“SWD is becoming a big problem for growers of soft-skinned fruits such as strawberries, raspberries, blueberries, and cherries all over the world,” Chiu pointed out. “With the need to satisfy insect damage standards and to reduce crop loss, the growers generally adopt high levels of insecticide usage for SWD control and risk reduction. In the long-term, this will lead to development of insecticide resistance, not to mention the damage inflicted on beneficial insects.”

“Current Drosophila suzukii management strategies rely heavily on insecticide usage, because other pest management tactics are still being development and optimized,” wrote Chiu and fellow authors Frank Zalom, integrated pest management specialist and professor of entomology; doctoral candidate Kelly Hamby of the Zalom lab; and graduate student Rosanna Kwok of the Chiu lab.

“From my point of view, what is particularly interesting is that insecticide detoxification of many insects including Drosophila suzukii is under circadian control,” Zalom said.  “This knowledge could be particularly interesting for organically acceptable insecticides like pyrethrum that are only effective for a short period of time after they are applied. Pyrethrum is one of the only organic options that can be used by farmers to control Drosophila suzukii, so if its efficacy can be improved by applying sprays at a certain time of day then this could be a positive development.”

Said Hamby: “The paper is a first look at Drosophilia suzukii daily activity rhythms under a temperature and light/dark cycle mimicking California raspberry growing conditions as well as a look at the daily cycling of insecticide susceptibility enzymes that could potentially detoxify insecticides. The next steps would be to include more temperature conditions, more insecticides, and attempt an experiment in the field.”

"For me, the importance of our research is that it allows us to move toward a more effective and efficient way of controlling this pest, which is rapidly becoming of prominent importance because of how fast Drosophila suzukii has been spreading throughout the western US since its initial introduction," said Kwok. "By recognizing temporal differences that may contribute to a difference in toxicity to certain pesticides, we may be able to move toward management programs that are tailored to target a specific species of insect. We may be able to spray less or less frequently if we can find out when these pests are most susceptible."

"As for the future," Kwok added, "I think that as we sequence and fully annotate the D. suzukii genome we can identify more genes that are implicated in toxicity and pesticide resistance."

Chiu praised the work of the graduate students. "I think Kelly and Rosanna really did a fantastic job on this project!" she said.

The study took place under laboratory conditions simulating summer and winter in Watsonville. The team found significant differences in the chronotoxicity of SWD toward malathion, with the highest susceptibility at 6 a.m., “corresponding to peak expression of cytochrome P450s that may be involved in bioactivation of malathion,” they wrote in their abstract.  “Chronobiology and chronotoxicity of D. suzukii provide valuable insights for monitoring and control efforts, because insect activity as well as insecticide timing and efficacy are crucial considerations for pest management.”

The spotted-wing drosophila was first observed in Japan as early as 1916. The females lay their eggs in ripe and ripening fruit, unlike other Drosophila species known to infest overripe and blemished fruit. The larvae feed on the fruit. “The adult is the only stage that can be targeted for control by conventional pesticides,” the UC Davis scientists wrote. The most commonly used insecticides are organophosphates, pyrethroids and spinosyns


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