Glischrochilus quadrisignatus Say Coleoptera Nitidulidae

Natural History

Distribution. This native insect is also sometimes called "picnic beetle'' because, like most sap beetles, it is attracted to sweet substances and the odor of food. It is found throughout the northern United States and southern Canada. Fourspotted sap beetle has been found as far south as Florida, but is infrequent in southern areas. A related species, G. fasciatus (Oliver), is similar in appearance and range, but it is not considered to be a primary pest.

Host Plants. The adults feed principally on damaged or decaying vegetables and fruits such as cantaloupe, sweet corn, tomato, apple, peach, and pear, and also on fungi. Late-season adults also attack ripe but undamaged fruits and vegetables, particularly corn and raspberry. Sometimes they also have been known to attack onion sets, potato, and strawberry.

Natural Enemies. Mortality factors are poorly known. General predators such as lady beetles (Coleoptera: Coccinellidae) and insidious flower bug, Orius insidiosus (Say) (Hemiptera: Anthocoridae), occasionally feed on sap beetle larvae, but there is no evidence that they are important. Similarly, the fungus Beauveria bassiana is associated with sap beetles, but its significance is uncertain.

Life Cycle and Description. This beetle overwinters in the adult stage. Oviposition occurs early in the spring, and in Ontario larval development is completed in May or mid-June, with new adults appearing in July and August. This pattern is similar in such mid western states as Minnesota, Iowa, and Illinois. Although only a single generation occurs annually in most of the northern regions, apparently a second generation occurs in Illinois (Dowd and Nelson, 1994), and a few insects go on to produce a second generation even as far north as southern Ontario (Foott and Timmins, 1977).

  1. The eggs are deposited in the spring, principally on decomposing ears of corn, though they also occur in the soil near food. Other oviposition sites include decaying cabbage, onions, and potato-seed pieces. Beetles dig in the soil to a depth of 15 cm to seek a suitable oviposition site. Females can produce about 300 eggs, which are deposited singly or in small clusters. Duration of the egg stage is about 3.4 days at 24°C, but about 8.3 days at 15°C. The developmental threshold is 6.5°C.
  2. The larval stage is brownish in color, with sparse hairs. The head and caudal plate are reddish brown. The tip of the abdomen bears a fleshy protuberance ventrally. The larval stage eventually attains a length of 5-6 mm. Three instars are reported, with mean development times of about 3, 4, and 13 days when reared at 24-28°C. The developmental threshold is 5.5°C, though larvae cannot complete development at 10°C or lower. Larvae are present early in the summer, and large numbers often are associated with decaying ears of corn.
  3. Pupation usually occurs within a small cell in the soil in the immediate vicinity of the larval food source. The pupa initially is white, and turns tan before adult emergence. Duration of the pupal stage is usually 8-12 days, and then the adult remains below-ground for about 12 days before digging to the surface. The developmental threshold is about 10.5°C.
  4. The adult is elongate and shiny black. The front wings bear four small orange spots—one at the base and one distally on each forewing. The front wings are truncate, exposing the tip of the abdomen. The antennae are club-shaped. The adult measures 5-6 mm long. Adults overwinter in clumps of grass, under rotting fruit and vegetables and under leaf mold and bark, but especially in the top 2.5 cm of soil. Areas with grass sod and tall weeds are preferred relative to areas with sparse vegetation or forest. Many of the females overwintering are already mated. Adults that emerge in the summer initially are tan rather than black. Adults are long lived, and at mid-summer both new adults and adults from the previous summer can be found. The pre-oviposition period of adults in the m

Adult fourspotted sap beetle.

spring is about 10 days. High humidity seems to be a prerequisite to oviposition. The oviposition period of females is about 55-70 days.

The biology was described by Luckmann (1963), Mussen and Chiang (1974), and Foott and Timmins (1977, 1979). Rearing was described by Mussen and Chiang (1974) and Foott and Timmins (1979). A key to adult nitidulids, including the northeastern species of Glischrochilus, was given by Downie and Arnett (1996). A bibliography of Glischrochilus was published by Miller and Williams (1981).


Fourspotted sap beetle is a significant nuisance at food processing plants, roadside fruit and vegetable stands, and when food is kept uncovered out-of-doors. It is reported to burrow readily into potato salad and bread, and to plunge into pickle jars. It readily attacks canning tomatoes that are harvested, and slightly injured. Fourspotted sap beetle attacks developing sweet corn during the silking stage, feeding down through the silk. Attack by these beetles is often followed by invasion of dusky sap beetle, Carpophilus lugubris. This beetle seems to be especially attracted to plants injured by European corn borer, Ostrinia nubilalis (Hubner), and Japanese beetle, Popillia japonica Neuman. It also is attracted to fields that are heavily infested by corn leaf aphid, Rhopalosiphum maidis (Fitch). Sap beetles may transmit the fungus Gibberella zeae, which is responsible for causing a plant disease known as corn ear rot.

Damage to corn is somewhat offset by destruction of young European corn borer larvae by sap beetles. Sap beetle adults are attracted to the fecal material of corn borers, enter their tunnels, and kill young borer larvae. McCoy and Brindley (1961) estimated that 8-17% of corn borer larvae were killed by fourspotted sap beetles.


  1. Food lures can be used to assess the population density of adults. Attractants such as banana, sweet corn, and whole wheat-bread dough are most effective. The chemical components of many fruits—butyl acetate and propyl propionate—also are effective lures. Traps placed close to the soil are more effective than elevated traps (Alm et al., 1986,1989).
  2. Protection of sweet corn ears during the period of growth can be attained by applying insecticides during and after silking. Insecticide residues are low at harvest time, however, and beetles frequently attack corn and tomatoes during this period. Food lures containing insecticide kill many beetles and offer the potential to reduce post-harvest infestation if adequate numbers of traps are present (Foott and Hybsky, 1976).

The attraction of beetles to vegetables during and after harvest sometimes creates problems with chemical-based suppression. It is often undesirable to treat close to harvest owing to the risk of excessive insecticide residues in the product. In processing the tomatoes harvested in Ontario, for example, beetles fly to the tomatoes that have been loaded into containers for transport to factories. The beetles burrow into cracked fruit and are difficult to detect. Because beetles usually land on the containers before crawling on the harvested fruit, however, it is possible to treat the containers with insecticides close to harvest, affect good suppression of beetles, and yet maintain low-insecticide residues on food (von Stryk and Foott, 1976).

Cultural Practices. The most important cultural practice is sanitation. All ears should be removed from the corn field after harvest, or crop residue plowed deeply to prevent development of beetles on discarded ears of corn. If beetles are found abundant in an area, it is also advisable to remove or destroy other potential oviposition sites such as old cabbage and onion crops.

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    Are picnic beetles native to minnesota?
    8 years ago

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