Sexual reproduction in the white pine weevil (Pissodes strobi [Peck] [Coleoptera: Curculionidae]): implications for population genetic diversity.

Controlled mating experiments in the white pine weevil (Pissodes strobi [Peck]) indicated that female weevils either stored sperm or fertilized eggs from one season to the next, and were able to colonize Sitka spruce (Picea sitchensis [Bong.] Carr.) trees without additional mating events. This was interpreted as being beneficial for the insect, in that population establishment in a new habitat could be initiated by dispersing previously mated females without participation of the male. This makes colonization and population/outbreak development more likely as it reduces the need for mate searching in the second season. Paternity identification, based on microsatellite molecular markers, established that the progeny produced in year 2 by females mated only in year 1, were often fathered by more than one male. Multiple paternity, coupled with a lack of parthenogenesis, which was also demonstrated herein, may help to account for the high degree of genetic diversity evidenced in this species.

Changes in volatile terpene and diterpene resin acid composition of resistant and susceptible white spruce leaders exposed to simulated white pine weevil damage.

Induced (traumatic) resin in white spruce (Picea glauca (Moench) Voss) leaders resistant or susceptible to the white pine weevil (Pissodes strobi Peck) was analyzed for volatile terpenes and diterpene resin acids after simulated white pine weevil damage. Leaders from 331 trees were wounded just below the apical bud with a 1-mm diameter drill, coinciding with the natural time of weevil oviposition in the spring. Leaders were removed in the fall, and the bark and xylem from the upper and lower regions of the leader extracted and analyzed by gas chromatography. Unwounded trees had low amounts of resin in xylem compared with bark. In response to wounding, volatile terpenes and diterpene resin acids increased in the upper xylem (area of wounding), with resistant trees showing a greater increase than susceptible trees. Wounding caused monoterpenes in particular to decrease in the lower region of the leader (away from the drilled area) in greater amounts in susceptible trees than in resistant trees. In response to wounding, the proportion of monoterpene to resin acid increased in the upper and lower xylem of resistant trees, and slightly increased in the upper xylem of susceptible trees. Monoterpene-enriched resin is more fluid than constitutive resin, and probably flows more readily into oviposition cavities and larval mines, where it may kill immature weevils. Loss of resin components in the lower xylem suggested catabolism and transport of these materials to the site of wounding; however, energetic and regulatory data are necessary to confirm this hypothesis. This study provides a basis for measuring the ability of a tree to undergo traumatic resinosis that could be used to screen for resistance to white pine weevil.

Insect feeding and oviposition deterrents from western red cedar foliage.

The feeding deterrent activity of fractions from the foliage of western red cedar,Thujaplicata Donn, was studied in laboratory bioassays using the white pine weevil,Pissodes strobi Peck, as a test insect. The most active fraction was the volatile mixture that comprises the leaf oil of this tree species. Further fractionation of the leaf oil indicated feeding deterrent activity in the monoterpene hydrocarbon, thujone, and terpene alcohol fractions. When tested alone, both (-)-3-isothujone and (+)-3-thujone, which made up 75-88% and 5-10% of the leaf oil, respectively, deterred feeding by the weevils. Western red cedar leaf oil also showed antifeedant activity with the alder flea beetle,Altica ambiens (Le Conte), and served as an oviposition deterrent for the onion root maggot,Hylemya antiqua Meigen. The leaf oil, however, had no inhibitory effect on the feeding of the leaf roller,Epinotia solandriana L., and the red-backed sawfly,Eriocampa ovata L.