Oviposition preference of Bactrocera dorsalis (Hendel) to five varieties of pitaya

Abstract: 【Objective】Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) can damage a wide range of fruit crops, and almost all pitaya fruits are included while the preferences of B. dorsalis to numerous pitaya species are unclear. To guide the selection of pitaya species and/or varieties and determine the critical window of population management for B. dorsalis in the pitaya producing areas, the oviposition preferences of B. dorsalis to five varieties (i.e.‘Meilong 2’,‘Meilong 6’,‘White Cinnamon Zeal’,‘Puhong’, and ‘Taiwanese Dahong’) and to their different maturity fruits (i.e., fully-ripe, half-ripe, and unripe fruits) were investigated in a laboratory.【Methods】The fruits of Psidium guajava L. damaged by B. dorsalis were collected from Xi’an village, Yuzhou district, Yulin city, Guangxi Zhuang Autonomous Region, and were put in the cage (length × width × height = 90 cm × 90 cm × 90 cm) until adults emerged. The adults were fed on the artificial diet (yeast extract: sugar = 1: 5) in the cage, and fully-ripe fruits of P. guajava and Musa nana Lour. were provided for egg laying. These damaged fruits were put in the plastic basin (radius = 8 and 13 cm for bottom and top, height = 11 cm) until the B. dorsalis off-spring developed to pupae. The pupae were randomly selected and placed in the plastic cup (radius = 4 and 6 cm for bottom and top, height = 15 cm) until adults emerged. Sexual maturity adults (15-20 days old) were paired in one cage, and mated females were chosen as experimental insects. Five varieties of pitaya and their different maturity fruits were used as experimental materials, which were collected from Xining village, Nachen Town, and Nanning Zhenqi Agriculture Technology Development Co. Ltd., Pumiao town, Nanning city, Guangxi Zhuang Autonomous Region. Thirty mated females of B. dorsalis were introduced into one cage, in which the arrangement of different pitaya varieties or different maturity fruits was equidistant diagonally. Each treatment was replicated for 10 times. These fruits were dissected and the number of eggs laid by B. dorsalis in these fruits was carefully counted after an exposure of 24 hours. The fruit hardness of different maturity fruits from the five pitaya varieties was measured using a fruit hardness tester. Each treatment was replicated for 5 times. The correlations be-tween the fruit hardness and number of eggs laid by B. dorsalis in different pitaya varieties were ana-lyzed using Pearson correlation coefficient with SPSS 22.0 software (IBM SPSS, USA).【Results】In the fully-ripe fruits, the number of eggs laid by B. dorsalis in‘Puhong’was the most (25.70±6.15), which was significantly more than all other treatments; in the half-ripe fruits, the number of eggs laid by B.dorsalis in‘Puhong’(18.45±5.13) and‘White Cinnamon Zeal’(20.80±7.03) was significantly more than other three treatments; in the unripe fruits, the number of eggs laid by B. dorsalis in‘Puhong’(10.13±1.25) and‘White Cinnamon Zeal’(12.45±4.80) was significantly more than all other treat-ments. As for the different maturity fruits from the five pitaya varieties, the number of eggs laid by B.dorsalis in the half-ripe fruits of‘Meilong 2’(83.67±3.61),‘Puhong’(119.67±10.52), and‘Taiwanese Dahong’(63.00±8.67) varieties was significantly more than that in other treatments; B. dorsalis laid more eggs in the fully-ripe and half-ripe fruits of‘Meilong’(51.67±6.42 and 58.40±5.40 for fully-ripe and half-ripe fruits, respectively) and‘White Cinnamon Zeal’(134.00±5.62 and 113.00±4.11 for fully-ripe and half-ripe fruits, respectively) varieties than in other treatments. Fruit hardness of‘Meilong 2’,‘Meilong 6’,‘White Cinnamon Zeal’,‘Puhong’, and‘Taiwanese Dahong’decreased significantly from (47.61±4.89), (49.20±1.78), (41.36±4.61), (47.34±3.80) and (47.61±2.75) kg · cm^{- 2} to (20.30±3.28), (20.23±4.65), (26.42±1.75), (20.23±1.95) and (20.94±2.00) kg·cm^-2, respectively, from unripe to fully-ripe. The fruit hardness of‘Meilong 6’,‘White Cinnamon Zeal’, and‘Puhong’varieties was negatively correlated with the number of eggs laid by B. dorsalis, respectively, while no correlation was found for the‘Meilong 2’and‘Taiwanese Dahong’varieties.【Conclusion】B. dorsalis preferred‘White Cinnamon Zeal’,‘Puhong’, and‘Taiwanese Dahong’to oviposite among all tested varieties and maturity fruits. Fruit hardness of the five pitaya varieties significantly decreased with the increase of fruit maturity, and the fruit hardness of‘Meilong 6’,‘White Cinnamon Zeal’, and‘Puhong’variet-ies was negatively correlated with the number of eggs laid by B. dorsalis, respectively. The results sug-gested that, in the cultivated area of‘White Cinnamon Zeal’,‘Puhong’, and‘Taiwanese Dahong’,those varieties should be reduced (especially under the context where the acceptance level of these vari-eties was average among consumers), and the critical window of population management for B. dorsalis was the color-changed period of these tested pitaya varieties, during which green prevention and control for B. dorsalis should be considered to avoid possible pesticide residue.