The effect of insect fauna on growth mortality and natality of broom, Sarothamnus scoparius.
Abstract
Two plots, each of 240 broom (Sarothamnus scoparius) seedlings were planted in England in March 1966. For 11 years, one plot was sprayed 1-3 times a year with a mixture of dimethoate and malathion; the second plot remained untreated. The aim was to reduce the insect fauna and to gauge its impact on the growth, mortality and natality of the broom bushes. The insect fauna was estimated three times a year between 1966-68, twice in 1969 and once a year during 1970-76. Colonisation of the plots was rapid and larger populations of insects developed in the unsprayed plot. The unsprayed bushes did not attain full growth; their mortality rate was higher and natality rate lower compared with the sprayed bushes. Aphids and psyllids in particular, aided by Leucoptera spartifoliella (Hb.), Miridae and Gonioctena olivacea (Forst.) (Phytodecta olivacea), reduced the vigour of the broom bushes. The seed yield of unsprayed broom over the average 10 year life-span of a bush was also reduced by 75%.