Targeting proctolin signaling pathways to control the small hive beetle

Abstract

The small hive beetle, Aethina tumida, is an invasive pest responsible for extensive damage to the European honey bee, Apis mellifera. This pest damages hives by feeding on honey and defecating its excrement contains yeast microbes that ferment the honey, causing it to leak from the hive. Fermented honey is irreparable, and if enough honey is lost, colonies will abscond in search of a new hive. The loss of honey and colonies can have a heavy impact on beekeepers and farmers, since A. mellifera -pollinated crops contributed to between $11.68 and $19.22 billion in yearly crop yield in the U.S. alone as of 2009. Current measures to combat A. tumida are often ineffective, can harm A. mellifera populations, negatively impact native species, or leave residues in honey. This underlines the need for a safe, effective, and targeted control method against the pest. RNA interference (RNAi) is a promising molecular tool for targeted pest management. By introducing double-stranded RNAs, essential physiological processes can be disrupted in a target organism without harming other species, such as A. mellifera. Prior research indicates that A. tumida has a robust RNAi response, suggesting that targeting a gene that A. mellifera lacks could prove fruitful for targeted pest control. Another burgeoning means of pest control is peptidomimetics. Peptidomimetics are synthetic peptides that can artificially disrupt the normal cascades of various systems by mimicking neuropeptides. These neuropeptide mimics can potentially nullify or extend processes, leading to a dysregulation of vital systems. Previous research suggests that Proctolin peptidomimetics are an effective control method for another hive pest, Varroa destructor, as application of the peptidomimetic achieved 100% mortality within 48 hours of exposure. If both RNAi and peptidomimetics are effective against A. tumida, this could provide two new control options against the pest. Initial trials demonstrated the effectiveness of proctolin receptor (Proc-R) dsRNA injection against A. tumida, with mortality rates comparable to those observed in groups injected with vacuolar-type ATPase subunit A dsRNA. Once Proc-R was established as a viable target, proctolin peptidomimetic injections and topical assays were conducted to determine the effectiveness of these peptidomimetics against A. tumida larvae. While the topical assays were inconclusive, the injection assays resulted in significant effects, including twitchy behavior and increased speed, which eventually would lead to complete mortality in one of the three experimental groups. These conclusions help support the idea that both RNAi and peptidomimetics are feasible means of control in A. tumida populations, suggesting further research is needed to develop these as commercial control methods.