The Effect of Insect Fauna on Growth Mortality and Natality of Broom, Sarothamnus scoparius

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Abstract
Two plots of 240 broom S. scoparius seedlings were planted in Mar. 1966. For 11 yr, one plot was sprayed 1-3 times a year with a mixture of dimethoate and malathion; the 2nd 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 3 times per year between 1966-1968, twice in 1969 and once per year during 1970-1976. Colonization 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, Miridae and Phytodecta olivacea reduced the vigor of the broom bushes. The seed yield of unsprayed broom over the average 10 yr life span of a bush was also reduced by 75%.