# Efficacy of Chlorobenzene as a New Fumigant for Control of Confused Flour Beetle (Coleoptera: Tenebrionidae) and Rice Weevil (Coleoptera: Curculionidae)

## TL;DR

Chlorobenzene is shown to be a safe and effective fumigant for controlling two major stored product pests, the confused flour beetle and rice weevil.

## Contribution

Chlorobenzene is introduced as a new, low-toxicity fumigant for postharvest pest control with high efficacy against stored product insects.

## Key findings

- Chlorobenzene achieved complete control of all life stages of the confused flour beetle in 24 hours.
- Rice weevil adults showed 100% mortality, and immature stages had 97.8% mortality after chlorobenzene fumigation.
- Chlorobenzene is low-cost, has low mammalian toxicity, and is technically feasible for large-scale fumigations.

## Abstract

There is a critical lack of safe and effective alternative treatments to replace methyl bromide fumigation for postharvest pest control on fresh and stored products. Current alternative fumigants, including phosphine and sulfuryl fluoride, have serious shortcomings in meeting the needs of postharvest pest control, and new fumigants are urgently needed. In this study, chlorobenzene, an industrial solvent chemical, was discovered to be an effective fumigant against two major stored product insects: confused flour beetle and rice weevil. In fumigation trials of 20 kg of corn in a 60 L fumigation chamber, the complete control of all life stages of the confused flour beetle was achieved. For rice weevil, the complete control of adults and 97.8% mortality of immature life stages were achieved in 24 h fumigations. These results indicated the high efficacy of chlorobenzene against stored product insects and the promising feasibility of being used on stored products for postharvest pest control. Because chlorobenzene has low toxicity to mammals, high volatility, and is commercially available at a low cost, it has good potential to be used as a safe, effective, and economical alternative fumigant for postharvest pest control and, therefore, warrants continued research and development efforts in the future.

Chlorobenzene is an industrial chemical with relatively high vapor pressure and has been used in the past to produce pesticide DDT (Dichlorodiphenyltrichloroethane). In this study, chlorobenzene was demonstrated to be an effective fumigant against two stored product insects: the confused flour beetle (Tribolium confusum) and rice weevil (Sitophilus oryzae). In small-scale fumigations in 1.9 L glass jars, the complete control of adults of both the confused flour beetle and rice weevil was achieved in 24 h at a dose of 150 μL/L at 21 °C. LC95 values of chlorobenzene vapor concentration for adults of the confused flour beetle and rice weevil were estimated to be 1121 and 1114 ppm, respectively. In large-scale fumigations in a 60 L chamber, all life stages of the confused flour beetle and rice weevil in 20 kg of corn were fumigated for 24 h with 30 mL (500 μL/L) chlorobenzene at 21 °C. The complete control of adults and immature stages of the confused flour beetle was achieved. For the rice weevil, adults had 100% mortality, and immature life stages had 97.8% mortality. These results demonstrated that chlorobenzene is effective as a fumigant against stored product insects, and it is technically feasible to conduct large-scale fumigations for postharvest pest control on stored products.