Search

Genetically marked insecticide-susceptible strains of the German cockroach, Blattella germanica (L.), were crossed to the Seasons-resistant strain to examine the inheritance and linkage of resistance to cypermethrin, fenvalerate, permethrin, and phenothrin. Tests on the F1 progeny from reciprocal crosses indicated that resistance to these pyrethroids is not sex linked and is incompletely recessive in each case. Backcrosses to the Seasons strain resulted in a 1:1:1:1 ratio with the black-body marker from linkage group IV. F2 crosses, involving the orange-body marker from linkage group VI, produced a 9:3:3:1 ratio. These results fit the hypothesis that resistance to each insecticide is inherited as a monofactorial, autosomal, incompletely recessive trait not linked to Bl or or . The data do not allow a distinction between whether 1 gene controls resistance to all 4 insecticides, or whether as many as 4 similarly acting genes are responsible. Other data are discussed that support the latter possibility.

Methods for detecting resistance to chlorpyrifos and cypermethrin in the German cockroach, Blattella germanica (L.), were evaluated. Results from the tarsal-contact method (jar test) are greatly influenced by the amount of insecticide used. In tests with high levels of insecticide, little or no resistance was detected. By using less insecticide, the existence of resistance was revealed. Recognition of this fact allows discrepencies between the lethal dose, lethal concentration, and lethal time methods to be largely resolved. These findings indicate that caution must be exercised in the use of the jar test to avoid misinterpretation of the results.

A simulated crack and crevice method of exposure to insecticides was developed to ascertain the relationship between mortality produced by field-application rates and resistance ratios obtained by the time-mortality method. Nymphal German cockroaches, Blattella germanica (L.), from strains of widely varying resistance backgrounds were tested with chlorpyrifos, acephate, cyfluthrin, and cypermethrin. I observed an inverse relationship between resistance ratios and 72-h crack and crevice mortality in all 4 cases. Gene frequency estimates paralleled resistance ratios for cyfluthrin and cypermethrin. I concluded that time mortality resistance ratios provide a good indication of the level of resistance in a given strain, and that resistance ratios >3.0 signal potential control failures in the field.

Twelve field-collected populations of German cockroaches, Blattella germanica (L.), were examined for resistance to dietary abamectin at 40 ppm. Half of these populations had significantly increased resistance ratios compared with the VPI-susceptible strain, but the highest value was only 2.4. Feeding inhibition was variable but nevertheless pronounced in all 12 strains. Feeding-choice tests with two strains revealed that each strain consumed treated and untreated food about equally. Mortality was reduced in both strains. Cross-resistance from cyclodiene resistance was not found. Low-level selections with abamectin did not result in increased resistance. Whereas resistance to abamectin does not appear to be a problem at present, two potential resistance mechanisms were identified and are discussed briefly.

The effects of three synergists on the level of resistance to eight pyrethroids were examined in field-collected populations of the German cockroach, Blattella germanica (L.). Resistance to allethrin was not affected by piperonyl butoxide (PBO), (2-(2-ethylhexyl)-3a,4,7,7a-tetrahydro-4,7-methano-1H-isoindole-1,3(2H)- dione (MGK 264), or S,S,S-tributyl phosphorotrithioate (DEF). Resistance to pyrethrins also was not affected by these synergists in the same or similar strains but was negated almost completely by them in strains resistant only to pyrethrins. Resistance to permethrin, cypermethrin, and cyfluthrin largely was negated by these synergists. Results were variable with esfenvalerate, fenvalerate, and especially phenothrin. For example, with phenothrin the synergists were partially effective against some strains but were totally ineffective against others. The results appear to be unrelated to the chemistry of the pyrethroids studied. I report evidence that indicates the possible presence of several independent resistance mechanisms. My results suggest that these synergists generally will not combat pyrethroid resistance in this species, although they are highly effective in some cases.

