Host-range testing of a mixture of two nucleopolyhedroviruses of Choristoneura fumiferana (Lepidoptera: Tortricidae)

The host range of a mixture of Choristoneura fumiferana (Clemens) nucleopolyhedroviruses (CfMNPV and CfDefNPV) was investigated using a per os bioassay of larvae of 29 species of Lepidoptera and adult males of Megachile rotundata (F.) (Hymenoptera: Megachilidae). Using a whole-genomic DNA probe, positive results were obtained in 8 of 10 Tortricidae: Archips cerasivorana (Fitch), Choristoneura fractivittana (Clemens), C. fumiferana, Choristoneura occidentalis Freeman, Choristoneura pinus pinus Freeman, Choristoneura rosaceana (Harris), Clepsis persicana (Fitch), and Cydia pomonella (L.); one Crambidae: Ostrinia nubilalis (Hübner); one arctiine Erebidae: Estigmene acrea (Drury); and two Noctuidae: Oligia illocata (Walker) and Pyrrhia exprimens (Walker). Mortality rates were highest among C. fumiferana, C. occidentalis, C. pinus pinus, A. cerasivorana, and C. pomonella. Sequenced polymerase chain reaction (PCR) amplicons from infected individuals from several species confirmed that the primer sets amplified the target viruses. CfMNPV was consistently found in virus-fed C. fumiferana; whereas, CfDefNPV was present only occasionally. The presence of CfMNPV and CfDefNPV in A. cerasivorana was confirmed by PCR and DNA sequencing. Significant treatment-mortality rates were induced in the noctuids P. exprimens and Acronicta impleta Walker; PCR determined that both viruses were present in treated P. exprimens but only CfMNPV was present in A. impleta. No virus was detected in M. rotundata.

The ecological interaction of the mountain pine beetle and jack pine budworm in the boreal forest

As climate change facilitates the range and host expansion of insect species into new ecosystems, the development of newstrategies for managing and preventing biological invasion is receiving considerable interest. In recent years, the range ofthe mountain pine beetle (Dendroctonus ponderosae Hopkins) has expanded from lodgepole pine-dominated forests eastof the Rocky Mountains into lodgepole x jack pine hybrid forest of western Alberta, and may soon invade jack pine forestsof the boreal. Our understanding of factors contributing colonization of jack pine by mountain pine beetle is far fromcomplete and several factors may limit its spread in these forests, including tree resistance and competitors. Among these,the jack pine budworm (Choristoneura pinus pinus Freeman) is one of the most important insect enemies of jack pine andan outbreak defoliator that potentially weakens jack pine trees, which may make them more susceptible to MPB attacks.To develop effective management strategies in the face of the short-run impacts of climate change, we need an in-depthunderstanding of factors influencing establishment and survival of the beetle in jack pine forests.Key words: Choristoneura pinus pinus, Dendroctonus ponderosae, jack pine, range expansion, invasion biology, climatechange in the boreal forest, conifer-mediated interactions, tree induced defences, tripartite interactions

Long-term effects of jack pine budworm outbreaks on the growth of jack pine trees in Michigan

Growth of jack pine (Pinus banksiana Lamb.) trees from the Raco Plains area in the Upper Peninsula of Michigan was examined over an 18-year period (1978-1995) that included two jack pine budworm (Choristoneura pinus pinus Freeman) outbreaks. Specific volume increments were calculated for 84 trees grouped into three classes based on their status in 1996; 36 trees were undamaged, 24 trees had been recently top-killed, and 24 trees had been recently killed. Average growth was converted to proportion of previous years' growth for three periods: before the 1983-1985 outbreak, between the 1983-1985 and 1991-1993 outbreak, and after the onset of the 1991-1993 outbreak. Differences in growth over these periods among undamaged, recently top-killed, and recently killed trees were evaluated. Growth did not differ among the three groups before the 1983-1985 outbreak. From 1983-1990, undamaged and recently top-killed trees grew significantly more than recently killed trees. There was no difference in average growth from 1983 to 1990 between undamaged and recently top-killed trees. Growth of undamaged trees was significantly greater than growth of recently top-killed trees following the onset of defoliation from the 1991-1993 outbreak. Patterns of growth loss suggest that a history of defoliation stress from multiple budworm outbreaks was an important determinant of tree mortality.

