Pepper Weevil: Are we in the clear?

Published on by Cara McCreary

If you grow peppers in North America, then I’m sure you are familiar with pepper weevil, Anthonomus eugenii. This economically damaging pest is always at the forefront of our minds through production.

Figure 1. Snout of a pepper weevil emerging from an aborted bud.

Available insecticides have limited efficacy largely due to the concealed immature life-stages, which develop inside the buds and pepper fruit (Figure 1), that go practically unscathed following an insecticide application. For best management results, it is critical to detect pepper weevil early in the initial infestation period, then respond promptly with diligent scouting, removal of infested fruit and buds, and use insecticides ONLY when necessary. One of the most reliable tools to assist in early detection are pheromone baited traps. Commonly used traps include large yellow sticky cards (Figure 2) and lures containing compounds found in naturally occurring aggregation pheromones.

These aggregation pheromones are released by adult male pepper weevils, telling both male and female pepper weevils “this is where the party’s at — there’s food, there’s mates, come on over”. As the lures tend to lose potency over time, especially during warm weather, be sure to change traps every two weeks to maintain maximum attractiveness.

Figure 2. Yellow sticky card that captured an adult pepper weevil.

How effective are pheromone baited traps?

Pheromone baited traps undoubtedly catch pepper weevil. Apart from the pheromones, it is widely known that volatiles released from pepper plants are what is drawing in the weevils to your greenhouse. These volatiles are even more attractive when weevils are actively feeding. Think about it this way, the peppers smell delicious to weevils and that smell draws them into your crop (for meat eaters, perhaps that’s comparable to the smell of grilling a steak). As pepper weevils begin to lay eggs and feed in the crop, the “smell” of the plant changes and smells EVEN MORE DELICIOUS to the weevils, thereby drawing in even more pepper weevil (so you have a steak grilling AND you’re grilling some veggies with garlic and onions). We stick some pheromone baited traps among all these delicious smelling plants and hope (fingers and toes crossed) that we catch a nearby weevil so that we know they are there. And it’s critical that we find them early. We don’t want them getting distracted by the yummy smelling pepper plants! Although pheromone baited traps are currently the best tool we have for early detection, is there room for improvement?

Figure 3. Pepper weevil lure experiment, conducted by Cassie Russell, MSc Candidate at the University of Guelph.

Cassie Russell (MSc graduate from the University of Guelph), studied whether it was possible to incorporate other attractive compounds such as these plant volatiles (aka kairomones) in monitoring traps to improve the likelihood of successful captures. Experiments adding specific volatile compounds found that additions of these compounds could increase overall trap attractiveness. More work is needed to determine suitability in a greenhouse system as well as optimal release rates of additional compounds.

If you’d like to learn more from Cassie Russell, listen in to her podcast episode on What’s Growing ON?

How to know when your weevil is evil: A guide to distinguishing the pepper weevil from its doppelgangers

One challenge encountered when monitoring pheromone baited traps is that other equally small weevil species are often observed, and sometimes well before any pepper weevils ever appear.

This is the conundrum: Failure to properly identify and promptly respond to the presence of pepper weevil could rapidly lead to a difficult-to-manage pepper weevil population (Figure 4).

Figure 4. Distinguishing features of pepper weevil.

But, misidentifying a non-pepper weevil as one, could lead to producers spending more time and money on a higher-than-normal rate of crop scouting, infested fruit removal, and the unnecessary application of insecticides (Figure 5).

Figure 5. Distinguishing features of cabbage weevil, a species that is commonly confused with pepper weevil.

For these reasons, the accurate identification of weevil species is essential to making informed and timely pest management decisions. But can you easily distinguish between pepper weevil and it’s doppelgangers? The Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) and Agriculture and Agri-Food Canada (AAFC) initiated a collaborative effort aimed at identifying the numerous other weevil species found on pepper weevil pheromone baited traps in southwestern Ontario. This work was focused on distinguishing close relatives of the pepper weevil, and other morphologically similar weevil species to better assist IPM specialists, scouts and producers in confidently identifying the evil weevil with ease. Since 2016, thousands of weevils have been collected from traps, cataloged and their prevalence and seasonal occurrence recorded. With this information, we can help narrow down the list of suspects.

To give you a taste of some of the commonly confused weevils we’ve found on these traps, we put together a preliminary visual guide showcasing their distinguishing features. Read the full article in Greenhouse Canada magazine here.

Are we in the clear?

By late summer or early fall, if you haven’t seen pepper weevil yet in your crop, are you in the clear? The answer is effectively, sort of. The good news is that the greatest level of damage is seen when it goes unnoticed early in the summer. Then populations grow exponentially through the heat and with access to many available hosts, it becomes much more difficult to manage. If you’ve made it this far, you are much less likely to experience serious economic damage due to this pest. But that doesn’t mean you are totally in the clear. Pepper weevil can still wreak havoc through the late summer and early fall. And it can survive clean out between crops, despite strict protocols. It is still important to assume that it’s out there somewhere and to continue diligent monitoring and following management recommendations. We continue to see cases each year and receive pepper weevil specimens caught on pheromone-baited sticky traps. Producers and industry allies have done an impeccable job responding to this evil weevil and as a community we must continue to be on guard.