Successive releases of male German cockroaches heterozygous for the translocation T(8;9) and the recessive deleterious gene sty were made into laboratory populations of Blattella germanica to study the effect of this genetic load on population growth.

Five experimental populations and one control were followed by monthly census for eight months. Individual progeny groups were held in separate containers. Various aspects of reproductive behavior of different genotypes were evaluated in separate experiments including fecundity, competitiveness and assortative mating. Linkage between T(8;9) and sty was also measured.

The translocation T(8;9) and sty were successfully introduced into the experimental populations by the introduction of heterozygous males. Experimental populations were only 50% the size of the control at the F₁ generation and only 25% as large by the F₂ generation. At the F₃ generation, experimental populations were only 15.4% as large as the control. Cross connected contingency table analyses of population data showed a significant retardation of population growth from releases of T(8;9) sty males. T(8;9) provided a successful mechanism for driving the deleterious gene, sty, into the normal segment of the population. The frequency of sty/sty females in F₂ groups was predicted at 0.20. Observed frequencies approached the expected frequency at 0.11 to 0.22. This deleterious gene provided additional genetic load by reducing possible F₃ progeny by approximately 15%. Linkage tests of T(8;9) with sty showed cross-over frequencies of less than 1% for both males and females.

Results were less than optimum due to the following: a possible reduction in competitiveness of released males; higher than expected fecundity in the sty· homozygote female; possible shift in the frequency of alternate disjunction in T(8;9) sty heterozygote males; possible assortative mating between non-translocation bearing wildtype males and T+/+sty females in the population as well as T+/+sty males and non-translocation bearing wild-type females; fewer T+/+sty males and more sty males released than planned due to phenotyping errors in larger releases.

Laboratory studies of the reproductive behavior of three genotypes involved in the experimental populations evaluated competitiveness among males, initial productivity, maximum number of matings per male, and assessed the prospect of assortative mating among the genotypes. Competitiveness of the T+/+sty males in small number tests was consistently better than wild-type males but in later assessments by mass mating and population studies, they demonstrated equal competitiveness with wild-type males. A statistically significant tendency toward assortative mating between VPI wild-type males and T+/+sty females was observed. The feasibility of techniques for mass rearing of semi-sterile males for releases of up to 10,000 males per month was demonstrated.