Determination of a Relationship Between Soil Moisture and Screwworm Fly (Diptera: Calliphoridae) Activity

To model screwworm fly (Diptera: Calliphoridae) population dynamics, it is necessary to quantify the relationship between soil moisture and screwworm fly numbers. Climatic data from one case study of Chrysomya bezziana (Villeneuve) and five case studies of Cochliomyia hominivorax (Coquerel) from tropical and subtropical areas were statistically analysed to determine the effect of soil moisture (corrected for temperature) on screwworm fly incidence. Significant relationships occurred in three of the six cases; in two cases the relationship was humped, and in the other linear. Both prolonged dry conditions and soil saturation cause reduced screwworm fly emergence whereas intermediate soil moisture is adequate for pupal development and adult emergence. the relationship previously used in the CLIMEX package was found to be biased because it did not adequately penalise saturated soil conditions. an improved function was estimated to correct for this bias.