The development of a semiochemical monitoring and detection system for the diamondback moth on canola

Project Summary

Overview

The overall objective of Dr. Evenden’s research was to develop a semiochemical‐based monitoring system for diamondback moth on canola in western Canada. This research was designed to establish a system to help producers determine the spatial and temporal distribution of diamondback moth and predict population densities of the damaging larval stage. The original proposal was broken down into two phases of research: 1. Pheromone‐based monitoring of diamondback moth males; and 2. Semiochemical‐based monitoring of diamondback moth females and natural enemies; and a third phase of research dissemination: 3. Communication of research findings and applications to the canola industry.

The majority of the research findings fall under the Phase I category, the scope of which has been greatly expanded since the initial application. There are limited findings in Phase 2 because the research team was unable to attract a significant number of female diamondback moths to semiochemicals.

Phase 1: Pheromone‐based monitoring of diamondback moth males

Two season‐long, pheromone‐based monitoring experiments were conducted at sites located in all major canola‐growing regions of Alberta to evaluate five different commercially available pheromone lures. Traps baited with lures from APT (now APTIV) and PheroTech (now ConTech) consistently captured the greatest number of male diamondback moths. Attractiveness of lures was inversely related to pheromone release rate as determined in laboratory studies. Based on these, and other trapping experiments that directly compared the APT and PheroTech lures, it is recommended that the Prairie Pheromone Monitoring Network continue to use the PheroTech lures.
Three experiments tested the longevity of pheromone lures under field conditions. All three experiments demonstrated that older lures were more attractive than fresh lures. It is therefore recommended that the Prairie Pheromone Monitoring Network change the lure rotation schedule from the current three‐week rotation to a six‐week rotation. This will reduce the overall cost of the monitoring system.
Grey rubber septa lures baited with the commercially‐available PheroTech blend were more attractive to male diamondback moths than red septa lures baited with the same blend. Laboratory studies indicated that the increased attractiveness of the grey lures may be the result of a difference in the ratio of the released components from the two lure types. It is therefore recommended that PheroTech (now ConTech) dispense pheromone into grey rather than the red lures that are currently sold. However, the current pheromone dose used in the commercial PheroTech lures (100 μg) was the most attractive of several doses tested in both lure types and should be retained in the commercially‐available lures
A season‐long experiment tested the attractiveness of differently positioned traps baited with PheroTech lures. Traps positioned at 50 cm above ground level and those positioned at canopy height throughout the season caught a similar number of diamondback moths which was greater than the number captured in traps positioned at 2 m above the ground. Therefore the researchers suggest that the Prairie Pheromone Monitoring Network change the currently recommended trap position of 2 m to 50 cm above the ground.
Trap catch in traps baited with the commercially‐available PheroTech lures was significantly related to densities of immatures sampled at the same sites when diamondback moth densities were moderate but not when they were low. This indicates that pheromone traps can be used to predict subsequent larval population densities but more research is required to establish an economic threshold based on pheromone‐based trap capture.
Although APT and PheroTech lures were consistently the most attractive commercially‐available pheromone lures tested, neither was as attractive as calling virgin female diamondback moths. The laboratory studies demonstrated that male diamondback moths detected the three previously identified pheromone components from female pheromone gland extracts. However, the field trapping studies demonstrated that lures releasing pheromone blends with the acetate as the main component were more attractive than lures releasing pheromone blends with the aldehyde as the main component. Interestingly, all of the commercial lures tested release the less attractive blends with the aldehyde as the main component. Therefore, the research team recommends that future research is warranted to commercialize of a new pheromone lure releasing a new pheromone blend in collaboration with ConTech.

