Impact of Spring Sawfly Defoliation on Growth of Loblolly Pine Stands

To estimate the impact of a single spring defoliation by loblolly pine sawfly (Neodiprion taedae linearis Ross), diameters of 3,006 loblolly pines from five locations in southeastern Arkansas were measured immediately after defoliation and two more times at 1-year intervals.The proportion of defoliation was assessed at each measurement. An insecticide was used in an attempt to prevent defoliation in subsequent years. Because tree growth depends on many factors, a multivariate multiple regression model was used to separate these effects. The model predicts thata single defoliation reduces annual diameter and volume increment by 17.4, 8.4, and 2.8% for the first, second, and third years after defoliation, respectively (the actual loss was 18.9 and 8.9% for the first 2 years). It was found that trees defoliated 20–40% actuallygrew faster than undefoliated trees. This response, called overcompensation, is a common reaction of plants to moderate stress. Potential losses from defoliation are greatest in sawtimber-sized stands between the ages of 25 and 35 years. The decision to control sawflies should take into accountstand age and time to final harvest. South. J. Appl. For. 29(1):33–39.

Transmission of Nuclear Polyhedrosis Virus Prior to Death of Infected Loblolly Pine Sawfly, Neodiprion taedae linearis Ross, on Loblolly Pine

Nuclear polyhedrosis virus (NPV) was transmitted by infected loblolly pine sawfly, Neodiprion taedae linearis Ross, larvae prior to death on loblolly, pine. Third instars reared on pine foliage previously fed upon for 24 h by NPV-infected larvae at densities of 4 and 16 per terminal resulted in up to 69.9 and 93.1% mortality, respectively, in previously unexposed cohorts. Third instars reared on pine foliage wetted with washings from frass of infected larvae also resulted in a high level of mortality. Results suggest that a high level of secondary transmission of NPV occurs before death of primary-infected larvae. This transmission appears to be the result of NPV in the digestive tract released either through regurgitation or in the feces.

INTRA- AND INTER-COLONY TRANSMISSION OF A NUCLEAR POLYHEDROSIS VIRUS OF THE LOBLOLLY PINE SAWFLY, NEODIPRION TAEDAE LINEARIS ROSS, ON PINE1,2

A high level (37 – 98%) of secondary transmission of a nuclear polyhedrosis virus from primary infected larvae (PIL) of the loblolly pine sawfly, Neodiprion taedae linearis Ross (Hymenoptera: Diprionidae), to other members of the same colony occurred on loblolly pine, Pine taeda L., in Arkansas. Intra-colony transmission was significantly (P < 0.05) related to PIL density (No. of PIL/colony) but not to PIL instar at death. Inter-colony secondary transmission from PIL-infected colonies was lower (2 – 50%) than intra-colony transmission. Inter-colony transmission was greater when the PIL colony was placed in the lower canopy than in the upper canopy. Regardless of placement of the PIL colony (upper or lower canopy), mortality in other non-PIL colonies, was highest in the upper canopy. Migration of infected larvae is discussed relative to these findings.

APPLICATION OF A NUCLEAR POLYHEDROSIS VIRUS OF NEODIPRION TAEDAE LINEARIS ROSS ON PINE: PERSISTENCE AND EFFECT OF TIMING ON LARVAL MORTALITY1,2,3

The persistence of a nuclear polyhedrosis virus (NPV) of the loblolly pine sawfly, Neodiprion taedae linearis Ross, on loblolly pine, Pinus taedae L., and the larval mortality in sawfly colonies sprayed from the ground during the egg stage were determined. When sawfly colonies and surrounding foliage on pine were sprayed with NPV one week prior to egg hatch, larval mortality was lower than in colonies treated as first-instar and was similar to mortality in colonies treated as third-instar. Percent larval mortality was not increased by the addition of 3.0% Shade® + 0.1% Trition CS-7 to the NPV suspension sprayed. Application of NPV at monthly intervals prior to egg hatch to either sawfly egg colonies and surrounding foliage or only to the foliage surrounding colonies resulted in loss of much of the NPV activity during the first month. Application of NPV at the highest rate (107 PIB/ml) to the eggs and surrounding foliage was the only treatment to significantly increase mortality over the untreated check at one and two months prior to egg hatch (P = 0.05).