A novel method for protecting slow-release sachets of predatory mites Neoseiulus californicus (McGregor) against environmental stresses and for increasing release of predators in greenhouses
Abstract: Release methods of predatory mites have been developed to enhance their effectiveness in spider mite control. A popular method is the use of predators kept in bottles with wheat bran or vermiculite carriers: one advantage is that predator dispersal throughout plants can occur quickly after release. Another popular method is “slow-release sachets” that contain predators, prey mites and their food, along with wheat bran: many predators can be released from sachets for several weeks. However, predator release using these methods is sometimes inhibited by environmental stresses such as pesticide sprays and severe wet conditions. To resolve these problems, we developed plant-attached shelters made of waterproof paper that hold the sachets (“sheltered sachets”). We conducted laboratory experiments to determine whether sheltered sachets can protect Neoseiulus californicus against drenching and pesticides. Predators in unsheltered sachets (i.e. sachets alone) were decreased after continuous spraying with water or after pesticide spraying, whereas sheltered sachets were not seriously affected. Furthermore, we found that more predators were released from sheltered sachets moisturized with a humidifier than from unsheltered sachets under dry conditions. These results indicated that sheltered sachets were potentially useful in protecting the predatory mites against environmental stresses and enhancing their release to crops.