Effect of summer irrigation on population dynamics and reproductive status of adult <i>Sitona lepidus</i> in the Waikato

Abstract

Populations of adult Sitona lepidus were sampled from five irrigated and five non-irrigated dairy pastures in the Waikato from November 1998 to April 1999. Under irrigated conditions, the presence of a second peak of adults with significantly more tenerals present provides evidence of a second generation over the summer months. The importance of the role of moisture in the development of S. lepidus was further demonstrated by the differences in the development of eggs in the calyces of sexually mature females. Egg development was significantly greater in females in irrigated pastures. Onset of rain after a dry period resulted in rapid egg development in females in non-irrigated pastures. These findings explain why the summer dry La Nina weather conditions in the Waikato led to farmer observations of a reduced impact of S. lepidus on clovers in Waikato pastures in 1998 and 1999.