| Summary: | 碩士 === 國立屏東科技大學 === 熱帶農業暨國際合作研究所 === 95 === The effectiveness and economic benefits of using different chemical application methods in the control of a mealybug, Planococcus minor Maskell, on the winter crop of sugar apple, Annona squamosa L., were evaluated. Also, the population dispersion and feeding habits of the mealybug were studied in hope that the results would facilitate the establishment of its early detection and control model. Comparing the results of manual and mobile fogger applications conducted in 2005, there was no significant difference in the rates of fruits infested with the mealybug. Both application methods were effective in controlling the mealybug in the winter crop of sugar apple. Based on the number of mealy bug counted (y) and the rates of fruits infested (x), the regression equation of y = 2.3769x – 3.5899 was calculated. Further, basing on the marketing standards of sugar apple, which are commonly practiced commercially that the number of mealybugs infesting a fruit covering over 30% of a fruit surface would render it non-marketable, the number was estimated at about 68 mealybugs per fruit. This estimated number did not include eggs found on the fruit in the calculations. Therefore, this regression equation is only applicable for the estimation of the number of the mealybugs found on a fruit. In comparing the estimated income, net income, and total losses, the differences between the two application methods were not significant. However, the total costs of the manual application method were 2.7 times more than that of the mobile fogger application method. Results of the analysis of their economic benefits showed that the mobile fogger application was a significantly better method. Comparing the data collected in 2006 on the use of three application methods; manual, mobile fogger and improved mobile fogger, their effectiveness in controlling the mealybug, in a descending order, was improved mobile fogger＞manual application＞ mobile fogger. Based on the two observations conducted in the field, the result showed that the earliest and most severe mealybug infestations were found on the fruits located in the mid section of a sugar apple tree. The mealybug is known to disperse by crawling. Results of the analysis of the rates of infested fruits collected respectively from the eastern, western, southern and northern directions of a sugar apple tree showed no significant difference among the four directions. It was concluded that the dispersal and food finding of the mealybugs were done randomly and were independent of the influence of sunlight and wind direction. As such, pesticide application on the truck from the root base to the branching of a stem of a sugar apple tree was most important in order to be effective in the control of the mealybug as this was a critical thoroughfare for its dispersal upward toward sugar apple fruits and this also provided the least protection or refuge for the mealybug. Five days after the mealybug had migrated to a sugar apple fruit, the results appeared to show that the rate of increase of its infestation area on a fruit was in line with the increase of temperature; 1.27 times under 20.0oC, 1.57 times under 22.2oC, and 2.3 times under 22.5oC. When the cumulative rainfall was 0.0 mm during the period of study, the rate of increase of the infestation area reached 2.3 times. However, when the cumulative rainfall was 29.0 mm, the rate of increase of the infestation area decreased 1.08 times. This indicated that rainfall would inhibit the mealybug infestation. Since the mealybug populations increased rapidly in the field, it took only 4.5 days for doubling the fruit infestation area; therefore, sugar apple growers should change from their common practices of using the results of monitoring mealybug populations over the entire tree as a basis for pesticide applications to relying on the result of monitoring the mealybug population density on the section from its root base to the branching of the main trunk of a sugar apple tree. This change in focusing on monitoring the mealybug populations on the tree trunk, instead of the entire tree, would enhance the effectiveness of the mealybug control by preventing its spread to sugar apple fruits. Based on the results of this study on the mealybug infestations in the field and its control costs and benefits, the best time for the control of the mealybug would be in the spring from March to April and in the fall from September to October, when the nymphs and adults of the mealybug were migrating by crawling upward from the root bases to the fruits. Also, the use of improved mobile fogger would be most effective in the control of the mealybug in an orchard.
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