Host Plants. Sap beetles have derived their name from their tendency to feed on sap and other sweet secretions. However, they also feed on fungi, pollen, damaged or rotting fruit, and occasionally on undamaged fruit. Among vegetables, corn is the crop most commonly injured, followed distantly by tomato. Dusky sap beetle is definitely a primary pest that feeds on uninjured corn; the other species are more likely associated with vegetable matter injured by other insects or by physical disruption.
Natural Enemies. Natural enemies of sap beetles seem to be few and their effects generally are unknown. The insidious flower bug, Orius insidiosus (Say), feeds on sap beetle eggs. A wasp, Cryptoserphus abruptus (Say) (Hymenoptera: Proctotrupidae), parasitizes beetle larvae. A nematode tentatively identified as Hexamermis sp. (Nematoda: Mermithidae) was found to infect up to 89% of adult beetles collected at certain sites during the spring in Illinois (Dowd et al., 1995), but it was absent from most sites. Some Carpophilus spp. are known to be affected by Howardula sp. nema-todes (Nematoda: Allantonematidae) and the fungus Beauveria bassiana. When sap beetle larvae occur in corn ears containing larvae of corn earworm, Helicov-erpa zea (Boddie), they are often killed by the caterpillars.
Life History and Description. Overwintering occurs underground in both the pupal and adult stages, usually in association with crop debris. The adults become active early in the spring, and enter corn fields about the time tassels are produced. Several overlapping generations may occur without distinct periods of abundance. In Washington and Maryland, eggs predominate in July, larvae in late July-early August, and adults are most abundant during August and taper off in September. Total generation time requires 1-3 months.
Some elements of dusky sap beetle biology were described by Connell (1956) and Tamaki et al. (1982). Description of several Carpophilus spp., and keys to common adult and larval sap beetles found in eastern states, were given by Connell (1956). Downie and Arnett (1996) also treated the adults of eastern species, and Hatch (1982) treated the western species. Rearing was described by Tamaki et al. (1982). Williams et al. (1983) published a bibliography of Carpophilus.
Sap beetles differ considerably in their tendency to attack undamaged vegetables. Among the Carpophilus spp., only dusky sap beetle is known to attack uninjured fruit frequently, whereas other species may be occasional contaminants of vegetable matter previously injured by caterpillars, grasshoppers, birds,
or other factors. Research in Delaware (Connell, 1956) and North Carolina (Daugherty and Brett, 1966) indicated that the attack in early season on the corn crop by sap beetles was independent of corn earworm damage. However, a positive association of sap beetles was found later in the season with corn ears exhibiting injury by corn earworm.
The presence of young sap beetle larvae in corn kernels is of particular concern because they are hard to detect. Sap beetles are responsible for rejection of considerable quantities of corn at canneries, and also transmit fungi which produce mycotoxins.
Cultural Techniques. Cultural practices affect dusky sap beetle damage. In North Carolina, early planted corn is more heavily infested than late planted corn. Sweet corn varieties differ in susceptibility to injury, owing primarily to different survival rates among larvae rather than selective oviposition behav ior by adults (Daugherty and Brett, 1966). Connell (1956) attributed increase in sap beetle damage to the loose husk found on some corn varieties, and to short husks that provide little coverage of kernels at the tips of the ears.
Sanitation is an important element of sap beetle management. Corn ears that are left unharvested, particularly those on or in the soil, support survival and overwintering of beetles. In Delaware, decomposing ears support larvae until December, when larvae leave the ears to pupate in the soil. Burying ears at a depth of 10 cm or greater inhibits sap beetle survival. Other decomposing crop debris, including lettuce and tree fruit, favors sap beetles, and they can be attracted to trees that are infected with bacterial wetwood (W. Cransaw, personal communication). Thus, windbreaks and wood lots can be an important source of beetles.
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