Biology Reference
In-Depth Information
Fig. 12.7
Summer rust
Puccinia melampodii
on seedling establishment, plant height, flower production, plant biomass and plant
density at the end of the first year was not significant (Dhileepan 2003b).
The biological control agents had a significant negative impact on parthenium at
both individual plant and population level, and the impact was more severe in central
Queensland than in north Queensland (Dhileepan 2001, 2003b). As a result, there was
a significant increase in grass biomass production due to biological control (Dhileepan
2007). In central Queensland, there was a 40% increase in grass biomass in 1997 due
to 96% defoliation by the leaf-feeding beetle
Z. bicolorata
and galling in 100% of the
plants by the moth
E. strenuana
. In north Queensland, grass biomass increased by
52% in 1998 due to reduced parthenium seedling emergence, and by 45% in 2000
(Dhileepan 2007), due to the combined effects of galling by the moth
E. strenuana
and the establishment of the summer rust
P. melampodii
in 72% of the plants. In eco-
nomic terms, benefits from increased grass production due to biological control have
been estimated to support an additional 0.002 of an animal ha/year, which is equivalent
