Measuring cypermethrin resistance in the German cockroach (Orthoptera: Blattellidae).

Cypermethrin resistance in the German cockroach, Blattella germanica (L.), was assessed by tests of surface contact and topical application. Topical application provided the most sensitive measure of resistance in a field strain. The resistance ratio (RR) measured by topical application was 122.6 for cypermethrin at LD50. As measured by surface contact, the resistance ratio at KT50 was 2.9. Differences between the walking movement of cockroaches of susceptible (VPI) and field (RHA) strains on deposits of cypermethrin influenced KT50 values. A bioassay with unrestricted movement resulted in RHA strain cockroaches accumulating a larger dose on the tarsal pads and subsequent reduction of the resistance ratio at KT50. Less walking by the VPI strain resulted in less insecticide accumulation on their tarsal pads. On a bioassay in which movement was restricted, the amount of insecticide accumulating on the tarsi was equalized, resulting in an increased resistance ratio at KT50. Differences in susceptibility were more accurately measured when the two strains were topically treated (either on the thorax or the tarsal pads) with known doses of insecticide.     

Evaluation of attractants for monitoring populations of the German cockroach (Dictyoptera: Blattellidae)

Lures that are used to attract German cockroaches, Blattella germanica (L.), to traps were compared in olfactometer assays in the laboratory and in trapping experiments in cockroach-infested homes and a swine farm. In olfactometer assays, AgriSense GP-2 was the most attractive lure, followed by peanut butter, and distiller's grain. Other lures, including Trapper tablet; Victor pheromone, a crude fecal extract that ostensibly contains B. germanica aggregation pheromone; and Victor food lure elicited upwind orientation from <50% of the test insects. Peanut butter and distiller's grain were equally attractive in trapping experiments in swine production barns and they captured significantly more cockroaches than the GP-2 tablet or the Victor pheromone lure; the commercial lures failed to attract significantly more cockroaches than the unbaited control traps. When tested against blank controls, cockroaches preferred to rest in shelters that contained the aggregation pheromone-based lure (Victor), but this lure was the least attractive to cockroaches in olfactometer assays. These results do not support claims that commercial crude fecal extracts attract cockroaches to traps, and they highlight a need for developing more attractive lures for detection of cockroaches and for monitoring populations.     

Influence of fenoxycarb on German cockroach (Dictyoptera: Blattellidae) populations in public housing

In a study examining three application rates for fenoxycarb, new interpretations of population age structure in relation to sterility levels and population reductions were used to establish important concepts in the management of German cockroaches, Blattella germanica (L.), with juvenoids. No significant differences in population reductions were noted when 0.5%, 0.25%, or 0.125% fenoxycarb was used to supplement propetamphos. However, significant differences in levels of induced sterility and in the age structure (measured as nymph-to-adult ratios) of treated populations were detected. The 0.125% rate caused lower, less consistent levels of sterility than the two higher rates, which maintained approximately 80% sterility from 4.5 mo and beyond. In addition, the 0.125% rate did not significantly reduce nymph-to-adult ratios in treated populations relative to that caused by the propetamphos alone (positive control). The two higher rates significantly reduced nymph-to-adult ratios, thereby lowering biotic potential and the capacity of a population to rebound from suppression. A relationship between the level of sterility induced by juvenoids and reductions in nymph-to-adult ratios permitted formulation of a biological action threshold for regulating treatment. This action threshold appears to be more meaningful than time intervals for scheduling retreatments in the long-term management of German cockroaches with juvenoids.     

Trail-following behavior in the German cockroach (Dictyoptera: Blattellidae)

The trail-following behavior of the German cockroach, Blattella germanica (L.), was evaluated by comparing the distance between cockroach movement paths and preapplied "trails" of fecal extract. For each cockroach group tested (adult males, females, gravid females, and late instars), the mean perpendicular distance of the cockroach from the trail was significantly less than the distance from a control trail. The results indicated that the German cockroaches did exhibit trail-following behavior. Trail- following accuracy varied among the cockroach groups. The mean distance from the fecal trail ranged from 18.45 to 110.05 cm with adult males < or = adult females < or = late instars < gravid females. Very dilute fecal extract could still induce trail-following behavior in adult male cockroaches. A 5.6% concentration of fecal extract in methanol was able to induce trail-following behavior in 50% of the cockroaches. Although German cockroaches have demonstrated trail-following behavior, fecal trails are still not thought to be actively deposited. Rather, the passive distribution of fecal material within the home range results in the accumulation of trails along frequently traveled routes (i.e., between resources and the cockroach harborage).     

Comparative toxicity and repellency of microencapsulated and other liquid insecticide formulations to the German cockroach (Dictyoptera: Blattellidae)

Responses of German cockroaches, Blattella germanica (L.) (Dictyoptera: Blattellidae), to microencapsulated (ME) formulations of six insecticides (bifenthrin, chlorpyrifos, cyfluthrin, deltamethrin, lambda-cyhalothrin, and permethrin) were compared with emulsifiable concentrates (EC) (chlorpyrifos, cyfluthrin, deltamethrin, and permethrin) or ready-to-use (RTU) formulations (bifenthin and lambda-cyhalothrin). Two rates were tested per comparison. Baseline toxicity (LT50 value) was determined by continuous exposure to residual deposits. Repellency, toxicity (LT50), and performance index (PI) values were determined using Ebeling choice boxes. Baseline toxicity of the permethrin formulations was similar, but all other active ingredients had significant toxicity differences at one or both formulation x dose comparisons. Baseline toxicity and repellency were negatively correlated. Choice box LT50 and the time to reach 50% of the maximum PI were positively correlated. The maximum PI was positively correlated (P < 0.06) with baseline LT50 and negatively correlated (P < 0.07) with repellency. Chlorpyrifos had the lowest repellency except for the EC at 0.25%. Bifenthrin ME and lambda-cyhalothrin ME had greater PI values than comparative RTU formulations. Cyfluthrin EC at 0.03% and deltamethrin ME at 0.01% had significantly lower PI values than comparison treatments. Permethrin PI value for the EC at 0.03% exceeded that for the ME, but at 0.05% the ME had a significantly greater PI. These data demonstrate the difficulty in making generalizations about the relative performance of ME compared with EC or RTU formulations. Variable results observed within, and between, formulations may be influenced by application rate, formulation type, other formulation components, and the toxicity-repellency of the active ingredient.     