Bendiocarb resistance was assessed genetically in the German cockroach, Blattella germanica (L.), by conventional crossing experiments. It is inherited as a simple, autosomal, incompletely recessive, Mendelian trait. Manipulation of the test procedure clearly identified the resistant homozygote. thus allowing gene frequency estimates to be made using the Hardy-Weinburg equilibrium expression. Gene frequnecies were estimated for 18 field-collected populations at two time intervals. In the initial tests, gene frequencies varied from 0.99 to 0.15. Significant decreases in gene frequency occurred in four populations over time; significant increases were observed in two others. Comparisons were made between gene frequency estimates of the level of resistance and conventional resistance ratios. I concluded that resistance ratios do not provide an adequate evaluation of the status of resistance. The results are discussed from the standpoints of their effect on resistance management and the effect of extended periods of laboratory culture on the assessment of resistance.

The response of a susceptible and two pyrethroid-resistant field strains of the German cockroach, Blattella germanica, to four emulsifiable concentrates (ECs)--Tempo (cyfluthrin), Demon (cypermethrin), Dursban (chlorpyrifos) LO, and XRM 5184 (chlorpyrifos)--was investigated. Application rates were 0.4, 0.1, 0.5, and 0.5%, respectively. Susceptible cockroaches avoided dried formulations of the pyrethroids Tempo and Demon, but resistant cockroaches did not; avoidance was greater with Demon than with Tempo. Filter papers freshly impregnated (wet) with Demon and Tempo flushed susceptible cockroaches (Demon greater than Tempo). Resistant cockroaches were flushed only by Demon, but less so than susceptible strain cockroaches. No mortality occurred in experiments with the pyrethroids. Dried formulations of Dursban LO and XRM 5184 had little, if any, repellency to nymphs of either the susceptible or resistant strains. Initially (1-3 h), most cockroaches settled on treated papers. Subsequent movement off treated papers was a step in the process leading to knockdown. At 24 h, mortality of susceptible cockroaches was 100% in the experiment with Dursban LO and 95% in the experiment with XRM 5184. Highest mortality in a resistant strain (40%) was in the contact experiment with Dursban LO. In contact repellency and flushing experiments, mortality was higher with Dursban LO than with XRM 5184. Neither chlorpyrifos formulation flushed cockroaches effectively. Mortality in flushing experiments was less than in the contact repellency experiments.

Selection experiments with a pyrethrins-susceptible and a pyrethrins-resistant strain of German cockroaches, Blattella germanica (L.), were conducted for 17 generations with either permethrin or fenvalerate as the selecting agent. Large nymphs were left on treated glass surfaces for extended periods of time each generation. Mortality was assessed at 24 h. The level of resistance was determined periodically by time-mortality testing. The VPI-susceptible strain served as the basis for comparison. The pyrethrins-susceptible strain developed resistance to pyrethrins early in the selection process; this strain ultimately became resistant to allethrin, phenothrin, permethrin, fenvalerate, cyfluthrin, and cypermethrin. Fenvalerate caused faster development of resistance than did permethrin. The pyrethrins-resistant strain, selected with fenvalerate, quickly became resistant to allethrin, permethrin, phenothrin, and fenvalerate. Ultimately, it developed resistance to all nine pyrethroids tested.

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).

The toxicity of synergism of and resistance to insecticides in four strains of German cockroach, Blattella germanica (L.), were investigated. Toxicity of nine insecticides by topical application to the susceptible strain varied greater than 2,000-fold, with deltamethrin (LD50 = 0.004 micrograms per cockroach) and malathion (LD50 = 8.4 micrograms per cockroach) being the most and least toxic, respectively. Resistance to pyrethrins (9.5-fold) in the Kenly strain was unaffected by the synergists piperonyl butoxide (PBO) or S,S,S-tributylphosphorotrithioate (DEF), suggesting that the metabolism is not involved in this case. Malathion resistance in the Rutgers strain was suppressible with PBO, implicating oxidative metabolism as a resistance mechanism. The Ectiban-R strain was resistant to all the pyrethroids tested, and cypermethrin resistance was not suppressible with PBO or DEF. These findings support results of previous studies that indicated this train has a kdr-like mechanism. Bendiocarb resistance in both the Kenly and Rutgers strains was partially suppressed by either PBO or DEF, suggesting that oxidative and hydrolytic metabolism are involved in the resistance. Trends between the effects of the synergists on the susceptible versus resistant strains are discussed.

