Phytoseiulus persimilis

Phytoseiulus persimilis is a specialized predator of spider mites (mainly those in the genus Tetranychus), and as such is the most commonly used biological control agent for two-spotted spider mite (Tetranychus urticae)_ The adults of P. persimilis are approximately 0.5 mm long (similar in size to adult spider mites), with a pear-shaped body and relatively long legs; adults are bright orange-red in colour, while the immature stages are somewhat paler.  The small oval eggs are Iaid close to (or in) the webbing of spider mite colonies, and hatch into a six-legged larval stage that does not feed; however, all subsequent stages (protonymph, deutonymph and adult) will prey on spider mite eggs, immatures and/or adults.

The activity and reproductive success of P persimilis is strongly influenced by temperature and humidity, with the optimum temperature range being from 20 to 26°’C (68—79°F) with relative humidities of 65-80%. At 26°C, the life-cycle (egg to adult) can be completed in approximately days, and the adults can be expected to live for 12—25 days; in that time, each adult may consume adult spider mites or 15-20 eggs per day_ Each female can lay a total of approximately 50-60 eggs.

Note that while P. persimilis is an excellent predator of spider mites, it will not eat alternative prey and hence cannot survive long when spider mites are absent. It does not thrive at temperatures above 30°C (86°F) and survival of the egg stage in particular is also greatly reduced by exposure to Iow relative humidity (55% or less). Reduced efficacy may be seen on crops with very waxy leaves (e.g. carnations), or those with high densities of glandular hairs (such as most tomato varieties).