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Cannibalism and intraguild predation (IGP) are two common interactions occurs in animal kingdom which influence their population structure and dynamics. Neoseiulus barkeri (Hughes) and Scolothrips takahashii (Priesner) are important natural enemies of citrus red mite Panonychus citri (McGregor). However, little was known about their interactions and how the availability of extraguild (EG) prey P. citri modulated their interactions. In this study, we determined incidences of cannibalism and intraguild predation of these two predators when different densities of extraguild prey P. citri were available. Our results showed that incidences of both cannibalism and IGP and were significantly reduced in the presence of the extraguild prey. The intraguild predation between N. barkeri and S. takahashii was bidirectional, but N. barkeri was a predominant intraguild predator over S. takahashii. The S. takahashii fed on immobile N. barkeri egg, and N. barkeri fed on inactive prepupa and pupa of S. takahashii, but the conspecifics seldom did. Our results indicated that the interactions of predators decreased significantly when prey was available. The predatory mite N. barkeri was a stronger interspecific competitor. The results of this study may be useful in developing effective biological control strategies against P. citri.

Organisms are always confronted with multiple stressors simultaneously. Combinations of stressors, rather than single stressor, may be more appropriate in evaluating the stress they experience. N. barkeri is one of predatory mite species that are commercialized for controlling spider mites. However, their biological control efficiency was often reduced because of high temperature and desiccation in summer. To understand how to improve the tolerance of N. barkeri to combined heat and desiccation stress, we pre-exposed the adult female of N. barkeri to high temperature, desiccation and high temperature &times, desiccation stress for acclimation. After proper recovery time, mites were subjected to high temperature &times, desiccation stress again to detect the acclimation effects. The results are as follows: (1) No decrease in mortality rate were observed under high temperature &times, desiccation stress after heat acclimation. Instead, it increased significantly with acclimation temperature and time. (2) Dehydration acclimation both at 25 &deg, C and high temperatures reduced mortality rate under high temperature &times, desiccation stress. Mortality rate was only significantly correlated with the amount of water loss, but not with temperature or water loss rate in acclimation, suggesting the increased tolerance is related to dehydration stress rather than heat stress. Among all acclimations, chronic dehydration at 25 &deg, C, 50% relative humidity were the most effective treatment. This study indicated dehydration acclimation is effective to enhance tolerance of N. barkeri to combined heat and desiccation stress, which can improve the efficiency of biological control under multiple stressors.

The predatory mite Neoseiulus barkeri (Hughes) is a good biological control agent for many small sucking pests. We aimed to determine whether rearing long term on alternative prey versus target prey species affected the performance of N. barkeri. Therefore, we investigated the prey preference, life tables, and population parameters of N. barkeri between alternative prey Tyrophagus putrescentiae (Schrank) and three species of spider mites, Tetranychus urticae Koch, Panonychus citri (McGregor), and Eotetranychus kankitus Ehara. We found that N. barkeri preferred the tetranychid mites to the alternative prey. Between the tetranychid mites, the predator consumed more P. citri and E. kankitus than T. urticae. When reared on T. urticae, the total developmental time and longevity of N. barkeri were the longest, whereas the intrinsic rate of increase was the lowest, indicating that the biotic fitness of predatory mite preyed on target of T. urticae was higher than on alternative prey of T. putrescentiae. However, total developmental time, longevity, and fecundity did not differ between N. barkeri reared on T. putrescentiae and P. citri, although these parameters were higher than those for mites reared on E. kankitus, indicating that the predatory mite reared on T. putrescentiae may not be affected to control P. citri, and that coexistence of P. citri and E. kankitus may enhance the control efficiency of N. barkeri. Altogether, our results demonstrated that long-term feeding on the alternative prey T. putrescentiae did not affect the performance of the predatory mite N. barkeri on various target spider mites.

Eotetranychus kankitus Ehara (Acari: Tetranychidae) is an important pest in Chinese citrus orchards. In the present study, we aimed to evaluate the potential of Neoseiulus barkeri (Hughes) (Acari: Phytoseiidae) for the biological control of E. kankitus. A two-sex life table of E. kankitus and N. barkeri was constructed to estimate development and fecundity. The functional response and stage-specific predation rate were analyzed to evaluate predation capacity. In addition, a timing model was used to project populations of E. kankitus with release of N. barkeri. Results showed that N. barkeri was able to develop and reproduce when fed on E. kankitus. The functional responses of N. barkeri on different stages of E. kankitus all fit the Holling II disc equation. When mixed stages of E. kankitus coexisted, N. barkeri mainly consumed larvae and nymphs. Based on the life tables and stage-specific predation rates, population projection revealed the stage structure and growth rate of N. barkeri on E. kankitus. Although E. kankitus had the higher growth rate, it was maintained at a low population level for several weeks after release of N. barkeri. The results highlighted the potential for utilizing N. barkeri as a biological control agent of E. kankitus.