Three clover root weevil (Sitona lepidus) adults infected with the entomopathogenic fungus, Beauveria bassiana, were collected from pastures in the Waikato in 1997. Genotyping using rDNA comparisons showed the strain from weevils to be a cosmopolitan type. Application of fungal conidia topically and by contaminating leaf, soil and root surfaces showed that both B. bassiana isolated from S. lepidus in New Zealand and commercial preparations of this species were pathogenic to adult and larval clover root weevil, with up to 100% mortality within two to four weeks of inoculation. Isolates varied in their effectiveness against larvae and adults, with two isolates effective against adults found to be less pathogenic to larvae than a third isolate.

The clover root weevil (CRW) (Sitona lepidus) has had, over the last two years, a major impact on pastoral farming in the greater Waikato area. Research into CRW biology, damage profile and financial impact is continuing and far from complete. A survey of farms in the affected areas in 1997/98 yielded a large volume of on-farm observations. A survey of the impact of CRW on clover on a single farm produced data that estimated the cost of CRW to this farming operation. These anecdotal findings are combined with initial results from a glasshouse experiment. Damage by CRW tended to be less on lighter (ash and pumice) soils than on heavier, more water-retentive (peat and clay) soils. Drought reduced CRW egg survival and the ratio of first instar larvae to number of eggs hatched. Damage was greater under hard than lax defoliation regimes and increased with increasing rates of mineral nitrogen application. Red clover appeared to be less affected by CRW than white clover. The general picture suggested that the level of stress placed on the clover plant played a major role in the impact of CRW on those clover plants: the higher the stress levels the greater the impact of CRW. Keywords: clover root weevil, farm survey, pasture pest, Sitona lepidus, Trifolium repens, white clover

Clover root weevil (Sitona lepidus), first identified in the Waikato in 1996, is currently distributed through the Auckland, Waikato and Bay of Plenty regions. This pest is perceived to be having a major effect on the sustainability of white clover in pastures in these regions. Two farmer surveys conducted in autumn 1996 and spring 1997 elicited over 300 responses. The surveys, in the form of a questionnaire, sought to define farmer perceptions of the impact of clover root weevil in terms of clover damage and survival. Farmer observations on the role of pasture age, pasture pugging, soil type, fertiliser inputs and management practices on clover productivity were sought. The survey demonstrated that clover content was generally lower in pastures where clover root weevil was present; however if red clover was present the estimations of clover content were generally higher. In the absence of clover root weevil, the highly stocked paddocks (3.4 -3.7 cows/ha) had the greatest proportion with a high clover content (20 -30%). However, in the presence of the weevil, the peak proportion was reduced to 10-20% clover content. Farmer observations suggested that soil type may affect expression of damage by clover root weevil. Peat and clay based soils had substantially less clover cover in the presence of clover root weevil than ash based soils.