Search

Laboratory bioassays were conducted to evaluate the sublethal effects of fenpyroximate and pyridaben on life-table parameters of two predatory mites species, Neoseiulus (= Amblyseius) womersleyi and Phytoseiulus persimilis. In these assays, young adult females were treated with three sublethal concentrations of each acaricide. The life-table parameters were calculated at each acaricide concentration, and compared using bootstrap procedures. For each acaricide, the LC estimates for both species were similar, yet the two species exhibited completely different susceptibility when the population growth rate was used as the endpoint. Exposure to both acaricides reduced the net reproduction rate ( R) in a concentration-dependent manner and their ECs were equivalent to less than LC. Two different scales of population-level endpoints were estimated to compare the total effect between the species and treatments: the first endpoint values were based on the net reproductive rate (fecundity λ) and the second endpoint values incorporated the mean egg hatchability into the net reproductive rate (vitality λ). The fecundity λ decreased in a concentration-dependent manner for both acaricide treatments, but the vitality λ decreased abruptly after treatment of N. womersleyi with pyridaben. The change in the patterns of λ revealed that the acaricide effects at the population level strongly depended on the life-history characteristics of the predatory mite species and the chemical mode of action. When the total effects of the two acaricides on N. womersleyi and P. persimilis were considered, fenpyroximate was found to be the most compatible acaricide for the augmentative release of N. womersleyi after treatment. [ABSTRACT FROM AUTHOR]

A 2-year survey of mite populations and pesticide use was carried out in Nova Scotia, Canada, in apple orchards where the two-spotted spider mite ( Tetranychus urticae Koch) was the dominant phytophagous mite. Fungicides were the only class of pesticides that affected cumulative number of T. urticae-days per leaf in tree canopies and colonization success — the ratio of T. urticae-days to number of immigrating T. urticae caught in sticky bands on tree trunks. In 2000, increased numbers of T. urticae-days in the tree canopy were associated with more frequent applications of ethylene bis-dithiocarbamate (EBDC) fungicides and with higher fungicide toxicity scores, which indicate cumulative level of suppression of the phytoseiid predator Typhlodromus pyri Scheuten by all fungicide applications. Higher rates of colonization success were also associated with higher toxicity scores. EBDC’s applied in 2000 promoted T. urticae immigration as indicated by their counts on sticky bands. In 2000 and 2001, number of T. pyri-days in the tree canopies was decreased by more frequent EBDC applications and by higher fungicide toxicity scores. Promotion of T. urticae in tree canopies by EBDC’s was attributed to their toxicity to T. pyri. Both T. pyri and another phytoseiid, Amblyseius fallacis (Garman), were found in ground cover vegetation. Hence, increased immigration from the ground cover attributed to the toxicity of EBDC’s to T. pyri and, especially, to A. fallacis, which is a specialist predator of spider mites and an effective natural enemy of T. urticae. [ABSTRACT FROM AUTHOR]

A new phytophagous mite species, Panonychus citri (McGregor) (Acari: Tetranychidae) (the citrus red mite), was found in Cyprus during spring 2008, infesting citrus plantations. Mites occurred in large numbers, mainly in the canopy of orange, lemon and mandarin trees. The adults and larvae preferred the upper surfaces of mature leaves of the above citrus species, although they occurred on both leaf surfaces. Orange, lemon and mandarin trees were greatly affected by this mite, as its high population densities under hot and dry conditions in the spring caused heavy leaf drop (firing) and twig dieback. [ABSTRACT FROM AUTHOR]