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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.

Crosses were made between the Asian cockroach, Blattella asahinai Mizukubo, and resistant strains of the German cockroach, B. germanica (L.), to assess the transfer of pyrethroid resistance to the progeny and to study the inheritance mechanism(s) involved. It was shown that the strain of Asian cockroaches studied was susceptible to four pyrethroids. F 1 progeny were essentially susceptible to the same compounds. Tests with F 2 progeny and those from backcrosses to the resistant parent indicated that the data for each pyrethroid fit an hypothesis of simple, autosomal, nearly completely recessive inheritance. The results are discussed from the standpoint of the impact of the Asian genome on the inheritance mechanism(s)

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.

Late instar German cockroach male and female nymphs were exposed continuously for two weeks to surfaces treated with fenoxycarb, diflubenzuron, and pyriproxyfen, singly and in combination. Concentrations were determined that eliminated or nearly eliminated reproduction in matings with untreated mates, either through mortality, effects on reproduction, or a combination of mortality and ‘sterility' (no hatch). The major effect of fenoxycarb, pyriproxyfen, and pyriproxyfen plus fenoxycarb was on reproduction. The major effect of diflubenzuron was mortality. No hatch occurred in matings of females that were exposed to low concentrations of pyriproxyfen and fenoxycarb (2 ng/cm² and 6 ng/cm², respectively); sterility was incomplete when females were exposed to 600 ng/cm² of diflubenzuron. Mortality and sterility acted together to eliminate productive matings (matings that produced nymphs) when relatively high concentrations of diflubenzuron were combined with one or both of the other insect growth regulators (IGRs). In the triple combination, very small amounts of fenoxycarb and pyriproxyfen (total 1.1 ng/cm²) combined with 200 ng/cm² of diflubenzuron eliminated productive matings of treated females, but similar results with treated males were found only at higher concentrations of each IGR.

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.

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.

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.

Food and water consumption by adult female German cockroaches has been examined in relation to the reproductive cycle. Daily consumption was recorded for individual insects and was related to certain landmark events in each of four egg-case production cycles. It was shown that peaks of feeding and drinking occur during the egg maturation period, but are abruptly terminated at the appearance of each egg case. During the period when females carry the egg case, they feed and drink sparingly. The possible role played by feeding and especially drinking in the regulation of reproduction in this important pest species is discussed. RESUME Consommation d'eau et d'aliments pendant le cycle reproductif des femelles de Blattella germanica L'examen de la consommation d'eau et d'aliments par les femelles adultes de Blattella germanica a ete lie au cycle reproductif. La consommation individuelle quotidienne des insectes a ete reliee a certains evenements marquants dans chacun de quatre cycles de production d'ootheque. Les pics d'alimentation et d'absorption se produisaient pendant la periode de maturation des oeufs, mais disparaissaient brutalement a l'apparition de chaque ootheque. Pendant la periode ou les femelles portent les ootheques, elles s'alimentent et s'abreuvent parcimonieusement. Le role eventuel joue par l'alimentation et particulierement l'absorption dans la regulation de la reproduction de cet important insecte nuisible est examine.

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.

By use of a recessive-genetic marker, it has been shown that adult female German cockroaches, Blattella germanica (L.), can be successfully inseminated by more than one male. Reinsemination was demonstrated to occur rarely between the first mating and production of the first egg case, while about 20% of the females examined remated between egg cases. The total impact of second matings on the offspring produced was small because of remating infrequency and the prevalence of incomplete sperm precedence in those that were reinseminated. RESUME DETERMINATION GENETIQUE DE LA FREQUENCE DES INSEMINATIONS ET DE LA COMPETITION ENTRE SPERMATOZOIDES CHEZ BLATTELLA GERMANICA Le marquage par un gene recessif a permis de montrer que les femelles de Blattella germanica peuvent etre inseminees avec succes par plus d'un mâle. La seconde insemination a rarement lieu entre la premiere copulation et la production de la premiere ootheque, tandis que 20% des femelles examinees recopulent entre la production des differentes ootheques. L'impact global des secondes copulations sur la descendance est faible parce que, d'une part, la frequence des nouvelles copulations est limitee. et que, d'autre part, les spermatozoides de la premiere copulation incomplete des femelles reinseminees sont avantages.

