Изменение видового состава и трофической структуры колеоптерофауны при уменьшении пестицидной нагрузки на биоценозы степной зоны Украины

Abstract

1. Agrocenoses are basic components to a more complex system, agrobiogeocenosis, or ‘agricultural landscape', and as such they do not incorporate the relationships fully developed in the latter. The principal difference lies in the reduced number of species involved in an agrocenosis of any particular cultivated plant. Besides that, the spatial distribution of agrocenoses in an agrobiogeocenosis is relatively stable, whereas each constituent agrocenosis occupies a discrete time span in their seasonal succession. Any generalizations based on studying agrocenoses cannot therefore by extension be applied to an agrobiogeocenotic study, which would require a more comprehensive approach. 2. According to existing nomenclature, an agrobiogeocenosis as a whole classifies under natural steppe biogeocenoses, except that it has been, and is being, modified by human agricultural activity. Due to a considerable measure of continuity in time of species comprised in it and stable patterns of their spatial distribution, agrocenoses are stable ecosystems. For that reason, only long-term longitudinal studies can reveal relationships existing between parts of an agrobiogeocenosis and the impact various external factors exert on them. 3. In the course of time preceding succession, an agrobiogeocenosis develops characteristic and constant herpetobiont beetle fauna, whose constituents form entomofaunistic complexes around them and are habitat- specific, relativelyvariegated compared to residualcomplexesofspecies formed inwild uncultivated grass layer. 4. Agrobiogeocenoses can maintain stability through self-regulating mechanisms inherent in any natural ecosystem and, to some extent, withstand human intervention. In a state of dynamical equilibrium of food chains and trophic groups, however, agrobiogeocenoses appropriated as cultivated lands are highly sensitive to any amount of pesticides brought into system. 5. Increasing use of pesticides to control populations of crop-damaging insects is thus the principal factor deteriorating the sustained equilibrium in an agrobiogeocenosis. 6. After a considerable(10–15 times) alleviationinpesticide pressureinUkraine,whichhastakenplacein recent 10–12 years, there has not been observed any comparable increase in phytophagous pest populations,much contrary to rather too straightforward predictions. This was the case virtually for all cultivated plants. Duringthis period, the overall population ofzoophagousinsectshasgrownalmost9times,while thisincreasefor several cultures was as high as 40 times, well exceeding effect of large-scale pesticide use at any previous time. Considering that in the observed gain in population density the weed-feeding species contributed the most, these latter may be regarded as beneficial. Also, lessened pesticide pressure in cultivated lands has led to proliferation of various Coleoptera; these were mostly zoophagous species, massively occurring as well as sporadically, butnot previously common in crop fields. Overall population density of saprophagous species in agrobiogeocenoses rose 6.1 times. 7. Following from the above is the conclusion that the main threat to sustained self-maintenance of crop fields, or agrobiogeocenoses, is in inconsiderate use of pesticides. The natural capabilities of agricultural ecosystems are nearly always sufficient to prevent irreparable destabilization potentially resulting from pest outbreaks; and hence, only minimal amounts of pesticide use can be reasonable. 8. Given the ultimate priority in cultivating any land resource remains in maximizing the volume of its produce, the use of pesticides is justified inasmuch as it is conducive thereto. Even then, the chemical method must never be thefirst choice, andshould onlybe resorted towhen predictionoflossesresultingotherwisewould exceed certain established limits, or when internal capacity of the agrobiogeocenosis to revert the effects of pest outbreak is inadequate. 9. Natural biodiversity conservation, however, is an overriding argument against chemical method, obviously in protected areas but also in steppe habitats converted to crop fields. In devising and implementing pest control measures, it is important to first carry out a long-term monitoring of population density and distribution fluctuations of every component species in the agrobiogeocenosis. Based on this, comprehensive assessment must be given to all available agrotechnical and biological methods, which should always be used in preference to the chemical method.