Effect of hot wind on insects in longan (Dimocarpus longan Lour.) orchard during off-season production in the Chao Phraya Delta

Abstract

Off-season longan is an important commercial frui crop grown in the alluvial plains of Chao Phraya Delta, Thailand. Hot winds during the off-season production period has been reported to significantly reduce shoot growth and cause flower buds to dry out and fall off. In addition, the effect of these hot winds on the bio-ecological environmental is still unknown. This study monitored the all year round (May 2018-April 2019) change in insect populations surrounding longan orchards. Five different insect trap sheets, four coloured (white, yellow, green and blue) and a transparant trap were located on the four compass directions (north, south, east and west) in Ban Phaeo District, Samut Sakhon Province. Apical shoots were induced in May (May pot) to initiated early flower buds to avoid the hot winds and compared with the flower buds initiated in June (June plot) that were exposed to the hot winds. The trap sheets were replaced and evaluated for insect population every month. The results showed, regardless of growth pattern differences between the two plots, insect populations in both plots clearly increased at the same time during June to November, when the annual hot winds blew at Ban Phaeo. Interestingly, during this period, insect populations increased in conjunction with situations of high-water vapour pressure deficit which is related to high temperature and low relative humidity. The insect category focused on, was those pests related to longan productivity, natural enemies, and water quality indicators. Trap location from the four compass directions showed the same trend. Major insect pests and enemies were found on yellow colour trap sheets. These results will benefit selective integrated pest management programs for controlling insect populations in longan orchards.