Insect-specific baculoviruses are increasingly used as biological control agents of lepidopteran pests in agriculture and forestry, and they have been previously regarded as robust to resistance development by the insects. However, in more than a dozen cases of field resistance of the codling moth Cydia pomonella to commercially applied C. pomonella granulovirus (CpGV) in German orchards, resistance ratios exceed 1000. The rapid emergence of resistance is facilitated by sex-linkage and concentration-dependent dominance of the major resistance gene and genetic uniformity of the virus. When the gene is fixed, resistance levels approach 100,000-fold. Our findings highlight the need for development of resistance management strategies for baculoviruses.

Analysis of amplified fragment length polymorphism (AFLP) has the potential to become a powerful new DNA fingerprinting technique for studying genetic relationships and genetic diversity in arthropods. Since DNA of high quality is a crucial prerequisite for AFLP analysis we evaluated the applicability of six protocols (one fast and four complex methods with phenol-chloroform treatments as well as one CTAB-based method) for extracting DNA from insect material and three additional DNA purification steps. The most rapid DNA isolation method did not produce DNA suitable for AFLP analysis. Among four complex methods tested, two protocols resulted in comparatively low yields of DNA that was therefore not used as template for AFLP analysis. The other two complex methods with phenol treatments and a CTAB-based DNA extraction protocol provided DNA suitable for AFLP assay. An additional purification of the DNA using spermine precipitation revealed a few extra bands in an AFLP gel that were masked in unpurified DNA. Therefore spermine precipitation is recommended for AFLP templates.

The toxicities of eight structurally different acaricidal compounds to six-legged larvae (first motile stage) of three laboratory strains of the two-spotted spider mite, Tetranychus uritcae, and the European red mite, Panonychus ulmi, were evaluated following spray application. The larvae of five field-derived strains of T urticae originating from France, Italy, Brazil, California and Florida were also tested for their susceptibilities to discriminating concentrations of several acaricides resulting in 95% mortality when applied to the organophosphate-resistant laboratory reference strain WI. The spray bioassay used was robust and gave repeatable results with a wide range of acaricidal compounds, irrespective of their mode of action (ovo-larvicides or primarily acting on motile life stages). Compounds tested were abamectin, azocyclotin, chlorpyrifos, clofentezine, deltamethrin, fenpyroximate, hexythiazox and pyridaben. Larvae of one of the laboratory strains of T urticae, AK, originally collected in Japan in 1996 and maintained without further selection pressure, exhibited 2000- and > 4000-fold resistance to the mitochondrial electron transport inhibitors pyridaben and fenpyroximate, respectively. Another strain of T urticae, AU, obtained from Australia and maintained in the laboratory under selection with hexythiazox and clofentezine since 1987 showed > 770- and > 1000-fold resistance to clofentezine and hexythiazox, respectively. The same resistance pattern was observed against larvae of a laboratory strain of P ulmi, CE, also selected with hexythiazox. Larvae of one of the field-derived strains of T urticae, BR, showed a lower susceptibility to a number of compounds, whilst the others were susceptible to all compounds except the organophosphates.