Yield and financial losses associated with a jack pine budworm outbreak in Michigan and the implications for management

Stand-level merchantable volume and financial losses resulting from a 1991-1993 jack pine budworm (Choristoneura pinus pinus Freeman) outbreak were quantified for 99 jack pine (Pinus banksiana Lamb.) stands in the Raco Plains area of the Hiawatha National Forest. Associations between standing value loss and stand inventory variables were evaluated. Stands were stratified into management groups based on age, site index, and stocking. Differences in standing value loss among groups were examined. Total standing merchantable volume loss and gross value loss were estimated to be 19 500 m3 and $289 800, respectively, for the 1480-ha sample area. Standing merchantable volume loss averaged 13.3 m3/ha or 14% of standing volume. Standing value loss within stands averaged $194/ha. Losses were concentrated in only a few stands with eight stands accounting for over half the total standing value loss. Standing value loss was positively associated with stand age and basal area and negatively associated with the proportion of open-grown, full-canopied "wolf" trees in the stand. A significant interaction in standing value loss was observed between age-class and site index class. No significant differences in standing value loss were observed among stocking classes. Results confirm overstocked stands over 50 years of age should be prioritized for harvest.

FEEDING BEHAVIOUR OF THE FIRST-INSTAR CHORISTONEURA FUMIFERANA AND CHORISTONEURA PINUS PINUS (LEPIDOPTERA: TORTRICIDAE)

We have discovered that, contrary to the long-held belief, 1st-instar spruce budworm, Choristoneura fumiferana Clemens, do feed. They display red alimentary tracts if they are provided with diet containing the red dye amaranth. They graze on the surface of balsam fir needles sprayed with rhodamine and ingest the fluorescent material, which can be detected in the frass pellets deposited inside the hibernacula. When emerging 1st instars were allowed to crawl on the inside surface of a glass tube coated with the polyhedral inclusion bodies of a recombinant C. fumiferana virus containing the gene for the green fluorescent protein, the larvae showed the characteristic green fluorescence, indicating that not only had they ingested the occlusion bodies but also the virus had replicated and infected different tissues. Similar results were obtained with the jack pine budworm, Choristoneura pinus pinus Freeman, which has an identical life history. The advantages of early-instar intervention to minimize defoliation by using control agents such as the ecdysteroid agonist, tebufenozide (RH-5992, Mimic® formulation), are discussed.

Association of within-tree jack pine budworm feeding patterns with canopy level and within-needle variation of water, nutrient, and monoterpene concentrations

The possibility that uneven within-tree feeding patterns by jack pine budworm (Choristoneura pinus pinus Freeman) larvae could be related to underlying variation in host jack pine (Pinus banksiana Lamb.) foliar water, nutrient, and monoterpene contents was considered. Choristoneura pinus pinus feeds disproportionately in the upper portion of the canopy and almost exclusively on the basal portions of needles. Within needles, the distribution of water, several nutrients, and monoterpenes varied significantly between the distal and basal sections. Water, nitrogen, sulfur, manganese, and zinc levels occurred in higher concentrations in the distal section of the needle, which would not be predicted based on C. pinus pinus feeding patterns. Phosphorus, potassium, calcium, iron, and copper were significantly higher in the basal section. Although the latter differences might be predicted based on C. pinus pinus feeding patterns, they were not strong (ranging from 7.8% to 36.4% relative differences, as compared with 10.7%-50.0% relative differences in the former group). By contrast, concentrations of foliar monoterpenes were more strongly associated with known feeding patterns of C. pinus pinus. These relative differences ranged from myrcene (26.8%) to limonene (44.79%). Thus, foliar differences affecting within-needle feeding selection appear more associated with allelochemicals than nutrients or water. In contrast with the within-needle associations between larval feeding and foliar chemistry, no associations between upper and lower canopy foliage were observed. Water, nutrients, and monoterpenes were evenly distributed across the upper and lower canopy locations. Thus, differential feeding between canopy locations cannot be explained by foliar constituents. Rather, it is more likely explained by other environmental factors, such as proximity to and density of reproductive and vegetative shoots.