A genetically marked insecticide-susceptible strain of the German cockroach, Blattella germanica (L.), has been developed by incorporating the orange-body trait into a stock containing the genomes of 2 of the most susceptible strains available. The new stock retained its susceptibility as indicated by tarsal contact tests with 12 insecticides. The integrity of the stock can be ensured by removing any wild type body color contaminants. This stock is well suited to become the standard-susceptible strain for the German cockroach and is available upon request.

Pyrethrins resistance was assessed genetically in the German cockroach, Blattella germanica (L.), by conventional crossing experiments. It is inherited as a simple, autosomal, incompletely dominant, trait. By manipulating the test procedure, the susceptible homozygote was clearly identified, allowing gene frequency estimates to be made using the Hardy-Weinburg equilibrium expression. Gene frequencies were estimated for four susceptible and 16 resistant field-collected populations. Values ranged from 0.10 to 0.18 for the susceptible strains, and from 0.34 to > 0.90 for the resistant strains. Changes in gene frequency over time for several resistant strains were not significant. The results are discussed from the standpoints of their effects on cockroach control and the stability of pyrethrins resistance even during extended periods with no selection pressure.

The level of resistance to seven pyrethroids was followed in a laboratory-selected population of Blattella germanica (L.) for 15 generations, during which time it was not exposed to any insecticide. As estimated by LT50 resistance ratios (RRs), resistance declined in a stepwise manner to preselection levels with all of the pyrethroids except pyrethrins. I also compared the levels of resistance as indicated by RRs and by gene frequency (GF) estimates. Results showed that GF estimates provide a more precise indication of the changes in resistance that occur over time than do RRs alone, especially when combined with RR and end-point mortality data. I discuss my results from the standpoints of the number of genetic mechanisms involved in pyrethroid resistance in this insect, and what the declines in resistance mean for future cockroach control.

Ten field-collected strains of the German cockroach, Blattella germanica (L.), with varying levels of pyrethroid resistance were tested for possible cross-resistance to abamectin administered as a bait. The time-mortality method was used for comparison of response with a known susceptible strain in 10-d feeding experiments. Essentially no resistance to abamectin was found. Extensive feeding inhibition occurred after a few days, but the amount of abamectin consumed varied substantially from strain to strain. Abamectin may have considerable potential as a cockroach bait insecticide.

Metaphase I cells from heterozygotes in eight reciprocal chromosome translocation stocks of Blattella germanica (L.) have been examined and counted. The data show that three stocks have random disjunction (adjacent and alternate orientations are equally frequent), but the cell types adjacent-1, alternate-1, adjacent-2, and alternate-2 are present in a ratio of 2∶1∶1∶2. Four stocks with directed disjunction have similar patterns, except for a heavy preponderance of alternate-2 cells. This difference is reflected in the finding that 60–65% of all cells in these interchanges are type II cells (alternate-2 plus adjacent-2), and the individual percentages agree closely with the percent directed disjunction in each case. One inter-change with directed disjunction is distinctly different in that the frequencies of both alternate-1 and alternate-2 cells are elevated and contribute to directed disjunction. It has also been demonstrated with two stocks that changes in disjunction frequencies can be brought about by genetic manipulation. These observations provide a better understanding of the differences between random and directed disjunction.

Two new reciprocal translocations in the German cockroach have been analyzed. They were identified cytologically to be T(3;12) and T(7;12). Linkage studies showed that groups XI, IX, and IV are on chromosomes 12, 3, and 7, respectively, and clearly demonstrated sex differences in recombination. Each of these chromosomes have distinctive morphological features that facilitate their identification, and permit breakpoint and centromere localization. A sex difference in fecundity is associated with T(7;12), but not T(3;12). About 40 percent mortality occurred when T(3;12) males or females and T(7;12) females were outcrossed. Outcrossing T(7;12) males produced the expected 50 percent mortality. Cell counts at metaphase I revealed that T(3;12) males exhibit directed segregation, while T(7;12) males do not. Tests for homozygosity indicated that the T(7;12) homozygote is viable. A map of chromosome 12 is presented showing the tentative placement of linkage group XI with respect to interchange breakpoints and chromosome morphology. The results are discussed in relation to possible sex differences in chiasma localization.

