Use of insectary-reared natural enemies for insect control has increased in popularity. We evaluated the release of a parasite (Goniozus legneri) for control of navel orangeworm (NOW), a moth pest of almonds. Previously, we showed that commercial release programs had variable results, from a 0 to 45% reduction in NOW. Some variation was attributed to poor release methodology and we now recommend release of adult, rather than immature, parasites to reduce parasite mortality. We also confirmed that leaving overwintered nuts on the tree did not consistently improve the ratio of G. legneri to NOW the following season. Overwintering sanitation is strongly recommended! In 1998, we focused on (1) establishing release guidelines that place viable G. legneri in the orchard at the most effective time and (2) studies of G. legneri biology with respect to overwintering survival. |
To improve release effectiveness, the release methodology can be manipulated. In 1998, we released adult G. legneri (marked with "mouse IgG") and found good movement throughout the tree canopy and orchard, with G. legneri moving up to 12 trees from the release point. We conclude that G. legneri can be released at only two to three locations per acre, thereby reducing labor costs. G. legneri biology was studied to determine optimal release periods. Results showed that G. legneri adults do not oviposit at temperatures <65 F, suggesting postharvest releases have little effect. Further, G. legneri larvae did not develop at <65 F (temperature cabinet study) and did not survive ambient winter temperatures in Fresno County (1997-1998). Therefore, parasite numbers, especially immature stages, will drop dramatically during the Central Valley winters.