Location: Tropical Crop and Commodity Protection Research
Project Number: 2040-43000-018-018-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 1, 2021
End Date: Aug 31, 2023
Objective:
1. Identify key bioactive deterrent compounds from crude deterrent mixture to B. dorsalis and other fruit flies.
2. Determine optimum and minimal effective doses of the key compound(s).
3. Evaluate the efficacy of the deterrent(s) on oviposition.
4. Determine the phytotoxicity and impact that the deterrent(s) have on host fruit quality.
Approach:
Insects and chemicals:
B. dorsalis will be reared on artificial diet. A mixture of 8 candidate oviposition deterrent mixture (OviX) and its individual components will be purchased.
Oviposition deterrence bioassay:
Oviposition bioassays will be conducted using laboratory two-choice cage experiments with guava juice infused agar as an artificial oviposition substrate in 30x30x30 cm screened cages using 20 mated OFF females per cage (12-18 d old) over 3 days. Each cage will be provided with water, sugar, and protein hydrolysate and two guava juice agar plates, each surface-treated with respective dose (e.g. 20, 2 or 0.2 mg/agar plate) of OviX or its individual components dissolved in 200 µl of hexane or 200 µl solvent control (hexane). After three days, oviposited eggs in the guava agar will be individually counted or estimated volumetrically (1 ml of eggs = 20,000 eggs).
Identification of key bioactive deterrent compounds from OviX:
Using two-choice bioassay, the oviposition deterrence of OviX on B. dorsalis will be evaluated at 20, 2, and 0.2 mg doses compared to solvent control. To determine candidate key-deterrent components of OviX, oviposition deterrence of individual components of OviX will be initially evaluated at 20 mg/agar plate compared to solvent control. Based on their effects on oviposition, individual compounds will be assigned to “negative” (i.e. oviposition reduced), “neutral”, and “positive” compound groups. We will then formulate “negative-compound” and “negative plus neutral-compound” blends and compare their oviposition deterrence with OviX at equivalent ratio and concentration as OviX.
Determination of minimum effective doses of the key compound(s):
We will conduct oviposition assays comparing the effect of solvent control and individual components of key-deterrent component blend at 2 and 0.2 mg doses on oviposition. Then, we will compare the oviposition deterrence of key-component blend formulated at lowest effective dose(s) of individual component(s) and the blend formulated at 20 mg dose of each blend component.
Evaluation of oviposition deterrence on host fruit:
We will evaluate oviposition deterrence of key-component blends for B. dorsalis applied to known hosts, papaya and guava, respectively, using a two-choice bioassay set-up as described above. For bioassays, each cage will be provided with two ripe papayas or guavas—one surface-treated with the key component blend at the equivalent dose of 2 mg OviX/200 µl/agar plate and the other treated with hexane control. Female flies will be allowed to oviposit on papaya or guava for 3 days. After 3 days, papaya or guava will be removed and stored in individual cages at 23°C. The numbers of larvae and pupae will be counted 2 weeks after the conclusion of the oviposition assay.
Evaluation of the effect of oviposition deterrents on host fruit quality:
After a key-component blend or blank control treatment on papaya or guava as conducted in laboratory bioassays (Objective 3), fruits will be stored at 23°C and weight and color parameters of each fruit will be measured at 3 day interval post treatment over 2 weeks.
