2-Methoxybenzaldehyde effectively repels ants

Abstract

Ants can particularly make for harmful pests, infesting human homes and reducing crop yields. The damage caused by ants and the efforts to mitigate the damage are hugely costly. Broad-spectrum insecticides are used most commonly; however, due to their negative side effects, there is increasing interest in nontoxic alternatives. One promising commercially available alternative is 2-hydroxybenzaldehyde, which is naturally produced by various arthropods as a means of chemical defense and effectively repels ants. Here we conduct a structure-activity relationship investigation, testing how different chemical modifications alter the repellence of 2-hydroxybenzaldehyde. We find that 2-methoxybenzaldehyde is considerably more effective than 2-hydroxybenzaldehyde at repelling the common black garden ant, Lasius niger. We next compare the most effective repellent chemicals against 4 particularly harmful ant species to confirm that the results obtained with L. niger are general to ants and that our results are relevant to mitigate the costs of ant damage.

Keywords: Solenopsis invicta; Wasmannia auropunctata; ant repellent; invasive ant; natural chemical control.

Fig. 1.

Chemical structures. A) Benzaldehyde; B) 2-hydroxybenzaldehyde; C) 3-hydroxybenzaldehyde; D) 4-hydroxybenzaldehyde; E) 2-methylbenzaldehyde; F) 2-aminobenzaldehyde; G) 2-bromobenzaldehyde; H) 2-methoxybenzaldehyde; I) 2-ethoxybenzaldehyde; J) 2-propoxybenzaldehyde; K) 2-butoxybenzaldehyde; L) 2-phenoxybenzaldehyde; M) cis-2-hexenol; N) trans-2-hexenol; O) hexanoic axid; P) AITC.

Fig. 2.

Testing a broad panel of molecules and mixtures. Most of the chemicals that we tested are structurally similar to 2-hydroxyBA, an established insect repellent, but we also included AITC and citrus essential oil to benchmark these chemicals against a recent study and an example DIY solution. Plotted are the distributions of median duration until exit of the chemical perimeter, over 30 trials for each chemical. The stronger the repellence, the longer the duration. Mean values are indicated with red points.

Fig. 3.

Testing the most effective repellent chemicals against harmful ant species. The first experiment revealed that 2-hydroxyBA, 2-bromoBA, 2-ethoxyBA, and 2-methoxyBA were the most effective repellents. We therefore tested these against various harmful species to establish whether the relevant receptor was conserved and therefore whether the identified chemicals could be relevant to combating harmful species. Plotted are the distributions of median duration until the exit of the chemical perimeter, over 20 trials for each chemical. The stronger the repellence, the longer the duration. The results are broadly consistent across species.

Fig. 4.

Survival analysis of L. niger data. A) Survival curves for the seventeen active chemicals and the negative control. B) Statistical comparisons of the survival curves based on Cox proportional-hazard models. For each chemical, the point indicates the hazard ratio relative to the reference (set here to be methoxyBA). Confidence intervals for the hazard ratios are plotted, and P-values are given.

Fig. 5.

Survival analysis of W. auropunctata data. A) Survival curves for the 4 active chemicals and the negative control. B) Statistical comparisons of the survival curves based on Cox proportional-hazard models. For each chemical, the point indicates the hazard ratio relative to the reference (the negative control). Confidence intervals for the hazard ratios are plotted, and P-values are given.

Fig. 6.

Survival analysis of P. longicornis data. A) Survival curves for the 4 active chemicals and the negative control. B) Statistical comparisons of the survival curves based on Cox proportional-hazard models. For each chemical, the point indicates the hazard ratio relative to the reference (the negative control). Confidence intervals for the hazard ratios are plotted, and P-values are given.

Fig. 7.

Survival analysis of S. invicta data. A) Survival curves for the 4 active chemicals and the negative control. B) Statistical comparisons of the survival curves based on Cox proportional-hazard models. For each chemical, the point indicates the hazard ratio relative to the reference (the negative control). Confidence intervals for the hazard ratios are plotted, and P-values are given.

Fig. 8.

Survival analysis of T. magnum data. A) Survival curves for the 4 active chemicals and the negative control. B) Statistical comparisons of the survival curves based on Cox proportional-hazard models. For each chemical, the point indicates the hazard ratio relative to the reference (the negative control). Confidence intervals for the hazard ratios are plotted, and P-values are given.