Repellents population effects

Brown-headed cowbirds, Molothrus ater, and red-winged blackbirds, A. phoeniceus, removed 95-98% less rice seeds sown in flight pens if the seeds had been treated with methiocarb. The effect was the same whether 100% or only 50% of the seeds had been treated. This shows that an entire prey population can be protected even if only a portion is unpalatable. Such automimicry may permit partial treatment of crops with repellents, which would be effective, environmentally sound, and economical (Avery, 1989). Batesian mimicry offers advantages over food aversion learning (Reidinger and Mason, 1983). 

Several strategies were employed in order to reduce this effect. Myers et al. described the use of a pulsed ion optic to limit the access of ions to the extraction region [28]. By application of a voltage pulse to one of the quadrupole optics, the ion beam was swept across the slit at the end of the primary optic chain. By correct choice of delay parameters, the extraction region was filled with ions only immediately prior to a repeller event. Mahoney et al. described a different approach that relied on differences in the energies of signal and continuum background ion populations [42]. 

At present, there is no vaccine to protect against dengue. The most effective method of prevention is to eliminate the mosquito that causes the disease. This requires removal of the mosquito breeding sites, a process known as source reduction. Proper disposal of solid waste helps to reduce the collection of water in discarded articles. Other control measures include preventing mosquito bites with screens, protective clothing, and insect repellents in epidemic risk areas, application of insecticide is practiced through an application method known as fogging to decrease the mosquito population. 

The inter-specific mediators, or allomones, may work in one of two directions some are attractant, or allelostimulant, whilst others are repellent, or allelopathic. This distinction is not always clear, since the effects of such chemical mediation varies according to the receiving species within natural populations. It may, however, be retained for clarity of account. 

Two possible sources of repellents from animals are the odors associated with mammalian carnivores and aggressive conspecifics. Rats actively avoid predator odors and this response appears to be innate. Trimethyl thiazoline extracted from fox (Vulpes vulpes) faeces caused an enclosed population of wild rats to alter their activities (Vemet-Maury, Constant Chanel, 1992). In the short-term, which may mean days or weeks, habituation to these predator odors appears to be slow. However, the odors may require reinforcement by some form of encounter with the predator itself to be effective in the longer-term (Muller-Schwarze, 1994). 

Laboratory mice have been used as the model rodent to demonstrate the potential of aversive social odors to manage populations. Chemical constituents in the urine of dominant male mice have been shown to inhibit the exploratory behaviour of subordinate mice in laboratory-based arena studies. Two constituents, a and P-famesene, have been patented as mouse repellents (Novotny, Harvey Jemiolo, 1993). However, we do not know what effect these chemicals have on free-living rodent populations, where dominance hierarchies may not always exist. The scent marks left by dominant male rats within family groups appear to act not so much as warning signals for strange rats, but as aids to orientation (Lund, 1975). In the context of controlling rat populations, social odors are unlikely to produce the immediate reduction in numbers required to control a troublesome rat... 

The early literature on repellents has been summarized many times (e.g. 1, 2, 3, ). The impression left on the reader of these reviews is that no consistently effective chemical repellent has been developed for use against vertebrate pests. The reasons for this are complex, but stem from the fact that we have tended to be anthropomorphic in the most basic assumption of repellent action. Most humans realize that when offered an array of foods, some of which taste bad, we alter our feeding pattern to consume only those that taste good. This basic human experience has been translated directly to wildlife populations. The original assumption in repellent development seemed to be that if a potential food could be made bad-tasting enough, the pest... 

Several studies have shown that chemical compounds containing specific functional groups or features are more effective arthropod repellents as measured by the duration of protection. - Recently, we reported a study of similar analysis of stereoelectronic properties (steric and intrinsic electronic properties) between natural insect JH, a synthetic insecticide (JH-mimic, undecen-2-yl carbamate), and deet and its analogs. Structure-activity studies on JHs have resulted in the discovery of JH-like compounds that mimic the morphogenetic activity of JH with the aim of controlling insect populations. 

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