Modification of Fitness in Species and Strains of Flour Beetles due to X‐Ray and DDT

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Abstract
Insecticides and ionizing radiations can induce population changes which under selection are beneficial or harmful. Such changes are known in some cases to have a genetic basis. Studies were designed to determine the early effects of DDT and x—radiation, singly and in combination, on mortality and productivity of flour beetle species and strains (Tribolium confusum Duval "Chicago standard" and T. castaneum Herbst "Brazil cI" an "Sooty"). Five replicate populations each containing ten pairs of virgin beetles x—rayed with 0, 1, 2 or 4 kR of x—rays (250 kvp, 30 ma, 0.25 mm Cu + 1.0 mm A1 filtration, 0.86 mm Cu HVL and 2.5 inches between target and subjects produced 1 kR/min) were cultured under standard conditions in food containing 0, 5, 10, 20 or 50 ppm DDT. Every two weeks for six weeks parental mortality was recorded and living adults were placed on fresh comparable food. The old food was reincubated and F1 adult biomass and numbers were the measures of productivity. Parental mortality was 1) unaffected by x—rays, 2) increased for "Brazil cI" at 50 ppm DDT, and 3) greater for females than males but unrelated to radiation or insecticide. Productivity measurements decreased with increasing x—ray or DDT. Productivity of T. confusum was, in general, more radiation—sensitive than that of T. castaneum strains, whereas, both T. castaneum strains were mor DDT—sensitive than was T. confusum. Radiation of 4 kR was almost sterilizing to T. confusum; of T. castaneum strain "Brazil cI" left no F1 at 50 ppm DDT. Proportions of lethals due to x—ray or DDT were considered genetic dominants and used to quantify the relationship between radiation and insecticide in combination. Observed lethality simulated that expected for genetic dominant lethal effects when "Chicago standard" and "Brazil cI" were stressed with x—ray plus DDT. In "sooty," observed lethality was consistently lower than that predicted on the assumption of dominant lethal effects; i.e., productivity was less adversely affected when both stresses were applied than that expected by multiplying the effects of singly stressed populations. Within a specie "sooty" populations showed more lethality due to x—rays than did "Brazil cI" populations; DDT had the opposite effect.

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