Population growth and development of the khapra beetle (Coleoptera: Dermestidae), on different sorghum fractions

Authors: LAMPIRI, EVAGELIA - University Of Thessaly; ATHANASSIOU, CHRISTO - University Of Thessaly; Arthur, Franklin

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/7/2020
Publication Date: 11/12/2020
Citation: Lampiri, E., Athanassiou, C.G., Arthur, F.H. 2020. Population growth and development of the khapra beetle (Coleoptera: Dermestidae), on different sorghum fractions. Journal of Economic Entomology. 114:424-429. https://doi.org/10.1093/jee/toaa235.
DOI: https://doi.org/10.1093/jee/toaa235

Interpretive Summary: The khapra beetle is one of the most destructive insect pests in the world today, and is subject to quarantine restrictions should it be detected in most developed countries, including the USA. It feeds on a variety of raw and processed commodities, but there is limited data on susceptibility of raw sorghum and milled sorghum fractions to this insect. We conducted a series of tests by first exposing adults of the khapra beetle on different milled sorghum fractions (bran, shorts, coarse grits, fine grits, red dogs and four) at 32 ' (about 86.5 deg F) and compared progeny production on these fractions to progeny production on wheat flour and whole wheat. In a second test, conducted at 27, 30, and 32 ' (about 80, 86.5, and 90 deg F), one-two-day old larvae were placed on the fractions and held until adult emergence. When parental adults were exposed, more live progeny larvae were found in the bran sorghum fraction compared to sorghum flour, wheat flour, whole wheat, with the lowest progeny production on the other sorghum fractions. More dead adults were found in the two wheat controls, indicating a slight preference for wheat and also indicating the larvae in the sorghum fractions could have entered diapause. Larval cannibalism could have been an issue as well. When individual larvae were exposed on the sorghum fractions, the wheat flour, and the whole wheat, few developed to the adult stage at 80 deg F, again indicating larvae could have entered diapause. At the other two temperatures, developmental time decreased as temperatures increased, and the shortest developmental time occurred on the shorts fraction. However, all fractions supported development of larvae to the adult stage. Results show that milled sorghum fractions will support population growth and development of the khapra beetle, which is important for international trade and import or export of milled sorghum fractions either into or from the USA. Results from these studies will also be of interest to US sorghum milling operations that are involved in export trade.

Technical Abstract: A series of tests was performed to examine the development ability of Trogoderma granarium Everts (Coleoptera: Dermestidae) on six different sorghum milling fractions: Bran, Shorts, Coarse grits, Fine grits, Red dogs and Flour. In the first bioassay, 20 adults and 20 g of each fraction were placed in vials of 60 ml at 30 ' and 60% relative humidity (r.h.) for a period of 65 days. In the second part of the experiment, a neonate larva (1-day-old) was placed in vials with 1 g of each fraction and exposed at 25, 30, and 32 ' until adult emergence. Significantly more live larvae were found in Bran compared to Flour and to the two grain controls, where most dead adults were recorded. The increase in temperature reduced both the time of adult emergence and larval mortality before the appearance of the first adult. Developmental times ranged between 25.5 and 37.5 days, and 23.2 and 29.0 days for 30 and 32 ', respectively. At 25 ', larvae in the milling fractions did not reach 100% adult emergence even after almost three months. However, the first adult appeared in the Shorts fraction at all temperatures tested. Our results show that all sorghum milling fractions support the development of T. granarium and that the optimal temperatures for growth and development are 30 and 32 '. These results also have important implications for phytosanitary regulations and international trade, given the quarantine restrictions on this insect.