Improving the control of Tetranychus urticae on edible glasshouse crops using a specialist coccinellid (Stethorus punctillum Weise) and a generalist mite (Amblyseius californicus McGregor) as biocontrol agents

Current glasshouse biological control practice relies on regular prophylact ic introductions of one or two 'best' species of natural enemy. Whilst this is effective for much of the time, occasional failures occur due to factor s such as differences in response to seasonal changes in environmental cond itions and/or host plant effects. This study looks at the predatory behavio ur of a specialist coccinellid, Stethorus punctillum Weise, and a generalis t mite, Amblyseius californicus McGregor (which predate on the two-spotted spider mite, Tetranychus urticae) in order to assess how they responded to temperatures and relative humidities typical of glasshouse conditions on fo ur edible crop plant species. Activity (distance covered, time spent walkin g, walking speed, angular velocity, and turning rate) was recorded at 20, 2 5 and 30 degrees C and at relative humidity (RH) levels of 33, 65 and 90%, on tomato, pepper, aubergine and cucumber leaves, and analysed using video- computer techniques. The results show that the activity of S. punctillum si gnificantly increased at higher temperature levels. Host plant species also strongly influenced the performance of the predator, with it being most ac tive on pepper and tomato and least active on aubergines. RH had no signifi cant influence. The activity and predation by A. californicus increased at low humidity levels, especially in terms of time spent moving and number of prey killed. Temperature levels had no significant influence, but host pla nt species strongly influenced the performance of the predator, which was m ost active on pepper, and least active on aubergines. Further research was conducted with semi-field trials to investigate the efficacy in controlling TSSM with different combination of predators. When contrasting the commerc ially available predatory mite Phytoseiulus persimilis, used alone, compare d with its use in a treatment with a combination of predator species, there was a stronger decrease in TSSM numbers on the crop plants in the latter t reatment.