Life History and Population Dynamics of Tetranychus Tumidus in Florida (Acarina: Tetranychidae)

F. Saba


Tetranychus tumidus Banks, is a polyphagous spider mite that can thrive in the laboratory on over 70 host plants of various families, especially on many belonging to the Leguminosae, Malvaceae, Compositae and Gramineae; those in the Solanaceae appear unpalatable. The female mite developed slowly at 19@* C and required 21.5 days (20 for male) as compared to its development at 29@* C which required 8 days (7.5 days for male). At 24@* C the average daily rate of oviposition (4.21 eggs) and average number of eggs per female lifespan (49.67 eggs) were both higher than at 19 and 29@* C. Optimal temperatures appeared to be closer to 24 than to 29@* C. Field populations appeared in spring once morning low temperatures climbed into the upper teens and day-time highs into the twenties. Populations decreased in early summer and virtually disappeared when rains appearing in May and June established, together with the high temperature, optimal conditions for a spider mite fungus, Entomophthora, epidemic. Precipitation also reduced the population mechanically if occurring at 3 in. or more per 24 hr. The population remained practically negligible until early autumn when precipitation ceased. The 2nd population growth in autumn was halted and its decline commenced once temperatures dropped in October, or if prior to that, optimal conditions for fungus infection were established again. Phytoseiulus macropilis (Banks) was the only predator found in significant numbers among several predatory species recorded.

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