Phase 2. Semiochemical‐based monitoring of diamondback moth females and natural enemies

In three field experiments the research team incorporated host cues into the pheromone‐baited traps in an effort to enhance male response to traps and to attract females and natural enemies to traps. The effect of trap colour (yellow vs. white) and the incorporation of a greenleaf volatile, Z3‐hexenyl acetate, into pheromone lures were tested. This greenleaf volatile was chosen as it has previously been shown to enhance male diamondback moth response to pheromone and it is not as toxic of some of the crucifer‐specific compounds that are implicated in host‐finding behavior in this species. However, the addition of host cues had no effect on the attractiveness of traps to male moths and did not result in the attraction of a significant number of females or natural enemies to traps. These cues were tested at two times in the field season when competing cues from the crop would differ (pre‐bloom and bloom). The addition of the greenleaf volatile to the pheromone blend did not increase the attractiveness of the pheromone to male diamondback moths at any of the doses tested. As a result of these conclusive findings, the research team did not further pursue the development of a semiochemical‐based lure targeting female diamondback moths.
The findings of this study have provided several easy to implement recommendations to improve the efficacy of the pheromone‐based monitoring system currently used to monitor diamondback moth activity in the prairie provinces. The findings also demonstrate that pheromone‐based monitoring is related to infestation levels, at least at moderate population densities. Therefore, pheromone‐based monitoring should be encouraged and should be followed by sampling of immature stages. Further, the research team has made several recommendations to improve the pheromone formulation that may result in the development of a more attractive, commercially‐available lure through future research and collaboration with ConTech.

Concluding discussion and findings

This research evaluated various commercial lures that are currently available to producers and determined the best lure type, age, and position in which to use these tools in the field. In addition, the research team tested other pheromone blends with various ratios of the known pheromone components with and without the addition a greenleaf volatile. Finally, this research evaluated the potential of diamondback moth trap capture in traps baited with commercially‐available pheromone lures to predict larval infestation in canola in Alberta.

Major findings include:

• Lures from APT (now APTIV) and PheroTech (now Contech) were consistently the most attractive of the five commercial lures tested in field experiments in canola and these lures had a lower pheromone release rate than the less attractive lures.
• Older lures (both PheroTech and APT) are more attractive to male diamondback moths.
• Although traps baited with lures from PheroTech and APT captured the most male diamondback moths of the commercially available lures tested, they were not as attractive as calling virgin female diamondback moths.
• Pheromone blends with the Z11‐16:Acetate component as the major pheromone component are more attractive than pheromone blends with the Z11‐16:Aldehyde component as the major pheromone component. All the commercial lures tested release Z11‐16:Aldehyde as the major component.
• The pheromone blend used commercially in PheroTech lures is more attractive to male moths when it is released from grey rubber septa, as compared to red rubber septa.
• The pheromone dose currently used in PheroTech lures (100 μg) is the most attractive dose to male diamondback moths.
• The addition of host cues (trap colour and greenleaf volatile) did not enhance the attractiveness of pheromone‐baited traps when tested early in the season or during full bloom.
• Traps positioned at 50 cm above the ground or moved with the crop canopy height captured more male diamondback moths than traps positioned at 2 m above the ground. The 2m height is currently the industry standard in the Prairie Pheromone Monitoring Network.
• Pheromone‐baited traps can be used to predict larval densities in the field, but this was only successful at moderate population densities.

Recommendations

1. PheroTech (now ConTech) lures were consistently among the most attractive of the commercial lures and their continued use in the Prairie Pheromone Monitoring Network is recommended.
2. Lures should be rotated on a 6‐week rotation schedule and not on the 3‐week rotation schedule as is currently used in the Prairie Pheromone Monitoring Network.
3. ConTech should dispense pheromone into grey rather than red rubber septa to improve the attractiveness of their product.
4. Producers should position traps at a height of 50 cm along the crop edge instead of the 2m height that is currently the standard used in the Prairie Pheromone Monitoring Network.
5. Development of a new pheromone blend that has the acetate as the major component should be the topic of future research and commercialization in collaboration with ConTech. All of the tested commercial lures release pheromone blends with the aldehyde as the major component and even the most attractive commercial lures are not as attractive as calling virgin females.
6. Producers are encouraged to use pheromone‐baited traps to monitor diamondback moth flight and this information can predict expected larval densities in their crop. However, further research is needed to develop an economic threshold based on moth trap counts and continued larval sampling after moths are detected in traps is recommended.