BIOSYSTEMATICS OF THE GENUS IPS (COLEOPTERA: SCOLYTIDAE) IN NORTH AMERICA: REVIEW OF THE IPS CALLIGRAPHUS GROUP

Abstract

AbstractThe recognition of four taxa within the calligraphus species group of the genus Ips DeGeer is supported by breeding experiments, karyology, morphology, ecology, and distributions. Ips calligraphus calligraphus (Germar) occurs in the eastern United States and adjacent parts of Canada. Ips c. ponderosae (Swaine) occurs in the range of Pinus ponderosa in the Black Hills, eastern Rocky Mountains, and in the northern Sierra Madre Oriental in Mexico. Ips c. interstitialis (Eichhoff) occurs in the Caribbean Archipelago but the homogeneity of populations on the islands of Hispaniola and Jamaica and the true type locality are uncertain. Ips apache Lanier infests various pines (excluding pinyon pines) at lower altitudes from southeastern Arizona through Mexico. Populations south of the Isthmus of Tehuantepec in Caribbean pines on the east coast of Central America are provisionally considered to be I. apache. Pairings of female I. calligraphus subspecies with male I. apache were infertile. Reciprocal pairing produced rare, sterile hybrids. Fertility of I. calligraphus subspecies was normal when I. c. calligraphus was the female but reduced when the female was either I. c. ponderosae or I. c. interstitialis. All members of the group had 15 pairs of autosomes plus a sex bivalent (2n = 32) that assumed a “parachute” configuration to give a male meiotic formula of 15 AA + Xyp. Second meiosis chromosomes of I. apache lack some of the heterochromatic arms present in I. calligraphus. Meiotic divisions of rare interspecific hybrids (I. apache ♀ × I. calligraphus s. lato ♂) had numerous autosomal rearrangements, a possible translocation, and oversized (probably tetraploid) spermatozoa. Meiosis was mostly normal in intersubspecific hybrids, but the presence of occasional anaphase bridges or nonmigrating chromosomes and alignment of pachytene homologs revealed inversions and other possible rearrangements. Univariate and multivariate analyses of pars stridens strial width, pronotal width, and male genitalia revealed significant differences among all four taxa.