Control of Pests in Glasshouse Culture by the Introduction of Natural Enemies

Abstract

While the predominately warm and sheltered glasshouse environment favors the rapid growth of pest populations, it also provides favorable conditions for their natural enemies. Thus, any interaction between a pest and its primary natural enemy can, in the absence of hyperparasites or secondary predators, proceed at a predictable rate. It is therefore surprising that, in the 30,000 acres of glasshouses in the world, biological control has been exploited to such a limited extent since the pioneering work by Speyer (1927) on the control of whitefly Trialeurodes vaporariorum Westwood by the parasite Encarsia formosa Gahan. In 1930 the Cheshunt Experimental Research Station (since transferred to the Glasshouse Crops Research Institute) was annually supplying 1½ million of these parasites to about 800 nurseries in Britain. At about the same time, 18 million Encarsia were shipped to Canada, and later this parasite was introduced into Australia and New Zealand and subsequently became widely dispersed in those countries. After World War II, distribution was discontinued in Britain as the newly-introduced insecticide DDT provided convenient and efficient control on most glasshouse crops. Later, Doutt (1951, 1952) demonstrated that the mealybug Planococcus citri (Risso) could be successfully controlled on gardenias by two encyrtid parasites (Leptomastix dactytopii Howard and Leptomasiidea abnormis Girault) and the ladybird Cryptolaemus montrouzieri Mulsant. Earlier, McLeod (1937) had defined the conditions in which Aphidius phorodontis Ashmead could control Myzus persicae (Sulz) in glasshouses and more recently Richardson and Westdal (1965) controlled this aphid with Aphelinus semiflavus Howard.