Comparison of the Brown Sugar, Hot Water, and Salt Methods for Detecting Western Cherry Fruit Fly (Diptera: Tephritidae) Larvae in Sweet Cherry

Abstract

Brown sugar and hot water methods have been developed to detect larvae of tephritid fruit flies post-harvest in fruit in order to maintain quarantine security. It would be useful to determine if modifications of these methods can yield better results and if less expensive alternatives exist. This study reports detection rates of Rhagoletis indifferens Curran (Diptera: Tephritidae) larvae separated from crushed sweet cherries (Prunus avium [L.] L.) by brown sugar flotation versus hot water and sodium chloride (salt) flotation methods. Cherries were crushed and shredded by a standard cherry crusher and submerged either in brown sugar solution, hot water, or salt solution. In sugar and salt solutions, extracted larvae floated, whereas in hot water they sank; and in all 3 visual inspections for larvae were made. The brown sugar flotation method detected more total larvae than the hot water method when using a clear dish or black pan after cherries were shredded through a 2-mm gap in a cherry crusher, resulting in 95, 85, and 85% detections, respectively. Brown sugar and salt flotation methods resulted in similar detection rates of 85–99% after cherries were shredded through either a 2- or 5-mm gap, even though the 2-mm gap resulted in greater shredding. In brown sugar, hot water, and salt solutions, 26–88% of first instars (when there were at least 8 individuals) were detected versus 77–100% of second and third instars. Results demonstrate that salt and brown sugar solutions are equally efficacious for detecting larvae of R. indifferens separated from crushed cherries. Salt solution is advantageous over brown sugar solution because it is less expensive. Should salt solution be used for detecting larval spotted wing drosophila (Drosophila suzukii [Matsumura]) in cherries, current results show that it would not compromise detection of R. indifferens.