Contents - LAC Biosafety

Africa where these conifers had been free of major pests until these aphids
arrived. Their arrival resulted in severe growth retardation and sometimes tree
mortality. Aphids were estimated to cause 50% loss of growth increment and up
to 20% tree mortality (CABI, 2005). According to Murphy (1996) the two pine
aphids were causing an annual loss of £1.5 million by way of increment loss in
plantations across Kenya, Malawi and Uganda. Outbreak of the conifer aphids
was characterized as a crisis in African forestry (FAO, 1991) and in 1991 the Kenya
Forestry Research Institute organized a regional workshop in technical
collaboration with FAO and the International Institute of Biological Control
to address the problem and develop a regional programme for conifer aphid
management.
Control Control attempts have mostly relied on classical biological
control although chemical control has also been tried with varying degrees of
success (Day et al., 2003). These aphids are not serious pests within their
natural geographic range and it is assumed that this is because of the pressure
exerted by indigenous natural enemies. They become pests in exotic
locations when released from the grip of natural enemies. P. boerneri has been
successfully controlled by introduced natural enemies in Hawaii, New Zealand
and Chile. The most effective natural enemy in Hawaii is the dipteran predator,
Leucopsis obscura. However, biological control with introduced alien predators has
been mostly unsuccessful in eastern Africa (CABI, 2005). In Kenya, indigenous
predatory coccinellid beetles have given some degree of control (Mailu et al.,
1980). Over the years, the severity of the problem has been reduced, apparently
due to a combination of factors including stabilization of the aphid population
due to the action of indigenous and introduced natural enemies, and the
slowing down of pine plantation establishment.
Knowledge gaps There is little published information on the current
status of pine aphids in Africa. This is partly because the problem has become
less severe after the initial escalation following the introduction of the exotic
aphids into Africa. There has been some confusion initially in the taxonomy of
pine aphids which affected the progress of biological control efforts (Day et al.,
2003). Obviously more research is needed on the taxonomy of conifer aphids.
10.15 Shorea species (Dipterocarpaceae)
Tree profile
10.15 Shorea species (Dipterocarpaceae) 287
Shorea is an important genus of commercial timber species of the family
Dipterocarpaceae, a dominant family in the lowland rain forests of Indonesia,