Chemosterilization of Culex pipiens fatigans Wiedemann by exposure of aquatic stages. I. Sterilization potential of certain aziridinyl compounds. (17/25)

The sterile-male technique has been considered to be a promising tool for the control of mosquito populations. Many chemosterilants are known to sterilize insects effectively in the same way as ionizing radiations. The sterilizing activity of 8 alkylating aziridinyl compounds has been assessed on the tropical house-mosquito, Culex pipiens fatigans Wiedemann. The chemosterilants employed for larval and pupal treatments were apholate, metepa, tepa and 5 diaziridinyl alkoxyphosphine oxides. In general, metepa was least toxic to the various life stages of C. p. fatigans during the treatment. Apholate was toxic only in pupal treatments while tepa was less toxic in pupal treatments and more toxic in larval treatments. Diaziridinyl compounds were moderately toxic in both larval and pupal treatments. The tepa and apholate treatments caused certain structural and moulting abnormalities in pupae and adults and also induced abnormalities in eggs and larvae.Among the polyaziridinyl compounds, non-toxic doses of apholate could produce about 100% sterility with larval treatment. Tepa was inferior to apholate, and metepa was least effective in larval treatment. Among the diaziridinyl compounds, the methyl ester was most promising. For pupal treatment, tepa was more effective than apholate and metepa at non-toxic doses, inducing almost complete sterility. The propyl and isopropyl esters of the diaziridinyl compounds also induced very high sterility in pupal treatments.  (+info)

Chemosterilization of Culex pipiens fatigans Wiedemann by exposure of aquatic stages. 2. Sterilization potential of certain phosphoramides and s-triazines. (18/25)

Many aziridinyl compounds are known to induce high sterility in Culex pipiens fatigans Wiedemann, but as the practical application of these chemosterilants is quite hazardous, compounds such as phosphoramides and s-triazines have been tried against this species. These compounds are relatively less reactive, thermally more stable and less toxic to mammals. The phosphoramides included hempa, N,N,N',N'-tetramethyl-P-piperidino-phosphonic diamide (ENT-51007) and a compound, ENT-60210, whose structure is not known to the authors. The s-triazines employed were hemel, 2,4-diamino-6-morpholino-s-triazine hydrochloride (ENT-51143), 2-amino-4,6-bis (dimethylamino)-s-triazine hydrochloride (ENT-51146), and a compound ENT-60433, whose structure is not known to the authors.The triazines were more toxic than the phosphoramides in both larval and pupal treatments. Among the phosphoramides, hempa and ENT-51007 were quite promising for larval treatment and resulted in 80% and 83% control of reproduction respectively at non-toxic doses. Hempa at a toxic dose induced complete sterility. ENT-60210 was least toxic and least effective. Among the triazines, hexa-substituted hemel was better than tetra-substituted ENT-51146 and cyclic-substituted ENT-51143 in inducing sterility. ENT-51143 was most toxic and least effective. For larval treatment, hempa was better than hemel in inducing sterility while for pupal treatment the latter was better than hempa. Both the compounds produced more sterility in treated females than in treated males. Oviposition was significantly lowered in treated females.  (+info)

The mating ability of males of Culex pipiens fatigans Wiedemann sterilized with apholate or tepa. (19/25)

The chemosterilants apholate and tepa are known to induce a high degree of sterility in the males of Culex pipiens fatigans. The studies reported show that 36-hour-old apholate-and tepa-sterilized laboratory-bred males can inseminate the same number of laboratory-bred or wild females as can normal laboratory or wild males in the first 48 hours of their lives. Males sterilized by either compound were found to be more competitive in mating with normal laboratory females than were the normal laboratory males. When normal virgin females were mated first with sterile and then with normal males or vice versa, the sperms of the first mating always decided the fate of eggs. Apholate-sterilized laboratory males were not only compatible with wild females but could even induce the same level of sterility in them and were fully as competetive in mating as normal wild males. The authors stress that it has still to be ascertained whether these encouraging laboratory findings would apply in field conditions.  (+info)

Studies on the population dynamics of the housefly, Musca domestica L. (20/25)

The population level and potential rate of increase of a population of houseflies, Musca domestica L., on Grand Turk Island was studied for about 2 years to determine what changes occurred when no control was applied (the first year) and when the population was totally suppressed by the application of chemosterilant baits (the second year). During the first year the population was relatively stable (the highest density occurred in June and the lowest in January) and the difference between the high and low levels was only 3-fold. When chemosterilant baits were applied over a 40-week period and total suppression was achieved, calculations based on the sterility achieved and the resulting control revealed that the population showed potential rates of increase ranging up to 4-fold during the period from June through October and from 4-fold to 11-fold from December through April. Thus, in the field, the potential rates of increase of the housefly are low despite its high biotic potential.  (+info)

