The influence of sublethal deposits of agricultural mineral oil on the functional and numerical responses of Phytoseiulus persimilis (Acari: Phytoseiidae) to its prey, Tetranychus urticae (Acari: Tetranychidae)

Abstract

Occasional pesticide application in integrated pest management to at least part of a crop requires that any biological control agents must re-invade previously sprayed areas in order that resurgent pests can be constrained. The ability of the phytoseiid predatory mite Phytoseiulus persimilis to feed on adult two-spotted spider mite (TSSM) Tetranychus urticae on excised leaf discs in both control conditions and in a treatment with a sub lethal residue of agricultural mineral oil (AMO) was assessed. The predator exhibited a Type II functional response with the asymptote significantly higher in the AMO conditions due to the fact that the prey grew slower and reached a smaller size in this treatment. In terms of prey volume eaten, the satiation level of the predator was unchanged by the AMO deposits. The numbers of eggs produced by adult P. persimilis females at densities of 4, 8 and 16 TSSM adult females/disc in the control were significantly higher than those in the AMO treatment, but were similar for the higher density levels, 32 and 64 prey per disc. Thus the functional response in terms of volume of prey eaten explained the numerical response in terms of predator eggs produced. The presence of AMO deposits when the prey were at high density had no effect on predator efficiency (volume eaten) but resulted in a lower intake than that in control conditions when there was a greater distance between prey.

Respuesta funcional de Phytoseiulus persimilis sobre Oligonychus punicae (Acari: Phytoseiidae, Tetranychidae) en hojas de aguacate

“…El tiempo de manipulación del depredador (Th) fue de 0.0317, 0.0556 y 0.1147 para larvas ninfas y adultos respectivamente. En este sentido, Xue et al (2009) mencionan un promedio diario de consumo de 5.45 adultos por depredador de P. persimilis en una densidad de 64 hembras de T. urticae ofrecidas en discos de hoja de frijol y un (Th) de 0.1734 y (a′) de 1.5573. Gharekhani et al (2014) registran una tasa de ataque y tiempo de manipulación de 2.415 y 0.00154 para estos mismos especímenes.…”

Herbicides Harm Key Orchard Predatory Mites

“…Given the potential of adjuvants to increase the harm of herbicides and other pesticides to natural enemies, this line of research should be further investigated to improve conservation recommendations. This is particularly true for the phytoseiids; many adjuvants are oils, which are known to have at least minor non-target effects on predatory mites [ 24 , 25 ].…”