Evaluation of Inundative Releases of Trichogramma exigum (Hymenoptera: Trichogrammatidae) for Suppression of Nantucket Pine Tip Moth (Lepidoptera: Tortricidae) in Pine (Pinaceae) Plantations
Inundative releases of Trichogramma exiguum Pinto and Platner were evaluated for suppression of the Nantucket pine tip moth, Rhyacionia frustrana (Cornstock), in first-year loblolly pine, Pinus taeda L., plantations. Three releases, spaced 7 d apart were made in three 0.4-ha plots during second-generation R. frustrana egg deposition. Each release included three cohorts of 7: exiguum developmentally separated by 25 degree-days. Mean ± SD field release rate for each cohort was 328 238 ± 88 379 females/ha. Mean T. exiguum emergence under laboratory conditions for released cohorts was 96 ± 2%, with 74 ± 3% females, of which 1 ± 1% of females displayed brachyptery; female longevity was 18 ± 3 d. Field emergence averaged 96 ± 4%. Parasitism of R. frustrana eggs was significantly increased, ranging from 40 ± 19 to 73 ± 22% in 1: exiguum-treated plots and 17 ± 17 to 67 ± 21% in control plots. Data from all treated plots combined showed R. frustrana egg survival (hatching) was significantly reduced by 46%, and larval populations were significantly reduced by 60%. There was no significant difference in the percentage of terminals damaged between T. exiguum-treated (31 ± 16%) and control plots (45 ± 10%); however, length of terminal damage was significantly lower in treated plots. The percentage of damage to top whorl shoots was significantly lower in T. exiguum-treated plots compared with control plots, but there was no significant difference in length of tunneling damage. Damage to remaining shoots was not significantly different between T. exiguum-treated and control plots. Microhabitat significantly influenced both mean maximum and minimum temperature and the number of consecutive hours per day that were at or above 35°C (critical temperature for T. exiguum survival). Soil surface with no cover had the greatest number of hours at or above 35°C. followed by soil surface with herbaceous cover, and canopies of small trees (0.4 m tall). Canopy habitats in larger trees (0.9-1.8 m tall) had the most moderate temperature conditions. Parasitoid emergence was significantly reduced in response to increasing number of consecutive hours at or above 35°C. Predation of parasitoids prior to emergence was significantly affected by microhabitat and by the length of time capsules were in the field before T. exiguum emergence (i.e. cohort number).