The use of entomopathogenic fungi to control agriculturally important pests, both in
greenhouses and in the field, has been demonstrated by various authors for a number of
years. This has been brought about by the development of resistance in certain pest
species to chemical applications and a growing public awareness of the safety
implications of residual insecticides. Several entomopathogenic fungi were tested
against four insect pests found in the Republic of South Africa (RSA), the greenhouse
whitefly, Trialeurodes vaporariorum, the rice weevil, Sitophilus oryzae, the grapevine
mealybug, Planococcusficus and the sugarcane stem borer, Eldana saccharina. Further
concentration, temperature and humidity studies were conducted with selected isolates
on the rice weevil, S. oryzae.
Sitophilus oryzae is considered one ofthe most important pests of stored grain. Several
fungal isolates were tested against the rice weevil, four of which, B1, PPRI 6690, PPRI
6864 and PPRI 7067, were selected for further testing based on the mortality results over
a 21 d period. Varying conidial concentrations were applied and at high doses of 1x10 -6
conidia ml -1 with mortality rates of to 84% achieved. LT 50 values ranged from 6 - 68d.
Increased spore concentration resulted in an increase in overall mortality.
Temperature and humidity was found to affect the infection potential of the four isolates
tested. Four temperatures ranging from 15 - 30°C were tested. The highest mortality
rates were obtained at 25°C where mortality ranged from 46 - 65% in 14d. Mortality
rates decreased with decreasing temperature, and no mortality was recorded at 30°C.
Temperature was found to significantly alter the LT 50 values, increasing the LT 50 with
decreasing temperatures. Decreasing the humidity resulted in an increased LT 50 and a
reduction in the overall mortality rates. The mortality of S. oryzae ranged according to
the RH and isolate. Isolates Bland PPRI 6690 resulted in the highest mortalities of 80
and 83% at 92.5% RH, with LT 50's of 6.3d and 6.4d, respectively.
Several entomopathogenic fungi were tested against T vaporariorum, P. ficus and E.
saccharina, three key pests of South African crops. Nine fungal isolates were tested
against the greenhouse whitefly, T vaporariorum, with mortalities ranging from 26.7 - 74.7% over 14d. Beauveria bassiana Isolates Bl and PPRl 6690 produced the highest
mortality rates and were recommended for further pathogenicity testing against T.
vaporariorum.
Planococcus ficus is a common pest ofvineyards in the Western Cape Province, South
Africa. Nine entomopathogenic fungi were screened against P.ficus, only two of which
produced mortality. Eldana saccharina is a stalk borer, which infests sugarcane in large
areas of Southern Africa. Five isolates were tested against second and third instar larvae,
three of which, B1, PPRl 6864 and PPRl 6690 resulted in mortalities. Mean percentage
mortality was low for all three isolates.
From the study it was evident that two of the isolates tested, Bland PPRI 6690 (B.
bassiana), showed potential against three of the four pests, and two isolates of
Lecanicillium lecanii caused mortality in P. ficus. Further research and understanding of
the effect of environmental conditions, spore concentration and epizootic potential
would result in the further development of these isolates as future biological control
agents. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/4062 |
| Date | January 2005 |
| Creators | Chambers, Craig Brian. |
| Contributors | Laing, Mark D. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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