FABI Articles : Gonipterus Scutellatus

"Gonipterus Scutellatus" Old pest, recurring problem

Gonipterus scutellatus, the Eucalyptus snout beetle, was first noted into South Africa in 1916 in Cape Town and by 1929 it had spread throughout eucalypt growing areas in South Africa. When initially reported it was causing severe damage, especially on E. globules and E. viminalis species but has since been recorded on the majority of Eucalyptus species growing in South Africa. Originating from Australia, this pest has spread throughout the world to all continents except Antarctica.

The Gonipterus beetle is a red brown colour, between 8 - 9 mm in size, with a characteristic "X" marking on the back. The larvae are yellow to yellow-green with black spots and two black lateral stripes. When feeding they produce a characteristic thin black thread of excrement. Egg capsules are dark brown in colour and contain, on average, about 10 eggs.

Between 1926 and 1929, an egg parasitoid wasp, Anaphes nitens (also from Australia) was released as a biocontrol agent for G. scutellatus. Through these release events and the ability of the parasitoid to spread on its own, it too spread throughout areas where G. scutellatus was present. Parasitism levels greater than 60% were reported from most areas with levels in some areas reaching 80 - 100%. Although largely effective, sporadic outbreaks still occurred and the parasitoid was not as effective in the higher altitude colder areas. Despite this, the program was and is one of the most successful biocontrol programs worldwide.

In recent years, however, the frequency and severity of outbreaks have increased. Severe outbreaks have occurred in areas where this pest was considered in control in the past. Possible reasons may include a decrease in efficacy or absence of the parasitoid in these areas. However, no current data on the spread and parasitism efficacy of A. nitens is available.

To address this, a monitoring project was initiated in May 2010. Monitoring sites were established where G. scutellatus egg capsules were collected once a month and A. nitens emergence recorded. Sites were located in the KwaZulu-Natal and distributed along an elevational gradient to incorporate different climate conditions in South Africa. Eucalyptus dunnii, Eucalyptus smithii as well as E. grandis x E. camaldulensis and E. grandis x E. urophylla hybrids were sampled. Egg capsules were collected and placed in plastic tubes for emergence, where after percentage parasitism was determined. The project will be ongoing for at least the next 2 years to gain as much long term data as possible.

During May 2010 - August 2011, 16526 egg capsules were collected. Parasitism levels varied across sites with average parasitism levels much lower than historically recorded by Tooke.

Despite low parasitism levels, damage due to G. scutellatus feeding is sporadic and less severe in the higher elevation cooler sites compared to extensive damage noted in the low elevation subtropical sites. This would indicate that higher temperatures at the lower sites may have an effect on parasitism success although this needs further investigation.