BUG OF THE MONTH: February 1997
Sawtoothed Grain Beetle
Order Coleoptera, Family Cucujidae
Copyright © 1997 by Rod Crawford
This article originally appeared in Scarabogram, February 1997, New Series No. 202, pp. 2-3.
I'm inspired to a contribution on these creatures because over the last few days I've eaten a large number of them! They were infesting a container of rice; they made no apparent contribution to the flavor, but doubtless marginally increased the protein content... You might say that "some inner voice" told me to write about them.
|Oryzaephilus surinamensis (figs. 9, 11); O. mercator (fig. 10); after Hatch|
The family Cucujidae are called "flat bark beetles" and have "a depressed elongate form adapting them for life under the bark of trees, where they probably feed on organic debris...Like some of the Ostomatidae and Tenebrionidae with similar habits, some of the Cucujidae have become important meal and stored product pests." (Hatch).
Two species of Oryzaephilus (Greek: rice-lover) are found in Seattle. Both are cosmopolitan in distribution and no one seems to know where they came from originally (or if anyone does know, they won't admit it!). O. surinamensis (so called by Linnaeus because his specimens came from Surinam: shades of the German cockroach!) is the commoner and infests a wide range of grain-like products, from rice to corn flakes to birdseed to pancake flour to tapioca. The first Washington records date from 1932. O. mercator ("merchant") was first found here in 1938 and is more likely to infest tropical products like cocoanut, dates, and coffee (Starbuck's take note! In fact, I've identified this species from Starbuck's coffee beans supplied to a restaurant!).
Both are small and inconspicuous (until you add the milk to the cereal and they float!), about 2.5-3 mm long, narrow and dark colored. Even under a miscoscope they are very similar, but surinamensis has tiny differences in the shape of the head and antennal club, and the 3 median ridges of the pronotum are not as convergent anteriorly. Also, in mercator the pronotum is somewhat constricted in front of the saw-teeth (see figures above). In both, the male has a tooth on the hind femur; the female does not.
Eggs "are laid singly or in small batches ... in some crevice in the food supply ... in Washington, D.C. the females emerge in April and lay from 45 to 285 eggs." (Mallis). The full grown larva is almost 3 mm long or slightly bigger than an average adult, paler colored, with a pair of abdominal prolegs in addition to the 6 true legs on the thorax. "It moves about nibbling hither and yon, and probably cannot feed on the whole grain." Thus, when these beetles are found in whole grains such as birdseed it is probably in association with other insects that perform the initial opening on the seeds. The larval cycle is 27-35 days, with 2-4 molts depending on temperature. On raisins in a California lab, the complete egg to egg generation time was 51 days. The adults are potentially long-lived (one was recorded living over 3 years; it is not known how the researcher knew it was the same individual!) but require relatively high (e.g. summer) temperature and humidity to breed.
Considered as a pest, this beetle has greater impact from making food unsalable and/or distasteful to the squeamish than from the relatively small amount of food actually consumed. Its size and shape makes it highly adapted for penetrating apparently intact packages. Mallis records a case where "the beetles and larvae have been known to enter every single package in a very badly infested grocery store."
As with other stored product pests, control is primarily a matter of identifying the infested packages and destroying (or, preferably, cooking and eating) them, then thoroughly vacuuming all cracks and crevices in the kitchen, storeroom, or whatever. At most a few cycles of this should suffice to exterminate any ordinary infestation.
A recent Internet correspondent inquired as follows: "I fed my two little kids rice-crispies this morning and didn't pay a lot of attention until the three year old said, "oh look, bugs!" The cereal was infested with little beetles, which I keyed out to Oryzaephilus surinamensis (Sawtoothed Grain Beetle). Any known worries about eating maybe 500 of these little beetles? Both my kids were kind of disgusted, as was my wife when she woke up. The fact that I had a microscope and all my bug books out on the kitchen table didn't exactly help..." To which someone responded, "A little protein never hurt anybody. I've eaten dozens myself. Got to the point where I didn't care any more. They're good in pancakes too!"
Hatch, Melville H. 1961. The Beetles of the Pacific Northwest, Part III. University of Washington Press. P. 206, 446.
Mallis, Arnold. 1990. Handbook of Pest Control. 7th edition. Cleveland: Franzak & Foster Co., pp. 524-6.