Effect of fasting and two different photoperiods on immune parameters in adult male and female house crickets (Acheta domesticus)

• A. domesticus reared in two different photoperiods were fasted for 48 h. • Haemolymph parameters phenoloxidase, lysozyme, haemocytes and protein were measured. • Both fasting and photoperiod affected haemolymph immune parameters. • Most affected was the haemocyte count (decreased) in fasted females. • Rearing practices could have effects on immune function, indicating welfare issues. Insects are often reared as a potential source of protein, both for human and animal consumption. However, food safety is a main concern and one common way of reducing the microbial load in insects is fasting them for 24–48 h. Fasting may pose a physiological stress with potential implications for welfare. Another parameter that can be manipulated in insect rearing facilities is the photoperiod, which affects maturation of the insects, and possibly immunity. In this study, adult Acheta domesticus of both sexes, reared in either 16 (16L:8D) or 12 h (12L:12D) of light, were fasted for 48 h or fed ad libitum prior to euthanasia. The immune parameters phenoloxidase (PO) activity, lysozyme concentration, haemocyte number and total protein content were investigated in haemolymph. The results revealed effects of both photoperiod and fasting on immunocompetence. Fasting lowered PO activity ( p = 0.002) and haemocyte count ( p = 0.005). The haemocyte count was especially affected by fasting in female crickets, and haemocyte count was correlated to protein concentration, and to PO activity in crickets reared in 16L:8D. A 16L:8D photoperiod lowered the protein content in haemolymph compared to 12L:12D ( p = 0.045). Protein content has been correlated to disease resistance in previous studies, and was herein found to be correlated with PO activity. These results need to be replicated and investigated further to make recommendations for future cricket rearing, but the results point to the fact that rearing practices could have consequences for insect immunity.