Dusky sap beetle (Carpophilus lugubris) Damage and Life Cycle
Adult and pupal stages of the dusky sap beetle overwinter in corn refuse in the soil or in protected places above ground. Adults are first noticed at about the time tassels appear on the earliest sweet corn. They invade corn borer tunnels and feed on frass. They also feed on the pollen as it ripens on the tassels and later as it lodges in the leaf axils. Mating and egg laying begin when the females are 5 to 6 days old. Eggs are deposited on worm frass and wet accumulations of pollen, which are suitable for larval development if these sites remain moist for 10 to 14 days. Sap beetle activity increases as the corn matures, and adults usually invade the ear when the silks begin to turn brown. The majority of eggs are laid on worm frass at the ear tip or scattered through the silk strands. As the larvae hatch, they move deeper into the ear where they penetrate and hollow out the developing kernels. Full-grown larvae leave the ear and burrow into the soil to pupate. At least 2 or 3 overlapping generations occur each year in the mid-Atlantic region (16). Frequency of Occurrence
Dusky sap beetle is a sporadic but important pest of sweet corn (7, 15). Previously, this pest was controlled by chemical applications made for key pests. It is an emerging problem in Bt sweet corn where these chemical applications have been reduced (3, 7). Winter survival is an important factor in determining the spring population. Many overwintering adults are killed by freezing temperatures during December and January. Sap beetle problems are most severe during late June, July, and into August (7, 25), particularly if corn is damaged by other pests, such as European corn borer or corn earworm. Sap beetle problems are most likely to occur on farms producing a variety of fruit and vegetable crops (10), which includes most of Maryland sweet corn producers (7). The number of beetles present each year affects management decisions, which are based on thresholds (13). IPM Program
Corn is sampled when fresh green silking is complete and wilted silks are present. The silk area at the tip of 20 primary ears at each of 5 sites per field are inspected to determine the percent of ears infested with adult beetles, eggs, or larvae. Insecticide treatments are applied as needed if more than 10% of the ears are infested with beetle adults, eggs, and/or larvae (5, 7, 10). Chemical Controls
Sap beetle populations are usually controlled by insecticides applied to treat the major ear-invading insects; however, there are times when densities of these major pests are low, but sap beetle populations are high enough to warrant insecticide treatment. Lambda-cyhalothrin (Warrior 2.56-3.84 fl oz 1E/A) is the first choice of growers, followed by diazinon (2.5 pt 4EC/A or other labeled formulations). Esfenvalerate (Asana XL 5.8-9.6 fl oz 0.66EC/A) and methyl parathion (Penncap-M 2-4 pt2FM/A) may be used in rare instances (7). Insecticides are applied more frequently to fresh market sweet corn, since less injury can be tolerated than in processing corn (13). Alternative Controls
Most Maryland growers minimize sap beetle problems by using tight husk varieties with good husk extension (7). Deep tillage in the fall to destroy overwintering stages and use of crop sanitation practices during the growing season minimize alternative food sources and help to reduce the build-up of sap beetle populations on a farm (3). No biological control strategies are used to control this pest in Maryland (13).
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