Figure 1.
Behavior and egg-laying response of B. dorsalis.
(a) Behaviour assay where B. dorsalis were presented with a filter paper disc containing γ-octalactone. Arrows show the hallmark oviposition behavior of extending the ovipositor and probing action (for better view watch video S1). (b & c) Egg-laying response of B. dorsalis to a pulp disc with γ-octalactone (Test) or without (Control) in a 24-h oviposition bioassay. More eggs were laid on the test disc (P<0.0001, one-tailed paired t test of non-transformed data). Error bars = Standard error of mean.
Figure 2.
γ-Octalactone is an oviposition stimulant and an oviposition site recognition cue.
(a) The clear discrimination of the untreated (No OL, γ-octalactone not present) half (A) and γ-octalactone treated (OL, γ-octalactone present) half (B) by B. dorsalis in a single plate two-choice assay. (b) Number of eggs laid into treated and untreated pulp (one-tailed paired t test, n = 30, t = 11.27, df = 19, P<0.0001). Error bars = standard error of mean.
Table 1.
EAG and ovipositional response of Bactrocera dorsalis to varying concentrations of γ-octalactone.
Figure 3.
Schematic representation of the response of flies with different rearing histories towards γ-octalactone. B. dorsalis was reared on 3 different hosts.
The final (third) generation gravid females were used in oviposition bioassays. A one-tailed t test revealed a significant difference (P<0.0001) between Test (OL, γ-octalactone present) and Control (No OL, γ-octalactone not present). One-way ANOVA between the tests of group 1 (mango), 2 (banana) and 3 (guava) showed no significant difference in the mean no. of eggs laid.
Figure 4.
γ-Octalactone is a crucial cue that elicits oviposition in B. dorsalis.
(a) Flies were allowed to oviposit into an empty agar disc. Area A contained all EAD active mango cues (cv. Alphonso) at natural ratios except γ-octalactone; Area B contained γ-octalactone alone. Flies could clearly distinguish between the untreated area (A) and the γ-octalactone treated area (B) (One-tailed t test, t = 6.610, df = 8, P<0.0001). (b) The mean number of eggs laid into A or B. Oviposition in B. dorsalis was mediated by γ-octalactone. Error bars = Standard error of mean.