Known as litter beetles, lesser mealworms, or “black bugs,” the darkling beetle (Alphitobius diaperinus) is found in large numbers in poultry houses, in the woods, and around feed bins. These black or reddish-brown beetles are troublesome in turkey and broiler production because deep litter and open-floor housing provide an ideal habitat in which the beetles can survive and reproduce.
The total effect of darkling beetles on poultry production is not known. They may be more problematic as a nuisance than as a vector (carrier of disease). However, beetles are thought to harbor a number of disease organisms — for example, fowl pox, E. coli, Salmonella spp., Newcastle disease, and avian leukosis — and to be involved in the transmission of the causative organism for Marek’s disease, although immunization against Marek’s disease is now available. Darkling beetles are also an intermediate host for poultry tapeworms and cecal worms. If they are in litter that is land applied, their possible effects on wildfowl must be considered.
An undisputed second concern related to the darkling beetle is that they can damage the insulation in poultry houses. Larvae bore into the insulation to find safe places to pupate. But adult beetles who eat the pupae soon enlarge the larval tunnels in their search for an easy meal. Birds and mice then claw at the insulation to get at the adult beetles, larvae, and pupae. In a severe darkling beetle infestation, as much as 25 percent of the insulation can be lost in a single year.
Another potential problem arises if infested litter is spread on crops. Adult beetles may migrate from the field into nearby residences; the result can be a nuisance complaint to the health department — and sometimes lawsuits.
Temperature and moisture affect the amount of time an insect needs to complete its life cycle. Temperatures between 60 and 100°F and moisture levels above 12 percent are optimum for its survival. Food sources, decaying litter, an occasional bird carcass, and the absence of major predator and parasite complexes in the poultry house help the beetle population increase.
The life cycle of the beetle takes 35 to 60 days to complete. The adult female lays eggs individually or in clusters at intervals of one to five days throughout her life cycle. The eggs hatch into tiny larvae after four to seven days and grow through five to nine stages, called instars. This period lasts for seven weeks; then the beetles pupate in cracks and crevices, in the soil and lower strata of the litter, and in building insulation. The pupal state lasts for seven to 11 days, after which a new adult emerges.
Controlling Beetles
To manage darkling beetles effectively requires monitoring, cultural practices, and some insecticide applications. Treatment should be maintained regularly, even if beetle numbers are low. Individual beetles or larvae (100 or fewer per house) pose no problem; however, their presence indicates a need for continued monitoring, ideally on a weekly basis, from the time the birds are brought into the house until they are removed. Visual inspection is the best way to monitor the open-floored, deep litter house. The grower should look at litter, carcasses, cracks and crevices, equipment, and insulation at intervals of 30 to 40 feet throughout the house.
- Litter should be examined along walls, around support posts, and under brooder hoods and feeders. Dig down 1 to 2 inches in caked litter to look for small, early instars.
- Keep litter dry and consider using recycled pa- per as the bedding material. Some recycled paper is treated with boric acid that creates a fog when first applied. The fog settles in about two hours. The litter can be replaced after the third flock each year, but no other treatment for darkling beetles should be necessary (i.e., when using the boric-acid treated recycled paper litter).
- Carcasses should be examined during daily collections. A large number of beetles on a large number of carcasses may point to a heavy infestation.
- Equipment and cracks and crevices are favorite beetle habitats. Be sure to check the framing joints and other cracks as well as the brooder guard, house dividers, drinkers, and feeders.
- Insulation in new houses should be checked for clusters of small holes along seams, in corners, at the eaves, and along the gable. Insulation board may also be discolored. If mice damage appears, look also for beetle tunnels. In older houses, it will be hard to distinguish between old and new beetle damage.
Trapping beetles has also been used to control their numbers. Traps can be made using a 2-inch schedule 40 PVC pipe, a 10-to-12-inch section for each trap. Put a roll of corrugated cardboard (brooder guard) inside the pipe, and place six or so traps between the wall, feeder, and brooder locations from one end of the house to the other. To prevent the birds from moving the traps, stake the traps in place. Remove the cardboard and count the beetles on a weekly schedule. Their presence or a rapid rise in their number indicates a need for treatment.
Cultural methods for controlling beetles are nonchemical ways to reduce the pest population. Cold weather is the most effective measure, and proper litter handling is also an essential for good control. If the weather cooperates, open the house to the cold between flocks. If the temperature drops below 30°F, all stages of the darkling beetle will die. As soon as the birds are moved, the grower can remove litter and litter cake from the poultry house. Darkling beetles will move to protected areas in the empty house within a few days; therefore, moving the litter before that time will more effectively control the beetle population.
Fresh litter that is applied to cropland should be incorporated to prevent any return of the darkling beetle. Stockpiled or composted litter should be turned every two weeks to promote enough heat to kill beetle eggs and larvae.
Although all insecticides registered as controlling darkling beetles will work, none controls the house for more than one flock. Therefore, a treatment program should be maintained year-round. Most products remain active about a week and are designed to be applied when the birds have been removed from the house. The best time for application is on the first day after the birds have been removed followed by cleanup immediately on the second day. Treating the house again — and its outside perimeter — just before the placement of a new flock, is also useful. Surface sprays, dusts, and baits are available for making these applications.
Beetles love temperatures between 70 and 90°F; they are nocturnal and can be found everywhere. Seeing them during the day is a sure sign of infestation — of their presence in great numbers. Young chicks will eat them. Darkling beetles can fly up to one mile at night. If a million or so are taken from a house, 15,000 of those taken will return in the direction of the house from which they came.
Beetles cause reductions in feed conversions and weight gains, and possible disease. Under dry conditions, they will eat the flesh of dead or down birds, and at night crawl up the feathers of resting birds and bite the skin around the feather follicals. Bitten birds may have weeping skin lesions or pink and swollen areas around the feather follicals that resemble skin leukosis. The birds are forced to wander all night instead of eating and sleeping as they would in properly managed houses. Darkling beetles are a general nuisance because they are attracted by light; therefore, they will crawl out of the litter and move toward the light at night. Large numbers of beetles on or in houses create a negative public image and give rise to complaints against the broiler producer. To prevent migration, spray the house walls and posts, or use well-sealed, angled, metal flashing attached to pit walls at posts and masonry frame wall joints.
Consult with your grow-out company about the approved insecticides to be used in your operation. Best control methods are careful cleanout and spraying.
References
Arends, J. No date. Darkling Beetle Control Using Disodium Octaborate Tetrahydrate (Red Zone). North Carolina State Newsletter. North Carolina Extension Service, Raleigh.
Gall, A. 1980. Are Lesser Mealworms Worth the Trouble They May Cause. Poultry Digest 39(456): 76-77.
Pennsylvania State University. No date. Darkling Beetles, and Pest Management Recommendations for Poultry. Lancaster, PA.
Skewes, P.A. and J.L. Monroe. 1991. Research Note: The Effects of Darkling Beetles on Broiler Performance. Poul- try Science 70:1034-36.