Why do mealybugs matter on cacao when they do so little direct damage?
Small sap-feeding insects that cause modest damage themselves and transmit cacao swollen shoot virus. They are the reason a virus problem in West Africa is also an insect problem, and the reason ants enter the discussion.
Where it is
- Present in cacao worldwide as sap feeders
- Agriculturally critical in West Africa, where several species transmit cacao swollen shoot virus
This one is genuinely everywhere. There is no producing region where it is not a consideration — which makes it the exception in this section rather than the pattern.
What causes it
Several mealybug species in the family Pseudococcidae, including Formicococcus njalensis, Planococcus citri and Ferrisia virgata
Established evidence
Supported by systematic review, meta-analysis or a regulatory or clinical position, from more than one independent original source.
What it looks like
Colonies of small, soft, white waxy insects clustered on shoots, pods and in the crevices of flower cushions, frequently with attending ants. Direct feeding damage is usually slight.
The symptom that matters is not the insect but what follows it: the vein-banding and swellings of swollen shoot appearing in a tree that carried mealybug colonies.
How it spreads
Mealybugs are poorly mobile and are moved substantially by ants, which tend them for their honeydew and carry them between trees. Wind and human handling move them too.
They acquire and transmit the virus semi-persistently in the course of feeding, which is what makes a modest sap feeder a major agricultural problem in West Africa specifically.
What it costs
Direct damage is minor. The agricultural significance is almost entirely as a virus vector, which means the impact of mealybugs is the impact of swollen shoot — cumulative, terminal for the tree, and requiring replanting.
How climate changes the picture
Population levels vary seasonally, with dry-season peaks reported in parts of West Africa. The interaction that matters is indirect — anything that raises vector populations raises virus spread.
How good is the evidence
The vector relationship, the species involved and the ant association are well documented in the West African literature. The relative transmission efficiency of different mealybug species is characterised but varies between studies.
Where informed people disagree
- How much practical control of virus spread is achievable through vector management alone, given that removal of infected trees remains necessary regardless.
How it is managed
These are categories of response, not instructions. This site gives no product, rate, concentration or interval for anything, and nothing here is a substitute for local agronomic advice — what works depends on the species present, the season and the regulations where the farm is.
- Managing the ants that tend and transport colonies, which is frequently more tractable than managing the mealybugs directly
- Removing infected trees to remove the virus reservoir, which is a swollen shoot measure rather than a mealybug one
- Biological control agents, which exist and are constrained by ant protection of the colonies
- Avoiding movement of infested planting material
Related
Affects
- GhanaWhere the vector relationship is agriculturally most consequential.
Pests and diseases
- Cacao swollen shoot virus diseaseRead alongside Cacao swollen shoot virus disease. Small sap-feeding insects that cause modest damage themselves and transmit cacao swollen shoot virus. They are the reason a virus problem in West Africa is also an insect problem, and the reason ants enter the discussion.
- Capsids and miridsRead alongside Capsids and mirids. Small sap-feeding insects that cause modest damage themselves and transmit cacao swollen shoot virus. They are the reason a virus problem in West Africa is also an insect problem, and the reason ants enter the discussion.
Sources
- Cacao Diseases: A History of Old Enemies and New Encounters — Springer, 2016(citation identity confirmed; passage not re-read)
- CABI Compendium: Theobroma cacao pests and pathogens — CAB International(citation identity confirmed; passage not re-read)
This page describes a crop pathogen or pest for readers of a chocolate reference. It is not agronomic advice. See the editorial policy.