Stable genetic transformation of a beneficial arthropod, Metaseiulus occidentalis (Acari: Phytoseiidae), by a microinjection technique.

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Abstract
A microinjection technique has resulted in stable transformation of the western predatory mite Metaseiulus occidentalis. Early preblastoderm eggs within gravid females were microinjected. The needle was inserted through the cuticle of gravid females into the egg, or the tissue immediately surrounding the egg. This maternal injection method resulted in relatively high levels of survival and transformation. Transformation was achieved without the aid of any transposase-producing helper plasmid. The predatory mite was transformed with a plasmid containing the Escherichia coli beta-galactosidase gene (lacZ) regulated by the Drosophila hsp70 heat-shock promoter. Putatively transformed lines were isolated based on beta-galactosidase activity in first-generation larvae. Transformation was confirmed in the sixth generation by polymerase chain reaction amplification of a region spanning the Drosophila/E. coli sequences. Amplification of a nested region, also spanning the interspecific boundary, provided further evidence for stable transformation. Maternal microinjection may be adaptable to other beneficial arthropods, particularly other phytoseiid mites. Genetic transformation of M. occidentalis may improve its efficiency as a biological control agent as well as provide a method for investigating details of its physiology and ecology.