Part 6

SOUTHERN PINE SAWYERS, Monochamus spp.

In the South, dying pines and fresh logs are quickly attacked by the pine sawyers. In sufficient numbers they may cause a significant loss of wood fiber and degrade sawlogs. These species are commonly found in the South infesting southern pine, fir, and spruce wherever the hosts grow.

The adults emerge in the spring or summer and begin to feed on the bark of twigs. After mating, the female gnaws pits through the bark of freshly felled or dying pine. The female beetle lays one to several eggs in each pit. After eggs hatch the larvae bore beneath the bark for 40-60 days, converting the inner bark into coarse, shredded frass. The larvae then enter the wood and make deep U-shaped cells through the heartwood and sapwood. The entrance is plugged with frass and the far end is excavated into a pupal chamber. The larvae pupate the following spring or early summer, transform into adults, and emerge that same season. The insect has two or three generations per year in the South.

Pine sawyers render storm- or fire-damaged pines unfit for salvage and are also a problem in wood-holding yards. Rapid salvage and utilization of dead or dying trees or green logs will reduce losses significantly.

NANTUCKET PINE TIP MOTH, Rhyacionia frustrana (Comstock)

The impact of the Nantucket pine tip moth on pine plantations varies widely with tree species, host vigor, and environmental factors. Heavily infested trees may be severely stunted or deformed but mortality is rare. Generally, the tree grows out of the susceptible stage within a few years. In seed orchards, the tip moth is receiving increasing attention because of its impact on height growth and, more importantly, because of its effect on flower and cone production. All species of pine within the range of the tip moth except white pine and longleaf pine, are attacked. It has been reported from all states in the eastern hard-pine region extending across east Texas, Oklahoma, Illinois, Indiana, Ohio, and southern New York State.

The tip moths overwinter as pupae in the tips of infested trees. In the South the adults emerge on warm days during the late winter months, mate, and the females lay eggs in the axils between needles and stem near the terminal bud of host trees. On hatching, larvae bore first into the base of developing needles, and later into the new terminal growth or buds. There are two to four generations per year in the southern part of the tip moth’s range.

Chemical control is generally not considered practical in forest plantations, but several pesticides have proved effective in reducing insect damage in seed orchards.

PALES WEEVIL, Hylobius pales (Hbst.)

Pales weevil is perhaps the most serious insect pest of pine reproduction in the southeastern United States. Losses in susceptible areas commonly run 20-25 percent, but exceed 90 percent under circumstances favoring weevil development. Pales weevil is found throughout pine-growing regions of eastern United States and Canada. Feeding has been reported on most coniferous species, and all species of southern pines appear to be susceptible in varying degrees.

Adult weevils are attracted by the odor of fresh pine resin, and quickly invade logging areas. Eggs are laid in lateral roots of fresh pine stumps, where they hatch in approximately five to ten days. Larvae feed on the inner-bark tissues of roots. At maturity, larvae usually construct a chip cocoon in a chamber cut into the wood, and pupate in the cocoon. On emerging, adults feed on the tender bark of seedlings, or twigs of trees. The small irregular feeding patches in the bark are characteristic of weevil damage. Heavy feeding girdles the stem or twig, causing wilting and eventual death. Newly emerged adult females feed for approximately one month before laying eggs. Females may lay eggs sporadically through two growing seasons. The average female lays about 50 eggs in her lifetime. In the South there are two peaks in adult weevil population each year; the first occurs in the early spring (March-May) followed by a second somewhat lower peak in July and August.

This insect can be controlled by delaying planting in cut-over areas for at least nine months, or by treating seedlings with a suitable insecticide.

WHITE PINE WEEVIL, Pissodes strobi (Peck)

The white pine weevil is generally regarded as the most serious insect pest of white pine. Although it usually does not cause mortality, trees suffering repeated attacks become stunted and deformed to the point of being commercially unusable. The weevil has become such a problem in some areas that it prohibits the growing of white pine. In addition to eastern white pine, the white pine weevils also attack Norway spruce and jack pine. Other pines and spruces are attacked to a lesser degree. The weevil is found throughout the range of eastern white pine.

