Abstract:

Monitoring populations of pests and their natural enemies under different management situations and seasonal
weather parameters provides extremely useful inl'orniation for taking preventive measures against pest outbreaks.
The abundance, spatial and temporal distributions of herbivorous insects and arthropod natural enemies on Alnus
species were monitored at four sites in Kahale district, Liganda between June 1999 and August 2000. Chewing
insects. dominated by Coleoptera (75%), constituted the trajority of insect herbivores sampled. Dominant and
potentially serious pests of Alitus included Apion globu/ipenne. an unidentified Chrysomelidac (Colcopt. 27),
Phvniateus viridipes, Coloborriics corticina and a Cacopsvila species (Homoptcra: Psyllidae). Spiders were the
predominant natural enemies accounting for 64% of the total natural enemies encountered, followed by parasitic
Hymenoptera (30%). There were marked spatial and temporal variations in arthropod abundance. Among sites,
mean abundance of total insect herbivores and total natural enemies on A. acu,ninala over IS months ranged
from 3.8-8.5 and 3.3-4.7 individuals per I-ni branch length respectively. Over the same period, mean number of
total insect herbivores and total natural enemies on A. nepalensis that was studied at only one site were Il .9
herbivores and 4.2 natural enemies per I -m branch length. Populations of most insect orders increased in the wet
season although the greatest herbivore abundance was evident in the dry season. Further studies are necessary on
the impact and management strategies of the potentially important insect pests and natural enemies on A/ntis.