Fitness costs associated with low-level dimethoate resistance in Phytoseiulus macropilis

Phytoseiulus macropilis Banks (Acari: Phytoseiidae) is an effective predator of tetranychid mites, but there are no data on its response to pesticides. We investigated the resistance of the predatory mite P. macropilis to the acaricides abamectin and dimethoate, and we examined the fitness costs associated with resistance. Two populations were tested: one from conventional cultivation and another from an area not commercially exploited. After the application of acaricides to the predator, we determined the lethal effects of the acaricides, the instantaneous rate of population increase (r(i)), the predation on Tetranychus urticae Koch (Acari: Tetranychidae) and its ability to locate prey in an olfactometer. P. macropilis exhibited resistance to dimethoate only. The low level of resistance (9.4x) of the predator did not affect their ability to locate prey. However, the dimethoate resistant population was not as effective in contatining prey population when in lower density and exhibited a more pronounced decrease of r(i) in the presence of this acaricide, due to the reduced oviposition of the predator, a likely consequence of the different genetic background of this population.

[Do Capsicum spp. trichomes influence the biological aspects of the broad mite, Polyphagotarsonemus latus Banks (Acari: Tarsonemidae)?]

Plant morphology traits can affect the feeding preference, oviposition choice and the vulnerability of herbivores to natural enemies. At long term, these plant variations may influence herbivore population dynamics due to the interference on their development, survival and reproduction. In this paper, the development of the broad mite Polyphagotarsonemus latus (Banks) was evaluated on five species of Capsicum with different density of trichomes. We tested the hypothesis that P. latus population growth has a negative relationship with the increase trichome density on leaves. It was assessed a decrease in the intrinsic growth rate (r m) of P. latus with the increase of trichome density on the leaves tested. The lower r m was measured in leaves of C. praetermissum (r m = 0.46), which has the highest trichome density among the assessed Capsicum species. The highest values of r m were observed on Capsicum species with intermediate densities of trichomes on leaves such as Capsicum frutescens (r m = 0.77) and Capsicum chinense (r m = 0.76). Capsicum spp. trichomes acted as a limiting plant trait for the development of P. latus when they were in higher densities and better distributed on the leaf surface. We also discuss the role of morphologic and chemical plant defenses on P. latus development.