Cross-resistance between dieldrin and fipronil in German cockroach (Dictyoptera: Blattellidae)

The toxicity of fipronil and dieldrin was determined in one susceptible laboratory strain and seven insecticide-resistant field-collected strains of Blattella germanica (L). The Zo960302 and Ga021001 strains were 1,270- and 2,030-fold resistant to dieldrin and 15- and 14-fold resistant to fipronil. The Su960304 and Od010803 strains were 15- and 13-fold resistant to dieldrin and two- and four-fold resistant to fipronil. Three strains showed no or a low level of resistance to dieldrin and fipronil. Crosses were performed between the susceptible strain Danish Pest Infestation Laboratory (DPIL)-SUS and the resistant strains Zo960302 and Su960304 and resistance to dieldrin and fipronil were intermediate compared with the susceptible and the resistant strains. Backcrosses to both of the parental strains showed cosegregation of dieldrin and fipronil resistance. The toxicity of dieldrin and fipronil was correlated when compared at LD50, and 93% of the observed variation in LD50 of fipronil can be ascribed to variation among predictions based on the value of LD50 of dieldrin. The frequency of the A302S substitution in the resistance to dieldrin (Rdl) gene in the highly dieldrin- and fipronil-resistant strains Zo960302 and Ga021001 and the moderately resistant Su960304 was 0.97, 1.0, and 0.38, respectively. We consider the connection between the frequency of the Rdl mutation and dieldrin and fipronil resistance a causal connection and not merely a coincidence.     

Differences in the response of German cockroach (Dictyoptera: Blattellidae) field strains to vapors of pyrethroid formulations.

Late-instar German cockroaches from an insecticide-susceptible field strain (Fairbanks) and four pyrethroid-resistant field strains were exposed to vapors of a cyfluthrin flowable concentrate (FC) and the formulation blank (formulation without the active ingredient). Experiments with other pyrethroid formulations were done with the Fairbanks strain and an insecticide-resistant field strain (K-851) because these strains exemplified the maximum interstrain variation in experiments with the FC. In these experiments, I used a cyfluthrin wettable powder (WP) and its blank, a cyfluthrin emulsifiable concentrate (EC), and a permethrin aerosol and its blank. Vapors of the FC and its blank caused the most rapid dispersal. Dispersal induced by vapors of the WP, EC, and aerosol formulations was low and variable. In general, less of a dispersal response occurred in the resistant strains than in the susceptible strain. The strain mostly highly resistant to pyrethroids (K-851) dispersed slowly compared with the other resistant strains in experiments with the FC and its blank. When vapor-induced dispersal was relatively low (less than 50%), a trend was still evident towards less dispersal in the K-851 strain than in the Fairbanks strain. Although dispersal in experiments with the FC did not differ significantly from that in experiments with the FC formulation blank, mean percentage dispersal at the end of the experiments was higher with the formulation blanks than with the complete formulations in experiments with the WP and permethrin aerosol.     

Secondary transmission of toxic baits in German cockroach (Dictyoptera: Blattellidae)

The death rates of three toxic gel baits (fipronil bait, 0.05%; hydramethylnon, bait 2.15%; and abamectin B1 bait, 0.05%) were estimated in Blattella germanica (L.). After ingestion, all three baits killed similar proportions of cockroaches, but they died more rapidly after ingestion of fipronil bait than after ingestion of abamectin B1 bait or of hydramethylnon bait. Laboratory experiments evaluated the impact of secondary transmission of fipronil bait and hydramethylnon bait. Mortality rates caused by secondary transmission were higher for fipronil bait than for hydramethylnon bait. Under controlled laboratory conditions, secondary transmission occurred mainly through direct contact with, or ingestion of, traces of baits dispersed in the environment by contaminated cockroaches. These traces were either deposited by "trampling" in the environment or on dead contaminated cockroaches. Social interactions and cannibalism played a minor role in secondary transmission of these two baits.     

Aspergillosis in German cockroach Blattella germanica (L.) (Blattoidea: Blattellidae)

Natural infection of Aspergillus flavus was observed in adults of Blattella germanica. Though the adult insects exhibited no external symptoms, they became hypoactive and later died. The dead and experimentally infected insects repeatedly yielded Aspergillus flavus in culture on Czapek's medium. Direct microscopic observation of the tissues of infected insects revealed fungal material. The blood films stained with Giemsa stain showed granulocytes (GRs) engulfing fungal hyphae. A remarkable increase in GR and plasmatocyte (PL) counts occurred in differential haemocyte counts (DHCs) of the infected insects. Two main types of immunological responses of the insect noticed were phagocytosis and encapsulation. DHC showed maximum involvement of GRs and PLs in immune mechanism. This revised version was published online in June 2006 with corrections to the Cover Date.