Nutritional status and insecticide tolerance in German cockroaches (Orthoptera: Blattellidae).

The interrelationship of two extrinsic factors-nutrition and pesticide exposure-was studied in German cockroaches, Blattella germanica (L.). Amount of dietary protein had no effect on susceptibility of male German cockroaches to propoxur and chlorpyrifos; however, the source of protein produced significant changes in insecticide susceptibility. Increased total body lipids, carbohydrates, and uric acid may have resulted in increased tolerance to these insecticides. Three days of food or water deprivation (or both) caused significant differences in susceptibility to chlorpyrifos and propoxur.     

Efficacy of chitin synthesis inhibitors on nymphal German cockroaches (Dictyoptera: Blattellidae)

Second- and fifth-instar Blattella germanica (L.), fed the chitin synthesis inhibitors triflumuron, chlorfluazuron, hexafluron, and UC 84572 (structure not disclosed) were examined for mortality and developmental abnormalities. All compounds were active against B. germanica (L.), with lower diet concentrations being required to kill second instars compared with fifth instars. Chlorfluazuron was significantly more active against second and fifth instars (LC50 = 0.000191 and 0.000363% AI, respectively for the second and fifth instars). UC 84572 also killed nymphs at extremely low concentrations (LC50 = 0.000508 and 0.000754% AI, respectively, for second and fifth instars). LC50's for hexafluron and triflumuron against fifth instars were more than 1,000 times higher than that for chlorfluazuron. Sensitive periods of exposure were determined by comparing effects when four different age classes of fifth instars (1-, 4-, 7-, and 10-d old) fed on the compounds for 3 d. Triflumuron was most effective when ingested during the first three age classes and hexafluron was most effective during the last three age classes. Chlorfluazuron and UC 84572 were most effective when ingested during the second age class (days 4-6). Adults surviving exposure during the fifth instar were often deformed and weak; they died at a greater rate than the controls. However, most surviving adults were able to reproduce normally.     

Effect of sublethal propoxur exposure on male German cockroaches (Orthoptera: Blattellidae) and their feeding behavior

Exposure of male German cockroaches, Blattella germanica L., to propoxur produced significant water loss at 2 and 24 h after treatment. This effect was dependent upon the state of hydration before insecticide exposure. Hydrated males lost as much as 10% of their total body mass in the form of water; dehydrated males lost about 4.3%; and untreated controls lost approximately 1.8% during the same time period. No significant compensatory feeding responses were observed 1-4 d after treatment. Water depletion associated with propoxur exposure resulted in increased water consumption for the first 2 d after treatment and then reached a plateau for the duration of the study. Males consumed water daily regardless of insecticide exposure.     

Efficacy of abamectin fed to German cockroaches (Dictyoptera: Blattellidae) resistant to pyrethroids

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.     

Ovicidal activity of noviflumuron when fed to adult German cockroaches (Dictyoptera: Blattellidae)

Ovicidal activity of the benzoylphenylurea noviflumuron was evaluated in the laboratory on three adult groups (virgin females, virgin males, and fertilized, nongravid females) of the German cockroach, Blattella germanica (L.), through ingestion of treated bait. Novifumuron caused significant ovicidal effects at concentrations ranging from 10 to 5000 ppm after 5-d feeding exposure to virgin and fertilized females. Untreated females produced little or no viable oothecae when mated with virgin males that had previously ingested bait (5-d exposure) with 1000 ppm or 5000 ppm noviflumuron. The highest tested concentration of noviflumuron (5000 ppm) caused 100% ovicidal activity through two ovarian cycles for all three adult groups. Noviflumuron seems to have broader ovicidal activity against B. germanica than reported for other benzoylphenylurea insecticides and can potentially impact cockroach populations through a combination of nymphal mortality and ovicidal activity.     

Effects of hydroprene exposure on the physiology and insecticide susceptibility of German cockroaches (Orthoptera: Blattellidae).

