The frequency of cannibalism by Spodoptera frugiperda larvae determines their probability of surviving food deprivation.
Evidence of cannibalism is usually associated with higher population density, or lower food plant quality, and has been reported in half of all terrestrial, herbivorous insects. However, we found that cannibalism can still occur in Spodoptera frugiperda when only two larvae had been provided with an abundance of corn leaves, a high-quality food. We analyzed the causes of cannibalism, its benefits and the nutritional physiology of the winner of cannibalistic contests. We found that there were different frequencies of cannibalism on five different plant foods, with the lowest incidence on corn leaves and the highest on rice leaves. Cannibalism is only beneficial to survival if fourth- to sixth-instar larvae cannibalize more than three conspecifics of the same age. Because of the higher incidence of partial pupation and a lower emergence rate in cannibal larvae, the probability of a newly molted sixth-instar larva subject to sudden food deprivation developing into a moth was about 5.42%. Transcriptome and real-time PCR suggest that the phosphoenolpyruvate carboxykinase (PEPCK) and putative solute carrier family 38 member 9 (SLC38A9) of cannibal larvae could be key hubs for gluconeogenesis and the utilization of amino acids from cannibalized conspecifics. In conclusion, cannibalism in S. frugiperda is essential for larvae to survive starvation, or to successfully colonize new, nutrient-poor, food plants. Further research on cannibalism in may allow the development of novel pest control strategies to control this major, invasive, global pest.