Dosdall: Improved Integrated Crop Management with Beneficial Insects
Date: April 2013
Term: 3 years
Status: Completed
Researcher(s): L. Dosdall, University of Alberta, O. Olfert, J. Soroka, Agriculture and Agri-Food Canada (AAFC), Saskatoon and K.N. Harker, AAFC Lacombe
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a
Project Summary
Diamondback moth is a serious pest of canola and mustard in Canada, and although there are important parasitoids for managing diamondback moth outbreaks in canola, very little is known of their life histories and habitat requirements. Researchers from the University of Alberta and Agriculture and Agri-Food Canada initiated a three-year project in 2010 to examine the biology, abundance levels and distributions of parasitoids of diamondback moth in prairie canola. As a result of the project, researchers have developed innovative practices and recommendations in insect pest management for farmers and agrologists.
Considerable progress has been achieved to develop integrated management strategies for several insect pest species that can infest canola crops, but one important area of research that has been largely overlooked involves identifying ways to enhance the effectiveness of beneficial insects. Beneficial insects can reduce infestations of insect pests, and in some cases, have been the primary agents responsible for ending outbreaks.
Diamondback moth is a serious pest of canola and mustard in Canada, and although there are important parasitoids for managing diamondback moth outbreaks in canola, very little is known of their life histories and habitat requirements. The parasitoid Diadegma insulare, a wasp species, is known to sometimes completely terminate diamondback moth outbreaks in western Canada. Two other parasitoid species, Microplitis plutellae and Diadromus subtilicornis, also attack diamondback moth and sometimes inflict high levels of parasitism.
Researchers from the University of Alberta and Agriculture and Agri-Food Canada initiated a three-year project in 2010 to examine the biology, abundance levels and distributions of parasitoids of diamondback moth in prairie canola. The aim of this project was to develop forecasting strategies to predict their abundance levels and distributions. Surveys of several commercial canola fields were conducted across Alberta and Saskatchewan to determine the parasitoid fauna of diamondback moth in canola, and to assess the levels of parasitism in different sites and eco-regions.
Laboratory studies were also conducted using colonies of diamondback moth and its dominant parasitoid, Diadegma insulare, previously established at the University of Alberta (Edmonton) and Agriculture and Agri-Food Canada (Saskatoon). Analyses of the developmental biology of the parasitoid under constant and fluctuating temperature conditions were conducted to determine developmental temperature thresholds for the insects and the effects of fluctuating temperatures on their development. Research was also conducted at the University of Alberta to determine the effect of plant stress on diamondback moth and parasitoid developmental and fitness parameters.
From the study results, researchers confirmed that canola fields vary considerably in the densities of diamondback moth and the species composition and abundance of its parasitoid fauna, even in the same year and among fields in the same geographical region. The principal parasitoids of diamondback moth were comprised of D. insulare, M. plutellae, D. subtilicornis, and an unknown species of braconid wasp, believed to be Cotesia vestalis. The discovery of Cotesia parasitizing diamondback moth larvae in western Canada is new, and this species appears responsible for a very substantial level of the total parasitism of diamondback moth.
The research showed that the most efficient approach for monitoring canola for diamondback moth and its parasitoid fauna is to take sweep net samples in production fields. Because populations of moths and parasitoids are not uniformly distributed, several locations within each field should be sampled. The survey results showed that levels of parasitism of diamondback moth larvae and pupae can be relatively high early in the season. It is therefore important for growers to carefully monitor pest and natural enemy populations to ensure that unnecessary insecticide applications are not made.
The study also showed that host plant density had no effect on the distribution of diamondback moth or its principal parasitoids. However, diamondback moths are attracted to the sulphur content of canola leaf tissue and this positively affects diamondback moth distribution. Therefore, canola producers should apply recommended levels of sulphur based on soil sample recommendations, and avoid applications that exceed recommended levels.
The temperature investigations in the study found that diamondback moth adults and larvae are more heat tolerant than adults of D. insulare and parasitized diamondback moth larvae. Both insects are able to tolerate high temperatures if these were brought on gradually rather than suddenly.
The study also showed that diamondback moth females lay more eggs on older (6-week- old) plants than younger (4-week-old) plants, and fewer eggs on moisture stressed plants. Therefore, fields that are drought-stressed at the time of diamondback moth influxes on winds from southern North America will likely be subjected to reduced infestation levels of these pests. However, parasitoids that develop in diamondback moth larvae reared on drought-stressed host plants require more time to progress from egg to adult, and are less fit than parasitoids that develop on unstressed plants. As a result, careful crop monitoring is important when water stress occurs, because control of diamondback moth by natural enemies may not be as efficient compared to conditions with sufficient soil moisture levels.
As a result of the project, researchers have developed innovative practices and recommendations in insect pest management for farmers and agrologists. They also developed a DYMEX climate model for predicting diamondback moth and D. insulare occurrence in the field. The DYMEX models for both diamondback moth and D. insulare await validation with field data.
Scientific Publications
Bahar, M. H., Soroka, J. J., Dosdall, L. M. and Olfert, O. O. 2013. Occurrence of diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae), and its larval parasitoids across Saskatchewan, Canada. Biocontrol Science and Technology Vol. 23, Issue 6. p 724-729.
Bahar, M.H., D. Hegedus, J.J. Soroka, C. Coutu, D. Bekkaoi and L.M. Dosdall. 2013. Survival and hsp70 gene expression in Plutella xylostella and its parasitoid Diadegma insulare varied between sudden plunge and slowly ramping extreme temperature regimes. PloS ONE. 8(9): e73901. DOI: 10.1371/journal.pone.0073901.
Bahar, M.H., J.J. Soroka, L.M. Dosdall. (2012). Constant versus fluctuating temperatures in the interactions between Plutella xylostella and its larval parasitoid Diadegma insulare. Environmental Entomology. 41(6): 1653–1661. DOI: http://dx.doi.org/10.1603/EN12156
Full Report PDF: n/a