Validation of an integrated pest management (IPM) strategy for pollen beetle to minimise the development of insecticide resistance

Abstract

This project was done in response to industry feedback to refine guidelines for pollen beetle control. It aimed to (1) investigate the impact of different numbers of pollen beetles on the yield of winter and spring oilseed rape (2) consider whether pollen beetle damage to the primary raceme results in increased yield loss (3 & 4) investigate whether the compensatory ability of crops is affected by pigeon damage or infestation by cabbage stem flea beetle (CSFB) larvae (5) calibrate numbers of pollen beetle caught on the monitoring trap with numbers in the crop (6) provide guidelines on how to best estimate pollen beetles levels in the crop and (7) assess the accuracy of an online tool to predict timing of pollen beetle immigration and investigate effects of its use on spray timing and pest control. 

In field experiments, pollen beetle numbers did not exceed threshold and did not justify insecticide treatment suggesting that that sub-threshold populations of the pest are the norm rather than the exception. 

In further experiments, pollen beetle damage was simulated by bud pruning and pigeon damage was simulated by mowing. There was no evidence to suggest that removing 100 per cent of buds from the primary raceme increased yield loss, whereas mowing reduced yield but less than anticipated.  Furthermore, mowing did not increase susceptibility to simulated pollen beetle damage and crops with low plant populations were no more susceptible to simulated pollen beetle damage than those with high plant populations. There was no evidence to suggest that crops with up to seven CSFB larvae/plant had an increased susceptibility to simulated pollen beetle damage. 

An Oecos pollen beetle monitoring trap with an attractive lure was more effective than unbaited yellow sticky traps. The trap can be used to detect pest movement and abundance but as yet it has not been calibrated to detect threshold numbers of pollen beetles. Pollen beetle immigration is usually greatest on the north-east side of the field (opposite to the prevailing wind) and this should be the focus for location of traps and crop walking. 

The Bayer Pollen Beetle Predictor (BPBP) accurately predicted the peaks of pollen beetle migration helping to focus monitoring effort to when it is most needed. It reduced monitoring effort by about a third compared with weekly in-field assessments and also provided early and accurate detection of when the threshold was exceeded. Monitoring (weekly or via use of the BPBP) resulted in a reduction in insecticide use by about one-third compared with prophylactic treatment. However, in line with other experiments in this project, insecticide use did not significantly increase yield in comparison with untreated controls.   

Overall the project has demonstrated that pollen beetle numbers are rarely damaging and that current thresholds and monitoring methods provide a good basis for an IPM strategy for this pest that minimises the need for insecticide treatment.