Phytoseiulus persimilis Athias-Henriot
Common name: None.
Geographical distribution: This predator has been dispersed around the world, initially by interested scientists and later through commerce, to wherever its main prey, the two-spotted spider, Tetranychus urticae, occurs. The predator has been introduced into the Middle East in the early 1960’s.
Host plants: Same as its prey.
Morphology: The brown-red, reticulated dorsum is about 0.3 mm in length, with 14 pairs of slightly-barbed setae plus two pairs of lateral setae. Five pairs of the dorsal setae (four laterals and one median) are much longer than the others. The sternal plate has three pairs of setae and is without preanal setae. A single, smooth macroseta is located on leg IV.
Life history: Phytoseiulus persimilis lives and places its eggs almost exclusively within the webbed colonies of T. urticae. It raises a generation in less than one week, oviposites ca 80 eggs/female (with a sex ratio of 0.84) in about 15 days at 26°C and 80% RH. The predator disperses by moving to the upper parts of wilting plants and “jumping” in to prevalent winds. It locates its prey by volatiles secreted by spider mite-infested plants.
Economic importance: Phytoseiulus persimilis is a major mainstay of greenhouse integrated pest management (IPM) programs intended to control spider mites on vegetables and ornamentals in many parts of the world. It has been introduced into many countries by trade and has become a notable biological control success. Trade names include “Phyto-line p” and “Spidex”, often sold in 500cm³ and 215cm³ bottles containing 2000 mites for application over wide areas, and also in 30 cm³ vials containing the same number of mites for treatment of ‘hot spots’. Trade names include “Phyto-line p” and “Spidex”. The predator reduces spider mite infestations on many crops, in temperate as well as subtropical regions, on ornamentals in greenhouses and on low-growing plants, such watermelons, in the open. It is a voracious forager for spider mites, an attribute that enables this predator to respond rapidly to changes in pest populations and to control them. But it swiftly kills all prey, and as P. persimilis cannot reproduce on other diets, its numbers then decline. In many cases P. persimilis is used like a pesticide (hence a ‘living pesticide’ or ‘biopesticide’), meant to provide rapid solutions to pest problems, but may have only a short-term (or single season) effect. This often occurs in greenhouses, glasshouses and in annual crop cultivation, where alternate host-plants for spider mites (e.g. weeds) have been removed. The scarcity of spider mites on alternate host plants causes a decline in spider mite numbers, followed by reductions in predator populations. If spider mite problems then recur, new releases of P. persimilis might be needed. In the field, where commercial plants are usually surrounded by other spider mite-infested crops or weeds, the predator can persist for longer periods. It is seldom used and rarely survives in arboreal situations, and efforts to control spider mites on fruit trees are seldom economically feasible. The predator is mass-reared in several facilities around the world and is available from many suppliers; they usually belong to strains that have become resistant to most pesticides in use.
An emerging problem in the use of P. persimilis is its susceptibility to contagious diseases with which it becomes infected while being mass-reared. Such diseases may reduce predator response to spider mite prey and reduce or curtail its fecundity.
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