Effects of bisphenol A in the ring-legged earwig, Euborellia annulipes.

Bisphenol A is a known endocrine disruptor in vertebrates that mimics the action of estrogens by interacting with hormone receptors. It also affects reproduction and development in many invertebrate animals, though mechanisms of action are unclear. Terrestrial insects, despite their abundance and profound ecological significance, have been largely overlooked as a group that might be affected by vertebrate endocrine disrupting chemicals. We evaluated potential effects of bisphenol A on the ring-legged earwig, Euborellia annulipes, as a model for terrestrial arthropods. Dosages of 0, 0.12, 1.2 and 12 microg bisphenol A were injected over a 6 day period into newly eclosed males and newly mated (7-day) females. The lowest dosage (0.12 microg) was most effective in eliciting significant effects including reducing weight gain while increasing testis size and seminal vesicle size; higher dosages were less effective or ineffective. In females, treatment with 0.12 microg bisphenol A enhanced clutch size but higher dosages were required to affect the duration of embryogenesis in offspring of treated mothers. Hatching success and the onset of the second reproductive cycle were not affected by treatments. No gross abnormalities were observed as a result of treatment in the reproductive structures of either males or females. Similarly, injection of varying concentrations of estradiol into males enhanced testis length, though it had no effect on seminal vesicle size. Lastly, we administered bisphenol A in drinking water for up to 2 weeks. Surprisingly, as little as 1 microg/L inhibited testis growth; 100 microg/L inhibited ovarian growth.

Effects of selected neuropeptides, mating status and castration on male reproductive tract movements and immunolocalization of neuropeptides in earwigs.

In earwigs, the male reproductive system is complex, comprising accessory glands and long dual intromittent organs for transfer of materials to the female and for removal of rival sperm. We investigated potential factors altering contractions of the male reproductive tracts in vitro. Tracts from 0-day (newly emerged) males displayed relatively little motility in vitro; however, those from 5-day (intermediate stage of sexual maturity) and 8-day (fully mature) males pulsed vigorously. Both 1 and 100 nM proctolin (RYLPT-OH) stimulated the rate of contraction of reproductive tracts from both 5-day and 8-day males. In contrast, 1 nM and 100 nM FGLa AST (cockroach allatostatin) did not affect pulsations. However, 10 microM FGLa AST decreased activity of reproductive tracts. Mating decreased motility of tracts from 5-day old males, but did not alter motility of tracts from 8-day old males. Castration of larvae significantly suppressed reproductive tract motility in subsequent 8-day old adults compared with those of intact or sham-operated adults. Castration also suppressed seminal vesicle size. Lastly, we assessed the presence and distribution of proctolin-like and allatostatin-like immunoreactivity in tissues. Immunoreactivity to FGLa AST and proctolin was widespread, occurring in the brain and ventral ganglia. Surprisingly, we did not detect immunoreactivity to either FGLa AST or proctolin within the reproductive system; however, proctolin immunoreactivity was evident in nerves extending from the terminal ganglion of 8-day, but not 0-day, males. Collectively, these experiments demonstrate that the male earwig reproductive system is an appropriate model for use in addressing sexual maturation and activities in male insects.

Effects of Manduca allatotropin and localization of Manduca allatotropin-immunoreactive cells in earwigs.

Manduca sexta allatotropin (Manse-AT) was first isolated on the basis of its ability to stimulate production of juvenile hormone in that insect. We examined whether this neuropeptide affects corpus allatum activity and visceral muscle contraction in adult females of the earwig, Euborellia annulipes. We also assessed the presence of allatotropin-like material in tissues using immunocytochemistry. Manse-AT at 1 nM to 10 muM stimulated juvenile hormone production in vitro by glands of low activity from 2-day virgin females. In glands of high activity from 12-day mated females, 1 and 100 nM allatotropin were effective, but 10 muM was not. Similarly, hindguts of 2-day and 12-day females significantly increased in motility in vitro in response to Manse-AT. A monoclonal antibody to Manse-AT was used to demonstrate allatotropin-like material throughout the nervous system of 2-day, virgin females. Immunoreactivity was most pronounced within varicosities of the corpora cardiaca and perisympathetic organs. No immunofluorescence was observed in gut tissue. Lastly, we showed that extract of retrocerebral complexes also enhanced in vitro hindgut motility from 2-day virgin females, in a dose-dependent manner. These results indicate material similar to M. sexta allatotropin in female earwigs and that such peptides may modulate juvenile hormone biosynthesis and visceral muscle contractions. Sensitivity to the peptides may change with physiological stage.