RNA interference suggests sulfakinins as satiety effectors in the cricket Gryllus bimaculatus

In the Mediterranean field cricket, Gryllus bimaculatus, the action of sulfakinin (SK) gene expression on food intake, food transport in the gut and carbohydrate digestion (α-amylase activity) was investigated by using the RNA interference (RNAi) method. Injection of SK double-stranded (ds) RNA into the abdomen of female adults and last instar larvae led to a systemic silencing of the SK gene, as was shown by RT-PCR studies. In adults, suppression of SK gene expression was effective from the first day after injection up to at least the third day. Treatment of the adult crickets by injection or feeding of dsRNA led to a stimulation of the food intake. Assuming that the gene silencing is followed by a depletion of the SK in tissues and/or haemolymph implies an inhibitiory role of the native SK peptides on food intake. The α-amylase activity in vitro in the midgut tissue and in the secretions of adult females was not affected by silencing the SK gene.