Trichogramma exiguum (Hymenoptera: Trichogrammatidae) releases in North Carolina cotton: Evaluation of heliothine pest suppression

Field studies were conducted in 1996 and 1997 to reevaluate the use of augm entative releases of Trichogramma wasps for heliothine management in cotton . In 1996, nine releases of Trichogramma exiguum Pinto & Platner, spaced 3- 4 d apart, were made into three 0.4-ha cotton plots. Six weekly releases we re made in 1997, each containing two T. exiguum cohorts developmentally sta ggered by 45 degrees C degree-days. Field release rates, estimated from lab oratory, and field quality control data, averaged 108,357 T, Exiguum female female per hectare per cohort per release in 1996 and 193,366 female femal e per hectare per cohort per release in 1997. In 1996, mean +/- SD adult em ergence under laboratory conditions for released cohorts was 92 +/- 7%; 62 +/- 5% of emerged adults were females, 3 +/- 2% of females displayed brachy ptery (nonfunctional wings), mean female longevity under laboratory conditi ons was 15 +/- 4 d, and mean +/- SD field emergence was 97 +/- 2%. Quality control measurements were similar in 1997. In 1996, mean +/- SD percent par asitism of heliothine eggs in field plots on the sampled dates ranged from 67 +/- 4 to 83 +/- 5% in T. exiguum release plots and 25 +/- 9 to 55 +/- 8% in control plots. In 1997, parasitism levels ranged from 74 +/- I to 89 +/ - 5% in T. exiguum release plots and 18 +/- 18 to 69 +/- 11% in control plo ts. Despite increased parasitism levels in T. exiguum release plots, there were no significant differences in density of fifth instars, boil damage, o r yield between T. exiguum release and control plots. Therefore, it is conc luded that Trichogramma augmentation is not an effective heliothine managem ent tool in North Carolina cotton.