Panonychus ulmi, the European red mite, is a major agricultural pest found in most deciduous fruit growing areas. It is the most important mite species attacking tree fruits in humid regions of North America. Bristle-like mouthparts of this mite species pierce the leaf cell wall and ingestion of their contents including chlorophyll causes bronzing injury to leaves. Heavy mite feeding early in the season (late Jun and July) reduce tree growth and yield as well as the fruit bud formation, thereby reduce yields the following year. Biological control of this pest species by predators has been a cornerstone of IPM . Phytoseiid mites, Neoseiulus fallacis (Garman) is the most effective predator mite in Michigan apple orchards and provides mid- and late-season biological control of European red mites. Achieving full potential of biological control in tree fruit has been challenging due to the periodic sprays of broad-spectrum insecticides. There have been cases of mite flaring reported by farmers in relation to the reduced-risk (RR) insecticides that were registered in commercial apple production in the past ten years. These insecticides are often used in fruit trees to control key direct pests such as the codling moth. Serious outbreaks of phytophagous mites occurring after insecticide applications indicate an imbalance of pest population dynamics. Several RR insecticides were used in this study to determine potential to flare ERM when applied on apple trees, which includes acetamiprid, chlorantraniliprole, spinetoram and novaluron. Two conventional insecticides esfenvalerate and carbaryl were incorporated into this study based on their traditional use in codling moth management programs or as an apple thinning agent. This research utilized field studies, laboratory bioassays and residue profiling of apple leaves. Season long field evaluations of ERM were made to observe the incidence of mite flaring and reduction of predator mites. Field-based bioassays and residue profile analysis were used to determine the temporal toxicity of insecticides to N. fallacis after exposure to field-aged residues. The most cases of mite flaring as evidence in this study were associated with esfenvalerate and carbaryl followed by acetamiprid, and limited cases in chlorantraniliprole, spinetoram and novaluron. Carbaryl in combination with other insecticides caused consistent reductions of predator mites populations. In addition, carbaryl caused the shortest lethal times and high mortality levels to N. fallacis from both topical spray and dry residue exposure. Esfenvalerate did not pose risk to N. fallacis under dry residue exposure, however exposure to wet concentration is very harmful. Spinetoram as dry residue showed moderate negative effects on N. fallacis and the likelihood of exposure is through grooming behaviour as this compound is active through ingestion. Acetamiprid, chlorantraniliprole and novaluron were not directly harmful to the predator mite N. fallacis through topical spray or exposure to dry residues.
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