Contents - LAC Biosafety

10.10 Leucaena leucocephala (Fabaceae: Mimosoideae) 265
Well-defined population peaks were recorded in maize-leucaena agroforestry
plantations in Kenya, where the abundance was lowest during months with little
or no rain and months with heavy rainfall, and higher during the intervening
period of moderate rainfall (Fig. 10.23) (Ogol and Spence, 1997). They found
no clear correlation with temperature, within the natural range obtained.
In Yogyakarta, Indonesia, H. cubana populations were higher during the dry
season than during the rainy season, which was attributed to incidence of
fungal disease during the wet season (Mangoendihardjo et al., 1990). In pollarded
leucaena plantations in the Philippines, the psyllid population was present
throughout the year, with wide fluctuations (Fig. 10.24), extreme wet and dry
periods reducing the numbers except in the cool and moist mountainous areas
(Villacarlos et al., 1990). It is evident that weather, pollarding and natural
enemies are the important factors influencing the leucaena psyllid populations.
Weather, mainly rain and temperature, in addition to their direct effect
on the dispersal and growth of the insect, exert indirect influence through
effects on the growth of the plant and the fungal pathogens of the insect.
The increase in the psyllid population following the monsoon rainfall is
probably also due to dispersal and arrival of the psyllids through the monsoon
wind system.
On a larger temporal and spatial scale, there has been a gradual decline in the
abundance of the leucaena psyllid since the outbreaks began. This has been well
documented in Thailand (Van Den Beldt and Napompeth, 1992). Following the
Fig. 10.23 Seasonal abundance of the leucaena psyllid Heteropsylla cubana, in
relation to rainfall at Mtwapa, Kenya. From Insect Science and its Application
(Ogol and Spence, 1997).