We determined nonlethal physiological effects of hydroprene on the German cockroach, Blattella germanica L., and the effects of hydroprene exposure on German cockroach susceptibility to traditional insecticides. Live and dry weights of German cockroach adults exposed as nymphs to the juvenile hormone analog hydroprene increased significantly (6-35%) in both sexes. The change in weight was affected by hydroprene dose and time after adult emergence. Hydroprene treatment did not affect total body lipids and carbohydrates consistently. However, total body urates of males and females increased significantly. The susceptible and multiresistant German cockroach strains were significantly more susceptible to propoxur at the lower hydroprene application rate (0.697 mg per tub) than the untreated cockroaches. Hydroprene application also significantly lowered the LD50 for chlorpyrifos of the multiresistant strain at the lower hydroprene application rate. However, hydroprene failed to affect chlorpyrifos susceptibility of the susceptible strain.     

Effects of moisture on the toxicity of inorganic and organic insecticidal dust formulations to German cockroaches (Blattodea: Blattellidae)

Toxicity of boric acid (40-99% [AI]), silica gel, eugenol, and deltamethrin dust formulations to adult male German cockroaches, Blattella germanica (L.), was evaluated at five different relative humidities ranging from 0 to 100% and in the presence of 0 to 1 ml of water. Victor boric acid dust was generally the most toxic boric acid formulation at all relative humidities, despite having the lowest percentage (40%) of boric acid; however, this was the only formulation to have sucrose and other edible ingredients. There was no consistent effect of relative humidity on dust toxicity; LT50 values of Roach Prufe (98% boric acid), Victor, and Drione (silica gel and synergized pyrethrins) increased significantly linearly with relative humidity, whereas other formulations were unaffected. The LT50 values of all boric acid-based dust formulations declined exponentially when wetted with increasing volumes of water. Water did not affect the toxicity of deltamethrin and eugenol dusts, but it caused a linear decline in toxicity of silica gel (Dri-Die). The toxicity of a formulation containing silica gel and synergized pyrethrins (Drione) increased exponentially with increasing amounts of water. Moisture in the form of relative humidity does not strongly affect the toxicity of most insecticidal dust formulations. Presence of water, however, increases the toxicity of boric acid dusts and Drione. Toxicity of the hydrophobic deltamethrin (DeltaDust) and eugenol (EcoPCO D) dusts were unaffected by water.     

Toxicity of several insecticide formulations against adult German cockroaches (Dictyoptera: Blattellidae)

Toxicity of bendiocarb, chlorpyrifos, cyfluthrin, cypermethrin, fenvalerate, hydramethylnon, malathion, propetamphos, propoxur, and pyrethrins against the adult German cockroaches, Blattella germanica (L.), was investigated. At LD50, cyfluthrin was the most toxic insecticide to adult males (0.53 microgram/g), adult females (1.2 micrograms/g), and gravid females (0.85 microgram/g). Malathion was the least toxic insecticide to adult males (464.83 micrograms/g), adult females (335.83 micrograms/g), and gravid females (275.90 micrograms/g). Males and gravid females were generally more sensitive than nongravid females to the insecticides that we tested. In tests with malathion, however, males were more tolerant. The order of toxicity of the insecticide classes varied among the stages of adult German cockroaches. The order of toxicity for males and nongravid females was pyrethroids greater than pyrethrins = organophosphates (except malathion) greater than carbamates = amidinohydrazone. The order of toxicity for gravid females was pyrethroids greater than pyrethrins = organophosphates (except malathion) greater than carbamates greater than amidinohydrazone. These differences in toxicity suggest that sex differences should be considered when determining insecticide toxicity for German cockroaches.     