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.

A pilot experiment in genetic control of the German cockroach was conducted aboard a small vessel based at Norfolk, Virginia. It utilized “sterile” ♂ ♂ (double translocation heterozygotes) whose sterility effects were due to embryonic lethality plus complete entrapment of any remaining viable embryos within the egg case. Initial infestations were reduced by insecticides prior to male release. Three releases of unmated ♂ ♂ were made at monthly intervals. Infested harborages, located in the course of insecticide application, were used as release sites. The experiment was terminated after 4 1/2 months. The results showed that released ♂ ♂ joined groups near release sites and that they competed well against wild type ♂ ♂. Apparently neither they nor ♀ ♀ ♀ ♀ with which they mated moved far from these sites. Sterility effects differed in respect to specific sites and general areas. Population growth was retarded markedly in the galley, the area of heaviest initial infestation. Terminal infestation was heaviest in the mess deck, although the highest sterility among ♀ ♀ ♀ ♀ occurred at/near the mess-deck release site (only one mess deck-infested site was found prior to initation of the experiment). It is suggested that a slight increase in the number released would have suppressed/eliminated groups inhabiting galley harborages, but that site selection was the major problem in the mess deck. Analyses of nymphal age classes and mating types among ♀ ♀ ♀ ♀ led to a hypothesis that insecticide-induced dispersal of nymphs resulted in the infestation of many new mess-deck harborages. Population growth was unchecked at these sites because they were too far removed from the sterile male release sites. RESUME Le lâcher de males steriles dans des populations naturelles de Blattella germanica Une experience pilote dans la lutte genetique contre Blattella germanica L. a ete realisee sur un petit navire encre a Norfolk, Virginie. La lethalite embryonnaire des mâles steriles utilises (heterozygotes a double translocation) etait associee au piegeage des quelques embryons viables dans les ootheques. Les pullulations initiales avaient ete reduites par des insecticides avant le lâcher des mâles. Des mâles vierges ont ete lâches a trois reprises a un mois d'intervalle. Les abris contamines, localises au cours des traitements insecticides, ont ete utilises comme lieux de lâcher. L'experience s'est achevee au bout de quatre mois et demi. Les resultats montrent que les mâles introduits rejoignent les autres blattes pres des lieux de liberation et qu'ils ne sont pas defavorises dans leur competition avec les autres mâles. Ni eux, ni les femelles avec lesquelles ils se sont accouples, ne s'eloignent apparemment de ces emplacements. Les effets de sterilisation varient en fonction des sites specifiques et des zones plus vastes. La croissance de la population est significativement retardee dans la cuisine, zone ou l'infestation initiale etait la plus elevee. L'infestation finale la plus importante est dans le pont du mess, bien que la sterilite des femelles la plus elevee s'observe a (ou pres) du lieu de liberation au pont du mess (seulement un lieu d'infestation avait ete observe sur le pont du mess avant le debut de l'experience). On pense qu'une legere augmentation de l'effectif libere aurait supprime (ou elimine) les groupes occupant des abris dans la cuisine, mais que la selection des sites etait le principal probleme pour le pont du mess. L'analyse des classes d'âges des larves et des categories de femelles accouplees laisse supposer que la dispersion des larves provoquee par l'insecticide a entraine la contamination de beaucoup de nouveaux abris dans le pont du mess. La croissance de la population n'a pas ete contenue dans ces sites parce qu'ils etaient trop eloignes des lieux de lâcher des mâles steriles.

