EFFECTS OF TRUNK BARRIERS ON LARVAL GYPSY-MOTH (LEPIDOPTERA, LYMANTRIIDAE) DENSITY IN ISOLATED-CANOPY AND CONTIGUOUS-CANOPY OAK TREES

The impact of sticky trunk barriers on the density of larval gypsy mot hs, Lymantria dispar (L.), in oak (Quercus spp.) trees with isolated a nd contiguous canopies was studied. Measurements of frass drop per uni t of area and frass yield per larva were used to estimate larval densi ty. The trunk barriers reduced larval density by an average of almost- equal-to 27%. The effect of the trunk barriers was the same on isolate d- and contiguous-canopy trees on the first sample date, when larvae w ere predominantly fourth instars. On the second sample date, when larv ae were predominantly fifth and sixth instars, the effect of trunk bar riers on larval density was greater on contiguous-canopy trees. These results indicate that reinfestation of trees from the canopy of adjace nt trees is minimal at low to moderate gypsy moth larval densities (up to almost-equal-to 80 larvae per square meter). Defoliation levels an d subsequent egg-mass density were not affected by trunk barriers. Whi le sticky trunk barriers appear to consistently reduce larval density on both isolated- and contiguous-canopy oak trees, they do not provide adequate foliage protection. Frass drop (number of frass pellets per square meter) was the most sensitive measure of treatment effects. The estimation of larval density by incorporating information about frass yield per larva introduced additional variability which made this a l ess sensitive measure of treatment effects.