During the latter half of April, the adults may be found on the terminal shoots of host trees where the female lays her eggs. Up to 200 eggs are deposited over a six-week period. The eggs are laid in feeding punctures in the bark, and hatch about two weeks later. Characteristically, the young larvae position themselves around the shoot and begin feeding as a group down the terminal through the inner bark. Small holes scattered over the bark are characteristic of white pine weevil attacks. After five or six weeks the larvae construct pupal chambers in the pith or wood of the terminal shoot and transform into adults. The young adults remain in the dead terminal until late October and November when they move to favorable overwintering sites on the ground, usually at the base of the host tree.

Control of the white pine weevil is difficult. It is possible, however, to reduce the damage by making conditions in a young stand unfavorable for egg laying. This is possible because the female weevil will only lay eggs within a rather narrow range of temperature and relative humidity. Various techniques involving the use of shade from “nurse trees” have been developed but require intensive management. Under certain circumstances, chemical control can be used.

PITCH-EATING WEEVIL, Pachylobius picivorus (Germar)

In the Gulf Coast States the pitch-eating weevil is probably the most troublesome insect pest of pine seedlings. No accurate figures are available on the damage directly attributable to this pest, but mortality losses are estimated to average about 30 percent in susceptible areas. All of the southern hard pines and other conifers are probably suitable breeding and host material for the pitch-eating weevil. Its range overlaps that of the pales weevil, being reported from Labrador, Canada, south to Florida and west to Texas. It occurs in damage-causing numbers only in the Gulf Coast States.

Pitch-eating weevils breed in the roots of freshly cut stumps. The adults burrow down through the soil, sometimes a considerable distance from the stump, and lay their eggs in niches chewed in the root bark. On hatching, larvae mine the inner bark, packing their galleries with frass. Pupal cells are excavated in the sapwood, and a chip cocoon is constructed from the excelsior-like material removed during the cells’ construction. Development time varies from six to ten months depending on when the stumps are initially infested. Emerging adult pitch-eating weevils feed by night on the tender bark of seedlings. Small irregular patches of bark are removed, eventually girdling the seedling and causing its death. The pitch-eating weevil exhibits a population trend similar to that of the pales weevil, and is a threat mostly in early spring and in the fall.

The most effective control for pine reproduction weevils is to wait nine months before replanting or until the stumps in an area are no longer attractive to the weevil. Chemical control can be used when such a delay is considered impractical.

DEODAR WEEVIL, Pissodes nemorensis (Germ.)

This snout beetle is very similar to the white pine weevil both in appearance and habits. It is found throughout the south- and mid-Atlantic states from southern New Jersey west to Missouri. Although deodar cedar is the preferred host, Atlas cedar, Lebanon cedar, and several species of southern pines are also attacked.

Adults emerge from April to May and feed briefly on the inner bark of leaders and lateral branches of host trees. Heavy feeding frequently girdles the stem and can kill small trees. The adults are dormant during the summer, but resume activity in the fall to lay their eggs. From one to four eggs are deposited in feeding punctures. The newly hatched larvae bore into the inner bark where they construct winding galleries which girdle the stem. Evidence of such infestations is often delayed until January when the branches begin to turn brown. Winter is spent in the larval stage. The larvae pupate in March or April and the cycle is complete.

Keeping shade trees in a vigorous condition by proper watering and fertilization helps reduce their susceptibility to weevil attack.

CONEWORMS, Dioryctria spp.

Coneworms are perhaps the most destructive insect pests of pine cones in the South. They are particularly serious in superior-tree seed orchards where they frequently cause substantial economic loss. There are five important species of coneworms in the South, one or more of which attack all of the native and exotic pines.

Although the number of generations per year varies with the species, their general life history is similar. Female moths lay their eggs around wounds, cankers, galls, etc., but also deposit particularly on terminal growth. Eggs generally hatch in about a week. Larvae may stay at a single feeding site, or move to several different sites before completing their development. This latter behavior often results in a single larva destroying several cones or shoots. Pupation takes place in a chamber constructed by the larva at the feeding site. Depending on the species and time of year, the adult may emerge in two to three weeks or overwinter in the pupal stage. Coneworms cause several kinds of damage. They may mine through the inner bark, bore up the center of a shoot, or completely hollow out a cone. Their attacks are sometimes marked by fecal pellets and large pitch masses.

Several parasites attack coneworms but are seldom effective enough to prevent population build-ups. Chemical control is often necessary on seed orchards to ensure adequate protection of the cone crop.