Can observation of climatic variables be used to predict the flight dispersal rates of Prostephanus truncatus?

Abstract

1. Attack by Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) on the maize and cassava stored by small-holder farmers in Africa is sporadic, varying considerably within and between years. The risk that food in store will become infested is related to the number of beetles dispersing by flight. A means of predicting years with high dispersal rates is needed to warn farmers when to be vigilant. 2. The relationship between climatic variables and pheromone trap catches was observed in a forest-savannah transition zone in Ghana. These observations were used to devise a model using a mix of biological and empirical rules that operate on temperature and humidity data. The predicted and actual trap catch deviated by only +5% to -1% in years when there were high dispersal rates. 3. The first part of the model estimates the numbers of beetles with potential for dispersal. The second part predicts the proportion likely to disperse. This is based on the apparent effect that those P. truncatus developing under low temperature conditions (about 24°C) have a lowered propensity for flight, a response previously observed in a related species. 4. The model was validated using climate data and trap catches from a woodland-savannah zone and a short grass steppe zone. With minor adjustment, the model worked well for these two habitats.