Resistant Cockroaches Research Articles

The Response of Susceptible and Pyrethroid-Resistant Blattella germanica (Dyctioptera: Blattellidae) to Shelter-Associated Cues.

In this work, it was studied the role of faeces in the location and permanence in a shelter in susceptible and pyrethroid-resistant individuals of Blattella germanica (Linnaeus 1767). Additionally, the effect of different concentrations of palmitic acid on the modulation of these behaviours was tested. A shelter constituted by a square cardboard structure was offered to susceptible as well as to resistant specimens. The shelter bases were treated with faecal extracts obtained from susceptible or resistant cockroaches, or with solutions of palmitic acid. The behaviour of susceptible as well as resistant specimens was analysed using infrared videography software. Susceptible's faecal extract attracted both specimens since the time spent by cockroaches to locate the treated shelters was lower, whereas the faecal extract from resistant insects did not elicit any effect on both strains. Faecal extracts showed an arrestant effect on both strains, suggested by the time spent inside the shelter that was significantly higher in their presence. On the other hand, treatment with palmitic acid produced an attractant or a repellent effect depending on the concentration and strain. The tested lower concentration was attractant to susceptible insects, but did not produce any effect on resistant ones. In addition, the higher concentrations did not produce any effect on susceptible individuals, but resulted repellent for resistant ones. Palmitic acid did not produce an arrestant effect on the strains as there was not an increase in time spent inside the shelter in the presence of this substance. An increase in the number of visits to the shelter and to the periphery was also observed in shelters treated with the faecal extract and with the lower concentration of palmitic acid. These results show that compounds of the susceptible faeces were attractant to cockroaches of both strains, while faecal extracts from resistant insects were not. Moreover, a dual effect of palmitic acid was observed, being attractant at low concentrations and repellent as concentration increased. Additionally, a difference in the concentration threshold at which the effect of this substance changes was observed between strains.

Role of social aggregation in the fitness cost of pyrethroid‐resistant German cockroaches

AbstractLiving in aggregations likely gives fitness benefits to resistant German cockroaches. We first investigated the trade‐offs in life‐history traits between six field pyrethroid‐resistant German cockroach strains and a laboratory susceptible strain (SUS‐1). Second, each strain was placed in groups of 2, 10, 20, 30 and 40 individuals with an equal sex ratio in each group to investigate the effect of social aggregation on fitness and overall population parameters. All resistant strains exhibited reduced nymphal survival (50%–83%) and a prolonged development period in both male (49–63 days) and female (47–62 days) nymphs when compared to SUS‐1 individuals (nymphal development period: 39 ± 2 days for male and 40 ± 3 days for female). Such fitness costs were minimized when the resistant cockroaches were in aggregations. Specifically, male (54 ± 3 days) and female nymphal development periods (52 ± 3 days) of German cockroach significantly decreased to 44 ± 1 days in the largest group. The nymphal survival was substantially enhanced (more than 80% survival) in German cockroaches with elevated cytochrome P450 monooxygenases, or both cytochrome P450 monooxygenases and esterases activities in the largest group. The effect of pyrethroid resistance on the life‐history traits of adult German cockroaches was limited; only adult male longevity was significantly prolonged. Group living did not significantly extend adult longevity and increase the number of offspring per ootheca. Contrary to expectations, the number of nymphs produced by a female and the oothecal hatchability were inversely proportional to the number of individuals in aggregations. Moreover, a lower proportion of viable oothecae were produced in German cockroaches when living in aggregations. Because of low fecundity, population parameters of German cockroaches living in aggregations (net reproductive rate and intrinsic rate of increase) were significantly lower than the parameters of those living in pairs.

Level of Pyrethroid-Resistance Associated with Cytochrome P450 Expression in German Cockroach Blattella germanica (Blattodea: Ectobiidae) in the Field Collected Strains.

