Evaluating the Efficacy of the Male Annihilation Technique in Managing Oriental Fruit Fly (Diptera: Tephritidae) Populations through Microscopic Assessment of Female Spermathecae

Abstract

The male annihilation technique (MAT) plays a crucial role in the pest management program of the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae). However, a suitable method for real-time and accurate assessment of MAT's control efficiency has not been established. Laboratory investigations found that motile sperms can be observed clearly under the microscope when the spermathecae dissected from mated females were torn, and no sperms were found in the spermathecae of virgin females. Furthermore, it was confirmed that sperms can be preserved in the spermathecae for more than 50 days once females have mated. Laboratory results also indicated that proportion of mated females decreased from 100% to 2% when the sex ratio (♀:♂) was increased from 1:1 to 100:1. Further observation revealed that there were no significant differences in the superficial area of the ovary or spermatheca between mated females and virgin females. Field investigations revealed that the proportion of mated females (PMF) could reach 81.2% in abandoned mango orchards, whereas the PMF was less than 36.4% in mango orchards where MAT was applied. This indicates that the PMF of the field population can be determined by examining the presence of sperms in the spermathecae. Therefore, we suggest that this method can be used to monitor the control efficiency when MAT is used in the field.

Keywords: Bactrocera dorsalis; male annihilation technique; proportion of mated females; spermatheca.

Figure 1

Reproductive tract of a Bactrocera dorsalis female showing the ovary, spermatheca, and ventral receptacle.

Figure 2

The geographic location of the field survey site in Yuanjiang County, Yuxi City, Yunnan Province, China. A indicates a wild mango orchard (untreated), and B indicates a wild mango orchard with the male annihilation technique (MAT) applied. Three trap points were established in each of the orchards, indicated by yellow dots.

Figure 3

The method of using a combination of mangoes and sticky boards to trap Bactrocera dorsalis in the field experiment area, showing the effectiveness of the lure at 7 PM. Before setting up the trap points, all the mangoes were collected on the ground within the experimental area. Five mangoes with intact skin and five mangoes with splits (caused by falling) or wounds (insect bites on the skin) were selected and gathered into a pile (approximately 600 g). A sticky board was fixed above the pile.

Figure 4

(a) Mean ± standard error (SE) ovarian superficial area of 10-day-old virgin Bactrocera dorsalis females and 10-day-old mated females (mated the previous day). (b) Mean ± SE superficial spermatheca area of 10-day-old virgin B. dorsalis females and 10-day-old mated females (mated the previous day). ns: not significant (p > 0.05).

Figure 5

Torn spermatheca of a 10-day-old mated Bactrocera dorsalis female (a) showing sperm mass dyed with acid fuchsin. Torn spermatheca of a 10-day-old unmated B. dorsalis female (b).

Figure 6

Sperms from torn spermatheca of a Bactrocera dorsalis female (dyed with acid fuchsin).

Figure 7

Pressed spermatheca of a Bactrocera dorsalis female (a) showing the spermatheca, spermathecal duct, and gelatinous matrix. The ventral receptacle of a B. dorsalis female (b) showing the alveolus.

Figure 8

Mean ± SE proportion of mated Bactrocera dorsalis females in experimental cages with different sex ratios (number of females/males). Bars topped by different lowercase letters indicate significant differences (p < 0.05) according to Tukey’s honestly significant difference (HSD) test.

Figure 9

(a) Mean ± SE proportion of mated Bactrocera dorsalis females in two orchards on 1 June (Orchard A, n = 41; Orchard B, n = 49) and 9 June (Orchard A, n = 38; Orchard B, n = 60), 2022. (b) Mean ± SE proportion of mated B. dorsalis females in two orchards on June 1 (Orchard A, n = 43; Orchard B, n = 30) and 8 June (Orchard A, n = 52; Orchard B, n = 38), 2023. Bars topped by different lowercase letters indicate significant differences (p < 0.05) according to Tukey’s honestly significant difference (HSD) test.