The predatory mite Phytoseiulus persimilis probably originates from Chile, but has currently been spread by man, on purpose or accidentally, throughout large areas of the world. A Phytoseiulus mite deposits her eggs in or close to a spider mite colony. They are distinguished from spider mite eggs by their oval shape, the light orange colour and because they are twice as big.

The larva, which has 6 legs, does not eat. Similarly to spider mites, the larval stage is followed by the protonymph, the deutonymph and the adult stage. Between the subsequent stages there is no quiescent stage. Once an adult, it takes at 20°C (68°F) about 2 days before the predatory mites start laying eggs. Under normal circumstances, the development time is shorter than for spider mites, and takes about 5 days at 30°C (86°F), 9 days at 20°C (68°F) and 25 days at 15°C (59°F).

Without fertilization the female cannot lay eggs. At 20°C (68°F) she deposits about 54 eggs during 22 days, but this can mount up to 75 eggs. So, under normal circumstances a Phytoseiulus population grows faster than a spider mite population. At higher temperatures (above 30°C or 86°F) or at dry weather (humidity below 60%) the spider mite is favoured and biological control is difficult. At low humidity the egg of the predatory mite shrivels.

The menu of Phytoseiulus nearly exclusively consists of spider mites. Only in case of lack of food the predatory mite eats its relatives. An adult Phytoseiulus devours all stages of spider mites, while Phytoseiulus nymphs only feed on spider mite eggs, larvae or protonymphs. The daily consumption of an adult Phytosiulus amounts to about 20 spider mite eggs or larvae, 13 protonymphs or 5 adults.

Although Phytoseiulus nymphs still stay at the same spot, adults readily move to other hot spots. If the plants touch each other, the predatory mite can spread relatively easily in the crop.

Application

Phytoseiulus can be applied on several greenhouse vegetables and ornamentals such as sweet pepper, cucumber, melon, eggplant, strawberry, bean, gerbera, rose and several pot plants. On tomato Biobest advises the use of the specially developed Phytoseiulus-T-System. For a successful biological control it is important to detect the pest presence on time and to act immediately. As a spider mite population grows faster in summer and it is then more difficult to keep pace with it, it is advised to control them early in the season as soon as the first spider mites wake up from hibernation.

After detecting the first spider mite hot spots, Phytoseiulus is released as soon as possible. Depending on the crop and the circumstances, an overall introduction of 3-6 Phytoseiulus/m² is advised. On and around the infested plants approximately 20 predatory mites/m² are released.

In order to be sure to obtain a biological balance early in the season, some growers prefer the Pre-Phytoseiulus-System. This consists of one tube of Phytoseiulus mites and two tubes of spider mites . On one plant two doses of spider mites are released on two different spots. In one of both introduction spots, one dose of Phytoseiulus is added. The predatory mites first exterminate the first spider mite colony, and then go looking for other spider mite colonies. Thanks to this early balance spider mite hot spots are kept down as from their emergence.

In normal conditions Phytoseiulus is able to protect the crop from spider mites for the rest of the cropping season. However, at dry and warm weather problems can still appear. Experience has shown that in this case, the control activity of Phytoseiulus can be supported by creating high relative humidity by spraying water with high pressure and through a fine nozzle.