Sabine Guichou

Morphological variation in the biological control agent Neoseiulus californicus (McGregor) (Acari : Phytoseiidae): consequences for diagnostic reliability and synonymies

The extent intraspecific variation among 42 morphological characters within Neoseiulus californicus (McGregor) (Acari : Phytoseiidae) is examined. Neoseiulus californicus is an important biological control agent used commercially worldwide to control pest mites in many crops. The correct diagnosis of this species is thus of prime importance for successful biological control and agricultural development. Incorrect interpretation of intraspecific variation could lead to misidentification and potentially to the description of new species that may be invalid. Three hundred female N. californicus representing ten populations collected from all over the world were measured and compared with the types of two morphologically close species: Neoseiulus marinus (Willmann) and Neoseiulus ornatus (Athias-Henriot). Significant differences between the populations were observed for almost all of the characters considered. However, these differences were small and low within-population standard errors in measurement data were observed. The mites collected in Chile were very different from the specimens of the other populations of N. californicus considered. The level of intraspecific morphological variation found within N. californicus indicates that caution must be applied to correctly determine species boundaries within this genus and morphological variation needs to be considered more in species’ descriptions. Based on our morphological analysis we conclude that N. ornatus, N. marinus and N. californicus are valid species. Redescriptions of these three species are given in this paper.

Resistance to fenazaquin and tebufenpyrad in Panonychus ulmi Koch (Acari: Tetranychidae) populations from South of France apple orchards

Abstract Following failures to control the European Red Mite ( Panonychus ulmi ) using METI-acaricides in some apple orchards in the south of France, resistance to fenazaquin and tebufenpyrad was studied under laboratory conditions. Resistance ratios ranged from 19.8 to 28.8 and from 16.8 to 39.8, respectively, for fenazaquin and tebufenpyrad when compared to the most susceptible of the 2 reference populations. An examination of bioassays responses showed that resistance was higher with tebufenpyrad than with fenazaquin. The recommended field rates for these compounds corresponded only to the LC 95 for fenazaquin and the LC 70 for tebufenpyrad. These results confirm resistance development to METI-acaricides in ERM field populations and suggest it could be responsible for reduced persistence of mite control and in some cases for control failure in apple orchards.

Assessment of the usefulness of eight DNA fragments for phylogenetic studies within the family Phytoseiidae

To determine the suitability of several molecular markers for taxonomic studies on the family Phytoseiidae, 5 nuclear and 3 mitochondrial DNA fragments were sequenced for several populations, species, genera, and sub-families. DNA sequences were obtained experimentally or taken from Genbank. Lowest nucleotide divergence was found for the two 18S fragments. No variability was observed between populations of one species (Neoseiulus californicus), between species of one genus, and between two genera of one sub-family. Variation between two sub-families was very low (0.6-1.2%). Poor variability was observed for the two 28S fragments between and within sub-families. Variability was higher for sequences of the fragment ITS-5.8S (intra-genus, 3-7%; inter-genera, 17-20%; inter-subfamily, 29-33%). Variation between intra-species populations was very low for this DNA fragment. Higher nucleotide divergences were obtained for the mitochondrial fragments. For the 12S fragment, the nucleotide divergence rate between two Neoseiulus species was 10%, 25-33% between genera of the same sub-family, and 27-33% between two sub-families. For the fragments of COI, variability between species of a single genus was ca. 20%. Nucleotidic divergence of species belonging to two genera was 26-36% within, and 26-43% between sub-families. Intraspecific variation was low (0-0.4%). The 18S and 28S regions seem to be too conserved for phylogenetic analysis within Phytoseiidae, and would be more suitable for deeper phylogenetic analysis. The mitochondrial fragments are too divergent for robust alignments and phylogenetic analysis between genera of the family, and would be more suitable to assess within-genus systematic studies and species discrimination. The ITS-5.8S fragment seems adequate for phylogenetic analysis within sub-families. However, nucleotide divergence is too high for assessing relationships between sub-families.