Efficacy of alpha-chlorhydrin in sewer rat control. (21/25)

A single application of the male chemosterilant, alpha-chlorhydrin, to a problem sewer rat infestation resulted in reductions of rat numbers and distribution which was comparable to effects of warfarin baiting methods. Rat numbers were reduced by more than 85% by both methods. More rapid mortality and recruitment were evident for warfarin effects; the alpha-chlorhydrin treated population had a longer lag phase of growth so that reinfestation of sewer habitat to pre-treatment numbers, and distribution over a 40 square block area, required approximately 1.5-2 times longer after alpha-chlorhydrin treatment when compared with warfarin treatment. Comparisons of changes in rat densities in infested sewers following the two treatments indicate that recovery of warfarin treated populations is achieved by reproductive recruitment followed by dispersal while alpha-chlorhydrin treated populations recover by slower immigration and later reproductive recruitment. Alpha-chlorohydrin should be a useful addition to a limited arsenal of rat control agents because of its specificity for the Norway rat, its single dose effectiveness as a toxicant-chemosterilant, and its short environmental half-life.  (+info)

Control and management of insect populations by chemosterilants. (22/25)

Chemosterilants, i.e., chemical compounds that interfere with the reproduction potential of sexually reproducing organisms, can be used in three new approaches to insect control. In the sterile-insect release technique, the principal problem is to develop compounds and methods for their application that would not result in introducing harmful residues into the environment. Because of the unusual and often unique circumstances connected with releasing large numbers of sterilized insects, the residue problem and its cost-benefit aspects must be examined individually for each intended control or eradication program. In the direct application technique, chemosterilants must meet the same efficiency and safety standards required from approved insecticides. Combined insecticidal and sterilizing activity is characteristic for some compounds now being investigated. In the genetic technique, chemosterilants may be used for inducing heritable changes in the insect's genome under laboratory conditions, and such procedures would not present any residue problems. Only the first two chemosterilant techniques are approaching practical application, and their safety aspects require detailed evaluation and assessment.  (+info)

Fertility control in laboratory rats and mice after feeding with the antigestagen RU486. (23/25)

The intermittent use of an antigestagen could prove to be a very effective way of controlling the fertility of rats and mice in the wild. This concept was tested by giving paraffin wax blocks containing cereal grains and the antigestagen Mifepristone, RU486 (150 mg kg-1 block) to male and female laboratory rats and mice in a series of free-choice feeding experiments. There was no significant difference in the consumption of blocks with or without RU486, showing that it was completely palatable to rats and mice, and no aversion developed following refeeding. The average consumption of RU486 by rats was 11 mg kg-1 day-1; mice consumed 37 mg kg-1 day-1. All the females showed persistent oestrous vaginal smears throughout the treatment. When male and female rats and mice were given continuous access to treated paraffin blocks for 30 days, no conceptions occurred. At the end of this time, there was a significant increase in ovarian weight in the treated rats and mice, but no difference in testicular weight. Treated blocks were given to rats for 3 days every 21 days for a total of 115 days. Four dead litters were produced following the first antigestagen treatment on day 21, but no more litters were produced and no treated rats were pregnant when autopsied on day 115. Mice were initially treated for 3 days every 21 days, but some animals continued to produce live young on this schedule. The treatment period was therefore reduced to 3 days every 18 days and no more litters were produced and none of the treated females was pregnant at autopsy.(ABSTRACT TRUNCATED AT 250 WORDS)  (+info)

Fertility control in wild mice after feeding with RU486 or methyl testosterone. (24/25)

Paraffin blocks containing either no steroid, 150 mg RU486 kg-1, 500 mg methyl testosterone kg-1 or 1500 mg methyl testosterone kg-1 were fed to wild mice (Mus musculus) in addition to the standard laboratory diet in four large (3 m x 3 m) outdoor pens for six months over the summer. The RU486 bait was provided for only 3 days every 18 or 21 days, whereas the methyl testosterone bait was available continuously. From a foundation stock of 20 mice (nine male, eleven female) in each pen, the population had increased to 253 (control), 72 (RU486), 249 (low methyl testosterone concentration) and 103 (high methyl testosterone concentration) at the end of six months, when 17%, 4%, 32% and 13% of the mature females were pregnant in the respective treatment groups. There was little evidence of an increase in the incidence of injuries in the androgen-treated animals. Daily estimation of water consumption in the pens proved to be a good non-invasive way of monitoring population growth during the course of the experiment. Intermittent feeding with a low concentration of RU486 appeared to be much more successful in inhibiting reproduction than continuous feeding with a high concentration of methyl testosterone, and it therefore offers a new method for controlling feral mouse populations.  (+info)