Laboratory Population Studies of the German Cockroach Using a Two-chromosome and a Three-chromosome Reciprocal Translocation1,2

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Abstract
The effects of repeated releases of a translocation, T(8;9), carrying a deleterious gene, st, and of a 3-chromosome translocation, T(4;8;10), on growth of laboratory populations were analyzed. P1 matings were between translocation-carrying males and 5 +/+ females. Subsequent nymphal groups were isolated and, in most cases, T/+ males were released so as to maintain ratios of ca. 5-6 T/+:1 +/+ male. Hatch, development, and other data were recorded for each progeny group in order to reconstruct total populations for the 1st 7 mo of growth. Mating types were studied by examining mature oothecae for normal embryonic development, semisterility, or sterility (T/+ × T/+). From linkage tests of T(8;9) with st, is was predicted that ca. 23% of the F2 females would be sterile st/st homozygotes. Observed frequencies generally ranged from 5-8%. T(8;9) did not provide a successful mechanism for driving the sterility gene into the population. Comparisons to control data showed the reductions differed little from those expected from the translocation alone. Progeny groups and population growth were severely limited by the T(4;8;10) releases. A 7-mo-old population reconstructed from 3 replicates was 2.1% that of the +/+ control; one based on a 4th replicate in which releases were increased was 1.3%. The latter grew by a factor of 10 in the 1 st-7th mo as compared to ca. 250X in the control. Certain F3 groups that hatched after month 7 were used to test the effects of 9-10:1 ratios. It appeared that releases of this magnitude would come close to population suppression. The reductions following T(4;8;10) releases resulted from the combined effects of high lethality (aneuploid gametes) and sterility from embryonic trapping (inability of low numbers of viable embryos to force open the ootheca at the time of hatch).

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