| dc.description.abstract | The biolo~y and control of the tomato russet mite,
Aculops lycopersici (Massee). (Acarina: Eriophy~d~a)
in Kenya.
One of the major constraints to obtaining high
tomato yields in Kenya is damage by the tomato russet
mite, Aculops lycopersici (Massee). Since there was
hardly any information concerning the bionomics of this
mite in this country,this study was initiatedto assess its
distribution and importance, determine its host plant
range, identify the natural enemies associated with
it, study the biology of this mite, evaluate resistance
levels of tomato varieties and to determine the nature
and source of resistance and screen several acaricides
for efficacy and to determine the optimum number and
intervals of their spray applications.
The results of the field survey showed that
A. lycopersici is a widespread and a serious pest of
tomatoes. The number of farms infested, the level of
infestation and the yield loss caused by its damage
was highest in Kajiado followed in descending order
by Nakuru, Kiambu and Kirinyaga districts.
\
Ten alternative host plant species, eight of which
belonged to Solaneceae family were identified. The
most common and prefered ones were irish potato,
Solanum tuberosum L. and the nightshade, Solanum nigrum L.
x
Developmental rate, fecundity, surviyal and adult
longevity of A. lycopersici were significantly affected
by the temperature. The shortest life-cycle (4.4 days)
o from egg to adult was recorded at 30 C and the longest
(10.5 days) at 15°C. The oviposition rate was 0.5 and
1.5 at l50C and 25°C respectively. Survival and adult
longevity were only significantly reduced at higher
temperatures (29°C and above). The most suitable
temperature for its development was 25°C. Two predatory
mites, Pronematus uhiquitus (Mac Gregor) and Typhlo<lromus
'spp.and a cecidomyiid maggot were ident ified.
The rate, of the tomato russet mite population
increase on the twelve tomato varieties tested indicated
that Roma, Rossol, Mecheast, Oxheart and Bonny Best
were generally less susceptible while Rutgers, Beauty
and Hybrid Beefmaster we~e more susceptible. Oviposition
preference was evident and was significantly and
positively correlated with leaf hair density. The
highest average number of eggs/female was recorded on
Roma and the lowest on Lycopersicon hirsutum 1.. gl.abrat.um,
Pronounced tolerance to leaf damage was obvious
in varieties Early Stone Improved and Beauty. Oxheart
and Bonny Best both of which had low mite densities
were highly sensitive. The tomato russet mite did
not significantly affect the flower bud formation
except in varieties Oxheart and Rutgers. However, its
damage on flowers and flower buds was highly significant.
The rmst affectedwere Oxheart, 1-echeastand Roma and the least
affectedwere Early stone Improved,Beauty and Penny Best.
xi
Average number of the fruits formed on infested
plants was significantly less than on the protected
ones in most varieties. Differences in the rate of
fruit formation among the varieties tested was probably
due to the interaction between the plant genetic
characteristics and response to mite damage. Russett lng
of young fruits was significantly and positively
correlated with the moisture content of their pericarp
(r = 0.738*). The highest average number of russetted
fruits was recorded on Red Cloud and lowest on Beauty
variety.
The yield loss due to mite damage was highest
on Oxheart and Hybrid Beefmaster both in the field and
in the greenhouse. Other varieties which were highly
susceptible were Bonny Best, Red Cloud and Mecheast.
Roma and Money Maker were the least susceptible in the
greenhouse. The observed field resistance was caused
mainly by pseudo resistance arising from phenological
asynchrony of some varieties with the mite.
Field evaluation of the acaricides showed that
amitraz, endosulfan, kelthane, triazophos and
cyhexatin were the most effective while dichlorvos
and karathane were moderately effective. Spraying
interval of 3 to 4 weeks during the warmer months was
regarded as optimum. | en |
| dc.description.department | a
Department of Psychiatry, University of Nairobi, ; bDepartment of Mental Health, School of Medicine,
Moi University, Eldoret, Kenya | |
