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PubMed1964

THE ASSESSMENT OF INSECTICIDAL IMPACT ON THE MALARIA MOSQUITO'S VECTORIAL CAPACITY, FROM DATA ON THE PROPORTION OF PAROUS FEMALES.

In malaria eradication the residual insecticide exerts upon the mosquito's vectorial capacity a direct insecticidal impact, the order of which may be measured by observing the decrease in the proportion of parous females. The impact is expressed as the product of the degree of reduction of the expectation of infective life (termed the longevity factor of impact) and that of the expectation of life (the density factor). To compute the factors from the proportion parous it is necessary to know also the mean difference in age between the nulliparous and the youngest parous females in the sample, and the sporogonic period of the parasite.Graphs are presented to enable the field worker, who has observed these parameters, to read off from his data the proportion surviving one day, the expectation of infective life and the expectation of life. Examples from the field are used to illustrate the manner of computing the direct insecticidal impact with the aid of the graphs. It is emphasized that this method can only measure the relative impact on vectorial capacity, and will not show whether the actual level of vectorial capacity is such that a malaria reproduction rate of <1 is indicated.

Animals↗
PubMed1964

THE MALARIA PARASITE RATE AND INTERRUPTION OF TRANSMISSION.

Present methods for assessment of the attack phase of malaria eradication are inadequate, particularly lacking any objective parasitological criteria of success. On the basis of previous observations and development of theory, the authors first postulate that the effects of complete interruption of transmission should, ideally, include a regular progressive decrease of falciparum parasite rates in the ratios of 1: 0.4 in 6 months, 1: 0.16 in 12 months and 1: 0.026 in 24 months. Analysis of a series of programmes in which complete interruption of transmission is known to have been achieved shows that this postulate is valid, and that it is not materially upset by strain differences of parasites or by differences in the ages of the subjects examined. Vivax rates appear to fall at approximately the same rate; the rarity of data for vivax malaria makes firm conclusions unsure, but the postulate can be extended to rates which are predominantly due to falciparum infection but include some admixture of other species. A second, arbitrary, postulate is made that the slowest acceptable rate of fall in 12 months should be in a ratio not less than 1: 0.22, which would secure ultimate eradication in about one-third more time than the ideal fall; on this basis statistical standards are set up for assurance of confidence that the minimum rate is exceeded. Slower rates of fall are then related to reproduction rates causing them, the findings being illustrated graphically and by mathematical theory.

Animals↗
PubMed1990

Apparent influence of the stage of blood meal digestion on the efficacy of ground applied ULV aerosols for the control of urban Culex mosquitoes. II. Laboratory evidence.

The susceptibility of adult Culex pipiens s.l., Culiseta melanura and Aedes aegypti to insecticide aerosols in wind tunnel exposures varied with time, depending on the stage of blood meal digestion. Greater than 2-fold differences were observed in the concentrations of malathion and synergized resmethrin required to kill test mosquitoes, depending on whether they had been given a blood meal and, if they had, the length of time following the blood meal. The period of lowest susceptibility varied from 24 h after feeding in Ae. aegypti to 72 h in Cs. melanura. The greatest variability occurred during the period when undigested blood was present. Data from tests with a malathion-tolerant strain of Cx. pipiens s.l. suggested little change in susceptibility regardless of blood feeding and the associated weight changes that occur from ingestion of blood.

Aedes↗
PubMed1990

Apparent influence of the stage of blood meal digestion on the efficacy of ground applied ULV aerosols for the control of urban Culex mosquitoes. III. Results of a computer simulation.

When posttreatment response to ultra low volume (ULV) application of insecticide has been followed for periods approaching a week, a damped oscillation in oviposition rates is observed, probably because females who have been recently blood-fed are more resistant to insecticides than their unfed siblings. We describe a simple model (ULVSIM) that incorporates physiologic changes in insecticide susceptibility and accounts for much of our field data. The model follows 30 cohorts over 30 days following insecticidal treatment. Multiple treatments or short-term residual activity can be evaluated. The model predicts that oviposition will follow a pattern of damped oscillations after an adulticidal treatment. The model gave a good fit to oviposition data obtained in 2 field trials of resmethrin for 7 to 9 days after treatment. It can be used to evaluate the effect of single and multiple treatments on the total female Culex population and on numbers of infected females surviving for different periods following an infective blood meal.

Aerosols↗