Predators associated with the twospotted spider mite, Tetranychus urticae, on strawberry at Abbotsford, B.C., and development of non-chemical mite control

D. A. Raworth


Populations of the two spotted spider mite, Tetranychus urticae Koch on strawberry were sampled from 1983-86. The predaceous mite, Amblyseius fallacis (Garman), was predominant. Active adults were observed in February and November, earlier in the spring and later in the autumn than any other predator. Amblyseius fallacis, cecidomyiid flies of Aphidoletes sp. and the ladybird beetle, Stethorus punctum picipes Csy., all responded numerically to introductions of the twospotted mite but A. fallacis responded to the greatest degree. The rate of increase of A. fallacis on a 10& scale was 1.0335 ± 0.0621 per 100 degree-days above 4C (DD4) in the spring and summer, and 0.5481 ±0.0845 per 100 DD4 in late summer, about 2.1 x and 1.6 x per week on an arithmetic scale. Slide dip tests showed that populations of A. fallacis in the Lower Fraser Valley were resistant to the chemical compounds cyhexatin, endosulfan and malathion, partially resistant to diazinon and very susceptible to carbofuran, demeton , dicofol and dimethoate. Biocontrol of T. urticae is discussed in the context of integration with the chemical control of aphids, and predator release rates.

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