Background:Cytochrome P450-dependent monooxygenases are a very important metabolic system involve in insecticide resistance. This study was conducted to find the association between the expression level of cytochrome P450 (CYP450) and permethrin-resistance level among four strains of the German cockroach Blattella germanica (L) (Blattodea: Ectobiidae).Methods:Three field strains of German cockroach with different frequency of exposure to pesticides, and a laboratory susceptible strain were used in the present study. Insecticide susceptibility bioassays were carried out to detect resistance to permethrin. The concentration of CYP450 in each strain was determined using ion-exchange HPLC chromatography. Biochemical assays was performed to analyse CYP450 activities.Results:The resistance ratios (RR) to permethrin among three field strains were 3.29, 4.10 and 6.17-fold comping with the susceptible stain. The CYP450 activity of three field strains was 1.6, 2.4 and 2.7 times higher than in the susceptible stain. The amount of CYP450 per mg of protein was significantly different between the susceptible and the three resistant strains. The resistant cockroaches showed a relatively high expression of CYP450 enzymes. A strong correlation was found between permethrin resistance level and total concentration of CYP450 enzymes.Conclusion:The results of current study show that more frequent usage of a pyrethroid insecticide cause the metabolic insecticide resistance to rise in German cockroach. Therefore, there is a ratio correlation between resistance level and monooxygenases activities in insect. Thus, the control program must be managed according to history of pesticide usage.

Characterization of the pyrethroid resistance mechanisms in a Blattella germanica (Dictyoptera: Blattellidae) strain from Buenos Aires (Argentina).

The use of chemical insecticides is the main control method for Blattella germanica worldwide. The prolonged and frequent use of insecticides produced the selection of insecticide-resistant individuals. The German cockroach is one of the most widespread urban pests in Argentina. In the last decades, resistance monitoring studies in this country demonstrated that there is a high prevalence of pyrethroid-resistant populations of B. germanica in the field. In this work, we studied the resistance mechanisms of a field-collected strain of B. germanica at toxicological, enzymatic, and molecular levels. A resistance ratio of 100 was obtained for the resistant strain when it was exposed to β-cypermethrin. The pretreatment with specific synergists (piperonyl butoxide and triphenyl phosphate) led to a significant increase in the toxicity of the pyrethroid, suggesting an involvement of oxidases and esterases in the detoxification of this insecticide. Moreover, esterase and oxidase activities in the resistant strain were 1.5-fold and 2-fold higher respectively, compared to the susceptible individuals. On the other hand, the voltage-gated sodium channel gene of the resistant cockroaches did not show nucleotidic substitutions in the domain II which are associated to knockdown resistance in this species. These results suggest that the main mechanism of resistance of the studied cockroaches' strain is metabolic, mainly due to an increase in the activity of oxidase and esterase enzymes. The results of this work in addition to other reports found in literature show that the extended use of a single active principle for cockroach control promotes the development of resistance leading to control failure in the field. In contrast, integrated pest management strategies include the use of different control tools in addition to chemical insecticides, which delay the appearance of resistance increasing the efficacy of pest control.

Topical Toxicity Profiles of Some Aliphatic and Aromatic Essential Oil Components Against Insecticide-Susceptible and Resistant Strains of German Cockroach (Blattodea: Ectobiidae).

Toxicity profiles of four aliphatic (α-pinene, cyclononanone, limonene, nerolidol), four aromatic (β-thujaplicin, carvacrol, eugenol, tropolone) essential oil components (EOCs), and permethrin were investigated against three strains of German cockroach, Blattella germanica (L.). The strains include a susceptible strain (S), and two multi-resistant strains - strains D and E. Also, a synergism bioassay, using piperonyl butoxide (PBO) was conducted. The most toxic EOCs were aromatic EOCs carvacrol, eugenol, and tropolone, followed by aliphatic EOC limonene; all had LD50 values of <0.7 mg/µl. Four of the EOCs were equally toxic against all the strains, with carvacrol being the most toxic, followed by eugenol, tropolone, and α-pinene. The other four EOCs were more toxic against strain S than against the two resistant strains. Permethrin was significantly more toxic to strain S (LD50 = 0.056 µg/µl) compared with the resistant strains (D = 2.138 µg/µl, E = 1.730 µg/µl). Toxicity of aliphatic EOCs correlated positively with their molecular weight against strain E only, whereas both molecular weight and vapor pressure of aromatic EOCs correlated significantly with toxicity in all strains. Strain D exhibited the greatest resistance (RR of 6.7) to EOCs, and synergism to the aliphatic EOC cyclononanone. Clear synergism with PBO was observed in permethrin against resistant strains, but not in all of the EOCs, suggesting multiple resistance mechanisms in the resistant cockroaches. These findings give insight on the potential of EOCs to be incorporated as parts of an IPM approach to managing insecticide resistant German cockroaches.

