Female performance towards offspring under starved conditions in four phytoseiid species (Acari, Phytoseiidae).

Abstract

There is an important difference between cannibalism between unrelated individuals and between a mother and its offspring, because the former can be defined as a form of intraspecific competition, but the latter affects the inclusive fitness of individuals. Many examples of cannibalism have been reported in predacious phytoseiid mites. Furthermore, sib cannibalism avoidance is known in several species. However, whether females' actually prey upon their offspring under starved conditions has yet to be established. Here, female performance towards their offspring under no-prey-other-than-offspring, water-available and humidity-selectable conditions, was observed in four phytoseiid species, Amblyseius eharai, Amblyseius swirskii, Neoseiulus cucumeris and Typhlodromus bambusae. Typhlodromus bambusae females only survived for 4.14 ± 0.42 days and there was a significant difference in survival duration between T. bambusae and the other three species (all survived more than 8 days). Neoseiulus cucumeris females survived longer than A. eharai and A. swirskii females, whereas there was no difference between A. eharai and A. swirskii females. On the other hand, the offspring (immature stages from egg to larva or protonymph) of A. eharai, A. swirskii and N. cucumeris died earlier in mother-presence than in mother-absence (egg alone) experiments, suggesting that cannibalistic interactions occur between mother and offspring. The survivorship of T. bambusae offspring in the mother-presence condition did not differ from the mother-absence condition, indicating that kin cannibalism is rare in this species. This must be related to the phenomenon that mothers tend to die before their offspring. The short longevity of T. bambusae mothers is one of the reasons why there is no significant difference in immature survival between the mother-presence and mother-absence experiments. Lastly, the reason(s) behind such variation in female phytoseiid performance towards their offspring is addressed in relation to the diet-specialization hypothesis.