Assessment of pesticide susceptibility for Typhlodromus exhilaratus and Typhlodromus phialatus strains (Acari: Phytoseiidae) from vineyards in the south of France.

Two species of Phytoseiidae predominated in and around vineyards in an experimental site in the south of France: Typhlodromus exhilaratus is the dominant species on grapes, whereas T. phialatus occurs in the uncultivated areas surrounding these crops. To help understand their distribution, this study aims to determine their susceptibility to a fungicide (dimethomorph + mancozeb) and an insecticide (chlorpyriphos-ethyl), which have been widely used at the experimental site for at least four years. The hypothesis tested is that the effects of these two pesticides differ between T. exhilaratus and T. phialatus. Two populations of T. exhilaratus, one collected on a vine crop where the two pesticides were applied and the other in an unsprayed orchard of Sorbus domestica, and one population of T. phialatus collected on Viburnum tinus from uncultivated areas adjacent to the vine crop, were tested under laboratory conditions. The fungicide seems to affect the females of T. phialatus more than those of T. exhilaratus from vine. However, at the recommended field concentration the female mortality rates of the three strains were low and female fecundities were not significantly different. Conversely, mortality rates were very high for the three strains at the recommended field concentration of chlorpyrifos-ethyl. The strain of T. exhilaratus from vine seems to be more tolerant and 20% of females survived the recommended field rate. This suggests better survival after insecticide application than females of T. phialatus (100% mortality at a lower concentration than the recommended rate). As extrapolation of laboratory results to the field is often irrelevant, these differences could be just one of several factors affecting the spatial segregation of the two species in the agrosystem considered. Possible explanations other than pesticides for the poor settlement of T. phialatus in vine plots are discussed.

Cannibalism and intraguild predation in Typhlodromus exhilaratus and T. phialatus (Acari: Phytoseiidae) under laboratory conditions.

Two species of Phytoseiidae are found in the same agroecosystem: Typhlodromus exhilaratus prevails in vine plots, while T. phialatus prevails in uncultivated surrounding areas. The objective of the present paper was to investigate whether the poor settlement of T. phialatus in vine plots can be explained by intraguild predation of these two species and/or cannibalism. Predatory abilities of the females on larvae and protonymphs were studied under laboratory conditions. A first experiment was conducted with only conspecific or heterospecific phytoseiid prey, in a second experiment Tetranychus urticae eggs were added to the phytoseiid prey. Oviposition, prey consumption, and escape rates of females were recorded. Oviposition and intraguild predation rates were higher for T. exhilaratus than for T. phialatus. Typhlodromus exhilaratus consumed fewer conspecifics than heterospecific phytoseiids, and oviposited when feeding on both diets. Typhlodromus phialatus consumed equal amounts of con- and heterospecifics. Although these two generalist predators belong to the type III defined by McMurtry and Croft (Annual Review of Entomology 42:291-321, 1997), our results suggest that they have different predation behaviour. However, because these results were obtained in experiments where no choice was given between the two phytoseiid species, they are difficult to link to previous studies conducted on the intraguild predation of the Phytoseiidae. The greater voracity and prolificacy of T. exhilaratus could partially explain the poor settlement of T. phialatus in vineyards and the predominance of T. exhilaratus. However, a full understanding of this phenomenon will require the study of other factors, such as susceptibility to pesticides and micro-climatic conditions, as well as the ability to cope with different food sources and host plants.

Effects of agroforestry on phytoseiid mite communities (Acari: Phytoseiidae) in vineyards in the South of France.

The abundance and diversity of phytoseiid mites were surveyed from April to September 2003 to 2005 in vineyards (Grenache and Syrah cultivars) co-planted with rows of Sorbus domestica or Pinus pinea and in monoculture plots of grapes in the South of France. Densities of phytoseiid mites were different on the two tree species, with P. pinea a more suitable host than S. domestica. Typhlodromus (Typhlodromus) exhilaratus was the dominant species occurring on grapes and on co-planted rows of S. domestica and P. pinea, whereas T. (T.) phialatus was the most abundant species in monoculture plots of both S. domestica and P. pinea. Factors determining the dominance of T. (T.) phialatus over T. (T.) exhilaratus in monoculture trees are discussed. In this study, agroforestry management did not affect phytoseiid diversity in vineyards, but did affect phytoseiid density, especially in 2005. The results obtained in 2003 and 2004 are not easy to discuss in this regard because of the low densities of mites observed during these 2 years (very dry climatic conditions and pesticide applications).