Background

To defend against the wide range of herbivorous insects that feed on them, plants have evolved a wide range of defenses that include direct and indirect defenses (Howe and Jander, 2008; Kariyat et al., 2012 and 2013). Among these, plant volatiles are a major group that falls under indirect defenses. Plant volatiles are low molecular weight high vapor pressure organic secondary metabolites emitted by plants as part of their normal metabolic activities (Pare and Tumlinson, 1999). However, when herbivores feed on them, they alter their volatile emission by varying it both qualitatively (number of compounds emitted) and quantitatively (amount and ratio of each compound in the blend) (Pare and Tumlinson, 1999; Kariyat et al., 2012). This altered volatile bouquet is also known as herbivore-induced plant volatiles (HIPV). HIPV are the major olfactory cues that the natural enemies (predators and parasitoids) of these herbivores use as signals to find their host–the herbivores (Kariyat et al., 2012), thereby indirectly improving host plant fitness. In addition, undamaged plants also emit volatile organic compounds that are used as cues by herbivores to locate their host plant for both feeding and oviposition (Kariyat et al., 2013 and 2014). A critical component of such insect-plant interaction studies involving plant volatiles is to examine and quantify the community of insects (herbivores, predators, pollinators, and other natural enemies) that gets attracted to their hosts under field conditions (Kariyat et al., 2012). Traditionally, such studies have employed one or a combination of insect traps such as commercial sticky traps, pheromone traps, and light traps to name a few. However, most of these traps have visual aid that interferes with olfactory cues. This can affect understanding the role of olfactory cues, and in many cases, the traps only collect only a subset of the actual insect community associated with the host.

This protocol provides detailed instructions to use inexpensive and easily available materials to build a combination of three traps-which when combined will carry out comprehensive trapping of the majority of insects associated with the hosts (Kariyat et al., 2012). These traps can easily be assembled and disassembled, and are also reusable. The basic methodology involves building a cage from hardwire cloth which encloses the host plant/s of interest, two pitfall traps made of plastic cups, and a pan trap made of aluminum that fits on top of the cage. Combined, these traps will collect insects flying above and at the canopy level, and insects that either crawl or are soil dwellers.