Food Security Department, Natural Resources Institute, Chatham, Kent, ME4 47T, UK.
The lesser grain borer, Rhyzopertha dominica (F.) is a destructive insect pest of stored grain. Males of this species produce a volatile aggregation pheromone that consists of two components, called Dominicalure-1 (D1) and Dominicalure-2 (D2). The ratio of D1 to D2 is generally stated as 1:2 but it varies considerably between pheromone collections. In the present studies it has been shown that external factors can affect the ratio of pheromone components produced by adult R. dominica males. To determine whether the type of food can affect the ratio of D1 and D2 in the blend, pheromone was collected from single R. dominica males present in wheat, maize or groundnut. It was found that males present in groundnut produced pheromone with a significantly lower percentage of D2 in the blend than those present in the wheat or maize. A lower percentage of D2 was also recorded when single males were confined with females; removal of females reversed this effect. A reduced D2 ratio was not simply the result of crowding since groups of males produced a similar pheromone blend as single males.