Agroforestry management and phytoseiid communities in vineyards in the South of France.

This study deals with the long-term effect of agroforestry management (trees within vine crops) on communities of phytoseiid mites. Several plots were considered: vineyards co-planted with Sorbus domestica or Pinus pinea, monocultures of vines and monocultures of S. domestica or P. pinea. All vine plots included two vine cultivars, Syrah and Grenache. Phytoseiid mites have been surveyed in these plots during several years within the previous 10 years. In 2010, samplings were again carried out in these same plots, from May to September, twice a month. Significantly higher densities of Phytoseiidae were observed on the cultivar Syrah (0.85 phytoseiids per leaf) than on Grenache (0.26 phytoseiids per leaf). Furthermore, significantly higher phytoseiid mite densities were observed in the monocultural grapevine plot than in the two co-planted ones. The main species found was Typhlodromus (Typhlodromus) exhilaratus in all vine plots considered. However, Kampimodromus aberrans was observed in the grapevine plots co-planted with the two trees, but never in the monocultural vine plot. Surprisingly, this phytoseiid species was not found on the co-planted trees, nor in the neighbouring uncultivated vegetation. Several hypotheses are discussed to explain such an unexpected distribution. Furthermore, contrary to what has been observed previously, agroforestry management did not seem to favour phytoseiid mite development, especially on the Grenache cultivar. Again, some hypotheses are developed to explain such observations and density modifications.

Tomato transgenic lines and Tetranychus urticae: changes in plant suitability and susceptibility.

A critical aspect dealing with the use of transgenic plants is the global evaluation of their environmental impact. The polyphagous mite Tetranychus urticae can be considered a suitable species to investigate unpredictable and undesirable effects on phytophagous arthropods. Three tomato near isogenic lines, that is, the cv. Riogrande (RIG), the transgenic lines RC332 (containing the Gox gene and showing high glucose oxidase activity), and MS498 (containing the KTI3 gene and exhibiting a high trypsin inhibition) were used in laboratory and greenhouse trials. Trichomes and contents of C and N of the leaves, differences in development and oviposition of T. urticae and damage caused were evaluated for each line. The laboratory trials evidenced that (1) the intrinsic rate of increase of two strains of T. urticae (T from tomato, B from bindweed), reared on the lower surface of tomato leaflets, was significantly lower in RIG than in transgenic lines and doubling time ranged between 6.9 and 11.6 days in the first and between 3.9 and 5.3 days in the latter; (2) the glandular four-lobed trichomes were always higher in RIG than in other genotypes; (3) the N leaf content was from 1.3 to 1.9 fold lower and the C/N ratio from 1.3 to 1.9 fold higher in RIG than in other lines. The greenhouse experiment, that lasted over a month and was performed by inducing an initially equal infestation of strain T, evidenced: (1) no significant difference between plant lines in the final mite infestation (motile stages per plant), nevertheless an almost double number of spider mites was counted in RC332; (2) a significantly higher percentage of damaged leaves and a significant higher average damage index on RC332 than on RIG (79% and 2.3 in the former, and 62% and 2.1 in the latter, respectively), even if in both transgenics a higher level of the most severe damages and a shorter time to approach them were observed; (4) a comparable number of mites causing the same damage level in all genotypes and a strong linear relation between the first four levels of damage and mite infestation. Although in the laboratory studies both transgenic lines enhanced the T. urticae population increase, the glasshouse studies were not as conclusive and they only suggest the possibility of any real difference between the transgenic and non-transgenic genotypes.