Evaluation of proxies for quality of Metaseiulus occidentalis (Acari: Phytoseiidae) reared on different stages of Tetranychus urticae (Acari: Tetranychidae)

•Quality of phytoseiids used in augmentative releases should be high.•Current evaluation methods (fecundity, longevity, sex ratio) are expensive.•Two diets produce Metaseiulus occidentalis females of known quality.•Size of dorsal shield and time to death of females were tested as quality proxies.•Both were different for females fed the two diets but were insufficient to predict. Experiments were conducted to determine if two different methods for assessing quality of the predatory mite Metaseiulus (=Galendromus or Typhlodromus) occidentalis (Nesbitt) (Acari: Phytoseiidae) could be used instead of the more-lengthy and tedious life-history assessment method. First, an experiment was conducted to confirm it was possible to develop females of confirmed different quality by rearing immatures on two diets (eggs only or actives only of Tetranychus urticae Koch (Acari: Tetranychidae). Metaseiulus occidentalis females had a higher total fecundity (15.6 vs. 8.5 eggs female−1), a higher daily fecundity (2.2 vs. 1.4 eggs female−1 day−1), a higher survival rate (100% vs. 56.7%) over 7days of evaluation, and a higher rate of developmental success of their progeny (96.4% vs. 69.5%) when fed eggs only rather than actives only, respectively. The results confirmed adult females of known different quality could be produced for evaluating potential quality-control assessment methods. Two potential quality-control metrics were investigated using these females: survival time of females when held without food and water, and size (length and width) of their dorsal shields. Starvation time and body size were influenced significantly by both diet type and mating status, but the differences obtained were insufficient to use as proxies for evaluating the quality of the M. occidentalis females of known different quality.