Contributions of diet quality and diapause duration to the termination of larval diapause in khapra beetle, Trogoderma granarium (Coleoptera: Dermestidae)

Citation

Shivananjappa, S., Fields, P., Laird, R.A., Floate, K.D. (2020). Contributions of diet quality and diapause duration to the termination of larval diapause in khapra beetle, Trogoderma granarium (Coleoptera: Dermestidae). Journal of Stored Products Research, [online] 85 http://dx.doi.org/10.1016/j.jspr.2019.101535

Plain language summary

Khapra beetle is a pest of stored grains with an unusual lifecycle. Their larvae can enter a state of diapause during which they may sporadically feed for several years, but not complete development. Diapausing larvae have an enhanced tolerance to starvation, insecticides and extreme temperatures. By identifying the factors that terminate larval diapause, it may be possible to ‘force’ larvae to end their diapause and become more susceptible to methods of control. In the current study, we fed diapausing larvae on five types of diet (ranging from ‘good’ to ‘poor’) to test the effect of food quality on larval diapause. For this test, we used larvae of different ages that had been in diapause for about 3, 10, or 14 months. For each combination of diet type and age, we held larvae at 30 °C for a period of 188 days and made observations on larval mortality and larval pupation (= diapause termination). We found that larvae were least able to survive on diets of poor quality. Larvae were most likely to terminate diapause on diets of higher quality. Larvae that had been in diapause for longer periods of time were least likely to terminate diapause and least likely to survive. These combined results suggest that when given the opportunity, larvae in diapause will accumulate the nutrients required to terminate diapause and complete development. However, the longer the larvae have been in diapause, the harder it is for them to accumulate the necessary nutrients and the greater the chances of them dying.

Abstract

Larvae of khapra beetle, Trogoderma granarium (Coleoptera: Dermestidae) have an unusual diapause during which they may sporadically feed for several years, but not complete development. Diapausing larvae have an enhanced tolerance to starvation, insecticides and extreme temperatures. Thus, knowledge of factors that terminate larval diapause may aid in the control of this pest. In the current study, we assessed the effect of diet quality (five mixtures of fresh and spent diet in a replacement series) on diapause termination for diapausing larvae from laboratory cultures aged 3, 10, or 14 months. Larvae (n = 10 replicates for each combination of diet quality and culture, 10 larvae/replicate) were held at 30 °C and observed at different intervals over the course of 188 days to record larval mortality and larval pupation (= diapause termination). Larvae were least able to survive on diets of lower quality; i.e., 88% mortality after 188 days on 0% fresh diet versus 8% mortality on 100% fresh diet (averaged across cultures). Larvae were most likely to terminate diapause on diets of higher quality; i.e., 87% termination after 188 days on 100% fresh diet versus 0% termination on 0% fresh diet (averaged across cultures). Diapausing larvae from older cultures were least likely to terminate diapause and least likely to survive. On 100% fresh diet, diapause termination of larvae from cultures aged 3, 10 and 14 months was 93, 91, and 78%, respectively. On 0% fresh diet, mortality of larvae from cultures aged 3, 10 and 14 months was 67, 97, and 100%, respectively. These results indicate that diapausing larvae can accumulate the nutrients required to terminate diapause and complete development when provided with an opportunity to do so. However, the window of opportunity continues to shrink the longer the larvae remain in diapause.