Tiny beetle, giant impact.

Contributor: Aaron Shurtleff, Maryland Department of Agriculture, Aaron.Shurtleff@maryland.gov

Photos: Natasha Wright, Cook’s Pest Control, Bugwood.org

The khapra beetle (Trogoderma granarium) is a small beetle in the family Dermestidae.  It feeds on a wide variety of dried plant and animal products, but its main target is stored grains, such as rice, wheat, and barley.  Khapra beetle is one of the most destructive pests of stored grain products in the world, and can cause the spoilage of up to 70% of infested products.  Although this beetle has not become established in the United States, it is occasionally found in incoming cargo and in prohibited agricultural products brought in by international passengers.  Due to the potential damage that the beetle can cause if allowed to become established, and the constant threat from accidental importation, the Maryland Invasive Species Council has chosen khapra beetle as the March invader of the month.

The native range of khapra beetle is thought to be India, although some researchers disagree.  Populations can currently be found throughout northern Africa, the Middle East, and South Asia; it seems to prefer areas where the temperature is at least 68OF (20OC) with relative humidity below 50% for at least four months out of the year.  In the US, khapra beetle was first discovered in California in 1953, and then in parts of Arizona, Texas, and New Mexico.  After expensive control efforts, it was eradicated from these areas in 1966.  Subsequent isolated infestations were found from 1980 until 1983 in California, Maryland, Michigan, New York, New Jersey, Pennsylvania, and Texas; all were quickly eradicated.  Currently, there are no known populations of khapra beetle in the US, however it is occasionally intercepted at ports of entry nationwide.  Some estimates suggest that 67% of the continental US has a suitable climate for khapra beetle.

Khapra beetle females produce an average of 50-90 eggs, randomly laid throughout the host material.  These eggs hatch in three to fourteen days.  At hatch, larvae are around 1.7 millimeters in length, and are typically pale yellow in color, except for the head and many body hairs, which are brown.  Larvae generally have a large number of these hairs that form a loose tail on their posterior end.  As the larvae feed and grow, they will molt four or five times.  As they age, their color tends to darken to a reddish-brown and they gain more body hairs.  Depending upon the temperature (and, to a lesser degree, humidity), the larval stage can last from as few as 18 days to as many as 200 days.  The beetle forms its pupa within the skin of the final instar larva, and pupates for three to five days.  Adult beetles are about two to three millimeters in length, and about half as wide (1-2 mm).  They are rather hairy beetles and dark brown to black in color, with indistinct patches of lighter brown along the back.  Females release a pheromone to attract males for reproduction, which may begin immediately after leaving the pupa.  The mated female can begin laying eggs right after mating, if conditions are ideal, but typically there is a 2-3 day pre-oviposition period, followed by up to twelve days of oviposition.  Females die soon after laying eggs, and males typically live for 2-4 days longer.

Adult, larva, larval skins of khapra beetle, showing damage to wheat grains. Photo: Ministry of Agriculture and Regional Development , Ministry of Agriculture and Regional Development, Bugwood.org
Photo: James D. Young, USDA APHIS PPQ, Bugwood.org

Damage from khapra beetle is mainly caused by the larvae.  Larvae display a behavior known as “dirty feeding”; they will feed a little bit on one grain, then move on to another piece of grain, and feed a little on that grain, and so on.  This allows them to very quickly spoil large amounts of stored grains.  In addition, if the larvae are in sub-optimal conditions, they can enter a diapause phase.  Larvae crawl into small crevices, after which the rate of metabolism drops drastically, and they become very inactive, only rarely needing to feed.  Diapausing larvae that have food available can live up to six years, while larvae without access to food can survive up to nine months.  Additionally, due to their extremely low metabolism during diapause, they are very resistant to contact insecticides and fumigants (the main means of controlling this pest), which make them much more difficult to eradicate once established. 

If you believe you have observed khapra beetle, it is important that you contact your state or federal regulatory agents immediately.  There are many beetles that look similar to khapra beetles, and a definitive identification can only be done by trained taxonomists, using specialized equipment. 

Links:

https://www.cabi.org/isc/datasheet/55010 http://entnemdept.ufl.edu/creatures/urban/beetles/khapra_beetle.htm