Interactions among exotic and native phytoseiids (Acari: Phytoseiidae) affect biocontrol of two-spotted spider mite on papaya

The two-spotted spider mite (TSSM), Tetranychus urticae is a major pest of papaya, in south Florida, where a newly naturalized predator, Neoseiulus longispinosus, has become the most abundant predator associated with this pest. Amblyseius largoensis and Neoseiulus californicus are other, phytoseiid predators on papaya and the exotic predator, Amblyseius swirskii, is often released to control other mite and insect pests. We investigated intra- and interspecific interactions among these four predatory mite species and their effects on biological control of TSSM. Cannibalism and intraguild predation were evaluated in the laboratory for all four predator species in the absence and presence of TSSM. Neoseiulus longispinosus was the most cannibalistic species in the absence of spider mites, and A. largoensis when spider mites were available. Amblyseius swirskii was the most aggressive intraguild predator, N. longispinosus was the least aggressive and most often the intraguild prey of other predators. Single and combined releases of A. swirskii and N. longispinosus were evaluated to assess the effects of cannibalism and intraguild predation on biocontrol of TSSM on potted papaya plants. Single releases of N. longispinosus significantly suppressed TSSM populations but releases of A. swirskii alone or in combination with N. longispinosus resulted in gradual increases in TSSM populations. Our results showed that N. longispinosus has potential to control TSSM on papaya, but the level of control can be negatively affected by 1) high levels of cannibalism at low prey densities, 2) intraguild predation by other mite predators and 3) releases of intraguild predators like A. swirskii.