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Abstract SUMMARY ======= Laboratory reared strains of two species of flour b~etleB i.e. Tribolium castaneum and Tribolium confuaum were reared for five generations under pressure of insecticides. The insecticides used were malthion, cypermethrin and decamethrin parent s ani Burvivals of insecticidal ~ selection were fUrther exposed to two levels of insecticides. the 1C50 level (sublethal dose) and a concentration causing no mortalities among adults (non lethal dose ) and the biology of each case was recorded. Rsults of rearing under pressure revealed various degrees and steps towards aquiring resistance in each insecticide. insect species, indicating a different gene set up in each case. In malathion selections, there waS a substantial increase in slope of the LD p-line in FS in T. castaneum whereas T.confusum under went slight changes in slope in the five generations investigated. This might be taken to indicate that T. castaneum would aquire resistance to malathion in lesS generations than re qlired by T. confusum. ~hen cypermethrin was tested, the results indicated that th~ five generations of both insect species reared under pressure represented a Lat ent period during which accumula’tion or subsid”~ J gene alleles takes plaae alongside a remodelling of the genotype as a whole to accomodate the new gene allele. --- ----- 140 Using decamethrin for selection in T. castaneum revealed th8t the first two generations served to eleminate tl~ extremely susceptible insects and the first steps towards tolerance could be detected from F) cnvards. In T. confuSUIn, however the five generations investigater were enough to produce a tipical tolerent strain with a low slope and ”LC50value being 7.3 folds longer than the parents. It was concluded that the two species of flour beetles were cupable of producing tolerent strains of the three insecticides investigated, although the pattern and number of generations required would differ in each species toxicant combination. ’rile slo’Nest build u, to resistance, would be expected with cypcrrnet””rin, while the fastest build up would eccurr e with dec me’~hrin andi.’. confusum. vnen the efi~ect of LC 5C and non lethal doses of the three toxic ants wer invest igat ed on the t’.0 insect specie s select ed for tolerance all the insecticides used excerted deleterious effect s on the biolog.y of the parent 8 and subsequent generat ions selected for tolerance. The degree of pre~nt. effect on oviposition, hatchability, Larva.L ani pupal development periods and longevity of adult s varied considerably with various insecticides. Selection for tolerance in BOI!l9 acases tended to partiall’ mitig te the effecta recorded for toe untreated parent s wni.Le in other case s an imp-ession was gained of the ~~~----- - - -------------- 141 presence of an adverse additive effect of selection for tolerance andexposure to sublethal doses • rne level of trel:1”tmentto produce activation of the biological activities, reported for other insects was not detected in the present work, it was concluded that if a threshold for stimulatory effects of malathion, cypermethrin and decamethrin on the two flour beetles, then if must be farbelow the range of concentration used to build LD-p-line. |