Potential new biocontrol for Gonipterus

Gonipterus snout beetles are leaf feeders. The adults feed on the edges of mature leaves causing defoliation of the tree crowns and stunted growth. Studies have shown that 50% crown defoliation can result in up to 85% loss of wood production over a 10 year period.

The Forestry and Agricultural Biotechnology Institute (FABI) team is testing a tiny fly that could turn out to be an important new biological control agent of the Gonipterus snout beetle, currently the most serious insect pest of Eucalyptus trees in South Africa.

The potential new biocontrol agent is a tachinid fly, Anagonia cf. lasiophthalma, which parasitizes the larval stage of the Gonipterus beetle. The flies were sourced from the Forest and Paper Research Institute in Portugal, which has been studying this insect for its potential use as a biocontrol for Gonipterus species for some time.

The parasitoids were imported into the FABI quarantine facility at the University of Pretoria and are showing great promise as an effective biocontrol for Gonipterus sp. n. 2, which is causing significant damage to Eucalyptus plantations across all major forestry regions in South Africa.

*Anagonia cf. lasiophthalma is a potential new biocontrol agent for the Gonipterus snout beetle, currently damaging Eucalyptus trees in South Africa and neighbouring countries.*

Gonipterus beetles are native to Australia. They were first identified in South Africa in 1916, rapidly spreading across the country and into neighbouring territories. This led to the release in 1926 of Anaphes nitens – a tiny wasp - which was the first biocontrol agent in South African forestry. Anaphes nitens was effective in controlling the spread of the Gonipterus beetles, but in the past few years damage from Gonipterus infestations has been increasing once again and it has become clear that on its own Anaphes nitens is not sufficient to suppress Gonipterus populations.

This has led to renewed interest in Gonipterus in South Africa and the discovery that it is not a single species, but one of several different taxa. Hence the one currently doing the damage in South Africa has not even been formally named yet.

Initially it was not known whether the fly Anagonia cf. lasiophthalma would parasitize Gonipterus sp. n. 2, the species present in South Africa, and whether it would be possible to rear it in quarantine. However, work at the FABI facility led by technical assistant Amy Collop and supported by Samantha Bush, Michelle Schroder and Brett Hurley, has confirmed that Gonipterus sp. n. 2 is a host of this parasitoid and the initial stages of a lab-reared population of the flies has been established.

This is very exciting news, according to the FABI team, as it confirms the possibility of using this parasitic fly as a biological control agent for Gonipterus - although there is still much work to be done before it can be safely released into the field.

According to Brett Hurley of FABI, what makes Anagonia especially exciting is that it parasitizes a different life stage of Gonipterus, namely the larvae, as compared to Anaphes which is an egg parasitoid. Thus it is more likely to add to the overall control of Gonipterus, as compared to releasing another agent that targets the same life stage.

Gonipterus larval stage. The larvae feed on the epidermis and mesophyll of young Eucalyptus leaves.

“The first step before releasing Anagonia in South Africa was to confirm that it would parasitize Gonipterus sp. n. 2 - this has now been done,” says Brett. “The second step is to establish a rearing population for experiments - this is ongoing. The third and very important step is to conduct host specificity tests, i.e. to assess if Anagonia will attack other native insects. This is the step where it is difficult to say how long it will take - it could be one year or it could be 3+ years, it depends on multiple factors such as our success with rearing the different insects needed for these studies. If the tests indicate that Anagonia is specific to Gonipterus and therefore safe to release, then we move to step 4 - applying to the government for permission to release Anagonia into the field. This application would be sent for comment from national / international researchers before a decision is made,” he said.

A number of Eucalyptus species, varieties and clones are negatively affected by Gonipterus including E. dunnii, E. grandis, E. nitens, E. urophylla, E.smithii and GUs.

Gonipterus is not the only pest on the FABI team’s radar, as there are many new potential insect pests and pathogens on the horizon!

“We are currently investigating the most likely future insect pests of eucalypts. One insect pest that is moving around, e.g. recently reported in Portugal and South America, is the eucalypt leaf feeding beetle, Trachymela sloanei. But the reality is that many of the new pests and pathogens are not currently known in their native range or anywhere in the world, so it is very difficult to predict,” concluded Brett.