Biological control with Trichogramma: advances, successes, and potential of their use.

Major contributions to the release of Trichogramma for biological control of lepidopterous pests have been made in the past 20 years. Most trials have used only five species of Trichogramma against two pests; Ostrinia in corn is considered the most universally feasible. All Trichogramma programs must address the following four aspects to be successful commercially. Selection of the appropriate population is based on inter- and intraspecific variation, as well as on current definitions of parasitoid quality. Mass rearing is comprised of both host and parasitoid components, although major emphasis is now on developing artificial systems. Effective distribution of Trichogramma requires supportive extension and advanced technology. Strategies for use in the field vary according to the approach desired (inundative or inoculative), the timing, frequency and rate of release, and the multiple factors that affect release, such as the weather, crop, host, predation, pesticides, and dispersal. The past difficulty in assessing the efficacy of Trichogramma should be improved with new guidelines for standardizing terminology and measurements.