14
zararlılarla doğal düĢmanları arasındaki etkileĢimleri araĢtırmak için uzun yıllar
çalıĢmak zorundadırlar.
2.3. Biyolojik Mücadelede ÇeĢitlilik
2.3 Diversity in biological control
Biological control differs significantly depending on whether the pests are invertebrates, vertebrates, plants, or microorganisms. For biological
control of invertebrates, hosts are usually small and sometimes mobile (at least in some life stages). Emphasis has been on planteating
arthropods and arthropods of importance to public health. Virtually all natural enemies used for biological control of arthropods kill pests
directly. Mortality of the pest is often very quick with predators but there can be a time lag with parasites or pathogens because they often first
develop using the hosts as food before killing them. Among pestiferous weeds, pests range from small herbs to large trees; these are stationary
and, at times, dense. Biological control of weeds requires many individual natural enemies to damage a weed, unless the natural enemy attacks
the so-called ‘‘Achilles heel” for that plant species (e.g., a part of the plant or its life cycle that is especially vulnerable), in which case fewer
individuals could be necessary. Mortality of the weed is always delayed, if the plant dies at all, although growth and seed production would be
reduced more quickly. Also, in contrast to biological control of arthropods, weeds do not move except through seed dispersal so herbivorous
natural enemies generally do not have as much difficulty locating their target pests. Weedy plants can ‘‘escape” from a natural enemy through
establishment of a disjunct population by means of long distance seed dispersal, but finding new isolated plant populations is often less of a
problem for weed-feeding natural enemies compared with the difficulty for arthropod-attacking natural enemies of finding and attacking
mobile arthropod pests. Weeds are also different from arthropods as pests because competition with other plants can be important in
mediating the outcome of biological control. If weeds can be partially suppressed by herbivory or disease then the weed can more easily be
outcompeted by other plants that are hopefully desirable. For the microorganisms causing plant disease, biological control is due to multitudes
of microbial antagonists that compete with multitudes of plant pathogenic microbes. Both plant pathogens and their antagonists are usually
tightly linked with specific habitats. For many programs, antagonists are applied preventively, so time before control is effective is not an issue.
Scientists working to control these diverse pests must adopt very different tactics with relation to the importance and immediacy of the pest
problem, the type of impact on the pest that is needed, and the ability of both natural enemy and host/prey to disperse.
ġekil XX. Sünger örücüsü,
Lymantria dispar L.‟ın temel biyolojik evrelerinde
görülen
bazı parazitoid türler.