BIOSYSTEMATICS OF THE GENUS IPS (COLEOPTERA: SCOLYTIDAE) IN NORTH AMERICA. HOPPING’S GROUP III

Publisher Website
Google Scholar
Abstract
Ips integer (Eichhoff) is removed from synonymy with plastographus (Leconte), which in turn is divided into two subspecies: p. plastographus (Leconte) and p. maritimus n. subsp. The former occurs in the subalpine zone of the Sierra Nevada, Cascade, and northern Rocky Mountain ranges; the latter is apparently restricted to the California coast.I. integer and p. plastographus are partially sympatric, but even in a mixed attack on the same host the two species were rarely found in the same gallery systems. In field experiments females showed strong preference for the sex pheromone of conspecific males. Laboratory-produced hybrid males were intermediately attractive to both species.In breeding experiments the plastographus subspecies were fully interfertile but fertility of backcross and F2 generations was reduced. Egg hatchability was low in interspecific combinations of integer and plastographus. However, results were different for the reciprocal pairings and the backcrosses showed increased fertility. These data defy explanation by nuclear genetics but may result from cytoplasmic incompatibility.Although integer and the two plastographus subspecies have the same karyotypic formula, 15 A A + Xyp, the three entities can be differentiated by the size of heteropycnotic segments in pachytene chromosomes and the shapes (centromere position) of some of the five largest chromosomes at second metaphase. Univalents, multivalents, bridged anaphases, and other abnormalities were common in hybrids of plastographus and integer. Heteromorphic bivalents, but no other abnormalities, were observed in hybrids of the plastographus subspecies.