The ecology of Raoiella indica (Hirst: Tenuipalpidae) in India and Trinidad: Host plant relations and predator: prey relationships

Abstract

Red Palm Mite, Raoiella indica (Acari:Tenuipalpidae) (RPM), an Old World species first recorded in India (1924), was reported historically on a small number of host species of Arecaceae (palms) throughout Asia and the Middle East. In 2004, the mite invaded the New World resulting in high population densities and apparent new host associations- including Musa spp. (bananas and plantains). Subsequently, RPM has become widely established in the tropical Americas. The aim of the work was to understand some of the factors underlying the differences in RPM population status between the two regions by comparing morphological and molecular characteristics, investigating Old World host relations and comparing predator–prey interactions in India and Trinidad. Field population densities on main host Cocos nucifera were significantly higher in Trinidad compared to India. Substantial RPM field densities and breeding colonies were confirmed on Musa spp. in Trinidad, but not India; although RPM was shown to survive and lay eggs on Musa spp. in vitro in India. Arthropod predator diversity in India was higher on C. nucifera and lower on Musa spp. compared to Trinidad. Surveys on both host species only recorded predatory mites in Trinidad, whereas predatory insects and mites were recorded in India. Although molecular studies were unsuccessful, morphological studies showed that, independent of host plant, RPM had significantly longer lateral setae in the Caribbean compared to India. Adventive range populations may have resulted from a genetic bottleneck upon introduction. Assays in Trinidad showed that RPM with droplets on dorsal setae were contacted and consumed by Amblyseius largoensis on fewer occasions than those without. Setae may also play a role in defence against A. largoensis. Studies confirmed differences in RPM severity and status on host plants between regions and suggest natural enemies play a role in maintaining a narrow host range in India.