Gaétan Bourgeois

Modelling the impact of climate change on disease incidence: a bioclimatic challenge

The potential impact of climate change on disease development was evaluated using mathematical modelling. Disease forecasting systems for late blight of potato [Phytophthora infestans], apple scab [Venturia inaequalis], and cercospora blight of carrot [Cercospora carotae] were selected to evaluate their relevance in predicting future events related to climate change. In general, if these models are to be valid for such predictions, they must predict adequately actual field observations. Many of the forecasting systems developed a few years ago are in need of updating. Disease forecasting systems using nonlinear responses to temperature and leaf wetness offer more potential to represent the impact of climate change and variability on disease epidemiology.

Effect of Soil Temperature and Moisture on Survival of Eggs and First-Instar Larvae of Delia radicum

ABSTRACT Edaphic factors such as soil temperature and moisture influence soil-dwelling insects, whose most vulnerable stages typically are eggs and young larvae. In this study, the survival of eggs and first-instar larvae of the cabbage maggot, Delia radicum L., was measured under laboratory conditions after exposure to a range of soil temperatures and moistures. When eggs were exposed to constant temperature (20–29°C) and humidity (5–200% [wt:wt]), temperature had no significant effect on survival, whereas humidity <25% [wt:wt] caused egg mortality. The gradual exposure of eggs to high temperatures resulted in low mortality below 33°C, but <5% of eggs survived at 40°C. When first-instar larvae were exposed to constant temperature (17–29°C) and humidity (5–100% [wt:wt]), both factors as well as their interaction had a significant effect on larval survival, which was nil at 5% (wt:wt) for all temperatures but increased from 21.9 to 42.8% at 17°C and from 34.1 to 55.0% at 29°C, for soil moisture contents of 15% and 100% (wt:wt), respectively. Eggs of D. radicum are resistant to low soil moisture and high temperature conditions. Larval survival tends to increase with an increase in soil temperature and moisture. It is suggested that soil temperature be integrated into insect development simulation models instead of air temperature, to build more effective models for cabbage maggot management.

Modeling Leafhopper Nymphs in Temperate Vineyards for Optimal Sampling

Abstract Cicadellids (Homoptera: Cicadellidae) are occasional pests of vineyards in temperate areas, and unchecked populations can build up to high densities to cause leaf burn followed by defoliation and yield loss. Therefore, an optimal sampling scheme would allow determination of risk at minimal cost. Because the development of leafhopper nymphs and feeding injury is closely tied to temperature, a model driven by the accumulation of degree-days was developed to predict leafhopper cumulative abundance at 5, 50, and 95% levels in vineyards. The model was based on 22 data sets collected over 7 yr in three vineyards in southern Quebec. It was based on the cumulative abundance of nymphs of the eastern grape leafhopper; the grapevine leafhopper; the threebanded leafhopper; the Virginia creeper leafhopper; and Erythroneura vitifex Fitch. The lower threshold temperature for development was 8°C. Paired t-tests and the forecasting efficiency confirmed the validity of the model. The model indicated that monitoring for leafhoppers in vineyards should be initiated at 630 DD (5% cumulative abundance) and terminated at 1,140 DD (95% cumulative abundance). Maximum abundance would be between 850 and 860 DD (50% cumulative abundance) calculated from 1 March.

Integrated assessment of climate change impact on surface runoff contamination by pesticides

Pesticide transport by surface runoff depends on climate, agricultural practices, topography, soil characteristics, crop type, and pest phenology. To accurately assess the impact of climate change, these factors must be accounted for in a single framework by integrating their interaction and uncertainty. This article presents the development and application of a framework to assess the impact of climate change on pesticide transport by surface runoff in southern Québec (Canada) for the 1981-2040 period. The crop enemies investigated were: weeds for corn (Zea mays); and for apple orchard (Malus pumila), 3 insect pests (codling moth [Cydia pomonella], plum curculio [Conotrachelus nenuphar], and apple maggot [Rhagoletis pomonella]), 2 diseases (apple scab [Venturia inaequalis], and fire blight [Erwinia amylovora]). A total of 23 climate simulations, 19 sites, and 11 active ingredients were considered. The relationship between climate and phenology was accounted for by bioclimatic models of the Computer Centre for Agricultural Pest Forecasting (CIPRA) software. Exported loads of pesticides were evaluated at the edge-of-field scale using the Pesticide Root Zone Model (PRZM), simulating both hydrology and chemical transport. A stochastic model was developed to account for PRZM parameter uncertainty. Results of this study indicate that for the 2011-2040 period, application dates would be advanced from 3 to 7 days on average with respect to the 1981-2010 period. However, the impact of climate change on maximum daily rainfall during the application window is not statistically significant, mainly due to the high variability of extreme rainfall events. Hence, for the studied sites and crop enemies considered, climate change impact on pesticide transported in surface runoff is not statistically significant throughout the 2011-2040 period. Integr Environ Assess Managem 2016;12:559-571.