Newly emerged adult female German cockroaches, Blattella germanica (L.) (Dictyoptera: Blattellidae) fed avermectin B1 at concentrations of 6.5 ppm and higher in the food exhibited high mortality at 10 days. Survivors of these dosages failed to reproduce. Lower dosages produced some mortality and inhibited mating and reproduction. Those individuals that did reproduce had normal-sized oothecae and the percent hatch was normal. The higher concentrations produced a marked inhibition of feeding which appeared to be related to toxicity rather than to unpalatability or repellency. When nymphs were fed avermectin B1 for short periods, higher dosages were required to produce mortality. Young nymphs were the most susceptible. Feeding inhibition also occurred in these short-term studies, but the survivors reproduced normally as did the progeny from the females fed avermectin continuously. The possible use of avermectin B1 in baits for cockroach control is discussed. RESUME Effets de la consommation d'avermectine B1 sur la mortalite et la reproduction de Blattella germanica (Dictyoptera: Blattellidae) Alimentees peu apres la mue imaginale avec une nourriture contenant 6,5 ppm ou plus d'avermectine B1, des femelles de B. germanica L. ont presente une forte mortalite a 10 jours; les survivantes ne se sont pas reproduites. Des doses plus faibles ont provoque quelque mortalite et quelque inhibition des accouplements et de la reproduction; les individus qui se sont reproduits avaient des ootheques de taille normale et le taux d'eclosion etait correct. Les concentrations plus elevees ont provoque une nette inhibition de l'alimentation, qui semblait etre plus due a la toxicite qu'a la repulsion ou au gout. Quand des larves âgees ont ete alimentees avec de l'avermectine B1 pendant de breves periodes, des doses plus elevees etaient necessaires pour provoquer la mortalite. Les jeunes larves etaient les plus sensibles. Une inhibition de l'alimentation apparut dans ces etudes a court terme, mais les survivants se reproduisirent normalement, comme le firent les descendants des femelles alimentees continuellement avec de l'avermectine. La discussion porte sur l'utilisation eventuelle de l'avermectine B1 dans des appâts pour lutter contre les blattes.

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 effects of food and water deprivation on survival and reproduction of adult female German cockroaches were examined. Females, maintained under constant conditions, were deprived of food or water following adult maturation, mating, during the oothecal incubation period, and after first oothecal hatch. It was found that both food and water deprivations caused increased mortality, delays in the reproductive cycle and decreased oothecal hatch. The relative importance of food vs. water deprivation on reproduction is discussed along with possible reproductive strategies for this species. RESUME Action du jeune et de la suppression d'eau sur la reproduction de femelles de Blattella germanica L. Les femelles, maintenues en conditions constantes, ont ete privees d'aliments et d'eau apres la maturite imaginale, l'accouplement, pendant la periode d'incubation et apres l'eclosion de la premiere ootheque. On a observe une mortalite accrue, un retard dans le cycle de reproduction et une diminution des eclosions de l'ootheque. L'importance relative de l'alimentation par rapport au jeune hydrique sur la reproduction est discutee en relation avec les strategies reproductives possibles de cette espece.

The toxic effects of 8 carbamate insecticides have been compared in susceptible and carbaryl-resistant strains of Blattella germanica (L.). Baygon® ( o -isopropoxyphenyl methylcarbamate) and UC-10854 ( m -isopropylphenyl methylcarbamate) effectively killed cockroaches of both strains with a topical method of application. Dimetilan and Isolan® (l-isopropyl-3-methyl-5-pyrazolyl dimethyl-carbamate) were less toxic, and there was little resistance to these materials in the carbaryl-resistant cockroaches. Susceptible cockroaches were killed effectively by UC-21149 (2-methyl-2-(methylthio)propionaldehyde O -(methylcarbamoyl)oxime) and Matacil® (4-(dimethylamino)-m-lolyl methylcarbamate), but there was evidence of cross resistance to these compounds in the resistant strain. Cross resistance to MC-A-600 (benzo[b]thien-4-yl methyl carbamate) occurred in carbaryl-resistant cockroaches when a topical method of application was used. There was no apparent cross resistance to this material when a dipping technique was employed for testing. Carbaryl was ineffective in killing cockroaches of either strain by the topical method; as expected, significant levels of resistance were demonstrated in the resistant strain with a dipping technique.

