Adult darkling beetles are being used as a bioindicator of environmental pollution after locust control operations involving the use of chemical insecticides. Distinguishing between the sexes of the darkling beetle, Pimelia senegalensis Olivier (Coleoptera: Tenebrionidae), is very difficult because the external morphological characteristics are quite similar between the sexes. To help determine the sexes of live beetles of P. senegalensis for physiological studies, we test a new and simple technique for easy sexing without subjecting them to chilling, anesthesia, microscopic observation, or dissection. Almost all the adult beetles extend their heads after adequately feeding on either boiled spaghetti (98.0%) or rice (98.1%). If the head of a beetle is gently pressed into its pronotum with the fingers, the reproductive organ will protrude, that is, the genitalia will be visible from the tip of the abdomen. The beetles are easily sexed based on the shape of the genitalia. This method does not result in mortality and is applicable for other two species of darkling beetles Pimelia angulata Olivier and Pterolosia squalida Solier. In P. senegalensis, the ratio of females to males deviates are ≈9:1. Although significant differences are found in several external morphological characteristics between females and males, the range of values greatly overlap. This time-saving method can be used for sexing of the three species of darkling beetles.
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