K. Dhileepan, Effectiveness of introduced biocontrol insects on the weed Parthenium hysterophorus (Asteraceae) in Australia, B ENT RES, 91(3), 2001, pp. 167-176
Six species of insects and a rust fungus have been successfully established
for biocontrol of the weed Parthenicum hysterophorus L. in Queensland, Aus
tralia. Effectiveness of biocontrol insects was evaluated at two properties
in Queensland during 1996-97 based on an exclusion experiment using insect
icides. Parthenium-infested plots with and without biocontrol insects were
sampled at monthly intervals and the impact of biocontrol insects on parthe
nium at individual plant and whole population levels monitored. Biocontrol
insects were more effective at Mt Panorama (central Queensland) than at Pla
in Creek (north Queensland). At Mt Panorama, the leaf-feeding beetle Zygogr
amma bicolorata Pallister caused 96% defoliation and the stem-galling moth
Epiblema strenuana Walker affected 100% of the plants, resulting in reducti
ons of 90% in weed density, 40% in plant height, and 82% in flower producti
on. Exclusion of biocontrol insects resulted in a 52% increase in seedling
emergence and a seven-fold increase in the soil seed bank in the following
season. At Plain Creek, E. strenuana was the only prominent agent. It affec
ted 92% of the plants and prevented 32% of plants from producing any flower
s, reduced plant height by 40% and flower production by 49%, but did not re
duce the plant biomass, weed density or soil seed bank. However, exclusion
of biocontrol insects resulted in an eight-fold increase in the soil seed b
ank in the following season.