Field Assessment of Mechanical Release of Green Lacewing Eggs (Chrysoperla rufilabris) for Management of Lettuce Aphid (Nasonovia ribis-nigri)

Lynn Wunderlich

The lack of affordable and predictable release techniques for natural enemies has hindered widespread use of augmentative biological control in pest management systems. Many natural enemy releases are done by hand and are therefore labor intensive and expensive. Prior to this field study, a mechanical technique for releasing green lacewing eggs in liquid suspensions was designed and evaluated in the laboratory and in a grape canopy (Wunderlich and Giles, 1999; Giles and Wunderlich, 1998; Wunderlich, 1997). Results showed that the design did not reduce viability of the lacewing eggs as measured by bioassays of larval emergence from discharged eggs. Mechanical release improves the cost-effectiveness of biological control and improves the uniformity of released natural enemies. This project adapted the prototype for use in lettuce (row crop) and conducted lacewing egg releases in commercial, unsprayed lettuce fields. The overall goal of this project was to evaluate the efficacy of augmentative biological control, specifically green lacewing eggs, for lettuce aphid, Nasonovia ribis-nigri, in unsprayed lettuce.

Nasonovia ribis-nigri, "Lettuce Aphid", is a serious new pest in California Central Coast lettuce. Since the aphid prefers feeding at the center of the lettuce head, it is difficult to control and infested lettuce is unmarketable. The aphid’s presence in conventionally farmed fields has increased applications of broad-spectrum pesticides, including organophosphates and carbamates. Some organic growers have been driven to reduce their lettuce acreage due to this serious new pest. In Germany, lacewing egg applications have successfully controlled Nasonovia in lettuce (Quentin et al., 1995; Rossmann and Fortmann, 1989.) Many conventional and organic lettuce growers in the Salinas Valley tried lacewing egg releases for lettuce aphid control during the 1999 season, but reportedly with mixed results.

We completed eight green lacewing egg releases in lettuce using the mechanical distributor in 1999 in cooperation with three different growers. Of the eight releases, three failed due to pre-release egg handling problems or problems with the mechanical distributor. Of the remaining five releases, only one resulted in recovery of lacewing larvae during field monitoring. In this field, the mean number of lacewing larvae was 1.2 larvae/plant one week after egg application in the release plot compared to 0 larvae/plant in an untreated control plot, and 65% of the treated plants had one or more lacewing larvae. The lacewings, however, did not control the Nasonovia population that had reached a mean of 65 aphids/plant on the same date.

Most information available on natural enemy releases is anecdotal; if a release fails, it is difficult to pinpoint why, and growers experiencing failure may be reluctant to try augmentation again. In this project, we have outlined "evaluation checkpoints", or points at which a release may experience failure, and we determined various methods for evaluating lacewing egg hatch at these checkpoints: 1) insectary quality, 2) pre-release handling and release effects, 3) environmental effects, 4) natural enemy survivorship, and 5) efficacy against the target pest. We also give suggestions to interested users for optimizing their lacewing egg releases.

This work was supported by the California Department of Pesticide Regulation Pest Management Grants Program and the Pew Charitable Trusts.

Lynn Wunderlich
Central Coast Vegetable IPM Project
Cooperative Extension
University of California
1432 Abbott Street
Salinas, California 93901
Tel: (831) 759-7377
lrwunderlich@ucdavis.edu

[Table of Contents]