Mineral oil and aliphatic alcohols: toxicity and analysis of synergistic effects on German cockroaches (Dictyoptera: Blattellidae)

Two mineral oils and 12 linear primary alcohols were studied, alone and in combination, to determine their contact toxicity to adult German cockroaches, Blattella germanica (L.) (Dictyoptera: Blattellidae). The more toxic oil, PD23 (LD50 = 1.45 mg per cockroach) was used for combination studies. Alcohols with carbon chain lengths of C3 and C8 through C12 were the most toxic, with LD50 values ranging from 0.3 to 0.6 mg. C1 (methanol) and C14 (1-tetradecanol) were least toxic, with LD50 values of 2.35 and 1.75 mg, respectively. Eight of the 12 combinations of a nonlethal dose of PD23 oil with an LD10 dose of alcohol produced significantly greater mortality than predicted under the assumption of additive effects. A sample of five synergistic oil + alcohol combinations, covering most of the alcohol carbon chain length range over which synergy occurred, was further studied by calculating LD50 values for three fixed mixture ratios (80:20, 50:50, and 20:80) of each combination. Results were analyzed using both graphical techniques (isobole analysis) and by nonlinear regression. At least one, but not necessarily all, of the three fixed ratio combinations of each oil + alcohol pairing indicated synergy. The conclusions drawn from the isobole and regression analyses were consistent.     

Contamination affects the performance of insecticidal baits against German cockroaches (Dictyoptera: Blattellidae)

The effects of contamination of insecticidal bait formulations, by using mint oil and silica aerogel, were evaluated in a series of laboratory experiments against the German cockroach, Blattella germanica (L.). Bait consumption at 3 d for uncontaminated baits ranged from 0.01 g for Avert dust to 0.399 g for Combat dry bait with hydramethylnon presented in a station. LT50 values for uncontaminated gel bait deposits ranged from 0.4 d for PreEmpt containing imidacloprid to 4.1 d for Maxforce containing hydramethylnon. As a group, significantly more gel bait was consumed than solid formulations even when both formulations had similar concentrations of the same active ingredient. As a result, gel baits were significantly more toxic than solid formulations. Application of mint oil directly to bait deposits significantly decreased bait consumption and increased overall LT50 values. When bait formulation types were examined individually, there was no difference in consumption or toxicity between contaminated and uncontaminated gel formulations. Contaminated solid baits, however, had significantly greater LT50 values and less consumption than uncontaminated solid baits. Gel formulations probably absorbed the contaminants and removed them from the surface of the bait deposits resulting in normal bait consumption and toxicity. Gel and solid bait deposits, inside plastic exposure stations or alone with no station and placed onto mint oil-contaminated substrates, had significantly lower bait consumption and greater LT50 values than baits placed on uncontaminated substrates. Contamination of a baited area is more likely than contamination of just the bait deposit and therefore a more realistic test of the effects of contamination on bait performance. The importance of contamination to the performance of cockroach baits is discussed.     

Behavioral responses and mortality in German cockroaches (Blattodea: Blattellidae) after exposure to dishwashing liquid

Behavioral responses and mortality of the German cockroach, Blattella germanica (L.), after exposure to solutions of common household dishwashing liquid diluted in tap water without other known insecticidal active ingredients are described. Soap solutions of 0.05, 0.1, 0.25, 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0% were tested on first and second instars, fifth and sixth instars, and adults. Cockroaches were treated individually or in groups. Behavioral observations after treatment included an immediate knockdown period, an awakening and a struggle period, an unresponsive period, and either death or recovery between 30 min and 18 h after treatment. Probit analysis gave an excellent fit of unresponsive rates 18 h after treatment with the various soap concentrations, and LD50 and LD99 values were calculated to be 0.4 and 3.0% soap, respectively. Adult females were the most difficult to kill, but at soap concentrations of 1% or higher, 95% or greater unresponsiveness and death occurred. Soap concentrations of 3% or greater resulted in 100% unresponsiveness after 3 min, and eventually resulted in 100% mortality within 72 h for all adults and nymphs treated. Observations on the mode and site of action for soap are consistent with the blockage of spiracles and/or tracheae that results in asphyxiation and death. Future investigations into the efficacy of soaps against other arthropod groups are warranted and may be beneficial in certain situations.