Production, Developmental Expression, Physiological Regulation, and Mitigation of German Cockroach Allergens

Abstract

The German cockroach, Blattella germanica (L.) (Dictyoptera: Blattellidae), produces several allergens, including B. germanica allergen 1 (Bla g 1). Although the clinical significance and abatement of German cockroach allergens continues to be extensively studied, little is known about their basic biology.

Using molecular and physiological approaches, my research elucidated where Bla g 1 is produced, its tissue distribution, developmental expression patterns, and its physiological regulation in the German cockroach. Bla g 1 is found predominantly in, and produced exclusively by, the midgut. Although it is produced by all stages and both sexes, adult females produce and excrete in their feces significantly more Bla g 1 than adult males and nymphs. Quantitative analyses of Bla g 1 mRNA expression in the female gut, and Bla g 1 content of the female and her feces showed a cyclic pattern in relation to the gonadotrophic cycle; Bla g 1 increased during the first 5 d after adult eclosion, when food intake increases, decreased before oviposition, as food consumption declines, and remained low while the female carried an egg case. After hatch, when the female resumed feeding, feces and Bla g 1 production increased. Forced starvation depressed both Bla g 1 mRNA expression and protein levels in adult females; Bla g 1 production increased and the gonadotrophic cycle resumed when food was returned. Bla g 1 mRNA expression also increased significantly in response to feeding compared to starved females. These data show that Bla g 1 is produced in relation to food intake and may be involved in digestion.

The best approach to allergen mitigation is to remove the source of the allergen, or cockroach control. Pest control in the confined swine production industry relies primarily on broad-spectrum residual organic sprays. However, recent regulatory restrictions that limit the use of organophosphate insecticides and a rising frequency of resistance to pyrethroid insecticides have led to a renewed search for alternative pest control methods. Furthermore, recent evidence suggests that integrated cockroach management in infested structures can reduce environmental cockroach allergen levels below clinically relevant thresholds. I sought to develop a liquid formulation of boric acid bait for the management of German cockroaches in infested swine farms.

The efficacy of various liquid borate solutions was assessed in no-choice and two-choice assays. While three borates provided effective kill under no-choice conditions, boric acid resulted in faster kill than sodium tetraborate or disodium octaborate tetrahydrate when cockroaches were given a choice between the borate-laced water and clean water. To evaluate whether various sugars could enhance the insecticidal activity of boric acid, solutions of 0.5% boric acid and 1 M sugar were tested. Finally, dose-mortality studies were conducted with the most promising sugars (maltose, sucrose, glucose, and fructose) at concentrations ranging from 0.01 to 2.0 M and boric acid concentrations of 0.5, 1.0, and 2.0%. From these studies, I concluded that a combination of boric acid and sucrose provided excellent control of the German cockroach.

In field evaluations, prototype J-shaped bait dispensers filled with liquid boric acid bait solution were applied in a cockroach-infested nursery of a swine farm. Results of this 2-year field study showed that the cockroach population was significantly reduced by >90% within 1–2 months. These data also showed that when baits were deployed continuously for ~10 months the cockroach populations declined by 90–99%. In addition to providing an alternative management strategy, this approach also provides an option for the potential mitigation of cockroach allergens in infested swine farms and homes.