Late-instar German cockroaches, Blattella germanica (L.), were used to evaluate the relative effects of single treatments and combinations of three
insect growth regulators (IGRs):
pyriproxyfen,
fenoxycarb, and
diflubenzuron. Groups of 15 males or 15 females were held for 2 wk on food treated with varying amounts of IGRs. After removal, newly mature adults were placed with untreated adults of the opposite sex. Mortality, adult phenotype (normal wings, divergent wings, curly wings, and nymphoids), and reproduction were assessed. Mortality occurred largely in the nymphal stage except when all three IGRs were combined. Neither the average number of nymphs per egg case nor hatch of egg cases from phenotypically normal cockroaches (normal wings, occasional darkening of the body) was affected in single treatments or in combinations of two IGRs, but nymphal numbers were reduced when the three IGRs were combined. Hatch from matings of insects with divergent wings varied. At low concentrations (3-10 ppm), hatch was generally normal; at high concentrations, most mating tests were unproductive. Mating tests of cockroaches with curly wings were almost always unproductive. When males with curly wings were mated, females dropped either unfertilized egg cases (no mating) or partially fertilized egg cases. Curly-wing females either dropped unfertilized egg cases or failed to form egg cases because of deleterious effects on ovarian development. Nymphoids did not mate.
Diflubenzuron at 100 ppm had no effect other than causing the appearance of a few insects with divergent wings. Effects on phenotype and reproduction began at 3 ppm of both
pyriproxyfen and
fenoxycarb and at a comparable concentration in the combination of
pyriproxyfen +
fenoxycarb (1 ppm each).
Female sterility was complete at 100 ppm of
pyriproxyfen and
fenoxycarb. When
pyriproxyfen or
fenoxycarb was combined with equal amounts of
diflubenzuron, the number of productive matings was not reduced at 6 ppm (3 ppm per each IGR). At 20 ppm (10 ppm per each IGR), a reduction in productive matings coincided with the appearance of curly wings. Complete
female sterility occurred only at 600 ppm (300 ppm per IGR). The most severe effects occurred in the experiment with equal amounts of
pyriproxyfen,
fenoxycarb, and
diflubenzuron. In addition to reduced hatch from normal phenotypes, this experiment caused complete
male sterility (300 ppm; 100 ppm of each IGR).
Female sterility was complete at greater than or equal to 90 ppm (30 ppm of each IGR).