Intraspecific variations on thermal susceptibility in the predatory mite Neoseiulus barkeri Hughes (Acari: Phytoseiidae): responding to long-term heat acclimations and frequent heat hardenings

Abstract Biological control of spider mites using phytoseiid mites is frequently being disrupted by high temperatures, which results in an important and urgent research topic. We hypothesized that this scenario could be ameliorated if the thermal tolerance of a certain phytoseiid mite is enhanced. In this study, a high temperature adapted strain (HTAS) of the predatory mite Neoseiulus barkeri Hughes was selected from its conventional strain (CS) via a long-term heat acclimation (maintained at 35 °C) and frequent heat hardenings (exposed at 45 °C for 2 h every 15–25 days) over multiple generations. As expected, heat acclimation greatly improved the survival probabilities of N. barkeri when a single heat stress event occurred, with a median lethal time (e.g., at 45 °C) calculated as 15.2 h for HTAS females and 1.9 h for CS ones, respectively. After the heat acclimatory, HTAS showed a faster growth and developmental rate, and a higher immature survival rate than CS did; a significant reduced total fecundity rather than longevity was observed at 35 °C; a shifting from larger females to smaller males was observed (about 21% reduced in female ratio). Meanwhile, single heat stress event (e.g., exposed at 42 °C for 4 h) had a detrimental effect on the reproductive traits of the newly-emerged females, particularly obvious for mites from CS colony, by delaying the onset of oviposition and reducing reproductive output. This is the first experimental demonstration that the artificially heat acclimatory can shape the intraspecific variations on thermal susceptibility in a phytoseiid mite. It is suggested that HTAS N. barkeri might be a promising strain for the biological control of the high temperature favored spider mites, and more field and greenhouse trials should be evaluated in the future.