Ecology and management of Sigastus weevil in macadamias (MC15010)

What was it all about?

Sigastus weevil was first found infesting macadamia nuts on the Atherton Tablelands in far north Queensland in 1994/95, but since then become a significant pest in other production areas. Some estimates put crop losses at 15 per cent, equating to around $15 million per year.

Sigastus weevil is long-lived so weevils that emerge in spring can easily live until the following winter. They are difficult to control by foliar insecticides as they spend most of their lifecycle hidden inside the developing nut.

This project investigated the biology and ecology of Sigastus weevil including its lifecycle and distribution, and reviewed literature that included the chemical, biological and cultural control of other important weevil pests.

Of particular note, the project found there are several promising bio-pesticides that may be successful in controlling weevils in macadamias. The most promising fungal option for control are entomopathogens, including the Beauveria bassiana strain, which has been used to successfully control other types of weevils overseas. Early research shows it produces high mortality in Sigastus in the laboratory when applied to feeding surfaces or as topical droplets.

The project also found… 

• Commonalities in management of the major weevil pests
• Sigastus weevil specimens in far north Queensland and New South Wales belong to the same species
• Sulfoxaflor and acetamiprid may be effective in controlling the weevil, but more insecticides need to be screened

The removal or destruction of infected nuts on the ground is crucial for controlling the weevil, as is managing out of season nuts to break the lifecycle.