Monitoring the Methyl Eugenol Response and Non-Responsiveness Mechanisms in Oriental Fruit Fly Bactrocera dorsalis in China

Abstract

Bactrocera dorsalis is a notorious polyphagous pest in China, and its management strategies largely depend on methyl eugenol (ME), which has been widely used as an attractant to monitor and eradicate B. dorsalis populations for seven decades. However, the non-responsiveness levels in field B. dorsalis populations to ME is unknown. In this study, we monitored the response to ME in field populations from the four most heavily infested provinces in China, and the results showed that the populations had lower sensitivity to ME relative to GZS susceptible strain. The percent responsiveness of the lowest sensitivity population was 5.88-, 3.47-, and 1.47-fold lower relative to the susceptible strain at doses of 1, 10, and 100 µL of ME, respectively. Gene expression analysis and inhibitor assays further revealed that odorant binding protein (BdorOBP2, BdorOBP83b) and the P450 enzyme system may be associated with the lower response to ME. To our knowledge, this work is the first to report that the P450 enzyme system confers a lower responsiveness to lure insects. These findings provided valuable insights for exploiting ME non-responsiveness to protect sterile males from ME-based control strategies and the use of lures combined with insecticides.

Keywords: P450; methyl eugenol; non-responsiveness; odorant binding protein; trapping.

Figure 1

The response of B. dorsalis males from the GZS-susceptible strain and the four field populations to ME. The assay was conducted by using three doses of ME (1, 10, 100 µL) and MO alone served as controls accordingly in trap cages (30 × 30 × 30 cm³) for 6 h. No flies were trapped in the control MO cages. Data are presented as the mean ± SE. Different letters on the histogram bars indicate significant differences based on one-way ANOVA followed by Tukey’s HSD multiple comparison test (p < 0.05).

Figure 2

Expression profiles of four genes in the antennae (ANT), maxillary palps (MP) and proboscis (PRO) of B. dorsalis males from the GZS susceptible strain and the four field populations (A) BdorOBP2, (B) BdorOBP83b, (C) BdorOrco, and (D) BdorOR88a. Relative gene expression was measured by qRT-PCR, and values represent the means ± SEs for three independent replicates. Different letters on the histogram bars indicate significant differences based on one-way ANOVA followed by Tukey’s HSD multiple comparison test (p < 0.05).

Figure 3

The effect of olfactory organs on the response of B. dorsalis males to ME. Assays were performed in trap cages (30 × 30 ×30 cm³) after the removal of the antennae (ANT), maxillary palps (MP) and proboscis (PRO) in a mixture of 100 μL ME and 900 μL MO, or 1 mL of MO alone (a control). No flies were trapped in the control MO cages. Data are presented as the mean ± SE. Different letters on the histogram bars indicate significant differences based on one-way ANOVA followed by Tukey’s HSD multiple comparison test (p < 0.05).

Figure 4

The effect of P450 inhibitors on the response of B. dorsalis males from the GZS susceptible strain and the two field populations to ME. Assays were performed in trap cages (30 × 30 × 30 cm³) using a mixture of 100 μL ME and 900 μL MO, or 1 mL of MO alone (a control). No flies were trapped in the control MO cages. Data are presented as the mean ± SE. The asterisks on the histogram bars indicate significant differences compared with the control (acetone) within each B. dorsalis line according to Student’s t test (p < 0.05).