Large nymphs of the German cockroach have been exposed to ionizing radiation at two similar Cobalt-60 sources. The insects received dosages ranging from 100r-9600r. A number of effects of these total body irradiations became apparent shortly after exposure, and are described. Data are given on mortality occurring at the 6400r and 9600r levels, on male and female sterility at 3200r, and on the progressive decrease in numbers of reproductive females, offspring per egg case and normal ovarioles at the lower dosages. Dissections of both normal and irradiated males and females, showing visible effects of irradiation on the ovaries, testes and on spermatogenesis, are also described. An explanation of the decrease in reproductivity and the occurrence of sterility is made on the basis of the probable presence of dominant lethals and on information obtained from dissection.

Pyrethrins resistance in Blattella germanica (L.) has been examined with respect to its development, inheritance mechanism, and linkage association. Laboratory and field-collected strains were tested to determine the extent and Level of resistance. A maximum of 75 × resistance Le50 was found. The most resistant strain was crossed with an unmarked susceptible strain and 2 susceptible marked strains. The progeny from subsequent generations were tested for resistance to pyrethrins: piperonyl but oxide (1:10 vol/vol) using a dipping technique and were classified by markers in linkage tests. The results showed that pyrethrins resistance ( R-Pyr ) is inherited as a simple autosomal incompletely dominant trait. Link age studies proved that R-Pyr is linked with the Group VI trait pallid eye at a distance of 32.8±0.9 units.

A search for mutants of Blattella germanica (L.) has led to the discovery of numerous heritable traits, 9 of which are described in this paper. These include 4 which affect body structures, 1 eye-color mutant, 1 resulting in loss of ocelli, and 3 which affect body color. Data concerning the patterns of inheritance and tests for linkage are presented. The work indicates that genes controlling color and color pattern will probably be the most useful markers owing to their frequency and the viability of insects with these traits. In addition, the morphology of 2 structural mutants is highly suggestive of the presence of genetic mechanisms leading to the appearance of apparently primitive body structures.

A new pronotal-win g mutant of the German cockroach, Blattella germanica (L.), has been described and studied. Morphologically, it is similar to previously described translocation proving traits (T(9, 10)Pw) in this species. Genetically it is inherited as an autosomal semidominant lethal with somewhat reduced viability especially through the males. Cytologically the trait is associated with a terminal deficiency of the ninth pair of meiotic chromosomes, and has been named Df(9)Pw. It is linked with the group VIII markers ru and st at average map distances of 3.4 and 1.5 units, respectively, thus allowing, for the first time, a positive linkage group-autosome correlation for the German cockroach. Comparative studies of the deficiency and translocation Pw traits have produced an approximation of translocation breakpoints and centromere location on autosomes 9 and 10, establishment of the relationship between the deficiency and the translocation, and a tentative assignment of specific traits to specific locations on chromosome 9. The genetic makeup of the prowing locus is also discussed.