Changes in the Peripheral Chemosensory System Drive Adaptive Shifts in Food Preferences in Insects

A key challenge in understanding the evolution of animal behaviors is to identify cellular and molecular mechanisms that underlie the evolution of adaptive traits and behaviors in polymorphic populations under local selection pressures. Despite recent advances in fish, mice, and insects, there are still only a few compelling examples of major genes and cellular mechanisms associated with complex behavioral changes. Shifts in food or host preferences in insects, accompanied by changes in the peripheral chemosensory system, offer some of the best examples of adaptive behavioral evolution. A remarkable example is the German cockroach, Blattella germanica, a major indoor pest with a highly diverse omnivorous diet. Strong and persistent selection pressure with toxic-baits has induced rapid evolution of behavioral resistance in multiple cockroach populations. While typical cockroaches detect and accept the sugar glucose as a feeding-stimulant, behaviorally resistant cockroaches avoid eating glucose-containing toxic baits by sensing glucose as a deterrent. We review the peripheral gustatory neural mechanisms of glucose-aversion and discuss how the rapid emergence of taste polymorphisms can impede pest control efforts and affect foraging and mate-choice in adapted cockroach populations.

Efficacy of fumigators in the field against insecticide-resistant German cockroaches (Blattella germanica)

The development of resistance to insecticides represents a serious issue in the field of pest control. Several studies have reported the development of pyrethroid resistance in the German cockroach (Blattella germanica). Populations that survive after insecticide treatments are considered to have acquired resistance. As a consequence, difficulties are now associated with exterminating the German cockroach using commercial insecticides. We herein report the efficacy of Earth Red® fumigators in the field. In the present study, we investigated the efficacy of these fumigators and the permethrin resistance ratio (RR) of German cockroaches in a number of restaurants in Tokyo. Efficacy was evaluated by surveying the number of cockroaches captured using the glue trap GOKIBURI HOIHOI® before and after the fumigator treatment. The permethrin RR was assessed by topical application on the captured population. The cockroaches captured in all restaurants treated had developed permethrin resistance, with a RR that was approximately 50- to 200-fold. However, even in restaurants with resistant cockroaches, Earth Red W® and Earth Red Pro alpha® containing d,d-T-cyphenothrin, a pyrethroid, and metoxadiazone, a non-pyrethroid insecticide, were very effective. This result was attributed to d,d-T-cyphenothrin exerting a stronger flushing-out effect, which drove cockroaches out of their hiding places more effectively than permethrin, and also to the combined effects of d,d-T-cyphenothrin and the non-pyrethroid insecticide metoxadiazone. This combination caused high lethality. Propoxur also enhanced the flushing-out effect. Although pyrethroids also exerted the flushing-out effect, the combination of pyrethroids and propoxur enhanced this effect.

Toxicity of Imidacloprid in the German Cockroach (Dictyoptera: Blattellidae), and the Synergism Between Imidacloprid and Metarhizium anisopliae (Imperfect Fungi: Hyphomycetes)

German cockroaches, Blattella germanica (L.), orally exposed to solid imidacloprid baits exhibited toxic symptoms rapidly (within 30 min). However, cockroaches recovered from this toxicity. The percentage of knockdown was positively correlated and the rate of recovery was negatively correlated with concentration. In the liquid bait tests, imidacloprid produced rapid moribundity (within minutes) in all exposed cockroaches, but this moribundity was transient. Topically applied imidacloprid also produced rapid but transient moribundity in both in the laboratory-snsceptible (JWax-S) and the field-collected resistant (Muncie'86) strains. In the topical application bioassay, recovery time was dependent on cockroach strain and presence of piperonyl butoxide (PBO). Resistant cockroaches recovered faster than susceptible cockroaches; cockroaches pretreated with PBO recovered faster than those not pretreated. The JWax and Lafayette (field-collected) strains were killed significantly faster with The entomopathogenic fungus, Metarhizium anisopliae alone, or Metarhizium + solid imidacloprid bait than imidacloprid bait alone in both the choice and no-choice bioassays. Combinations of direct contact to the conidia of Metarhizium and feeding on imidacloprid bait indicated synergy when compared with the activity of the individual components. We found no differences in mortality when the JWax cockroaches fed on either 500 or 1,000 ppm imidacloprid baits. The presence of alternate food slowed the lethal time for imidacloprid against the JWax and Lafayette strains. Both strains were killed significantly faster when cockroaches lind on imidacloprid after a topical application of spore suspensions of Metarhizium than when insects fed on imidacloprid bait alone, indicating possible synergistic interaction (i.e., greater than expected mortality) between imidacloprid bait and Metarhizium The mortality of cockroaches inoculated topically with spore suspensions of Metarhizium increased significantly with an increase in the number of fungal spores. No significant differences in daily cockroach mortality were detected among imidacloprid concentrations for each Metarhizium dose. Imidacloprid; d bait alone has a limited potential for use in controlling cockroaches, but it may have a potential if used in combination with a fungal pathogen such as Metarhizium.

