The biology and control of the tomato russet mite, Aculops lycopersici (massee) (acarina: eriophyidea) in Kenya.
Kamau, Alice W
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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.