The biochemical defenses of <i>Pomacea</i> snail eggs are effective against mealworm beetles

Eggs of freshwater snails from the genus Pomacea (Caenogastropoda: Ampullariidae) are rarely predated because of their strong anti-predatory defenses present in the perivitelline fluid (PVF) that surrounds the embryos. There are clade-specific defenses: the Bridgesii clade expresses enterotoxic lectins, whereas the more derived Canaliculata clade produces the neuro-enterotoxin perivitellin-2 (PV2). While the toxic effects of Pomacea PVF on vertebrates are well documented, its impact on invertebrates remains completely unexplored. Here, we assessed the toxicity of PVF from Pomacea canaliculata (Canaliculata clade) and Pomacea scalaris (Bridgesii clade) eggs on the mealworm beetle (Tenebrio molitor) larvae (Coleoptera, Tenebrionidae). PVF was administered both by injection and orally, and mortality, feeding preference, life cycle, reproduction and histological alterations of the digestive tract and fat body were assessed. Injection of P. canaliculata PVF caused 30% larval mortality, with an LD50 of 56.5 µg g-1 for its PcPV2 toxin, whereas P. scalaris PVF was non-lethal. Although oral administration of PVF from both species did not cause direct mortality, it led to midgut damage, fat body alterations, changes in the insect life cycle with delayed pupation and reproduction alterations in fecundity. Additionally, we provide evidence that the toxic proteins interact with and passage across the larval peritrophic matrix barrier. Notably, beetle larvae displayed feeding avoidance behavior of P. scalaris PVF. These findings provide the first experimental evidence that Pomacea egg biochemical defenses can affect invertebrates, demonstrating the broad-spectrum efficacy of their biochemical strategies and expanding current knowledge of their defenses beyond vertebrate models.