Defensive chemicals of prey can be sequestered by some coevolved predators, which take advantage of prey toxins for their own defence. The increase in the number of invasive species in the Anthropocene has resulted in new interactions among non-coevolved predator and prey species. While novelty in chemical defence may provide a benefit for invasive prey against non-coevolved predators, resident predators with the right evolutionary pre-adaptations might benefit from sequestering these novel defences. Here, we chose a well-known system of invasive species to test whether non-coevolved predators can sequester and use toxins from exotic prey. Together with the invasive prickly pear plants, cochineal bugs (Dactylopius spp.) are spreading worldwide from their native range in the Americas. These insects produce carminic acid, a defensive anthraquinone that some specialized predators sequester for their own defence. Using this system, we first determined whether coccinellids that prey on cochineal bugs in the Mediterranean region tolerated, sequestered, and released carminic acid in reflex bleeding. Then, we quantified the deterrent effect of carminic acid against antagonistic ants. Our results demonstrate that the Australian coccinellid Cryptolaemus montrouzieri sequestered carminic acid, a substance absent in its coevolved prey, from exotic cochineal bugs. When attacked, the predator released this substance through reflex bleeding at concentrations that were deterrent against antagonistic ants. These findings reveal that non-coevolved predators can sequester and use novel toxins from exotic prey and highlights the surprising outcomes of novel interactions that arise from species invasions.
Keywords: ants; carminic acid; chemical defence; coccinellid; cochineal bugs; invasive species.