Multiple Mechanisms of Pyrethroid Resistance in the German Cockroach, Blattella germanica (L.)

Pyrethroid-resistant German cockroaches known as the Village Green strain were compared to a susceptible (Orlando Normal) strain in respect to possible mechanisms of insecticide resistance. Male adults of the resistant strain weighed 15% more than susceptible roaches of the same cumulative age from adult eclosion. Based on the topical application of different concentrations of permethrin, the KD 50 for resistant roaches was 20-times greater than that for susceptible insects. Reduced penetration of [ 14C]permethrin was observed in resistant insects during 24 hr after treatment along with increased in vivo metabolism as compared with susceptible controls. The cytochrome P450 content and monooxygenase activity when measured with methoxyresorufin and benzo[ a]pyrene was elevated in resistant roaches by as much as 6.9-fold but no difference was found with benzphetamine. The glutathione transferase activity was also increased (1.6-fold with chlorodinitrobenzene) and elevated esterase activity was detected with the substrates, 1-naphthyl acetate (1.7-fold) and p-nitrophenyl acetate (2.1-fold). Using isoelectric focusing, a novel E 2 esterase was identified in resistant cockroaches not found in the susceptible population. E 2 may be partly responsible for the increased esterase activity observed in resistant roaches. Increased esterase activity toward p-nitrophenyl acetate was used to develop a kinetic, diagnostic assay that could rapidly discriminate resistant from susceptible individuals.

Strain differences in the response of German cockroaches (Dictyoptera: Blattellidae) to emulsifiable concentrates.

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.

Residual Efficacy of Chlorpyrifos and Diazinon Formulations for German Cockroaches (Orthoptera: Blattellidae) on Panels Placed in Commercial Food Preparation Areas2

Ceramic and stainless steel panels were treated with chlorpyrifos (Dursban LO or ME) or diazinon (Knox Out 2FM) and aged in a commercial kitchen. Type of surface (ceramic tile or stainless steel) did not significantly affect residual performance of formulations used for control of adult male German cockroaches, Blattella germanica (L.). Microencapsulation stabilized the residues of both chlorpyrifos and diazinon and caused 100% mortality of susceptible German cockroaches for 8 weeks and resistant cockroaches for 4 weeks. The emulsifiable formulation provided only 0–67% mortality after 1–2 weeks.

Evaluation of Experimental Propoxur Baits, 1988

Abstract Three experimental baits were prepared using peanut butter, flour, Propoxur, and boric acid. Effectiveness of the experimental baits on susceptible and resistant cockroaches was compared to commercial Combat bait stations containing 1.65% hydramethylnon. The experimental baits tested were 2% Propoxur in peanut butter, 2% Propoxur + 25% flour in peanut butter, and 2% Propoxur + 40% boric acid in peanut butter. Fifty susceptible or Propoxur-resistant adult male German cockroaches were introduced into 22- by 12- by 8-inch clear plastic cages with water, harborage, dog food, and experimental bait that had been placed in a sealed plastic bait tray. Experimental conditions were maintained at 25°C with a photoperiod of 12:12 (L:D). Insects were considered dead if they did not move when gently prodded with forceps. Mortality readings were taken hourly for the first 8 h, and daily thereafter for 1 wk. Probit analyses generated LT25, LT50, LT95 values in h, and 95% fiducial limits for each treatment.