Oviposition Pattern of Early and Late-Emerging Genotypes of Delia radicum (Diptera: Anthomyiidae) at Different Temperatures

ABSTRACT The cabbage maggot, Delia radicum L., has a bimodal pattern of emergence caused by the presence in populations of early and late-emerging genotypes that differ in their pupal development time. These genotypes could also express different egg-laying strategies. To examine oviposition patterns between genotypes and, particularly, their response to temperature, the egg-laying activity of females and egg mortality from each genotype were evaluated at temperatures from 12 to 30°C. Several criteria were used to describe the oviposition pattern: longevity of females, preoviposition period, lifetime fecundity, number of oviposition bouts, duration and number of eggs for each oviposition bout, duration of an oviposition cycle, and time interval between oviposition bouts. All criteria were similar between genotypes, except the preoviposition period and time interval between oviposition bouts. The preoviposition period was 1–4 d longer for the early emerging genotype than for the late-emerging genotype at temperatures <25°C, but similar at temperatures ≥25°C. The time interval between oviposition bouts of early emerging genotype was a few hours longer than for the late-emerging genotype at all temperatures. All oviposition pattern criteria responded to temperature, except the duration of oviposition bouts (≈6.5 d) and egg mortality (≈11%). The duration of a bout could be a compromise between oogenesis duration and the risks associated with egg deposition. According to these results, early and late-emerging genotypes express similar egg-laying strategies for all temperatures tested.

Probabilistic climate change scenarios for viticultural potential in Québec

Climate conditions for Québec’s viticultural potential (VP) during upcoming decades are estimated through high-resolution probabilistic climate scenarios (PCS) based on a large ensemble of simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5). VP is investigated through four temperature-related indices identified as current limiting factors for cold, northern latitudes: length of frost-free season (CNFD), growing degree-days (DDB10), annual winter minimum temperature (AWMT), and annual number of very cold days (ANVCD). Results show that by 2040–2050, most of southern Québec can reasonably expect favorable climatic conditions, with enough consecutive frost-free days and growing degree-days for growing current hybrid-grape varieties, as well as some Vitis vinifera grape varieties. Regions with new VP are identified, for example southern Outaouais and along the St-Lawrence River. Cold winter temperatures remain problematic, but technical solutions to this limiting factor exist.

Modeling phytophagous mirid nymphs in cool-climate vineyards

In temperate regions, mirids may be occasional pests of vineyards where risk-averse growers use control measures. In that context, an optimal sampling scheme would allow determination of risk at minimal cost. A model driven by the accumulation of degree-days (DD) was developed to predict cumulative total captures of mirid nymphs (mainly the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois)) at 5%, 50%, and 95%. The model was based on 23 data sets collected over 4 years in three vineyards in southern Quebec. Lower and optimum temperatures for development were set at 10o and 32°C, based on experimental results and previous studies. Cumulative total captures at 5%, 50%, and 95% levels occurred, respectively, at 229, 331, and 479 DD for the first generation and 630, 806, and 1000 DD for the second generation. Paired t-tests and the forecasting efficiencies confirmed the reliability of the predictive model. The model indicated that monitoring for mirid nymphs of cool-climate in vineyards should be initiated at 200 and 500 DD calculated from 1 March for the first and second generations, respectively. Using the same lower and optimum temperatures for the development of mirids, another degree-day model was developed to predict grapevine phenological stages in relation to the modified Eichhorn-Lorenz system. Superimposing the mirid model over the grapevine model allows relating mirid total captures to grapevine phenological stages, and thus optimizing resources to monitor mirid populations in cool-climate vineyards.