Evaluation of inundative releases of Trichogramma exiguum (Hymenoptera : Trichogrammatidae) for suppression of nantucket pine tip moth (Lepidoptera :Tortricidae) in pine (Pinaceae) plantations

Inundative releases of Trichogramma exiguum Pinto and Platner were evaluate d for suppression of the Nantucket pine tip moth, Rhyncionia frustrana (Com stock), in first-year loblolly pine, Pinus taeda L., plantations. Three rel eases, spaced 7 d apart, were made in three 0.4-ha plots during second-gene ration R. frustrana egg deposition. Each release included three cohorts of T. exiguum developmentally separated by 25 degree-days. Mean +/- SD field r elease rate for each cohort was 328 238 +/- 88 379 females/ha. Mean T. exig uum emergence under laboratory conditions for released cohorts was 96 +/- 2 %, with 74 +/- 3% females, of which 1 +/- 1% of females displayed brachypte ry; female longevity was 18 +/- 3 dr. Field emergence averaged 96 +/- 4%. P arasitism of R.frustrana eggs was significantly increased, ranging from 40 +/- 19 to 73 +/- 22% in ir: exiguum-treated plots and 17 +/- 17 to 67 +/- 2 1% in control plots. Data from all treated plots combined showed R. frustra na egg survival (hatching) was significantly reduced by 46%, and larval pop ulations were significantly reduced by 60%. There was no significant differ ence 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. exiguumtreated plots compared wi th control plots, but there was no significant difference in length of tunn eling damage. Damage to remaining shoots was not significantly different be tween T. exiguum-treated and control plots. Microhabitat significantly infl uenced both mean maximum and minimum temperature and the number of consecut ive hours per day that were at or above 35 degrees C (critical temperature for T. exiguum survival). Soil surface with no cover had the greatest numbe r 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 con secutive hours at or above 35"C. Predation of parasitoids prior to emergenc e was significantly affected by microhabitat and by the length of time caps ules were in the field before T. exiguum emergence (i.e., cohort number).