Suppression of German Cockroach (Orthoptera: Blattellidae) Populations with Cypermethrin and Two Chlorpyrifos Formulations1

Cypermethrin and two new chlorpyrifos formulations (Dursban LO and ME) were evaluated in the laboratory and field to determine effects on German cockroaches, Blattella germanica (L.). Initially, continuous exposure of adult males on cypermethrin- or chlorpyrifos-treated surfaces for 24 h resulted in total mortality of susceptible cockroaches. Dursban LO was less effective than the ME formulation 2 wk after treatment. Multiresistant cockroaches were more difficult to kill with both chlorpyrifos formulations, but cypermethrin killed 100% of both strains within 30 min. In modified choice arena tests, cypermethrin killed 100% of German cockroaches (susceptible and multi resistant). Chlorpyrifos applied as a micro emulsion (Durban LO) and as a micro encapsulated (Durban ME) formulation resulted in 92% and 95% mortality of susceptible cockroaches and 81% and 39% mortality of resistant cockroaches, respectively. Weekly sampling of populations demonstrated that chlorpyrifos (Durban LO) resulted in significantly fewer cockroaches per harbor ager than untreated controls, whereas chlorpyrifos (Durban ME) results were variable. Field evaluations resulted in percent reductions of 91% for cypermethrin, 66% for chlorpyrifos (Durban ME), and 15% for chlorpyrifos (Durban LO) at 4 wk after treatment.

Effects of propoxur treatment on populations containing susceptible and resistant German cockroaches (Orthoptera: Blattellidae).

Three experiments on the effects of propoxur treatment on German cockroach, Blattella germanica (L.), populations were conducted on an inactive ship. In one, all members of the population except adult males were from a resistant field strain; in the others, populations were equally divided between genetically marked susceptible and resistant cockroaches. Each population was established at a known site. Treatment with propoxur caused immediate dispersal. Most movement was into nearby untreated locations. The majority of cockroaches in each population returned to their original site in 1–2 weeks. However, small groups appeared and remained in previously uninhabited harborages. Some of the new spot infestations were near the original site; others were in relatively distant locations. No difference in pre- or posttreatment distribution of susceptible and resistant cockroaches was found. Kill of resistant cockroaches did not appear to vary greatly with age or sexclass. In the susceptible strain, mortality for adults was considerably higher than nymphal mortality. The experiments demonstrated that a 7- to 8-fold resistance to propoxur reduced mortality of adults and nymphs compared with that of susceptible cockroaches under conditions where the cockroaches were free to escape from the insecticide treatment.

Difference in the picrotoxinin receptor between the cyclodiene-resistant and susceptible strains of the german cockroach

As a result of toxicity tests, it was established that all cyclodiene-resistant strains of the German cockroach are also resistant to picrotoxinin, a plant-origin neurotoxicant. Two of the cockroach strains which exhibit a distinct cross-resistance pattern to picrotoxinin (i.e., LPP and FRP) are the ones that have been purified genetically by backcrossing against the susceptible (CSMA) strain. This cross-resistance pattern appears to be specific to picrotoxinin and does not extend to other neuroexcitants such as bicuculline, beta-bungarotoxin, and DDT. The nervous system of the resistant cockroach was found to be less sensitive to picrotoxinin. Furthermore, it was determined that nerve components from the resistant cockroaches have significantly lower binding capacity to [ 3H]α-dihydropicrotoxinin. The most likely explanation for the above phenomenon is that these cockroaches have developed the cyclodiene resistance by altering the nerve receptor for picrotoxinin.

Comparative Life Histories of Chlordane-Resistant and Nonresistant German Cockroaches12

