Evaluation of secondary killing effect of Imidacloprid Gel Baits to control Blattella germanica (Linné 1767) (Blattaria: Blattellidae)

Blattella germanica (L.) (Blattodea: Blattellidae) is one of the major household pests worldwide, commonly named German cockroach. Application of gel baits is one of the most efficient management methods. This study investigated the effect of 3 commercially available Imidacloprid gel baits on the palatability of dead cockroaches and, consequently, on the efficacy of secondary killing. German cockroaches killed by the gel baits and others killed by freezing were offered to conspecifics, the numbers of cannibalistic cockroaches and dead cockroaches, as well as weight loss were recorded. Despite the content of Imidacloprid is identical in all the baits, the palatability of the cockroach killed by the gel consumption and used as food was different between the 3 commercial products, with consequences on the secondary killing effect. These results suggest as the bait co-formulants play an important role not only on the palatability of the bait but also in the palatability of the dead cockroaches which are eaten by conspecifics, and therefore, in the result of a pest control application.

Differential microbial responses to antibiotic treatments by insecticide-resistant and susceptible cockroach strains (Blattella germanica L.)

The German cockroach (Blattella germanica L.) is a major urban pest worldwide and is known for its ability to resist insecticides. Past research has shown that gut bacteria in other insects can metabolize xenobiotics, allowing the host to develop resistance. The research presented here determined differences in gut microbial composition between insecticide-resistant and susceptible German cockroaches and compared microbiome changes with antibiotic treatment. Cockroaches received either control diet or diet plus kanamycin (KAN) to quantify shifts in microbial composition. Additionally, both resistant and susceptible strains were challenged with diets containing the insecticides abamectin and fipronil in the presence and absence of antibiotic. In both strains, KAN treatment reduced feeding, leading to higher doses of abamectin and fipronil being tolerated. However, LC50 resistance ratios between resistant and susceptible strains decreased by half with KAN treatment, suggesting gut bacteria mediate resistance. Next, whole guts were isolated, bacterial DNA extracted, and 16S MiSeq was performed. Unlike most bacterial taxa, Stenotrophomonas increased in abundance in only the kanamycin-treated resistant strain and was the most indicative genus in classifying between control and kanamycin-treated cockroach guts. These findings provide unique insights into how the gut microbiome responds to stress and disturbance, and important new insights into microbiome-mediated insecticide resistance.

Effectiveness of Ethyl Formate as a Fumigant of Blattella germanica and Periplaneta americana (Blattodea: Ectobiidae, Blattidae) in Cross-Border Trade Transportation

Cockroaches cause problems as pests not only locally in residential areas but also internationally, as they can disperse across borders in transport vessels. We investigated the effects of the ethyl formate (EF) fumigant on all developmental stages of Blattella germanica and Periplaneta americana. For B. germanica eggs, the hatching inhibition rate increased directly proportionately with the increasing treatment concentration of EF, but the 100% control was not observed. P. americana eggs did not show any fumigation effect, even after exposure to 60 mg/L of fumigant in a 12 L desiccator. Adults and nymphs of the two species showed various fumigation effects dependent on the concentration in the 12 L desiccator. When EF was applied at the lethal concentration for 99% mortality (LCT99) values of 35 mg/L for 4 h (78.5 mg·h/L) and 60 mg/L for 2 h (70.8 mg·h/L), respectively, adults and nymphs of both species had 100% mortality in a 0.65 m3 fumigation chamber with a 20% loading ratio. However, no significant difference from the control was observed in the egg stage of either species of cockroach. The results of this experiment indicate that EF can be used as a fumigant for cross-border transport vessels if the control period occurs during the cockroach developmental stage and continuous refumigation is performed.

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.