|Van Duyn, John|
Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2001
Publication Date: N/A
Citation: Interpretive Summary: Trichogramma are minute wasps that primarily attack eggs of moths, some of which are considered agricultural pests. Because they attack many pest species, Trichogramma wasps are the most widely used insect natural enemy in the world. Typically, immature stages of wasps are released in fields with adult wasps emerging soon after release. An important consideration when releasing Trichogramma is the environmental condition (microclimate) into which they are released. This study examined the effect of plant size on cotton microclimate, and subsequent effect on Trichogramma emergence. The objective of this study was to design more effective strategies for releasing Trichogramma wasps into cotton and other crops. We found that the plant canopy provided the most suitable microclimate for releases of Trichogramma wasps. Suitability of the soil surface as a release site for Trichogramma wasps significantly increased when the soil surface was shaded by plants, when Trichogramma wasps were placed within rows, and when Trichogramma adults were timed to emerge one day after field release. Our results indicate that these factors should be considered to increase adult Trichogramma emergence and reduce application costs.
Technical Abstract: Field studies were conducted in 1996 and 1997 to determine if cotton plant size and canopy closure altered cotton microclimate and subsequent emergence of inundatively released encapsulated Trichogramma exiguum Pinto and Platner. Atypical applications of a plant growth regulator, mepiquat chloride (Pix), were used to manipulate cotton plant size and canopy closure to produce a range of plant sizes that might be present in North Carolina when Trichogramma releases for suppression of third generation heliothines were made. Pix treatments had a significant effect on canopy closure, which significantly influenced the number of hours soil surface temperatures between rows were greater than or equal to 35 C. The mean daily number of hours temperatures were greater than or equal to 35 C was greatest on the soil surface between rows, followed by in the canopy, then soil surface within rows. A significant correlation between the number of hours preimaginal Trichogramma were exposed to temperatures greater than or equal to 35 C and Trichogramma emergence was found in 1997. Consequently, suitability of the soil surface as a release site for Trichogramma capsules depended significantly on the level of canopy closure, location of capsules relative to the center of rows, and length of time capsules remained in the field prior to parasitoid emergence. Our results indicate that these factors should be considered when implementing augmentative releases of Trichogramma wasps in cotton.