# Reticulitermes flavipes (Blattodea: Rhinotermitidae) Response to Wood Mulch and Workers Mediated by Attraction to Carbon Dioxide

## TL;DR

This study shows that subterranean termites are attracted to wood mulch and termite workers mainly because of the carbon dioxide they emit.

## Contribution

The study identifies CO2 as a key attractant for Reticulitermes flavipes, showing it is both necessary and sufficient for attraction.

## Key findings

- Termites showed significant attraction to wood mulch and workers, which was eliminated when CO2 was removed.
- CO2 concentration elicited a quadratic response in termites, peaking at around 14,000 ppm.
- CO2 alone, at the same concentration as emitted by mulch and workers, replicated the termite attraction response.

## Abstract

The global economic impact of subterranean termites is estimated to top USD 30 billion annually in damage to wood structures and costs of control measures. For insects living in the soil, resource finding brings special challenges not faced by above-ground species. These challenges include the limited cues available to provide information about the resource, physical obstructions to their detection in the soil, and the high energy costs of tunneling. The termite Reticulitermes flavipes has evolved a locomotory program of steering that increases the search area and thus the probability of an encounter with potential food substrates. Nevertheless, the integration of a directional response to resource-associated cues is predicted to further increase the energetic efficiency of this search strategy. In this study, we demonstrate that R. flavipes show attraction to moist wood mulch or mulch combined with termite workers. Solvent extracts of these materials elicited at best a partial response, while CO2, when presented at the concentration emitted by mulch, produced a termite response comparable to the mulch itself. Understanding the full suite of the mechanisms used by subterranean termites in finding resources for feeding and colonization is important for the development of new strategies for monitoring and control.

The eastern subterranean termite, Reticulitermes flavipes, is challenged by the significant energy expenditures of tunnel construction for resource discovery. Subterranean termites use idiothetic mechanisms to explore large spaces, while the use of resource-specific cues for localized search is disputed. Here, termite response to wood mulch, termite workers, extracts of wood mulch, and CO2 alone were tested using a bioassay design that distinguished between attraction and arrestment. Termites showed significant attraction to wood mulch with workers or to wood mulch alone. They did not respond to workers alone at the initial dose tested, but were attracted to workers at higher densities. Termites did not respond to water or the acetone extracts of wood mulch, but did show a partial response to hexane extract compared to intact wood mulch. More significantly, when CO2 was removed from the emissions of wood mulch and workers using soda lime, attraction was eliminated. Furthermore, termites showed a quadratic response to CO2 concentration that peaked at ca. 14,000 ppm. The response to CO2 alone predicted by the model matched termite response to mulch + workers when compared at the level of CO2 they emitted. The results suggest that CO2 is both necessary and sufficient to explain the attraction response of R. flavipes to mulch and workers we observed. It is argued that orientation to food cues complements the previously demonstrated idiothetic program to maximize the efficiency of resource location.