History, Distribution, Damage, and Life Cycle of a Pine Shoot Gall Sawfly, Xyela gallicaulis (Hymenoptera: Xyelidae)

Larvae of Xyela gallicaulis Smith cause shoot stem galls in young pines. Loblolly pine, Pinus taeda L., is the most seriously damaged, but galls have been observed on slash pine, P. elliottii var. elliottii Engelm., and shortleaf pine, P. echinata Mill. Studies in Virginia and Georgia confirm a 2-year life cycle. Larval development takes 4 - 6 wks. After feeding, larvae bore out of the galls and drop to the ground where they form a papery cocoon in the soil to pupate, and where they remain for 22 - 25 months. Adults emerge from cells constructed in the soil from early-December to mid-January of the second year. Eggs are inserted into the vegetative buds during odd-numbered years. Insect associates found feeding in or on gall tissues are the Nantucket pine tip moth, Rhyacionia frustrana (Comstock) (Tortricidae), and the weevil Conotrachelus carolinensis Schoof (Curculionidae).

Control of Low-Level Nantucket Pine Tip Moth Populations: A Cost-Benefit Analysis

The Nantucket pine tip moth, Rhyacionia frustrana, an important pest of intensively managed loblolly pine, can cause significant long-term volume loss in plantations. The primary objective of this study was to establish an economic damage threshold beyond which chemical control of this pest becomes cost-effective. Tip moth damage estimates were obtained from 200 trees for each generation over a 3-year period after planting on two sites in the Georgia Piedmont. A volume index (D2H) was obtained for each of these trees at the end of the study. Significant reductions in volume were observed among trees with relatively low damage levels (10–30% of shoots infested on average over a 3-year period) compared with those trees sprayed with insecticide throughout the study. Growth projection models were used to extrapolate 3-year volume differences among treatments to a full rotation. These and other parameters were used to calculate land expectation values and, subsequently, willingness to pay values for tip moth control at the beginning of the rotation using various discount rates. The results of this analysis suggest that an economic injury level for R. frustrana may be reached when damage levels, on average, exceed 30% infested shoots. South. J. Appl. For. 30(4):182–187.

Variation in Developmental Synchrony of the Nantucket Pine Tip Moth (Lepidoptera: Tortricidae) with Implications for Chemical Control

Regional variation in developmental phenology of the Nantucket pine tip moth, Rhyacionia frustrana (Comstock), was studied at four locations in southeastern Virginia and northeastern North Carolina. A companion study assessed the effects of developmental asynchronony on insecticide spray timing efficacy. Substantial variation in developmental synchrony was found within a relatively small area, with more synchronous development at Greensville and Isle of Wight Co., VA sites, and high levels of asynchrony at Sussex Co., VA, and Hertford Co., NC, sites. The Greensville Co. site showed a typical three generation developmental phenology, while the Isle of Wight Co. site had a more atypical two generation phenology. The Sussex and Hertford Co. sites appeared to have phenologies that were a combination of the other two sites. Spray timing evaluations with permethrin at the Sussex Co. site suggested that mid-April to early May and early to mid-July periods offer opportunities for effective chemical control of tip moths. These dates corresponded to the presence of high proportions of eggs and early-instar larvae in the field. Later season sprays were largely ineffective due to high developmental asynchrony, which resulted in the presence of high proportions of late-stage tip moths on virtually all collection and spray dates. Results suggest that multiple late-season treatments likely would be more effective. Overall, optimal spray dates at the Greensville Co. site, which had a typical three-generation tip moth developmental pattern, agreed most closely with published optimal spray period predictions which are based on historical temperature data.