Retrogressive moulting in khapra beetle, Trogoderma granarium (Coleoptera: Dermestidae)

Insect larvae typically moult to grow, but here we investigate insect larvae that moult to shrink; that is, retrogressive moulting or retrogressive development. We demonstrate this phenomenon in khapra beetle, Trogoderma granarium Everts (Dermestidae), among the world's most invasive pests of stored grains and cereal products, and a quarantine pest of interest for many countries. Larvae survived a 3-month period of starvation, moulting up to six times and reducing their body mass by about half, on average. When reprovisioned with food, most larvae resumed the normal trajectory of development and pupated within a month. Thus, retrogressive development is a mechanism that may favour species whose resources exhibit feast-or-famine dynamics. By enabling survival during periods of privation, retrogressive development contributes to the invasiveness of the khapra beetle by allowing them to persist for long periods in empty storage facilities or empty containers used for international grain shipments.