The impact of thigmotaxis deprivation on the development of the German cockroach (Blattella germanica)

Abstract

Thigmotaxis is required in small animals. In this study, we examined how the shelter angle affects the development of German cockroaches, Blattella germanica. Groups and individual cockroaches showed a strong preference for shelters with an angle of ≤40° after 15 min or 24 h in shelter-selection trials. For cockroaches that developed in 90/180-degree shelters, survival and fecundity were low, and the nymphal stage lasted longer. Post-molting transcriptomes of second- and sixth-instar nymphs were analyzed at 12 h and 2 days post-molting. Upregulation was observed in genes related to ATP metabolism and cellular amide metabolism. Chitin-based cuticle development and postembryonic development-related genes were downregulated. The stress responses of cockroaches that developed in shelters with angles of 90° were similar to those of gregarious cockroaches experiencing social isolation. For German cockroaches, environmental tactile stimuli are crucial to development and homeostasis.

Keywords: Entomology; Molecular mechanism of behavior.

Graphical abstract

Figure 1

Shelter selection of groups of German cockroaches after 24 hours An acrylic cylinder with a lid (inside diameter × height = 59 × 11.5 cm; outside diameter × height = 60 × 20 cm) was designed as the test environment (the 60 cm cylinder). Copper shelters with fold angles of 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, and 90° were evenly distributed inside the acrylic cylinder at a distance of 18 cm from the center of the cylinder. A total of 20 nymphs, 10 adult males or 10 adult females were placed at the center of the acrylic cylinder for shelter selection. The angle of the chosen copper shelter was recorded 24 h later, after which the cockroaches were removed. X axis: the angle of the copper shelter; Y axis: the percentage of cockroaches choosing a shelter. ∗p < 0.05, Student’s t test.

Figure 2

Shelter selection by individual German cockroaches after 15 minutes One nymph (N), adult male (M), or adult female (F) German cockroach at a time was placed at the center of the acrylic cylinder for shelter selection. Copper shelters with angles of 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, and 90° were distributed evenly inside the 60 cm cylinder at a distance of 18 cm from the center of the cylinder. The angle of the chosen copper shelter was recorded 15 min later, after which the cockroach was removed. X axis: the angle of the copper shelter; Y axis: the number of cockroaches choosing a shelter.

Figure 3

Shelter selection by individual German cockroaches after 24 hours One male or female German cockroach at a time was placed at the center of the acrylic cylinder for shelter selection. Copper shelters with angles of 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, and 90° were evenly distributed inside the 60 cm cylinder at a distance of 18 cm from the center of the cylinder. The angle of the chosen copper shelter was recorded 24 h later, after which the cockroach was removed. X axis: the angle of the copper shelter; Y axis: numbers of cockroaches choosing a shelter.