Global trade has enabled societies to benefit from the exchange of species worldwide — agriculture, forestry, fisheries and horticulture all depend on species native to distant regions. While this has enriched livelihoods, it has also introduced serious threats to ecosystems and economies.
A major concern is the introduction of Invasive Alien Species (IAS) — insects, plants and pathogens that disrupt native ecosystems, harm agriculture and pose risks to human health. Zimbabwe has been invaded by two key eucalyptus pests:
International Treaties
Two international agreements coordinate the global response to invasive species. Despite these measures, IAS continue to spread rapidly due to increasing global trade.
Convention on Biological Diversity
CBD
The international framework for the conservation of biodiversity, sustainable use of its components, and equitable sharing of benefits arising from genetic resources.
International Plant Protection Convention
IPPC
A multilateral treaty for cooperation in plant protection — aimed at securing common action to prevent the spread and introduction of pests of plants and plant products.
Leptocybe invasa
Blue gum chalcid
A wasp that attacks young eucalyptus trees. Native to Australia, it is now found across Africa, Asia, Europe and the Near East. Known to infest Eucalyptus camaldulensis, E. grandis and E. tereticornis.
Adult females are small brown wasps (1.2 mm) 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.
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.
There are no effective chemical treatments yet. Research on biological control is ongoing in Israel and South Africa. Zimbabwe participates through its membership in the Forest Invasive Species Network for Africa (FISNA).
Thaumastocoris peregrinus
Bronze bug
A sap-sucking insect that feeds on eucalyptus leaves. Native to Australia, it has since spread nationwide and into Kenya, Tanzania, Brazil and Argentina.
Adults are light brown and ~3 mm long. Eggs are black, laid in clusters in protected areas of leaves. Nymphs and adults are often found on the same leaf and prefer white-coloured surfaces.
Five nymphal stages, completing its life cycle in ~20 days at 17–20°C. Fecundity is about 60 eggs per female. Highly active and spreads rapidly.
Affects both pure eucalyptus species and hybrids.
In Zimbabwe, the pest is found mainly on E. tereticornis, E. camaldulensis and E. grandis.
Feeding causes bronzing, leaf whitening, curling and defoliation. Severe outbreaks can cause branch death and overall tree decline.
Likely introduced via infected clonal eucalyptus material from South Africa. Local spread may occur via birds, vehicles transporting logs or firewood.
No definitive control methods. Chemical pesticides may offer some relief, but biological control is the long-term goal. Zimbabwe may benefit from research conducted in Israel and South Africa.
Report a Suspected Infestation
If you notice galls, bronzing, leaf curl or other symptoms described above, contact our entomologist directly.
I. Makowe
Entomologist · Forest Research Centre
-
Postal Address Box HG 595, Highlands, Harare