Searching behaviour and the egg production of the coconut mite, Aceria guerrernis on selected coconut varieties in Sri Lanka

Abstract

Coconut is a major livelihood crop in many tropical countries in the world. Its production is affected by many biotic and abiotic factors and among the biotic factors, pests play a major role in reducing the coconut production. The coconut mite, Aceria guerreronis (Keifer) is one of the major pests of coconut in many countries causing severe yield losses including immature fruit drop, deformed fruits, empty fruits, and reduced fruit weight. Chemical and biological methods have been mostly used to control A. guerreronis. In Sri Lanka, some commercial varieties are known to show least damaged compared to other varieties. But the reason for this observation is not known. The varieties used in this study, Ran Thembili (RT), Gon Thembili (GT), Sri Lanka Green Dwarf (SLGD), Sri Lanka Yellow Dwarf (SLYD) and Sri Lanka Tall (SLT) are used as parent palms in producing hybrid coconut varieties in Sri Lanka. Therefore, it is worthwhile to understand the mechanisms behind the different susceptibility levels of these varieties to A. guerreronis and this information can be used in selecting parental palms in future breeding for A. guerreronis tolerant/resistant coconut varieties. Therefore, the experiments reported in this paper were conducted to understand whether different coconut varieties provide volatile or non-volatile cues for A. guerreronis or whether their egg production is affected by different varieties. The preference of A. guererronis towards the coconut varieties RT, GT, SLGD, SLYD and SLT were tested on a 5-arm runway arena and the egg production was also measured on young fruits of the above varieties. The results revealed that A. guererronis do not prefer any of the varieties tested. Their egg production was higher on RT compared to SLYD and SLT. Although A. guerreronis populations and their damages were shown to be higher on SLGD and SLT in previous study, it was not reflected in the egg production on them in the present study. Therefore, we conclude that volatile or non-volatile cues of different coconut varieties do not provide signals for A. guerreronis to select certain coconut varieties over other varieties and their egg production is affected by the coconut varieties. However, apparently susceptible coconut varieties (SLGD and SLT) are not preferred by A. guerreronis for the selection for colonization or for the egg production. Other physical barriers in different coconut varieties such as the shape of the fruits and perianth tightness appear to affect the varietal susceptibility of coconut varieties to A. guerreronis.