Over the course of evolution, plants have developed a broad spectrum of defense mechanisms against herbivorous insects to protect themselves and ensure their survival and reproduction. These defenses include the emission of herbivore-induced plant volatiles (HIPVs), which are plant scents that serve as attractants to natural enemies of herbivores, such as parasitoids or predators.
Natural enemies use these olfactory cues to search for hosts or preys. Thus, HIPVs play an important role in population dynamics; because they might affect the behavior of natural enemies, and natural enemies can consequently suppress herbivores population in an ecosystem. Because of that, it has been proposed to study of plant volatiles as a new focus for sustainable pest management in crops.
In general, there are two kinds of HIPVs: the early and the late volatiles. The early volatiles, called green leaf volatiles, are immediately released from freshly damaged leaves, and they provide a fast clue about herbivore location. The late volatiles, mostly terpenoids are more indicative of actual herbivore damage due to involving specific metabolic routes in plants.
Earwigs are insects, which many of them are recognized as important predators in agricultural systems worldwide due to this voracious consumption of crop pests such as African stem borers, leaf-chewing caterpillars, as well as gardens and orchards herbivores, such as aphids, scales, and mites. Despite this potential, until now earwigs have not been used in integrated pest management programs due to few studies conducted with these species. The earwig Doru luteipes has shown great potential to prey on lepidopteran larvae such as the fall armyworm (Spodoptera frugiperda) and the sugarcane borer (Diatraea saccharalis), both of the major pest of maize crops in the Americas. We believe that the earwig contribution in the agrosystems could be maximized from understanding the mechanisms that affect predatory behavior and olfactory communication.
Within this context, in our recent work, we study the predatory behavior of D. luteipes. In addition, we questioned whether earwigs have the ability to use HIPVs released by maize plants when attacked by the fall armyworm and the sugarcane borer to find their prey and if so, what kind of plant scents they prefer. To investigate this, we performed predation and olfactive experiments in the laboratory during the day and night.
Our results support the notion that herbivory by both lepidopteran larvae results in the emission of maize’s HIPVs that can recruit D. luteipes during the night. These findings suggest that earwigs use a nocturnal predation strategy that allows them to explore different niches than diurnal predators and consequently avoid the competition with them. Likewise, earwigs could prey on different herbivores in diverse crop systems. Earwigs preferred the early plant scents over late ones, which possibly increases the chances of the earwig finding suitable prey, quickly at a very premature stage of herbivory.
It may be possible that the observed predatory behavior is also common in other earwig species, which greatly expands the potential range of those insects as biological control.
These findings are described in the article entitled Nocturnal herbivore-induced plant volatiles attract the generalist predatory earwig Doru luteipes Scudder, published in the journal Naturwissenschaften. This work was led by Natalia Naranjo-Guevara and José Mauricio Simões Bento from the University of São Paulo.