Study on the optimal field trapping period of Bactrocera minax

Abstract: 【Objective】In order to monitor the dynamics of adult population and predict the optimal field trapping period in the citrus orchards. At present the food trapping is the main method for monitoring the dynamic occurrence of citrus fruit fly adults in the citrus orchards. Because the adult citrus fruit fly early emerged (2 or 3 days after emergence) showed the habit, which flew away from the citrus orchard and then returned to the citrus orchard to lay eggs after a period of time. The dynamic occurrence of the adult in the citrus orchard was obtained through the real-time monitoring method of trapping. The occurrence was found a serious lag, which made some limitations for guiding the trapping and killing control of adults. Some scholars have proposed the possibility to predict the dynamics of adult occurrence in citrus orchards at constant temperature, indoor room temperature, and an outdoor screening house, using the fly pupal rearing method to monitor the adult emergence dynamics. Monitoring of adult emergence using constant temperature and an outdoor screening house can predict the appropriate timing of thetrapping in citrus orchards. Constant temperature cannot be synchronized with the natural adult eclosion period in the field due to the difference between the constant temperature and the natural temperature.The natural temperature often results in low emergence rate due to uncontrollable outdoor humidity while indoor room temperature preservation eliminates the problem of inconsistent eclosion periods and low emergence rate.【Methods】Citrus fruit fly larvae were collected in Yidu city of Hubei province (Zhicheng town) in late October of each year from 2009 to 2012. The larvae pupated in a fine sand container with a water content of 15% and stored at natural temperatures (4.8-22.6 ℃) . Adult emergence was monitored in the second year. Citrus orchard trapping test field was selected in Yidu city (Zhicheng town Zhifang village) , Hubei province with an area of 40 000 m2. Sixty traps were evenly distributed in the orangery and the attractants (Jufeng) in the trap were changed every 7-10 d. The trapped adults were monitored to examine the trapping dynamics in the citrus orchard. We compared the dynamics of indoors adult eclosion and trapping in Yidu, and the SPSS data processing software was used to fit the logistic equation. The beginning, apex and ending of the adult peak period were recorded during the eclosion and the citrus orchards trapping pattern was figured out by the logistic equation in 2010—2013, and the delay degree between eclosion and trapping was calculated. The climatic factors influencing the delay degree were analyzed according to the correlation between the climatic factors (temperature, humidity and rainfall amount) and the delay degree.【Results】For the emergence of adults, the logistic equations were Y=100.713/[1+Exp (10.163-0.707 X) ], Y=100.452/[1+Exp (4.096-0.718 X) ], Y=123.36/[1+Exp (2.996-0.484 X) ] and Y=118.632/[1+Exp (6.994-0.564 X) ], respectively in 2010—2013. In these four years, the beginning of the adult peak period during the eclosion was at May 24, May 14, May 15 and May 11, the apex day was at May 26, May 16, May 18 and May 13, and the end day was at May 28, May 18, May 20 and May 15. However, for the adults captured in citrus orchards in 2010—2013, the logistic equations were Y=94.054/[1+Exp (3.962-0.294 X) ], Y=102.328/[1+Exp (4.57-0.206 X) ], Y=99.727/[1+Exp (2.023-0.27 X) ] and Y=100.468/[1+Exp (4.584-0.375 X) ], respectively. In these four years, the beginning of the adult peak period was at Jun. 5, May 30, May 30 and May 28, and the apex day was at Jun. 10, Jun. 6, Jun. 5 and Jun. 2, and the end day was at Jun. 17, Jun. 14, Jun. 11 and Jun. 6. The doomsday lagged 20, 27, 21 and 22 d, respectively compared to the last days of emergence. The beginning of the adult peak period of trapping lagged 11, 16, 16 and 17 d and the apex day lagged 15, 21, 18 and 20 d and the end day lagged 20, 27, 21 and 22 d, respectively, after the eclosion peak in 2010—2013. So there was a relatively stable delay degree between eclosion and trapping. The delay degrees of the beginning, apex and ending of the adult peak period were (15 ± 1.35) days, (18.5 ± 1.32) days and (22.5±1.55) days, respectively. There was no significant correlation between the delay degree and the temperature, humidity and rainfall amount.【Conclusion】There was a relatively stable delay degree between eclosion and trapping, which was not affected by the temperature, humidity and rainfall amount during the delay degree. Therefore, in the field management of citrus fruit fly, we can monitor the dynamic eclosion at normal temperature and then foresee the optimum trapping period of citrus fruit fly in orchards. This will enhance the accuracy of trapping of citrus fruit fly in the citrus orchards.