The pregnancy rate in Glossina palpalis (R.-D.) in southern Nigeria

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Abstract
Females of Glossina palpalis (R.-D.) were dissected and examined for pregnancy at the Ugbobigha field station of the West African Institute for Trypanosomiasis Research in southern Nigeria between January 1958 and October 1959. Of 2,490 females dissected, 46 (2%) were virgin; 764 (31%) had an egg in utero and 221 (9%) a larva in utero. Highest pregnancy rates were found in months with heaviest rainfall and lowest mean temperature, saturation deficit and evaporation rate.The pregnancy rate in G. palpalis near Kaduna, in Northern Nigeria, was nearly twice that found at Ugbobigha, the major difference being in the number of females with a larva in utero. It is suggested that in the Ugbobigha area an adverse factor operates in the late egg or early larval stage, causing abortion; this is probably not a direct effect of climate or of insufficient food but may partly be related to the possible inability of females to obtain a blood-meal at just the right stage in gestation. Low pregnancy rates may, at least in part, explain the low densities of G. palpalis commonly found in the forest belt of West Africa, despite the wide distribution of the species in such areas.