Entomological studies of a reliable and regular nature have now been going on at five fixed stations in Zone 94, East Bauro, since June 1971. The graphs show the population densities of Anopheles farauti, as measured by man-biting catches carried out on a whole-night basis. The densities are the total numbers caught by two baitcatchers, one working indoors and the other outdoors. At one of the five fixed stations, Tawani, the population density of An. farauti has remained very low throughout the study and the results are not shown.

What is noteworthy from the graphs is the basically similar seasonal patterns of vector population density at each of the four fixed stations, the only significant exception would appear to be the high figures for March and April 1972 at Arohane. A study of the monthly rainfall figures, recorded at Ngorangora, near Kira Kira, for the period since June 1971 shows no obvious relation with the apparent seasonal peaks of vector numbers. The effect of cyclical spraying operations at the times indicated would appear to be marginal in affecting the vector population densities. The timing of the October-November cycle is unfortunate in that it comes at the time of peak vector population levels and thus is likely to be too late to prevent resumption of transmission if, in fact, this takes place.

The peak levels of the malaria slide positivity rate since July 1970 have been in September 1970, April-May 1971, September-October 1971 and May 1972. The P. falciparum rates during the entomology study period, June 1971 to the present, show the peak population densities to be some 6 to 8 weeks in advance of the malaria peaks. It would seem desirable, therefore, to spray East Bauro at the beginning of January and July rather than in October and April as at present.

My memorandum 18/1-1707 of 17th November also indicates that the last two months of the spraying cycle are vulnerable in that the potency of DDT may have lessened. If this is true, spraying in October gives a minimum effect of DDT in February and March when the vector population is potentially going to rise. Similarly spraying in April gives a minimum effect of DDT in September and October again when the vector population is potentially increasing.

These results serve to underline the poverty of the base-line data obtained before the onset of spraying operations elsewhere in the Protectorate. Entomological data is available for Choiseul, Santa Ysabel, Nggela and Malaita but this was all on a half-night basis as laid down by Slooff (Assignment Report, 1969) and usually with only a single technician at post. No long-term malariometric pre-spraying data is available for any of these areas.

Dr. B. Taylor
Government Entomologist
8.1.73

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