Malathion resistance in the German cockroach has been examined with respect to its inheritance pattern and linkage relationship. A resistant strain was crossed reciprocally with an unmarked and two marked susceptible strains. The progeny from F1, F2 and backcrosses were tested for resistance to malathion by exposure to toxicant-impregnated filter paper, and were classified according to marker traits where appropriate. Malathion resistance (R-Mal) is inherited as a simple autosomal dominant trait. Linkage studies showed R-Mal to be independent of or in group IV, pld in group VI, and T(9, 10) Pw marking both groups III and VIII. A possible malathion-resistance mechanism for this insect is discussed. Resume HEREDITE DE LA RESISTANCE AU MALATHION CHEZ LA BLATTE GERMANIQUE La resistance de la Blatte germanique au malathion est repuTEe se manifester a la fois dans les conditions naturelles et dans les lignees elevees en laboratoire. Dans le present travail cette resistance est etudiee en vue de determiner le mecanisme de sa transmission hereditaire et de commencer a etablir la carte chromosomique de ce caracTEre. Une lignee presentant un haut niveau de resistance au malathion est croisee avec une lignee sensible non marquee et avec deux autres lignees sensibles possedant un gegne marqueur. Les descendants de F1, de F2 et des croisements de retour sont tesTEs pour leur resistance au malathion en soumettant les larves a un contact avec du papier filtre impregne de malathion; ils sont classes en se rapportant aux caracTEres marqueurs. Les genes marqueurs utilises sont or sur le groupe IV, pld sur le groupe VI, et T(9, 10) Pw, marquant a la fois les groupes III et VIII. Les resultats montrent que les descendants F1 provenant de croisements reciproques sont identiques et ressemblent au parent resistant. Cette donnee ajouTEe aux resultats concernant F2 et les croisements de retour avec les parents R et S, indique que la resistance au malathion est transmise comme un caracTEre dominant, monofactoriel et porTE sur un autosome, caracTEre designe R-Mal. Les etudes relatives au linkage du caracTEre R-Mal aves les genes marqueurs, ont montre l'independance de R-Mal. Il est suggere que le mecanisme le plus probable de la resistance au malathion resulte d'une activiTE accrue de la carboxyesterase.

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.

Differential embryonic development, as seen within egg cases of the German cockroach, serves to distinguish matings of interchange heterozygotes from those of wild type. In T (3;12), one group of fertilized eggs ceases development during stage I of embryonic development; a second group, during stage VII. The frequency of the two groups correlates closely with that of adjacent-1 vs adjacent-2 disjunction. It also does not differ significantly from the expected frequency if zygotes fertilized by one of the two types of adjacent-1 gametes reach a more advanced stage of development than those of the other three types of duplication-deficiency gametes. The absence of a sex difference in the stages of embryonic death indicates that it makes little difference whether aneuploid gametes are of maternal or paternal origin.

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.

Several field-collected strains of German cockroaches, Blattella germanica (L.), were tested for resistance to bendiocarb or pyrethrins or both in the presence or absence of synergists. Large nymphs were exposed to toxicants on glass surfaces. All strains tested had high-level resistance to bendiocarb: a few were highly resistant to pyrethrins. The synergists piperonyl butoxide and MGK 264, 2-(2-ethylhexyl)-3a,4,7,7a-tetrahydro-4,7-methano-1H-isoindole-1,3(2H)-dione, both successfully negated resistance to bendiocarb and pyrethrins. Combinations of these insecticides with either synergist also effectively eliminated resistance. A commercial product (Ficam Plus) containing bendiocarb, pyrethrins, and piperonyl butoxide rendered eight bendiocarb-resistant strains susceptible. These results indicate that the resistance mechanism to both bendiocarb and pyrethrins probably may be attributed to an enhanced microsomal mixed-function oxidase system which is effectively inhibited by either synergist.

The synthesis and properties of a new double translocation heterozygote in B germanica, combining T (8;9) with the progressive interchange T (4;5;10), are described. Competitiveness and sterility data indicate that males are promising candidates for a "field" experiment in genetic control of a cockroach. Sterility from genetic load and embryonic trapping is complete. Disjunction properties of the parental interchanges are similar to those found in cells of the double males, but chiasma frequency of the interchanged chromosomes is increased. Evidence of a possible relationship between chiasma formation and disjunction type is discussed.

