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Biology |
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Pales weevil adults are large beetles (7 to 12 mm; 0.3 to 0.5 inch long), and are dark reddish-brown with scattered patches of long, yellow-white hairs on the wing covers (figure 1). The pitch-eating weevil is about the same length as the pales weevil, but it is more robust and it appears darker because the hairs on its wing covers are sparser and shorter (figure 2). The pitch-eating weevil can also be distinguished by its widened hind leg; that of the pales weevil is slender. Pitch-eating weevils are similar to pales weevils in their biology, behavior and seasonal occurrence. Adults of both species are attracted to areas where pines have recently been cutover or killed by bark beetles, fire, or some other agent. Here they feed nocturnally on the inner bark of freshly cut slash and stumps. Later, after the logging residue or dead pines dry out, the insects feed on the inner bark of small twigs of residual pines and stems of small pine seedlings (figure 3). [ top ] This feeding on seedlings may result in small isolated patches of bark missing near the base of the stem or may be extensive enough to girdle the stem. Often seedlings are totally stripped of stem bark and needles. Feeding below the root collar may occur, especially on seedlings planted in duff or having loosely packed roots. According to one report, pitch-eating weevils feed more extensively on the root than above it. The immature stages of the pales and pitch-eating weevils are similar in appearance (figure 4). Eggs are usually laid in small niches chewed in the bark of subterranean parts of stumps and roots. The larva bores an irregular tunnel under the bark, scoring the wood more deeply than the phloem. After passing through 5 to 6 larval stages, the insect pupates in a shallow cell in the outer surface of the wood.
[ top ] In the South, active adult pales and pitch-eating weevils are found all year round, usually within flying distance of any potential pine cutting area. Adult pales weevils begin to migrate into an area with the onset of cutting, with the probable exception of areas harvested during the cooler months. In eastern North Carolina, egg laying, and thus perhaps even migration, were found to cease from November to February. Weevils probably migrate into winter cuts in the spring (figure 5). In eastern North Carolina, new pales weevil adults emerge from stumps and roots 3 to 12 months after trees are cut. Emergence on pine sites cut before June occurs from late summer to mid fall of the same year. In pine cut in June, part of the population emerges in the fall and part the following May and June (figure 5). On sites cut in July or later, emergence occurs from May through August of the following year. A similar pattern of emergence for pitch-eating weevils, in relation to timing of cut, has been observed in east Texas. Since serious weevil-caused seedling damage on the Atlantic and Gulf Coastal Plain occurs from February through May, before new adults emerge, this damage is caused by overwintering adults rather than new adults produced in the area. The weevils originally attracted into areas cut after June overwinter there. During warm periods, even in mid-winter, overwintering adults feed on pine seedlings and small pine twigs. Subsequent feeding in summer and fall is probably increasingly that of brood adults produced in the area. Cutting begins when indicated and lasts up to 2 weeks. The black bars indicate when adults migrate into stands cut at several different times of the year and how long they are present in the areas. Brood development depends on the time eggs are laid, which in turn, depends on the time of cutting. Brood from early eggs reach the adult stage from late summer to mid-fall (open bar), while brood from later eggs overwinter as larvae and emerge the second year (gray bar). E indicates when egg laying begins; A indicates when brood adults begin to emerge. In areas cut before July, the brood which emerges by fall and any surviving parent adults (black bars) will migrate to fresh cuttings before the planting season (shaded area); therefore, feeding damage on seedlings does not occur. In areas cut in July or after, migrating parent adults remain in the area through the following winter and spring, causing seedling damage. [ top ] |
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