Construction of the fecal armor of larvae of Podontia quatuordecimpunctata (L.) (Chrysomelidae, Galerucinae, Alticini) and its role against insecticides in pest management.

Abstract

Five subfamilies within Chrysomelidae (leaf beetles) have larvae that retain their feces as a coat or armor which serves for thermoregulation, camouflage, or barrier to enemies. The construction, retention and repair of these fecal structures are associated with specialized larval morphologies in the tortoise beetles (subfamily Cassidinae) and in the Cryptocephalinae + Lamprosomatinae (Camptosomata), but morphology associated with fecal encrustations on larvae in the Blepharida-group flea beetles (Galerucinae: Alticini) and in Criocerinae have not been examined. Experiments with live larvae of Podontia quatuordecimpunctata (L., 1767) (or sineguelas leaf beetle, SLB; Blepharida group) reveal the anus opens dorsally and deposits feces directly to the larva's dorsum; the armor is maintained and is reconstructed. Scanning electron microscopy reveals integumental microtrichia that presumably hold on the feces. This invasive beetle has become an introduced tree-crop pest in the Philippines, so ongoing research seeks to mitigate its population. Insecticidal chemical assays show that fecal armor does not fully protect SLB larvae but delays potency slightly. The study recommends rotating the insecticides (Imidacloprid, Cypermethrin, and Buprofezin) to prevent the development of resistance. Specialized morphology for fecal retention is known in Cassidinae, Camptosomata and is now documented in the Blepharida group. Such morphology and the fecal-building behavior can offer additional phylogenetic information for these beetles.