"Gonipterus Scutellatus" Old pest, recurring
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
We would like to thank Sappi
and Mondi for their use of their sites and assistance in collecting samples.