Erythritol sprays reduce Drosophila suzukii infestation without impacting honey bee visitation nor fruit quality

BACKGROUND

Spotted-wing drosophila, Drosophila suzukii, is an economic pest of small fruits and cherries. Insecticides primarily control this pest while alternative controls are in development. Laboratory studies show that erythritol is insecticidal to D. suzukii and other pests while approved for human consumption. Moreover, erythritol combined with sucrose or non-caloric sucralose can stimulate feeding and quicken mortality. Before growers can use erythritol, the impact on crop protection, non-target insects, and fruit quality need evaluation.

RESULTS

In three blueberry and cherry field cage trials, oviposition on fruit sprayed with erythritol:sucrose or erythritol:sucralose formulations was lowered by 59%-81% compared with unsprayed controls. Fly infestation (larval or adult counts from fruit) was 90% lower in a greenhouse blueberry trial, and 49% lower in an open field blueberry trial with 2 m erythritol : 0.5 m sucrose. Infestation was also 57% lower in an open field cherry trial with 1.5 m erythritol:0.5 m sucrose. Other field trials with very low pest pressure or frequent rains revealed no differences from controls. Field trials consistently revealed that honey bees did not preferentially visit plants sprayed with either erythritol formulation, although yellow jackets visited plants sprayed with erythritol:sucrose more frequently. Erythritol formulations consistently led to more leaf spotting, but there was no reduction in the quality of treated blueberries or cherries in terms of mold development, firmness, diameter, epidermal penetration force, and Brix° (total soluble solids) at harvest.

CONCLUSION

Eleven trials conducted over four years show that erythritol formulations can reduce D. suzukii pressure without attracting foraging honey bees nor negatively impacting fruit quality. © 2023 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Insecticidal Properties of Erythritol on Four Tropical Tephritid Fruit Flies, Zeugodacus cucurbitae, Ceratitis capitata, Bactrocera dorsalis, and B. latifrons (Diptera: Tephritidae)

Tephritid fruit flies are among the most destructive agricultural pests of fruits and vegetables worldwide and can impose trade barriers against the movement of fresh tropical commodities. Primary pre-harvest control methods for these flies rely on the spraying of conventional chemical insecticides or bait sprays. However, resistance to these control methods has been reported in fruit flies. Erythritol is a non-nutritive sugar alternative for human consumption, which has been tested and confirmed for its insecticidal properties against various insect pest species. In this study, using laboratory bioassays, we evaluated the insecticidal effect of erythritol alone or various erythritol formulations containing sucrose and/or protein on four tropical fruit fly species established in Hawaii (e.g., melon fly, Mediterranean fruit fly, oriental fruit fly, and Malaysian fruit fly). In addition, the effects of other non-nutritive hexose and pentose sugar alcohols, such as sorbitol, mannitol, and xylitol, were tested. Among the different standalone and combinatory treatments tested, 1M erythritol and a combinatory formulation of 2M erythritol + 0.5M sucrose appeared to be the most detrimental to the survival of all four species of tested flies, suggesting the potential of using erythritol as a non-toxic management tool for the control of tropical tephritid fruit flies.

Effect of Erythritol on Drosophila suzukii (Diptera: Drosophilidae) in the Presence of Naturally-Occurring Sugar Sources, and on the Survival of Apis mellifera (Hymenoptera: Apidae)

Previous studies have demonstrated various combinations of non-nutritive erythritol and sucrose having detrimental effects on Drosophila suzukii (Matsumura). Fly mortality is likely caused by 1) starvation from feeding on non-metabolizable erythritol; and 2) physiological imbalance with abnormally high osmotic pressure in the hemolymph. While erythritol kills D. suzukii in controlled environments, flies in the field can access naturally-occurring sugar sources. We evaluated fly mortality in the presence or absence of wounded fruits, and an erythritol mixture of 2.0 M erythritol:0.5 M sucrose (E+S), or erythritol- and sucrose-only controls. When provided E+S, survival was consistently lower than sucrose controls with/out wounded fruit, suggesting that this mixture still has a detrimental effect in the presence of competing sugar sources. Our second study examined the effects of diet on fecundity and egg load of female D. suzukii. Females laid fewer eggs on blueberries when fed E+S or erythritol-only than sucrose. Unexpectedly, females fed E+S had more ovarial eggs than sucrose-fed females, suggesting that erythritol might inhibit D. suzukii laying eggs. Lastly, we evaluated honey bee survivorship by enclosing bees with one of four diets in a cage. The erythritol mixture had no discernible impact on adult survivorship during 7 d.