The Effect of DDT and BHC on the Population of the Lucerne Flea, Sminthurus viridis (L.) (Collembola) , and its Control by predatory Mites, Biscirus spp. (Bdellidae)

Wallace, M.M.H.

Aust. J. agric. Res, Melbourne 5(1): 148-155


Accession: 013855992

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An account is given of further tests in Western Australia on the effect of top-dressings of BHC and DDT in superphosphate on Smynthurus viridis (L.) in pastures, and also on their toxicity to the Bdellid mites that prey on it. The pastures selected consisted chiefly of subterranean clover and contained high populations of S. viridis. The Bdellids present were Biscirus australiens Wom., which was numerous, and B. symmctricus (Kramer), which was scarce. The BHC contained about 13 per cent, y isomer. In the first test, superphosphate alone or with 0.5 per cent. p, p'DDT or BHC was applied at a rate of 1 cwt. per acre on 31st July 1947, and the populations of S. viridis and the mites were estimated by aspiration from metal cylinders pressed into the ground. In the control plots treated with superphosphate only, the numbers of S. viridis declined steadily throughout the season, whereas those of Biscirus were trebled, and similar trends occurred in the plots treated with BHC, though the initial decline in S. viridis was rather more rapid. In the plots treated with DDT, the numbers of S. viridis fell during the first 12 days, though no more rapidly than in the controls, and subsequently showed no significant change; the Bdellids were rapidly reduced and eventually died out completely, and at the end of the season, S. viridis was five times as numerous as in the controls. In the second test, superphosphate alone or with 0.5, 1 or 2 per cent. BHC or 1 per cent. p, p'DDT was applied at 90 lb. per acre on 28th July 1950, and the populations were estimated 23, 45 and 69 days later by sweeping with glass tubes, and, in the case of the mites, by collection from under trap boards; the former method was not very reliable when the plants were tall, owing to the vertical distribution of the insects. Populations of S. viridis decreased in all the plots, but the reduction was less rapid for DDT than for any other treatment and numbers were eventually 19 times as great as in the controls. BHC gave reductions increasing with concentration, and significant differences were found between 2 per cent. BHC and 0.5 or 1 per cent., and between these and the controls, after 23 days. The differences decreased after 45 days, and none of the BHC treatments differed significantly from the controls after 69 days. The Bdellid mites were significantly fewer after 23 and 45 days in the plots treated with DDT than in any others, but there were no significant differences after 69 days. The control given by BHC applied in this manner was thus limited, and higher concentrations are not considered economically practicable. A further test was attempted in 1951, when 50 per cent, dispersible BHC applied in sprays at 2 lb. per acre reduced S. viridis by 30 per cent, in three days, but the results were inconclusive owing to low infestation in the controls. S. Davies obtained only moderate control in experiments in which emulsion sprays containing BHC were applied by low-volume spraying equipment. Other investigators have obtained satisfactory results from BHC sprays applied from the ground or from the air, and the poor results of the experiments reported are attributed to the height of the vegetation, giving increased cover, at the time of application.