Lesser Cornstalk Borer

Family: Pyralidae

About the Lesser Cornstalk Borer

Reproduction and Life Cycle

The lesser cornstalk borer has 2 generations per year. This pest overwinters as larvae or pupae in the ground. When they emerge as adults in the spring, they will mate and the female will lay her eggs underground beside host plants. Sometimes; however, they are placed on leaves, stems, or on the soils surface. A female can lay around 200 eggs over her lifespan, sometimes more. The eggs will hatch within 3 days. Larvae live in the ground, creating silken tunnels that they remain in, except for when they feed off of the plants stalk and stems. The larvae will mature within 20 days. On average they go through 6 instars, but this can be modified to 5 or up to 9, contingent on climate conditions. The mature larvae will then enter the pupal stage of development, which takes on average 10 days to complete, but can range anywhere from 7 to 13 days. When the adult emerges, their lifespan is approximately 10 days.

Lesser Cornstalk Borer Identification and Habitat

Identification

This pest as an adult will develop a wingspan of about 17 to 22mm in length. You can easily distinguish the males from the females. The male’s forewing is generally yellow-brown with a band that is darker than the body on the inner margin and has purple scales. The females are black with purple or red scales at the forewing’s base. The thorax is also darker on the females. At rest, wings are held close to the body on their back. The adults tend to be the most active during the evening as long as temperatures are above 80 degrees Fahrenheit, and especially when it is humid, as these conditions are ideal for oviposition and mating. The eggs are only about 0.6mm long and 0.4mm wide. They are oval and start off as a green colour, but will later change to pink and then red. Once they have matured, the larvae are typically 16mm in length. During this stage, they are extremely active and will wiggle aggressively when disrupted. When they first hatch, larvae are yellow-green with red pigmentation on their back. Later in their development they will have white stripes running lengthwise down their body (mainly noticed during the fifth instar). Fully mature larvae will be a blue-green or red-brown with yellow-white stripes on its back. Their heads are black. When they enter their pupal cells, they will be about 8mm long. They construct their pupae out of silk and sand, creating the cocoon which is 16mm long. They start as a yellowish colour and will then turn brown and black right before the adult emerges.

Habitat

The lesser cornstalk borer is common in the western hemisphere, mainly in the southern areas of the United States. They tend to prefer plants that grow in poor soil types, especially those that are sandy. They are attracted to grasses, and a variety of crops, mainly corn. They thrive in hot, dry weather. These warmer temperatures can lead to higher cornstalk borer populations since eggs are laid at a quicker rate in that type of condition. If there are more than 10 days in the summer that have temperatures of at least 95 degrees Fahrenheit with precipitation less than 2.5mm, an outbreak is very possible. If there are 5 to 9 days with the above mentioned conditions, there is still a possibility of an outbreak and lesser cornstalk borers should be scouted for in your fields. The larvae will tunnel into the plants stem and feed from within, whether above or below ground. The plant will often be stunted, will wilt, and buds sometimes wither. This can eventually lead to the plants death. Another way to tell that this pest has infested your crops is silken webbing that forms a tube by the stalks base in the soil.

Lesser Cornstalk Borer Management and Control Methods

Cultural Control

For preventative measures, ensure you are practicing clean cultivation. Keep weeds along the fields edges to a minimum. Plowing in the fall can help kill any borers who are overwintering. Early planting can also keep their population in check. Always make sure weeds are removed from the field before planting. However, it is important to note that conservation tillage can also lessen plant injury because when crop residue remains at the soils surface, the larvae will sometimes feed on this instead of the newly seeded plants. Keeping the soil moist through irrigation can also be a useful deterrent for the females from laying their eggs. You can plant RIB (refuge in a bag) corn seed; this seed helps in the protection from corn pests while still having 5% seed that has not been treated with Bt in order to keep this method effective, as that 5% refuge seed does not allow the pest to grow immune to this treatment plan. Not a lot of natural enemies have been overly successful at controlling the lesser cornstalk borer. Note that having satisfactory control is often dependent on using an integrated management system that includes the use of cultural and chemical methods.

Chemical Control

Granular insecticide types are often used to control this pest. They are typically applied in the seed furrow. Liquid pesticides can work as well, but must be aimed at the plants roots. In the past, chlorpyrifos, chlorantraniliprote and bifentrhin have been helpful in suppressing the cornstalk borer. Be sure to carefully read the label for cautions and proper application. It is important to never spray on days that are windy. After applying insecticides, it is important to irrigate sprayed area to increase the insect control. That being said, a large rainfall or irrigation soon after the application can reduce the concentration insecticides.

Latin / Alternative Lesser Cornstalk Borer Names

• - Elasmopalpus lignosellus
• - Jumping borer

Sources