Effect of the pseudostems of five banana varieties on banana weevil

Abstract: 【Objective】Banana weevil is one of the most destructive insect pests in most of banana growing areas in the world and almost all banana species have been suffered from its damage. It has been reported that the infestation of banana weevil in banana groves can reach up to 50% by causing up to 60%-70%yield loss in Chinese banana production areas. In recent years, banana weevil has been causing serious damage to banana production in Hainan, Guangdong, and Guangxi provinces and the damage in these provinces is getting worse. Banana weevils, including Odoiporus longicollis(Oliver) and Cosmopolites sordidus(Germar), mainly feed on pseudostem and corm of banana at larval stages, causing criss-cross larva gallery and therefore impeding the upward transport of nutrient flux. Feeding damaged banana plants normally show weak, fruitless and are easy to lodge in windy weather. Banana weevil normally occurs 4-5generations a year in Hainan province and generations are usually overlapped. Chemical control is currently the primary way to manage banana weevil in banana-growing regions, which has several advantages including low cost, quick effect, high efficacy, and being able to control secondary pests in the same period.However, the negative impact of long-term use of chemical pesticides include not only serious environmental pollution, which pose a great threat to human health, but also a large number of natural enemiessuppression, which leads to the destruction of ecological balance, and causee various problems and issues in the control of banana weevil. Therefore, ecological, environment friendly and biological means is necessary to be developed for banana weevil control. Previous studies have shown that banana pseudostem has attractive effect to banana weevil and it is useful to develop the traps for banana weevil control. Hence, we selected five banana varieties including‘Baxijiao',‘Baodaojiao'etc and their pseudostems as traps to determine the attractive effect of banana pseudostems to banana weevil. The current study will provide practical guidance for control of banana weevil by using banana pseudostem to prevent damage of banana production from banana weevil.【Methods】Field trapping tests were conducted in April 2014 when population of the banana weevil adult occured at peak in the banana growing season at the Haikou Experiment Station, Chinese Academy of Tropical Agricultural Sciences in Chenmai, Hainan. The planting area was6.67 hm2 with variety of‘Baxijiao'. Three types of traps were used as treatments, including pheromone trap, elongated pseudostem trap, and disc pseudostem trap. These three traps were deployed in a total of11 trap plots with trapping area of 400 m2 each. For pheromone trap plots, three tubbish traps were randomly deployed in the plot and each trap contained a banana weevil attractant. Then the three traps were randomly hanged in petioles of three plants respectively, with 10 meters above ground level and with spacing of 10 meters between traps. For pseudostem trap plot, three elongated pseudostem traps or three disc pseudostem traps, were randomly placed in the shade of the three plants close to the roots, with spacing in 10 meters between pseudostem traps. The test repeated three times and the number of trapped banana weevil in five days and ten days were counted and then analyzed. Under the laboratory conditions,the bioassays of selection response of banana weevil to different banana pseudostem were conducted by using double pitfall olfactometer. Pure air(blank control),‘Baxijiao'pseudostem,‘Baodaojiao'pseudostem,‘Haigongjiao'pseudostem,‘Guangfen 1'pseudostem, and‘Guangdongxiangjiao 1'pseudostem were paired into 15 different combinations for this experiment. The total number of insects tested in each treatment was 50 and the experiment was carried out in two parts, with 25 insects each time. When tested,one hundred gram of pseudostem was placed in the glass bottle of olfactometer and 25 banana weevils were released in the bottom center of the olfactometer box. After an hour, the number of banana weevil making choices to either of the two treatments in the glass bottle was counted. The position of the pitfall and the glass bottle of the olfactometer were shifted and another 25 banana weevils were released in the bottom center of the olfactometer box. After an hour, the behavior and choices making of the banana weevil in the glass bottle were observed and recorded. The data were analyzed by testing goodness-of-fit in chi-square analysis.【Results】Results from field traps indicated that the Banana weevil attractants had significant stronger attractive effect on banana weevil when compared with the other five banana pseudostems. Specifically, the number of the trapped banana weevils in 5th and 10 th day by using banana weevil attractants was 24.0 and 32.7 per trap, respectively. Furthermore, field trapping results also showed that.The significant trapping effects on two banana weevil species were found in the five banana pseudostems traps, and the number of trapped banana weevils in 5th and 10 th days reached 4.7-11.3 and 9-18 per trap, respectively. The number of banana weevils trapped in different traps was significantly different,however, the shapes of pseudostems showed little effect on the amount of trapped banana weevils. Moreover,‘Baxijiao'and‘Baodaojiao'showed significantly higher attractant effect than the‘Haigongjiao'‘Guangfen 1'and‘Guangdong xiangjiao 1'. Under the laboratory conditions, host selection experiment results showed that both banana weevil species showed significant choice to the five pseudostems whencompared with the blank control and the attractiveness of the five pseudostems from the most to the least to the two banana weevils could be arranged by:‘Baxijiao'>'Baodaojiao'>'Haigongjiao'>'Guangfen1'>'Guangdong xiangjiao 1'.【Conclusion】All five banana pseudostems could have a great potential to be used as an attractant to control the two banana weevil species, particularly the‘Baxijiao'and‘Baodaojiao'pseudostems. Furthermore, because trap shape was not significantly different in attractive effect on the two banana weevil species, for the convenient purposes, it is recommended to apply elongated trap rather than disc trap in the field, along with either of the two effective attractants mentioned above.