Forest Protection
Forestry Invasive Alien Insect Pests in Zimbabwe
Global trade has enabled societies to benefit from the exchange of species worldwide. Industries such as agriculture, forestry, fisheries, and horticulture now depend on species native to distant regions. While this biodiversity has enriched livelihoods, it has also introduced serious threats to ecosystems and economies.
A major concern is the introduction of Invasive Alien Species (IAS), including insects, plants, and pathogens. These can disrupt native ecosystems, harm agriculture, and pose risks to human health. Zimbabwe has been invaded by two key eucalyptus pests: Thaumastocoris peregrinus (Bronze bug) and Leptocybe invasa (Blue gum chalcid).
The 1992 Convention on Biological Diversity (CBD) and the 1952 International Plant Protection Convention (IPPC) are international efforts to address IAS. Despite these measures, IAS continue to spread rapidly due to increasing global trade.
Leptocybe invasa (Blue gum chalcid)
Leptocybe invasa is a wasp that attacks young eucalyptus trees. Native to Australia, it is now found across Africa, Asia, Europe, and the Near East. First reported in Zimbabwe in 2008, it is known to infest Eucalyptus camaldulensis, E. grandis, and E. tereticornis.
Identification
Adult females are small brown wasps (1.2mm) with a metallic blue-green sheen. Males are rare. Larvae are white and legless. The wasps form bump-shaped galls on midribs, stems, and petioles.
Biology
Eggs are laid in the epidermis of new leaf tissue. Galls begin developing within 1–2 weeks and go through five stages. Multiple generations occur yearly. Severe infestations cause stunted growth, dieback, and even death of young trees.
Control Measures
There are no effective chemical treatments yet. Research on biological control is ongoing in Israel and South Africa. Zimbabwe participates in this effort through its membership in the Forest Invasive Species Network for Africa (FISNA).
Please check for L. invasa symptoms in nurseries and report suspected outbreaks.
Thaumastocoris peregrinus (Bronze bug)
This sap-sucking insect feeds on eucalyptus leaves. Native to Australia, it was first identified in Zimbabwe in 2007 (Chegutu). It has since spread nationwide and into countries like Kenya, Tanzania, Brazil, and Argentina.
Identification
Adults are light brown and ~3mm long. Eggs are black, laid in clusters in protected areas of leaves. Nymphs and adults are often found on the same leaf, and they prefer white-colored surfaces.
Biology
T. peregrinus has five nymphal stages and completes its life cycle in ~20 days at 17–20°C. Fecundity is about 60 eggs per female. It is highly active and spreads rapidly.
Hosts
It affects both pure eucalyptus species and hybrids, including E. camaldulensis, E. grandis, E. tereticornis, E. viminalis, and others. In Zimbabwe, the pest is found mainly on E. tereticornis, E. camaldulensis, and E. grandis.
Symptoms and Damage
Feeding causes bronzing, leaf whitening, curling, and defoliation. Severe outbreaks can cause branch death and overall tree decline.
Dispersal and Introduction Pathways
Likely introduced via infected clonal eucalyptus material from South Africa. Local spread may occur via birds, vehicles transporting logs or firewood.
Control Measures
There are currently no definitive control methods. Chemical pesticides may offer some relief, but biological control is the long-term goal. Zimbabwe may benefit from research being conducted in Israel and South Africa.
Report Suspected Infestations
Contact:
I. Makowe (Entomologist)
Forest Research Centre
Box HG 595, Highlands, Harare
Email: idea.a.makowe@gmail.com or idea@frchigh.co.zw
Cell: 0774 639 714 / 0716 184 557