Not normally effective

Press, Volume CXI, Issue 32720, 24 September 1971, Page 13

Not normally effective

Bonfires are not usually an effective method of controlling grass grubs at the time of beetle flights, according to Mr P. E. C. Read, a technician with the sub-station of the Entomology Division of the Department of Scientific and Industrial Research at Lincoln. Mr Read has recently been working with a sex attractant for grass grub beetles. He was commenting on a letter recently written to the editor of “The Press” by “Ex Farmer.” • “Ex Farmer" suggested that fanners who had a grass grub problem could alleviate their problem by a concerted effort in lighting rings of bonfires after

dusk at the time of the beetle .flights. "There are old motor tyres at every garage in the country and a few gallons of waste oil will do the job. Try it. It works. What about Federated Farmers doing some organising,” added the correspondent. The writer of the letter told “The Press” that when he was fanning at Courtenay he had lit a gorse fire across the fence from a first year paddock of grass and oats that was badly affected with grub. It was about early November in 1922 and the beetles were attracted to the fire in their thousands. “Ex Farmer” said that he had used this method of catching beetles often since. But Mr Read said that on the basis of figures recorded by Mr J. M. Kelsey, formerly officer in charge of the Lincoln sub-station, normally only 2 per cent and very occasionally up to

5 per cent of female beetles flew to light traps. These were usually unmated females. The majority of the beetles flying to traps or a bonfire were, therefore, male beetles and they had mated the females before flying to the light so that there was really no advantage in their being trapped by a fire. However, in 1955, Mr Read said that Mr Kelsey had recorded an unusual sex ratio in his trappings. Then when flights each night had been of from one and three-quarters to two and three-quarters hours duration instead of the usual 30 minutes, 87 per cent of the beetles flying were found to be females and 85 per cent of these were unmated. This phenomenon was a rarity but in such a season bonfires could have had some effect in reducing the population.