Dendroctonus rufipennis (Kirby, Coleoptera: Curculionidae) uses pheromone blends containing aggregative components (frontalin, verbenene, 1-methyl-2-cyclohexen-1-ol [MCOL], and seudenol) and an anti-aggregative component (3-methyl-2-cyclohexen-1-one [MCH]) to coordinate attacks against host trees, but little is known about the influence of external stimuli on pheromone production. We conducted feeding experiments followed by pheromone extractions to determine if feeding duration and mate presence affected pheromone production in D. rufipennis. Unfed beetles of both sexes produced very little of any pheromone component. Females fed for 48 h produced significantly more MCH and MCOL compared to those which fed for 24 h. Males fed for 48 h produced significantly less seudenol than those which fed for 24 h. Male presence did not significantly affect female pheromone production. We propose that the pheromone blend produced by beetles transitions from aggregative to anti-aggregative shortly after colonizing a host, regardless of mate presence.
We used the red flour beetle, Tribolium castaneum Herbst (Coleoptera: Tenebrionidae), to compare three feeding bioassay techniques using flour disks. The area (scanner or digital photographs) and mass (sensitive balance) of the same flour disks were measured daily for 1 or 2 wk to assess feeding by insects. The loss in mass and area over 4 h was measured, as some variation over time was noticed in the disks with no insects feeding on them. The gravimetric method correlated well with both measurements of the area for the disks held in a growth chamber: scanner (R2 = 0.96), digital photography (R2 = 0.96). There was also a high correlation (R2 = 0.86) between the disk weight and area scanned at normal lab conditions. There were differences in the percentage of the disks remaining over time depending on the temperature and whether they were weighed or scanned. Measuring the mass of the disks resulted in a relatively larger percent of disk remaining compared with the scanned area. Mass measurements required a sensitive balance, handling of the disks and the insects, and appeared slightly more sensitive to humidity and temperature changes over time. Scanning the disks requires flat bed scanner access but less handling of both insects and disks. Digital photographs could be taken quickly, requiring less equipment, although photographs had to be further processed to determine area Scanning or taking digital photographs of flour disk area was an effective technique for measuring insect feeding.
The geographical exchange of non-native insects can be highly asymmetrical, with some world regions 'exporting' or 'importing' more species than others. Several hypotheses have been proposed to explain such asymmetries, including differences in propagule pressure, environmental features in recipient regions, or biological traits of invaders. We tested aspects of these hypotheses in the context of the exchange of non-native insects between North America, Europe, and Australasia. Europe was the dominant exporter of non-native insect species between the three regions, with most of this asymmetry arising prior to 1950. The European dominance could not be explained by differences in import value, source species pool sizes, or native plant richness in the recipient regions. We identified that the introduction of non-native plants, driven in part by European colonization, best explains the asymmetrical exchange of non-native insects between our focal regions.
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