| dc.description.abstract | Ophiomyia phaseoli Tryon and Ophiomyia spencerella Greathead
were the two Beanfly species that infested Canadian Wonder plants
at Kabete Kenya. The latter, was the most abundant species 'I
throughout the experimental period. Beanfly females first attacked
bean seedlings immediately after emergence and reinfest at ion
and increased colonisation continued for the following two weeks.
The attacked plants were recognised by punctures made in their leaves
by ovipositors of the female Beanflies. Such plants when two to
four weeks old, were characterised by lea! yellowing, co110used
stem bases and wilting. Increases in the Beanfly infestation
rates were estimated by the percentage o! infested plants per 9m2
plot per week, female Beanf1y punctures per plant per week and pest
larvae plus pupae per plant per week. The highest infestation
rate was recorded in the December sown crop where all the plants
were invested within the first 7 days after emergence. Initial
Beanfly population density and oviposition behaviour of their
females were probably the two main factors that influenced the rates .•
of infesting bean fields. Peak infestation intensities of bean
fields were recorded during the third week of each crop stand.
Infestation intensities also varied from one bean crop season
to the next. The highest infestation intensities were recorded in the
crops sown during the short rain (October to December, 1976) season.
In the short rains and long rains (February to July, 1977) seasons, the
early planted bean crops were less infested than the late planted
ones. Infested plants had their potential leaf development reatarded
and had overall stunted growth. The potential seed yield performance
of infested plants were lowered. The threshold infestation levels
of the beanfly were found to lie between 85 and 120 larvae per m of
crop stand. The low seed yields were caused by few pods per plant
and few seeds per pod from such plants. The lowest seed yields were
recorded from infested plants of the December crop. The recorded low
seed yields were mainly caused by small photosynthetic capacity and
stunted growth infested plants. Multiple linnear regression analysis
showed that, changes in the rainfall intensities considerably
influenced the effects of the Beanfly infestation densities on the
growth rate and seed yields of infested bean plants. Birlane 2G
was the least effective at controlling the Bean flies when compared
to aldrin 40%, Birlane, Miral and Furadan. None of the four
chemical sUbstances tested completely protected bean fields against
Beanfly invasion. But, Furadan was the most effective at controlling
Beanfly infestations. All these chemical substances protected
beanfields against the Beanflies for only two to three weeks. | en |
