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Title: TRICHOGRAMMA EXIGUUM (HYMENOPTERA: TRICHOGRAMMATIDAE) RELEASES IN NORTH CAROLINA COTTON: EVALUATION OF HELIOTHINE PEST SUPPRESSION

Author
item Suh, Charles
item ORR, DAVID - NC STATE
item VAN DUYN, JOHN - NC STATE

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Trichogramma are minute wasps that primarily attack eggs of moths, some of which are considered agricultural pests. Previous studies using releases of Trichogramma wasps for suppression of cotton bollworm and tobacco budworm in cotton have been unsuccessful. The lack of success has been attributed to a number of factors including improper selection of Trichogramma species and use of poor quality wasps. This study reevaluate the use of Trichogramma releases for suppression of cotton bollworm and tobacco budworm populations in cotton with a high quality source of a known Trichogramma species. Trichogramma wasps killed 70 to 85 percent of cotton bollworm and tobacco budworm eggs, but did not reduce damage to cotton bolls or increase yield. Based on the lack of damage suppression provided by released Trichogramma wasps and relatively expensive cost of using Trichogramma, it is concluded that releases of Trichogramma wasps are not an effective management tool for cotton bollworm and tobacco budworm in cotton.

Technical Abstract: Field studies were conducted in 1996 and 1997 to reevaluate the use of augmentative releases of Trichogramma wasps for heliothine management in cotton. In 1996, nine releases of Trichogramma exiguum Pinto and Platner, spaced 3-4 d apart, were made into three 0.4 ha cotton plots. Six weekly releases were made in 1997, each containing two T. exiguum cohorts developmentally staggered by 45-Celsius degree-days. Field release rates, estimated from laboratory and field quality control data, averaged 108,357 T. exiguum females/ha/cohort release in 1996 and 193,366 females/ha/cohort /release in 1997. In 1996 mean (+/- SD) adult emergence under laboratory conditions for released cohorts was 92 +/- 7 percent, 62 +/- 5 percent of emerged adults were females, 3 +/- 2 percent of females displayed brachyptery (non-functional wings), mean female longevity under laboratory conditions was 15 +/- 4 d, and mean (+/- SD) field emergence was 97 +/- 2 percent. Quality control measurements were similar in 1997. In 1996, mea (+/- SD) percent parasitism of heliothine eggs in field plots on the sampled dates ranged from 67 +/- 4 to 83 +/- 5 percent in T. exiguum release plots and 25 +/- 9 to 55 +/- 8 percent in control plots. In 1997, parasitism levels ranged from 74 +/- 4 to 89 +/- 5 percent in T. exiguum release and 18 +/- 18 to 69 +/- 11 percent in control plots. Despite increased parasitism levels in T. exiguum release plots, there were no significant differences in density of fifth instars, boll damage, or yield between T. exiguum release and control plots. Therefore, it is concluded that Trichogramma augmentation is not an effective heliothine management tool in North Carolina cotton.