Summary1. The fecundity of the forest tent caterpillar varies considerably across its geographic range. Field data indicate that populations in the southern United States (Gulf States) produce nearly twice as many eggs as females from Canada or the Lake States, with little or no difference in the size of adult females.2. In controlled rearing experiments, female forest tent caterpillar from the southern United States (Louisiana) had much larger clutch sizes than same sized females from northern populations in Michigan or Manitoba, Canada. Increased fecundity in Louisiana females was achieved through a significant reduction in egg size and a concomitant increase in the allocation of resources to egg production.3. Comparison of 10 forest tent caterpillar populations spanning a 27° latitudinal gradient, validated the results of detailed comparisons among the three populations above by confirming the strong negative correlation between latitude and clutch size.4. Neonate forest tent caterpillars from Manitoba were significantly larger than larvae from either Michigan or Louisiana. Michigan larvae were intermediate in size. It is postulated that large neonates are advantageous in thermally limiting environments. More than three times as many degree‐days are available to Louisiana neonates during the first 2 weeks after hatching. A consistently favourable climate during the vulnerable post‐hatching period may have allowed the evolution of larger clutches at the expense of neonate size in southern populations.

No abstract

The importance of visual silhouettes for host finding by the southern pine beetle (SPB), Dendroctonus frontalis (Coleoptera: Scolytidae), and the potential for disruption of this process using visual deterrents were evaluated with multiple‐funnel traps, painted white or black, and with clear, white, or black Plexiglas sticky panels. All traps and panels were baited with the SPB attractant frontalure. The effect of combined semiochemical and visual disruption was evaluated in funnel traps by including the antiaggregation pheromone verbenone, or the repellent/inhibitory host compound 4‐allylanisole, in addition to the attractant. Visual treatments had a highly significant effect on catch of SPB and the predatory clerid beetle Thanasimus dubius. In attractant‐baited traps, white paint alone reduced the average number of SPB caught by 72% in Florida and 68% in Louisiana. The repellent 4‐allylanisole reduced catch of SPB by 56% in Florida and 45% in Louisiana. Verbenone was eluted at 25% of the targeted rate and did not affect total catch in either place. White panels trapped 79% fewer SPB than black, and 55% fewer than clear, with both differences significant. Clear panels also caught significantly fewer (−54%) SPB than black panels. Capture of T. dubius was reduced significantly by clear (−61%) or white (−56%) panels compared to black but did not differ significantly between clear and white panels. The percentage of female SPB captured was not significantly changed by visual treatments but was, as expected, reduced by verbenone. Neither visual nor semiochemical treatments influenced the sex ratio of T. dubius. The potential for using visual disruptants for protection of trees was assessed in front of a single SPB infestation by painting trees either white or black to 4.5 m. White trees showed fewer landings by SPB and a reduced density of successful and total SPB attacks within, but not above, the painted area. These results show that both SPB and T. dubius can be significantly affected by altering visual silhouettes, and that visual and semiochemical treatments, especially used in combination, may increase effectiveness of bark beetle disruption strategies.

No abstract

Olfactory deterrents have been proposed as tree protectants against attack by bark beetles, but their development has been hindered by a lack of knowledge of host selection behavior. Among the primary tree‐killing (aggressive) Dendroctonus, vision appears to be an integral part of the host selection process. We evaluated the importance of vision in host finding by D. brevicomis LeConte, and our ability to affect it by modifying the visual stimulus provided by attractant‐baited multiple‐funnel traps. White‐painted traps caught ∼42% fewer D. brevicomis than black traps in California, USA (P < 0.05). Visual treatments were less effective (P < 0.0001) than olfactory disruptants (verbenone with ipsdienol), which reduced catch by about 78%. When combined, olfactory and visual disruptants resulted in ∼89% fewer D. brevicomis being caught, but this combination was not more effective than olfactory disruptants alone (P > 0.05). Our results demonstrate that the visual component of D. brevicomis host finding behavior can be manipulated, but that D. brevicomis may be more affected by olfactory than visual disruptants. In contrast, visual disruption is more pronounced in the southern pine beetle, Dendroctonus frontalis Zimmermann, suggesting that non‐insecticidal tree protection strategies for these related species should differ.