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Biological Studies on Galendromus flumenis (Acari: Phytoseiidae), a Predator of Banks Grass Mite


The predatory mite, Galendromus flumenis (Chant) (Acari: Phytoseiidae), is the most abundant predator and the only phytoseiid species on date bunches infested with Banks grass mite, Oligonychus pratensis (Banks) (Acari: Tetranychidae). Biological studies were conducted on this predatory mite in order to develop and optimize biological control strategies against the Banks grass mite.

In the first chapter, studies showed that G. flumenis feeds on all immature stages of Banks grass mite, but it prefers eggs over the other stages. Functional response studies indicated that the predator displays a type II response on all immature stages of the prey. The mutual interference study in Chapter 2 revealed that total predation increased with increasing G. flumenis density in two arena sizes. However, there was not a proportional increase in per capita predation due to mutual interference. The interference effect was high in small arenas due to higher encounter rates between predators. Also, higher predator density and smaller arena size caused significantly higher dispersal rate of predators.

In Chapter 3 data show that G. flumenis develops under a wide range of temperatures from 18°C to 42°C, but survival rates were highest between 26°C and 38°C. The optimal temperature for development (Topt) was calculated to be 37.6°C. Further work on the population growth and reproduction of G. flumenis (Chapter 4) showed that predators cannot oviposit at 38°C (Topt). At 34°C, the next temperature with the shortest developmental time for the predator, G. flumenis showed medium reproductive capacity (1.6 eggs/ day and 19.9 eggs/ ovipositional period), which is inferior to its prey. The net reproductive rate of prey can reach three times the maximum potential of G. flumenis, contributing to an intrinsic rate of natural increase of the prey that is more than double that of the predator.

In the final chapter, treatment with the miticide hexythiazox had little or no effect on immature development and reproduction of emerging adult predators. Hexythiazox did not have any adverse effect on the fecundity of treated females, hatch rate of eggs, progeny development, or sex ratio.

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