Effect of Larval Instar on Intraguild Predation and Cannibalization in Herbivorous Scarab Beetles

Intraguild (IG) predation (IGP) appears to offer multiple benefits for IG-predators from the viewpoints of predation and resource competition. Similarly, herbivores may also gain benefits such as resource monopoly and utilization in the form of food through IGP. We examined IGP among the larvae of two species of herbivorous beetles in eastern Japan belonging to the family Scarabaeidae: the increasing invasive species Anomala albopilosa and the decreasing endemic species A. cuprea. Regardless of species, older larvae preyed on younger larvae; however, third-instar larvae did not kill each other but performed vibratory behavior as a warning. These results show that IGP does not explain the mechanism of decreasing A. cuprea populations, which is contrary to our initial expectations because A. cuprea emerge earlier than A. albopilosa in the field and older larvae of A. cuprea are expected to exhibit IGP toward younger larvae of A. albopilosa. To the best of our knowledge, this study is one of the few case studies proposing the occurrence of IGP as an interspecific interaction among herbivores.