Mass rearing the weevil Hylobius transversovittatus (Coleoptera : Curculionidae), biological control agent of Lythrum salicaria, on semiartificial diet

Lythrum salicaria L., purple loosestrife, an invasive Eurasian perennial, i s degrading wetlands across temperate North America. Chemical, physical, an d mechanical methods failed to provide long-term control. Therefore, four h ost-specific insect species (two leaf feeders, a root feeder, and a flower feeder) were introduced as biological control agents. To increase the avail ability of adults of the root feeding weevil Hylobius transversovittatus Go eze for field releases. we developed a semiartificial diet. Suitability of different diet formulations (varying vitamin mixes, salt mixes, antimicrobi als, water content, root content) and temperatures for larval development w ere evaluated. We also monitored how rearing on artificial diet and the num ber of larvae per container affected larval development time, larval surviv al, adult weight, and incidences of deformities. Rearing larvae on artifici al diet reduced development time from 1-2 yr to 2-3 mo. Larval development was fastest and survival rates highest under constant temperatures of 25 de greesC. Hatch rate and larval survival decreased if eggs were surface steri lized. Using FABCO antimicrobials could not prevent fungal contamination; u se of methyl paraben and sorbic acid was successful in suppressing fungal a nd bacterial growth throughout larval development time to <10%. The moistur e content of the diet did not significantly affect larval survival, develop ment, or adult weight Decreasing the proportion of purple loosestrife roots in the diet reduced adult weight and the proportion of larvae completing d evelopment, and increased development time; no larvae were able to complete development in root-free diet With an increase in the number of larvae per cup, survival rates were reduced. Te experiments revealed a female biased sex ratio: females consistently developed faster and were heavier than male s. Incidence of adult deformities was consistently below 5%. Increased avai lability of adults for field release as a result of mass production using t he semiartificial diet will accelerate the biocontrol program targeting pur ple loosestrife. We are able to produce several hundred weevils per week an d have adapted the diet to rear other root-feeding weevils.