Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/19/1996
Publication Date: N/A
Interpretive Summary: The diamondback moth (DBM) is the most important pest of cabbage and other cruciferous crops worldwide. Virtually all stages of plants from seedlings to mature, harvestable crops are attacked by DBM larvae. Larval control with pesticides started failing in the 1980's and has since spread to all classes of insecticides. Scientists at the IABBBRL, Gainesville, FL are developing alternatives to conventional pesticides that can be used in Integrated Pest Management programs to control DBM on cabbage. Tests with Diadegma insulare, a naturally-occurring, highly-effective parasitoid of DBM were conducted to evaluate the viability of field-collected cocoons stored in a cold room at 39 F. and also the effects of parasitism by D. insulare on the feeding rate of DBM larvae on collard plants. D. insulare cocoons were stored successfully for up to 3 weeks, but storage for longer periods sharply increased cocoon mortality. Consumption of collard foliage by parasitized larvae the first day after stinging was ca. the same as for non-parasitized larvae; but the parasitized larvae became sluggish and fed very little until cocoons formed. Cold storage of cocoons can be used to provide a supply of parasitoids for research on methods for rearing D. insulare artificially during periods when the parasitoid is unavailable in the field. The reduced feeding observed for parasitized larvae indicate that D. insulare could become a significant control agent for DBM when used in conjunction with other biorational tactics such as mating disruption technology.
Technical Abstract: Laboratory tests with Diadegma insulare (Cresson), a parasitoid of the diamondback moth (DBM)(Plutella xylostella (L.)), were conducted to evaluate the viability of cocoons stored at 4oC for varying lengths of time and also the effects of parasitism by D. insulare on the feeding rate of DBM larvae. More than 50% adult emergence occurred from cocoons stored up to 21 d at 4oC. Beyond 21 d in storage, emergence of adults declined steadily until day 49 when no emergence occurred. There was a significant difference in feeding rate between parasitized DBM larvae and non-parasitized larvae. Consumption of collard foliage by parasitized larvae (86.25% of them were parasitized) the first day after stinging was about the same as for non-parasitized larvae but the parasitized larvae then became sluggish and fed very little on days 2-5 when the experiment was terminated.