Influence of temperature and humidity on the survival of eggs of the thrips predator Amblyseius cucumeris.
1995
Houten Y.M. van | Lier A.M.M. van
The predatory mite Amblyseius cucumeris (Oudemans) is used for biological control of western flower thrips, Frankliniella occidentalis (Pregande), in greenhouse cucumbers. Under certain circumstances, however, this predator fails to control the pest. One possible cause for this failure is the susceptibility of the predator's eggs to low humidity conditions, which in greenhouses mainly occur during frost periods in winter or at bright hot days in summer. In the present study, the eggs of Ambleysius cucumeris were investigated, with respect to the following features: development time at 20 degrees, 25 degrees and 30 degrees C in order to obtain the maximum exposure time in the humidity experiments; tolerance to drought at 20 degrees, 25 degrees and 30 degrees C; tolerance to fluctuating humidities at 20 degrees and the survival of eggs on a cucumber crop at low humidity condition in a greenhouse. At 80 percent relative humidity the mean development time of A. cucumeris eggs was 4, 2, 4 and 1,8 days, at 20, 25 and 30 degrees C, respectively. The SD 50 (saturation deficit at which only 50 percent eggs hatch) increased at higher temperatures. The critical relative humidity for the suvival of eggs, however, was nearly the same at all temperatures. Eggs survived a period of extreme drought when it was followed by a period of high humidity. In a small greenhouse experiment on a cucumber crop it was shown that almost all eggs of A. cucumeris survived at relative air humidity of 45 percent.
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