain more eggs, which resulted in a higher per capita survival of the eggs. We therefore hypothesized that N. californicus would prefer oviposition sites with more G. liturivorus eggs. Indeed, N. californicus preferably laid their egg at oviposition sites containing more than six G. liturivorus eggs, which corresponds to the average number laid by a female G. liturivorus during 1 day. Our results suggest that N. californicus uses egg volatiles to localize oviposition sites of G. liturivorus, where the eggs of the former are effectively protected against egg predators.

Many animal species protect their eggs against predators, and other species may profit from this by adding their eggs to those of the protecting species. We studied two tiny species of predatory mites that share a food source, are engaged in intraguild predation, and which eggs are attacked by the same egg predator. One of these predatory mites (Neoseiulus californicus) adds its eggs to those of the other species (Gynaeseius liturivorus) which guards its eggs from egg predators, resulting in reduced predation of the eggs of the nonguarding species. The guarding species experiences costs in the form of intraguild predation of her offspring, and the addition of eggs to the guarding species therefore qualifies as brood parasitism. In the presence of egg predators, the brood parasite preferentially adds its eggs to those of the guarding host species, not to those of another, nonguarding mite species. This cuckoo behaviour comes with a cost for the parasite when egg predators are absent, and therefore only occurs when egg predators are present. Our findings emphasize the importance of the risk of egg predation as a factor driving facultative brood parasitism. Read the free Plain Language Summary for this article on the Journal blog.