Raoiella indica Hirst (Acari: Tenuipalpidae) is a pest species that has expanded not only in geographical distribution but also in the number of host plants. Control measures are still being evaluated in recently invaded countries. In some countries and for some crops, spraying with botanical extracts has been used to reduce R. indica populations. Laboratory and field studies point to the predatory mite Amblyseius largoensis (Muma) (Acari: Phytoseiidae) as promising for combating R. indica. However, this predator has not yet been commercially available. Thus, the present study aimed to evaluate the potential of another predatory mite Neoseiulus barkeri Hughes, a commercially available generalist predator as a biological control agent of R. indica. The consumption and oviposition rate of N. barkeri were determined across the developmental stages of R. indica. The predation and oviposition capacity of N. barkeri and A. largoensis when fed R. indica eggs in the laboratory were compared. In the field, releases of the predator N. barkeri at densities of 900, 600 and 300 predators per plant were compared to spraying with botanical extracts such as cottonseed oil and azadirachtin to control R. indica. Our results suggested that N. barkeri is an effective predator to control R. indica. The consumption of N. barkeri was inversely related to the life stage of R. indica, and all developmental stages of R. indica enabled the reproduction of N. barkeri. The predation and oviposition of N. barkeri were higher than those of A. largoensis, and the releases of N. barkeri at densities of 900 and 600 predators/plant resulted in significant reductions in R. indica populations.

The mechanisms involved in the acceptance and choice of prey by predatory mites are still poorly understood. The present study was designed to determine whether previous feeding experience of Amblyseius largoensis (Muma) (Acari: Phytoseiidae) on Raoiella indica Hirst (Acari: Tenuipalpidae) eggs could influence the predator’s functional response and related parameters. The consumption of R. indica eggs by experienced and naïve female A. largoensis was evaluated under increasing densities of eggs. Regardless of the predators’ previous experience, a gradual increase in the number of eggs consumed and a tendency to stabilize at higher densities were observed. Proportionally, egg consumption decreased with increasing egg densities, indicating a type II functional response for both experienced and naïve predators. Experienced and naïve predators also had the same attack rate. However, naïve predators had a handling time almost 50% longer than experienced predators and showed lower variation in egg consumption and lower peak egg consumption. The results of the present study demonstrate that previous feeding experience may alter parameters of the functional response of A. largoensis to R. indica eggs but not the type of response. Possibly, longer associations between native populations of A. largoensis and R. indica results in more aggressive predator populations.

The coconut mite, Aceria guerreronis Keifer, is one of the main pests of the coconut tree (Cocos nucifera L.) worldwide. Its control is mainly based on the use of acaricides. However, due to the habitat of this pest mite, which is protected by fruit bracts that act as a physical barrier, chemical control is often inefficient. Thus, natural enemies have been studied as an alternative to acaricides. We evaluated the functional and numerical responses of Amblyseius aerialis (Muma) to increasing densities of A. guerreronis (40, 80, 160, 240 and 360) and additionally the oviposition rates of the phytoseiid A. aerialis over 11 days on different food sources: coconut pollen, A. guerreronis and a mix of pollen and A. guerreronis. Our results showed that Amblyseius aerialis showed a type III functional response, where prey consumption increasing as the density of A. guerreronis increased, with a maximum consumption of up to 175 prey per predator. All the prey densities allowed female oviposition. The number of eggs laid by A. aerialis increased with increasing prey density and stabilized between 240 and 360 A. guerreronis individuals, with an average oviposition of 1.7 eggs/female. Furthermore, our results showed that all the food sources (coconut pollen, A. guerreronis and a mix of pollen and A. guerreronis) supported oviposition. The mean oviposition was approximately 1.5 eggs/female on all the food sources. Our study suggests that A. aerialis can be effective in the biological control of A. guerreronis. However, further studies are needed to investigate whether A. aerialis can explore the habitat of A. guerreronis and if that prey can support the development of immature stages and the reproduction of A. aerialis.

Raoiella indica Hirst (Acari: Tenuipalpidae) is a polyphagous pest widely dispersed worldwide and a particular threat to crops from the Arecaceae family. Control measures are still being evaluated in recently invaded countries. A possible control strategy for this pest is the use of predatory mites. A recent study has suggested Neoseiulus barkeri Hughes (Acari: Phytoseiidae) as a potential biological control agent of R. indica. In the present study we determined the prey stage preference of N. barkeri when offered different stages of R. indica besides its functional response and numerical over its prey stage preferred. The predatory mite N. barkeri showed a marked preference for eggs over other stages of the prey. The regression analysis indicated that the predatory mite N. barkeri exhibited a Type II functional response. The prey density needed to start the oviposition was 10 R. indica eggs. The number of eggs laid by N. barkeri females increased with an increase in the prey density and tended to stabilize when prey availability was greater than 80 R. indica eggs, with average oviposition of 2 eggs/female. Our study suggests that N. barkeri shows potential to reduce populations of R. indica, especially at low prey densities. However, further studies are needed to investigate whether R. indica supports the development of immature stages of N. barkeri.

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