At the start of my work term in January, I spent time in the IPM lab processing pitfall and sweep-net samples collected the previous field season. To process samples we grouped insects by taxon, a group of organisms described by taxonomists. Identification requires knowledge of shared characteristics within a taxon. In this case, we sorted based on Order, Family, genus and species levels which required attention to detail and manipulating the specimens. Characteristics ranged from obvious, such as the presence of sets of iridescent red dots on the elytra (Fig. 1), to subtle or as in the degree of curvature of the pronotum (i.e., the shield-like plate on top of the thorax). By learning to identifying some insect groups, I began to appreciate just how diverse they are in the environment.
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| Figure 1. Dorsal view of a Calosoma calidum collected in a pitfall trap. Photo: T. Malloff 2020 |
Insects are small and usually dispersed throughout a habitat. They have evolved mechanisms and strategies to communicate with conspecifics and locate both hosts and mates even over great distances. Many insects emit volatile semiochemicals to communicate. Conspecifics or similar species of an insect can sense semiochemicals, even at small concentrations. Semiochemicals, known as pheromones, act as alarm signals, help insects aggregate, and facilitate mate location. For example, a female moth releases a sex pheromone from glands in her abdomen when she is ready to mate, alerting male moths to her location (Fig. 2 A). Insects even sense semiochemicals released from other species. For example, plants can release volatile chemicals when attacked by herbivores. These volatile chemicals can help attract natural enemies including predators or parasitoids who respond by preying upon or attacking the insect pest feeding on the plant. By understanding how insects communicate, insect pest management strategies can be enhanced to become more targeted.
The IPM program used semiochemicals in pest detection and seasonal monitoring. Lures filled with species-specific synthesized sex pheromones or aggregation pheromones were used. In most cases, the pheromone lure attracts the target insect to the sticky surface of a delta trap or in proximity to a vapona insecticide strip. Pheromone-baited traps are important tools for insect monitoring when populations are hard to detect owing either to the large distances they traverse or great difficulty in detecting or catching them (e.g., if exceedingly low populations are present). It can be enormously helpful to take advantage of an insect’s mating behaviour to ‘lure’ a pest of interest to a specific trap. Early detection of insect pest populations is crucial to detect economically damaging densities. Growers depend on monitoring as part of an integrated pest management strategy to protect their crops.
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| Figure 2. Female sphynx moth (Family: Sphingidae) calling for a mate (A) and male green midge (Family: Chironomidae) resting on a leaf. Notice the fuzzy antennae, the increased surface area allows for more chemoreceptors and therefore more sensitive detection of semiochemicals such as sex pheromones. Photos: A. Harpe 2020 (A) and T. Malloff 2020 (B) |
Semiochemical communication is facilitated by structural and behavioural adaptations in the insect world. Insects have sensory equipment or chemoreceptors on antennae and other parts of the body. Chemoreceptors are generally highly specific: each often only responds to one compound. The specificity of chemoreceptors can make synthesis and commercialization of semiochemicals or pheromone lures quite difficult. However, the specificity is also useful as highly specific or targeted pheromone lures tend to reduce by-catch in traps. Even more importantly, specific pheromone lures avoid attracting beneficial insects such as pollinators and natural enemies. As control methods continue to evolve, I am interested to see how semiochemicals will be integrated in to future insect pest management strategies.
I am grateful for an introduction to the incredible world insects within agricultural environments. Learning about the diversity of insects and how they communicate has widened my perception of the natural world and has sparked an interest for further study into insects. The interactions between insects and their environments are vast and diverse. There is so much more for us to learn.
- Tia Malloff
Thanks to Isaac Hudson Foy, Amanda Jorgensen and J. Otani for reviewing this Post
Read more about the Students working in the IPM Program from May-August 2020.