Two-spotted spider mite, Tetranychus urticae Koch (Acari: Prostigmata), is one of the most economically important mite species, mainly controlled by chemical acaricides. Natural enemies have been assessed as reliable alternatives for management of this phytophagous mite. In the current project, demographic characteristics of Neoseiulus californicus McGregor (Acari: Phytoseiidae) to sublethal concentrations (LC10 = 6.76 × 102, LC20 = 8.74 × 103 and LC30 = 55.38 × 103 conidia ml−1) of entomopathogenic fungus, Beauveria bassiana (Bals.) Vuill. TV strain were investigated under laboratory conditions at 25 ± 2°C, 70 ± 5% RH and a photoperiod of 16:8 (L:D) h. Our results indicated that when adult predators were exposed to LC20 and LC30 of B. bassiana, the oviposition period was significantly reduced compared with other treatments. Neoseiulus californicus fecundity was significantly greater in the control (37 eggs) than in LC30 (24 eggs). Life table analysis revealed that the net reproductive rate (R0) declined as the sublethal concentrations of B. bassiana increased. The most striking result to emerge from the data is that not only intrinsic (r); but also, finite rate of increase (λ) was not significantly affected by different concentrations of B. bassiana. Our findings revealed some potential interactions of B. bassiana and N. californicus during their combinations for managing T. urticae that may be helpful for optimising control of this important pest.

Better performance of generalist predators, as well as an increase in their density, may be an incentive factor in the ability of the predators to exploit more than one food item or mixed diets. In this study, the effects of four pollen grains (cedar, pear, apricot, and pistachio) when provided to Neoseiulus californicus in mixed diets with prey, Tetranychus urticae, were evaluated. The result indicated that the fastest female developmental time was observed on pistachio pollen + T. urticae, together with apricot pollen + T. urticae. Females reared on the mixed diet comprising pistachio pollen reflected the longest total life span duration, while the shortest total life span was observed in those on the diet that included pear pollen. Furthermore, the lowest fecundity, as well as the shortest reproduction period, was determined on the diets that included pear pollen, while the highest fecundity and the longest reproduction period were observed in pistachio pollen + T. urticae. In addition, the intrinsic (r) and finite rate of increase (λ), net (R0) and gross (GRR) reproductive rates were highest in pistachio pollen + T. urticae. These findings have important implications for developing a comprehensive biological control program of T. urticae, which will be discussed.

Predators are important determinants of the spatiotemporal distribution of prey within a given habitat. The predator effects may vary with diet specialisation, the associated risk posed to prey and, if multiple predators are present, the predator-predator interactions. We examined the spatiotemporal distribution of the herbivorous spider mite Tetranychus urticae and the associated specialist and generalist predators Phytoseiulus persimilis and Neoseiulus californicus on bean plants. Tetranychus urticae is a key pest on numerous agricultural crops. Both predators are used singly and in combination for biological control of spider mites. Population development and within-plant distribution of the spider mites and the predators were compared among five treatments: T. urticae without predators, with either predator alone and with both predators in combination at full and half densities. The spider mites were suppressed to zero density in both predator combination treatments but not in the single predator treatments. The predators determined the spatiotemporal distribution of the spider mites through density- and behaviour-mediated effects, and these effects were linked to diet specialisation. The specialist P. persimilis exerted stronger density-mediated effects on the spider mite distribution than did the generalist N. californicus. Either predator induced in the spider mites early upward migration on plants. The predators also affected each other's distribution. The aggregation level of N. californicus was lowered by P. persimilis but not vice versa. In combination, the predators were more dispersed than when alone, reducing the predator-free space and leading to the local extinction of T. urticae.