The life histories of chlordane-resistant field-captured and chlordane-susceptible laboratory-reared Blatella germanica (I,,) were compared. German cockroaches highly resistant to chlordane, were collected en masse from Raleigh. N. C., dwellings (summer and winter) and transferred to a room maintained at 26.7°C and 55% relative humidity for comparison with a susceptible colony. There was no significant difference in the egg incubation period, 25-29 days. Nymphs emerged from egg cases while attached, and up to 15 days after detachment. Egg case mortality was highest among winter-collected females. Fewer nymphs emerged from egg cases of winter-collected females than from the susceptible females, and more nymphs emerged from egg cases of summer-collected, than from winter-collected females. No difference existed in the F1, generations. A fairly constant number of nymphs emerged per case for the first 3 egg cases of a female and decreased in succeeding cases. Development of nymphs from a given egg case to first adult and to all adults did not differ, with means of 59 and 99 days, respectively. Sex ratio approached 1:1. No correlations in time existed between the introduction of a virgin male to a virgin female and the first visible egg case, or between successive cases by a female. Fewer egg cases per female were produced by susceptible females than by females developing from summer-collected nymphs. Females maturing from resistant nymphs lived longer than their susceptible counterparts. Environmental conditions, such as food, water temperature, humidity, type of activity in infested buildings, and control procedures may be the cause of reported “change in habits and biology of resistant cockroaches,” rather than the change being due to the development of resistance.

Alicyclic and heterocyclic carbamates

The development of heterocyclic carbamates with insecticidal activity is illustrated. The variation of compounds with a repellent effect range from aromatic amides to carbamates with pronounced insecticidal properties. Enolisable heterocyclic compounds, based on 3-methyl-pyrazolon or hydroxy-pyrimidine, were tested, and dimetilan (2-dimethylcarbamoyl-3-methylpyrazolyl-5-dimethylcarbamate) with strong stomach poison activity against houseflies, and PyramateR (2-n-propyl-4-methyl-pyrimidyl-6-dimethyl-carbamate) with a good contact activity against houseflies and a low toxicity for warm-blooded animals, were developed. The synthesis and purification of these two compounds led under certain conditions to isomers. A comparison of the insecticidal and toxicological properties is given. The insecticidal activity of a further class of carbamates (1-alkylthio-methyl-3-methyl-pyrazolyl-5-dimethylcarbamates) is specified. For this type of compound, isomers with differences in activity and toxicity were obtained. A further class of compounds of low mammalian toxicity is obtained by condensation of 3-methyl-pyrazolyl-5-dimethylcarbamate with esters of the acrylic acid: they have a pronounced effect on Diptera and Homoptera. More favourable lack of toxicity toward warm-blooded animals combined with a good insecticidal activity was observed in monomethylcarbamates compared with the corresponding dimethyl analogues, but the monomethylcarbamates proved to be much more susceptible to hydrolysis. The search for new compounds without this disadvantage led to other carbamates, i.e. those of the quinolines, from which GS 13798 is so far the most noteworthy representative. Despite its rather narrow spectrum, it has outstanding activity against sensitive and resistant cockroaches.

Penetration, excretion, and metabolism of carbaryl in susceptible and resistant German cockroaches.

Carbaryl metabolism was compared between susceptible and resistant, Blattella germanica (L.). Rates of penetration, excretion, and metabolism and nature of metabolites were determined at various time intervals after topical application of known amounts of carbaryl. Both susceptible and resistant cockroaches degraded carbaryl to 1-naphthol and 1-naphthol conjugates. Other unidentified metabolites were detected in minute quantities. Penetration of carbaryl was slower, less carbaryl was retained in the tissues, and more carbaryl was excreted in the resistant cockroaches. Slightly larger amounts of internal and excreted 1-naphthol were found in the susceptible cockroaches but more conjugated 1-naphthol was recovered from resistant cockroaches. It is hypothesized that more rapid hydrolysis of carbaryl to 1-naphthol and subsequent conjugation play an important role in the carbonyl-resistance. Slower penetration and more rapid excretion of carbonyl in the resistant cockroaches may be minor contributing factors to the resistance.

Insecticide absorbed by the Central Nervous System of Susceptible and Resistant Cockroaches exposed to Dieldrin

PENETRATION and metabolism studies carried out in this Department on susceptible and resistant houseflies, using the sulphur analogue of dieldrin or a non-insecticidal bromine derivative of aldrin1; aldrin, dieldrin, isodrin or endrin2; failed to reveal any differences between the strains which would explain the mechanism of resistance. There is some evidence that dieldrin acts on the central nervous system of susceptible insects3 and it seemed possible that dieldrin failed to reach the sensitive cells of this system in the resistant insect due to some internal local barrier, for example, a dieldrin impermeable neural lamella.

The Dehydrochlorination of DDT by Resistant Cockroaches

The Dehydrochlorination of DDT by Resistant Cockroaches