Authors: Cara McCreary, Greenhouse Vegetable IPM Specialist, OMAFRA and Tracey Baute, Entomologist – Field Crops, OMAFRA

What is European Corn Borer (ECB) (Ostrinia nubilalis)?

In a nutshell, ECB is a small nocturnal brown moth. Problem is, they may choose pepper plants as hosts for egg-laying and larval development. Since larvae feed and develop inside the pepper fruit, which is the marketable portion of your plants, it’s important to be on the lookout for them. ECB overwinters as fully-grown larvae in corn stubble or other plant material and complete development the following spring. When adults emerge, they take flight to look for mates and suitable hosts such as corn, wheat, potatoes, hemp and unfortunately greenhouse peppers to feed and reproduce.

Figure 1. European corn borer larva feeding inside pepper fruit

What do we know about ECB in Ontario?

There are three different ECB areas in Ontario…a 1-generation area (univoltine), a 2-generation area (bivoltine), and an overlap area that has both univoltine and bivoltine populations (Baute 1999). Sound confusing? See the map in Figure 2 for a visual representation of which populations are found where.

Figure 2. European corn borer generation map, Baute Thesis 1999.

ECB Pheromone Races

As if having univoltine, bivoltine and overlap areas isn’t enough… ECB also has two different pheromone races that co-exist in the United States, Canada and Europe. Each race releases slightly different chemical compounds than the other to serve the same purpose — attracting mates. Historically, Z-race was assumed to prefer corn, though since the introduction of Bt corn, experts are questioning if that has changed as a survival mechanism. New research is looking into ECB on other hosts to determine what pheromone race they are from. The E-race has been known to pursue other available hosts, which may include greenhouse peppers. There is also a hybrid race that evolved from the E- and Z-race mating with each other that responds to another slightly different chemical blend. It is currently unclear which hosts it prefers.

Lucky for us, ECB is predictable!

Degree Days (DD) are heat accumulations using a base temperature (i.e. a minimum temperature required for development). A degree day model was validated to predict flight patterns of ECB in southwestern Ontario (Baute 1999) (Figure 3). This model gives us an idea when ECB flight begins, peaks and ends based on moth catches and can be used to guide scouting and management decisions. (Weekly updates on DD accumulations will be posted to this blog).

Figure 3. Degree day model for European corn borer in southwestern Ontario

Monitoring for ECB

Aside from using the model for ECB DD, monitoring can be done using light traps and pheromone traps (Figure 4). All three approaches can help make efficient use of scouting efforts. You can also think of trapping as a form of physical management, since every adult that is captured is not mating or laying eggs.

Figure 4. European corn borer pheromone trap.

Pheromone traps or light traps will be attracting adult moths which are approximately 2 cm (0.8 in.) long, light-brown with dark wavy lines running across each forewing. Males are typically darker and smaller than females.  Pheromone traps only catch males (lure is the female sex pheromone) but there are other look-alike moths that can also end up in the traps. For more details on setting up pheromone traps and to view adult moths and their look-alikes click here.

Scouting for ECB should include close observations of pepper fruit, specifically looking for signs of larval entry. When larvae chew their way into the pepper fruit, they leave holes that may be hidden beneath the calyx or they could be entirely visible. They do leave some evidence in the form of frass (i.e., poop) near their entry point (Figure 5). Mature larvae are approximately 2.5 cm (1 in.) in length, creamy white to pale grey with two small spots on each abdominal segment, with a black head. If infested fruit are found, remove and discard properly (e.g. crush, freeze, or bury deep) to intercept the larvae from completing development.

Figure 5. European corn borer larva feeding and boring into pepper fruit with piles of frass around the calyx.

Observing signs of larval entry is most likely although you may encounter ECB egg masses under leaves (Figure 6).

Figure 6. European corn borer egg mass under a leaf.