A new chromosome translocation in the German cockroach, Blattella germanica, was studied. Cytologically, it involves chromosomes 9 and 11 and was designated T(9,11). The approximate positions of the breakpoints were determined. In chromosome 9, the distance between the breakpoint and Df(9)Pw was measured. Genetically, linkage of T(9,11) with the chromosome 9 marker, ru, was estimated at 1.1 ± 0.6%. The new chromosome 9 breakpoint and available linkage data were used to approximate the location of the linkage group on the chromosome. An attempt to correlate map and chromosome distances indicated chromosome 9 probably has a total of at least 50 crossover units.Crosses between T(9, 11) heterozygotes and wild type showed significant sex differences in oothecal size and percent hatch. In males, the hatch data suggested preferential alternate disjunction. This was confirmed cytologically by examination of metaphase I and prophase II cells. In females, the hatch data suggested random disjunction. Similar hatch and cytological data are included for T(9,10)Pw and T(2,11)Cu. Intercrosses of T(9,11) were largely sterile, precluding the attempt to test for a viable homozygote.

Reciprocal crosses have been made between an insecticide-susceptible strain and a DDT-resistant strain of the German cockroach ( Blattella germanica (L.)) in order to study the mechanism of inheritance of resistance to DDT. Parental and F1 populations were tested with DDT by dipping in insecticide suspensions of various concentrations. Dosage-mortality data were obtained and plotted as fitted regression lines. Data from back-crosses and F2 crosses have also been obtained. It was concluded that the data are strongly indicative that one major locus and perhaps a number of modifying factors are responsible for DDT resistance. An explanation for the sexual difference in resistance is given.

During the investigation of a wing mutation in the German cockroach (Cochran & Ross 1961), sib-matings of some of these mutant roaches were made for several generations. From certain of these crosses there appeared roaches in which the body was twisted in a most unusual but consistent manner. Thus far attempts to mate twisted males and females have been unsuccessful. Twisted cockroaches have been successfully crossed with normal cockroaches, however, and normal-appearing offspring were produced. Most of these roaches were accidentally lost prior to maturation, but the trait has continued to appear in the inbred line which first produced it. More recently a few specimens have been found in other inbred lines as well. To date 15 twisted roaches have appeared in the original inbred line (3 in the F1, 3 in the F2, and 9 in the F3). A genetical basis for the trait is thus indicated, but as yet the mechanism is not clear. Therefore, the present note is primarily a morphological description of the abnormality.

In the course of certain investigations dealing with the German cockroach, Blattella germanica (L.), it became necessary to separate males and females prior to the final molt. To our knowledge, no method of sex determination in nymphs has previously been reported for this species. It is usually quite easy to distinguish the sexes in the last one or two nymphal instars by gross appearance, however, and this means has probably been used in the past. In the present paper a method is described by which it is possible to sex the nymphs in all instars including the first. The distinguishing characters are the presence or absence of a notch in the ninth sternum in the early instars and, in later instars, the presence or absence of the eighth and ninth sterna. Over 800 nymphs have been sexed by this method without error.

Genetic analyses of crosses between each of the 4 eye-color mutants, red (r) , rose (ro), ruby (rw), and pallid (pld), of the German cockroach, Blattella germanica (L .), were presented in earlier studies (Ross and Cochran 1966, 1967, 1968a). This work was reviewed recently, and it was pointed out that the several double homozygotes either resemble the paler of the parental types or are paler than either parent (Ross and Cochran 1968a). One possible exception is the double homozygote of r and ro. These traits, on the basis of their respective distances from prowing (Pw), appear to be closely linked (Ross and Cochran 1967). This assumption is supported by the fit of F2 repulsion data to a 2:1:1 ratio (Ross and Cochran 1966). No phenotypically distinct double homozygous recombinant could be identified among these F2 progeny. Of course, it is possible for linkage to be so close that none was present in the specimens examined. The purpose of this note is to report an attempt to (1) identify the phenotype of the double homozygote, (2) detect the occurrence of crossingover, and (3) make an estimate of the map distance separating these loci.