Insertion of a yeast metallothionein gene into the model insect Drosophila melanogaster (Diptera: Drosophilidae) to assess the potential for its use in genetic improvement programs with natural enemies

The use of copper-containing fungicides, such as Kocide, negatively affects nontarget beneficial insects in Florida citrus. To determine if the insertion of the yeast metallothionein gene (CUP1) into the genome of beneficial insects could produce populations resistant to copper, the model insect Drosophila melanogaster Meigen (Diptera: Drosophilidae) was transformed with the Drosophila metallothionein promoter Mtn fused to the CUP1 open reading frame. Two transformed lines, confirmed by high-fidelity polymerase chain reaction and Southern blot analysis, were assessed for tolerance to copper hydroxide (CuOH). Transgenic lines 8 and 14 exhibited 1.5- to 2-fold increases in tolerance when held at 24 °C, not, vert, similar75% RH, and 14L:10D. In the absence of copper, lines 8 and 14 exhibited fitness costs as compared to the ww control line. In addition, each line (ww control, lines 8 and 14), when pretreated with 2.5 mM CuOH and held at not, vert, similar22–24 °C, not, vert, similar50–75% RH, and 14L:10D, was more tolerant to copper, with line 14 exhibiting the greatest increase. The increased copper tolerance of the pretreated transgenic lines could be a result of induced transcription of both the CUP1 and native metallothionein (MT) genes whereas the increase in the pretreated ww control could be a due to induced transcription of native MT genes. Both transgenic lines exhibited reduced fitness compared to the ww control line, which could be due to the effects of inbreeding or to the insertion of the CUP1 construct into the genome. The data suggest that CUP1 may be useful for the genetic improvement of natural enemies where copper is applied.