Adaptability and efficacy of transgenic and wild-type Metaseiulus occidentalis (Acari: Phytoseiidae) compared as part of a risk assessment

Comparisons between transgenic (T) and wild-type Metaseiulus occidentalis colonies (COS) were made under laboratory conditions as part of a risk assessment effort prior to proposed field releases. There were no differences between the transgenic T18 colony and the COS strain in the daily egg production, hatchability at three temperatures and four relative humidity (RH) conditions, diapause incidence, or proportion of female progeny produced. Metaseiulus occidentalis eggs do not hatch at 38°C under any RH tested, nor at 33.5°C under 100% RH, indicating that high temperature and extreme RH affect egg hatch negatively. At 28.5 and 33.5°C, fewer eggs hatched at 32.5% than at 75.5 and 93% RH. Metaseiulus occidentalis cannot survive on any plant tested without prey nor on a diet of pollen alone; adult female mites cannot prey or survive on a diet of eggs and larvae of two lepidopteran species, indicating that the suitability of food sources has not been altered in the transgenic strain. Two subcolonies, derived from two transgenic strains using single females, differed in the rate of egg hatch at 28.5°C under 32.5 and 100% RH, indicating that reduced genetic variation and/or random genetic drift in the two lines may have led to differences in some biological characters. Since we did not find any significant differences between the T18 and COS colonies in the traits tested, the T18 colony is not expected to exhibit any new biological attributes in a proposed short-term field release.