Abundance and diversity of white grubs in KwaZulu-Natal: interim results of the 2017-2018 monitoring programme

Authors
Sivparsad BJ, Germishuizen I, Colong Des E, Webster T and Morris AR
Publication Type
Technical Note
Publication Year
2018
Source
TN06-2018

In KwaZulu-Natal, white grubs are dominant soil pests that can contribute to serious transplant mortality at re-establishment. A two-year monitoring programme was initiated in summer 2017 to determine temporal trends of white grub activity. From February 2017 to January 2018; six sites planted to pine, eucalypt and wattle and located in sugarcane and non-sugarcane areas of KZN were sampled bi-monthly for white grub larvae, pupae and adults. An additional site that had been planted to sugarcane was surveyed as a control. Over the one-year survey period, a total of 1 023 white grub stages were recovered from 900 pits, representing an average area-wide density of 1.14 white grub/ pit. The greatest abundance of larvae (3.51 larvae/pit), pupae (0.05 pupae/pit) and adults (0.57 adults/ pit) was observed in the wattle site located in the sugarcane area. In general, a low number of larvae (≤0.19 larvae/pit), pupae (≤0.01 pupae/pit) and adults (≤0.02 adults/ pit) were recovered from all pine and eucalypt sites. Distinct seasonal fluctuations in the abundance of different white grub stages in relation to rainfall and harvesting were observed in all sites where a greater number of larvae was found prior to harvesting operations during the summer rainfall months. A total of nine morphospecies were identified based on species-specific raster patterns of collected larvae. The identification of these species using molecular markers is currently underway at the Forestry and Agricultural Biotechnology Institute (FABI). The greatest species richness was found in wattle sites with the non-sugarcane wattle site being the most diverse and composed of all morphospecies. The pine site in the non-sugarcane was the least diverse with only one species being identified. Monitoring will continue to March 2019 and results will then be further analysed to develop a risk assessment model for white grub infestation of forestry in KZN.