Forty-five field-collected strains of German cockroaches, Blattella germanica were tested for resistance to 12 different insecticides by the time-mortality response method in comparison with a known susceptible strain. Only low to moderate resistance to diazinon, chlorpyrifos, and acephate was detected. Resistance to malathion was widespread; about half of the strains tested showed high resistance. High resistance to the carbamates propoxur and bendiocarb also occurred. High resistance was uncommon with propoxur, but about 35 strains were highly resistant to bendiocarb. High resistance to pyrethrins was observed in about of the strains tested. Resistance to the pyrethroids allethrin, permethrin, phenothrin, fenvalerate, and cyfluthrin was detected in some of the strains examined. All of the strains tested were susceptible to one or more of the insecticides used. These results indicate that, although resistance is a serious problem in this species, satisfactory control should be possible by selection of an appropriate insecticide.

The evidence in support of two types of alternate disjunction in translocation heterozygotes from the German cockroach, Blattella germanica(L.), is reviewed. When unique cytomorphological features occur in the translocation figure, the two types of alternate disjunction are identifiable regardless of the angle of observation. Photographs supporting this contention are presented for alternate-1 and alternate-2 disjunction in T(7;12)/7;12. Other evidence in support of the existence of alternate-2 disjunction is also presented.

Experiments were designed to compare growth and development of Piophila casei (L.) under sterile, unsterile, and sterile-inoculated conditions. A millipore-filter modification of an egg-sterilization technique was used. In unsterile treatments, eggs were washed only in tap water. For the sterile-inoculated condition, eggs were sterilized and inoculated with 0.5 ml of a 5-h culture of Proteus mutgaris (VPI strain no. 3). Chicken embryos served as growth medium. Use of the millipore-filter technique eliminated the transfer of eggs from one chemical to another, and allowed continual checks of egg survival. The results indicate that the normal flora accompanying eggs has no beneficial influence on the growth and development of P. casei, and that limiting the number of bacteria present may be advantageous to the insect. P. vulgaris has very little influence on growth and development of the cheese skipper.

A pyrethrins-susceptible and a pyrethrins-resistant strain of German cockroaches, Blattella germanica (L.), were selected with either permethrin or fenvalerate over several generations to determine if resistance would occur. Large nymphs were left on treated glass surfaces until about half were killed each generation. The level of resistance was determined periodically by time-mortality testing. The VPI-susceptible strain served as the basis for comparison. The pyrethrins-susceptible strain developed resistance to pyrethrins in six to seven generations with either selecting agent. This strain also showed resistance to allethrin when fenvalerate was the selecting agent. The pyrethrins-resistant strain developed resistance to allethrin with both selecting agents; in addition, resistance to permethrin, phenothrin, and fenvalerate developed when fenvalerate was used. The synergists piperonyl butoxide and MGK 264 (2-(2-ethylhexyl)-3a,4,7,7a-tetrahydro-4,7-methano-1H-isoindolel, e(2H)-dione) largely negated resistance to pyrethrins, but neither they nor the esterase inhibitor DEF (S, S, S tributyl phosphorotrithioate) were effective after development of resistance to allethrin. While resistance to pyrethroids can easily develop in this species, both the selecting agent and the previous history of resistance appear to have a bearing on how resistance develops.

Adjacent-1, alternate-1, adjacent-2, and alternate-2 disjunction configurations were observed cytologically at metaphase I in heterozygotes from two reciprocal chromosome translocations in the German cockroach, Blattella germanica (L.). T(7; 12) shows random disjunction and the frequencies of the above four types were in a ratio of 2:1:1:2 (p greater than 0.90). T(3; 12) has directed disjunction (about 70% alternate) which is attributable to a heavy preponderance of alternate-2. No interpretable ratio occurs here except for the equality of alternate-1 and adjacent-2 types. These observations confirm the existence of two types of alternate disjunction, and provide insight into the basis for random vs directed disjunction.