Update on foxglove aphid control: seeking greenhouse collaborators!

foxglove aphid 3_SJ

Investigating biocontrol options for our industry is always important, given the lack of registered insecticides in this country.   Currently, we are relying heavily on two closely related chemicals –  Beleaf (flonicamid) and Endeavor (pymetrozine) – for control of the foxglove aphid (Aulacorthum solani).  If our battle with thrips (and Bemisia whitefly) have taught us anything, it’s to be prepared for chemical failure.

Unfortunately, biological control of foxglove aphid has been challenging so far.  For example, my own research showed that Aphidoletes, a “generalist” aphid predator, actually has lower preference for foxglove aphid than other species, and is less effective for this pest. However, a long-term project by Dr. Michelangelo La-Spina (Vineland Research and Innovation Centre) has found some results that get us closer to being able to control foxglove aphid WITHOUT resorting to pesticide sprays.

One way YOU can help move this research forward is by filling in this quick, 10 question survey if you’re a grower (even if you’ve never had problems with foxglove aphid before).  Read on for more details on exactly what Dr. La-Spina has found.

One of the most interesting things Michelangelo’s research has revealed is that foxglove aphid defensively drops in the presence of the parasitoid Aphidius ervi.  Almost 50% of the foxglove aphid population leave the plants when disturbed by this parasitoid. Check out this video of A. ervi making foxglove aphid scatter.

At first, we were concerned this would potentially spread the aphid problem. But follow up trials demonstrated that A. ervi was able to control the foxglove aphid infestation in 3 weeks.  Supporting previous research, Aphidoletes aphidimyza, a “furtive” predator that does not cause foxglove aphid to fall from the plant, only controlled 50% of the foxglove aphid populations.  Although these trials were done in cages, it suggests that A. ervi CAN have an impact on foxglove aphid if given some time.

A ervi for foxglove aphid control

Compared to no treatment,  the presence of A. ervi caused foxglove aphid to disperse more to nearby plants (yellow and grey bars) from a centrally infested plant (dark green bars).  However, A. ervi was also able to bring the aphid population down to near zero in 3 weeks in cage trials.

It also suggests that A. ervi might be using a combination of parasitism and non-consumptive effects to control foxglove aphid. “Non-consumptive effect” is a nice word in the insect world for “harassment”.  Even though the parasitoid  may not be “consuming” the aphids, by chasing them off the plant, the aphids may die from other factors (not being able to get back onto plants; spending too much energy running instead of feeding; coming into contact with pathogens, etc.).  For an example of how non-consumptive effects help control thrips, see this post.

If you’ve used A. ervi for foxglove aphid before and found it unsuccessful, ask yourself if you didn’t think it was working because A) you hardly saw any aphid mummies? Or B) you actually looked at the size of the aphid infestation?

If you only looked at the presence of mummies, that may not actually be a good indicator of A. ervi control with foxglove aphid. Recent small greenhouse trials by Dr. John Sanderson at Cornell University corroborate that A. ervi can control foxglove aphid, even if very few mummies are observed.

Johns data FGA control by ervi

Dr. Sanderson’s data from Cornell.  Foxglove aphids were allowed to infest pepper plants and reproduce for 1 week. Bio’s were released at 2/square feet; a single release was used.  Although lacewing larvae had the best results, they are unlikely to disperse well in the greenhouse, and are better used for aphid “hot spots”.  A. colemani were released for green peach aphid (data not shown) and likely didn’t affect foxglove aphid numbers.

Michelangelo has also been looking at the best release method for A. ervi.  Should you release it preventatively (when aphid densities are low) or curatively (once you know you have a significant infestation)?  Contrary to release strategies for other aphids, curative releases seem to work better for foxglove aphid.   In the curative scenario foxglove aphid populations were held steady, AND A. ervi was able to establish in the crop over time.  However, in the preventative scenario, foxglove aphid numbers increased by 500% and no adult wasps could be recovered.  Not good.

curative vs preventative _Ervi for foxglove

Releases of 2 A. ervi / square meter were made when foxglove aphid populations were at 2/plant (preventative treatment; bottom line) or 20 aphids/plant (curative treatment; top line).  Although aphid numbers/plant in the curative treatment were higher, A. ervi prevented them from increasing further.  In the preventive treatment, there was no clear effect of A. ervi and aphid populations steadily rose.

Obviously, just holding aphid numbers steady is not what we’re looking for in the end, which is why Michelangelo is looking at combining releases of A. ervi with applications of Met-52, along with a novel biopesticide and/or a predatory mite VRIC is looking into (more on that at a future date!).

The other thing that’s obvious is that research greenhouse trials are NOT actual commercial greenhouse trials.  To make sure his results are applicable to YOU, the Vineland Research and Innovation Centre is looking to compare their IPM strategy with previous strategies used in commercial trials.  So, we are asking you to please fill out this survey to a) answer some general questions about foxglove aphid in the industry and b) see if we can find some suitable greenhouse collaborators for the next step.

For a second project relating to aphids, Biobest is performing a survey on the hyperparasitoid population in Ontario.  If you come across a substantial clump of aphid mummies, please email myself or Sebastian Jacob at Biobest (sjacob@biobest.ca) to coordinate sampling.  If you’d rather sample yourself, put the entire leaf with mummies into a ziplock, write down the greenhouse (or use a code name!), crop, week number, and date, and keep it cool until you can drop it  off at Vineland Station (4890 Victoria Rd N) c/o Sarah Jandricic or Rose Buitenhuis.

As always, we thank the greenhouse growers in Ontario and Quebec who are willing to host commercial research trials.  YOU are why Canada is a leader in the application of biocontrol in the greenhouse industry world-wide.

 

 

 

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This entry was posted in Aphid control, Aphids, biological control, Foxglove aphid and tagged , , , , . Bookmark the permalink.

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