The cost of sexual coercion and heterospecific sexual harassment on the fecundity of a host-specific, seed-eating insect (Neacoryphus bicrucis)

Two species of seed-eating true bugs, Neacoryphus bicrucis (Heteroptera: Ly gaeidae) and Margus obscurator (Heteroptera: Coreidae) co-occur on ragwort, Senecio tomentosus. in southern Georgia, USA. Males of both species someti mes engage in chases and protracted grappling with females that flee initia l mountings. Sometimes genital coupling occurs while the wriggling female i s restrained in the male's grasp. Chases, grappling, and mounting attempts are misdirected toward heterospecific females, heterospecific males, or con specific males. In a laboratory study, confinement of mated. N. bicrucis fe males with either conspecific or heterospecific males reduced fecundity by approximately one-half relative to mated females confined only with other f emales. Perhaps as a consequence of this. N. bicrucis females frequently le ave areas of high host plant density, where they prefer to oviposit, when m ales are abundant. The abundance of each species is positively correlated w ith host plant density but the two species rarely occur together on the sam e plants. This may be an effect of heterospecific courtship which induces t he flight of N. bicrucis more than the flight of M. obscurator:The laborato ry results suggest that copulations following chases and grappling represen t sexual harassment, not a mechanism of active female choice for a vigorous mate. As sexual harassment imposes high fitness costs that favor abandonme nt of host plants, it may, when misdirected, incidentally limit habitat use by ecologically similar species.