Clarifying the identity of Amblyseius swirskii and Amblyseius rykei (Acari: Phytoseiidae): are they two distinct species or two populations of one species?

The generalist predator Amblyseius swirskii is an efficient natural enemy of small insects and phytophagous mites, particularly thrips and spider mites. This phytoseiid species was considered for a long time as a subtropical species and Amblyseius rykei as a sub-Saharan African species. A recent revision of phytoseiid species of the subtribe Amblyseiina from sub-Saharan Africa Zannou et al. (Zootaxa 1550:1-47, 2007) determined that the two species are identical and synonymized them. To confirm or invalidate that morphological study, we crossed a Benin population of A. rykei and an Israel population of A. swirskii through two generations and back-crossed their hybrids to their parents. We also compared demographic parameters of both species on maize pollen, and their predation and oviposition rates on first larval instars of Frankliniella occidentalis. All females of homogamic and heterogamic crosses produced viable progeny, fertile F1 and viable F2. All the laid eggs hatched and sex ratio was female-biased for all crosses. Demographic parameters of the two species on maize pollen, and their predation rates and development times (egg to adult) on first instars of F. occidentalis were similar. Only oviposition of A. swirskii on larvae of F. occidentalis was significantly higher than that of A. rykei. These results indicate that A. rykei and A. swirkii are conspecific, and thus are a single species as concluded by Zannou et al.