Elements of integrated control involved in maintaining the biological balance of lucerne crop agrobiocenose

Some 40 phytophagous insect species live and breed in lucerne crops, as a pest complex. The integrated pest control requires knowledge on the agroecosystem components. These are the natural (environmental) and crop management practices, both strongly influencing fluctuations of beneficial and harmful entomofauna. Among the environment factors, the biotic ones are mainly governing evolution of pest population levels. Pest-parasite relationships are highly important, the role of parasites in maintaining pest populations below the EDT being essential. In lucerne crops 45 parasitic Hymenoptera species have been found, of which 23 Braconids, 3 Chalcidoids and 13 Ichneumonids, and 6 Diptera-Larvaevoridae. Seven of these are new for Romanian fauna: Apanteles jugosus Lyle, A. lineola Curt., A. immunis Hal., A. pallipes Reisch. (Braconidae), Diadegma variegata Szepl. (Ichneumonidae), and Carcelia tibialis R.D. (Larvaevoridae). The wide variety of their hosts raised the problem of specificity and parasitic efficiency of some of these entomophages. Thus, Bathyplectes curculionis Thoms. destroyed Hypera variabilis Herbst. larvae to an extent of 19-30 percent, Contarinia medicaginis Kieff. Larvae can be reduced by 30-50 percent by Sistasdis encyrtoides Walk., while Apantheles praepotens Hall. parasitizes the larvae of Semiothisa clathrata L. and Tephrina arenacearia Den. et Schiff. by more than 70 to 50 percent, respectively. Among the crop and soil management practices contributing to prevention of pest outbreaks and hindering their reproduction there are: choosing proper land and labour practices before sowing, cropping cvars resistant to diseases and pests, suitable planting, various agricultural works (ploughing, tillage, hay mowing, weed control, harvest). Another outstanding cropping practice in lucerne seed production is pest control. At present, the biological control is rarely applied and its efficiency is reduced. Chemical control with selective compounds, important and necessary in the integrated control, is practised as preventive (seed dressing) and curative measures (season treatments). Application in agriculture of these pest control measures result in a significant reduction of detrimental influences on the ecosystem. Consequently, due to increase of parasite and predator numbers, a natural lessening of pest population is noticed; also pollinators poisoning with pesticides has dropped