Flour Beetles Description & Biology Common flour beetles include the confused flour beetle and the red flour beetle. They are similar in habits and appearance. Both beetles primarily infest flour and, to a small extent, foods made of processed grains. Confused flour beetles and red flour beetles are often found together. Even though they cannot attack whole grains, there are usually enough broken kernels and grain dust, caused by the rubbing of grain during handling, for these beetles to survive. Any home can be invaded by these beetles through the transportation and storage of grains or grain products such as cereals, macaroni, flour, etc.
Flour beetles are not known to carry or spread any diseases that affect humans. Nor do they attack anything other than grain or starch foods (at least not for long). However, in search of their favorite foods, they may become an annoyance, invading all areas of a home.
The beetles (adults) are shiny, flattened, reddish brown insects about 1/7" long, and very active. The larvae are brownish to yellowish white, worm-like insects with three pairs of legs. They are about 1/16" when fully grown.
Both beetles can live up to three years. Unlikely to survive winter temperatures, they seek protection in heated areas or areas where high moisture grain is heating. Generally, these insects are considered weak fliers, but warm temperatures make them more active and, with the help of a wind, they can apparently move long distances.
Larder beetles, as their name implies, prefer meat or meat by-products. This could be decomposing animal, poultry, insect or other non-plant materials. Mounted animals may also become infested. However, larder beetles can survive on other organic materials too. Infestations in homes most likely come from infested dry dog and cat food or bird feed. It is not unusual to find new infestations where rat or mouse baits have been used. The beetles can infest the baits and also the vermin carcasses.
Grease from food preparation and cooking also attracts larder beetles. Any food that is not in a tight container, and has not been used for a month or more, should be checked for infestation whenever beetles or larvae are found.
The adult larder beetle is about 3/8 inch long, black with a lighter stripe across the middle on which there are six small black spots. A full grown larva is about 5/8 inch long, somewhat fuzzy, with two distinct spines on top of the back end that curve backward. When mature, the larvae can become even more destructive by chewing holes into wood, in which they pupate.
The lesser mealworm may be found in any area where there is damp or moldy manure, litter, grain, milled products, or spoiling food. These conditions are usually found wherever there is livestock or poultry. High populations of the beetles may become a nuisance to farms and surrounding communities.
Adult lesser mealworms are black or dark reddish brown and are about 1/4" long. They can move quite rapidly. The yellowish brown larvae, look wormlike and are about 3/8" long. The 200 to 400 eggs laid by each female are usually found in crevices of grain.
While feeding and growing, the larva will molt 7 to 11 times in the 48 days it takes to become a pupa. The pupal stage will last an average of 7 days, adding up to a total of 60 days from egg to adult. The newly emerged female will start egg laying in about 11 days. The lesser mealworm will complete one cycle, egg to egg, given generally favorable temperatures and diets, in approximately 71 days. The larvae and pupae are rarely seen because they hide under boards, in litter, etc. The adults are nocturnal. Few commercial poultry operations are free of these beetles. Because the creatures live in litter, it is generally believed that they cause no damage or problems. However, lesser mealworms are known to attack the digestive tracts of sickly birds. Also, mealworms are aggressive, destroying the eggs and larvae of beneficial insects such as predaceous mites and pseudoscorpions that may also be attracted by the litter. Mealworms are also credited with destroying the eggs and larvae of nuisance insects such as fly eggs and maggots. In some states, the insect is introduced into new chicken houses or freshly cleaned houses to aid in fly control. But in many cases, high populations of beetles have failed to reduce or control fly populations.
One concern regarding the use of mealworms to control indoor flies is that some larvae will migrate to walls, where they may chew holes in foam and fiberglass insulation and wood to create spaces for pupation. However, most of the pupae are found in manure. Of greater concern is the dispersal of beetles when litter is piled or spread in fields. Some areas have had severe problems as a result, with hundreds of these beetles invading nearby homes.
Because lesser mealworms are widely distributed and their food and habitats are found in many rural areas, it seems unlikely that a farm could ever be kept entirely free of the insects. Populations must be kept as low as possible because lesser mealworms can spread certain poultry diseases and damage insulation.
When areas around homes are infested with lesser mealworms, reduce the light visible from the house and put on a light elsewhere to attract the mealworms. Sevin, diazinon, or malathion may be used to treat a 5-to-10 foot perimeter around the house to kill beetles hiding in grass, under shrubbery, siding, porches, etc., during the day. A blacklight electrocuting unit placed in an area away from the house may also help.
Adult root weevils eat notches in the leaves, but this damage is seldom important. The larvae, however, cause serious damage by tunneling in the roots and crowns as they feed on strawberry plants. Most damage to the roots is caused by the later instars of larvae in March and April. Plants become stunted and darkened, and this damage can weaken or kill the plant. Injured plants have a stunted appearance; the leaves are closely bunched and are dark and blue-green. The fine roots have been destroyed, and sometimes even the hard fibrous roots have been eaten.
Heavily damaged areas in the field can be large--sometimes up to 0.2 ha (.5 acre)-- and circular, because of the beetles' behavior of gathering in groups. Without control, damage can be so severe by the second fruiting year that early termination of the planting is necessary. Newly transplanted strawberry plants can be particularly susceptible to black vine weevils.
As with all root-feeding insects, control of the root-feeding stage is very difficult. Therefore, control measures for strawberry rootworm should be directed toward the adult stage of the insects. Presence of adults can be detected by the feeding injury or direct sightings of the adult beetles in the field. Sticky traps used for monitoring tarnished plant bug may aid in sighting strawberry rootworm adults since they feed primarily at night. Some of these beetles find their way onto the traps.
If feeding injury is observed in May or June, an insecticide spray at this time will reduce the number of egg laying females and therefore, the number of grubs feeding during the summer. When the next generation of adults emerges in July or August, control measures may be needed again.
Because overwintering cucumber beetles are around by the time cucurbits are up or transplanted, it is important to check at least daily to control the pest. Handpicking is most effective if done early in the morning when most feeding occurs. These beetles are easy to kill, but because more keep arriving on the plants, it sometimes seems as though controls are not effective. Barriers of row covers, cheesecloth, etc., can protect your plants; remove by midsummer to permit pollination.
Removal of goldenrod, aster, etc., from the vicinity of cucurbits helps reduce the number of beetles. Removing plant debris or keeping it to a minimum is also advisable.