About the Bollworm Complex
Reproduction and Life Cycle
Bollworms will spend the winter in their puparium underneath the soils surface; usually 5 to 10cm below. They will begin the overwintering process starting late in August or in September, and emerge sometime between April and May. When they emerge, they will mate and then the females will begin to produce eggs, often close to 1,000 over their lifetime. Host plants of the bollworm are often not in enough abundance at this time for the females to select a single site to lay her eggs on. As a result, eggs are laid in modest clumps on several different hosts such as in the whorl of corn plants, cotton, different weed types, and tobacco. However, if oviposit occurs when corn plants start silking or when tobacco is flowering, the females will only place their eggs within these field types. The eggs take between 2 and 5 days to hatch. When the later generations of this pest hatches and the corn silks have dried up, they will move to other host plants like cotton. However, the bollworm still prefers tobacco and corn to cotton, making it less likely for cotton to have an infestation. When the larvae hatch, it will take them about 17 to 25 days to reach full maturity. They will pupate near host plants in the soil taking about 16 days, when the moths will emerge. This pest can have 4 generation per year.
Bollworm Complex Identification and Habitat
The adult bollworm is a moth with a wingspan ranging from 25 to 39mm in length. Their forewings are a pale yellow to olive in colour with a dark mark in the center. The hind wings are white and have a border that is brown along the wing. The thorax and head both have hairs that are similar in colour to the forewings. There abdomen tends to be slightly lighter in colour. The eggs are dome-shaped, small, and are white when the female first lays them, developing rust brown coloured bands close to hatching time. The newly hatched larvae are relatively hairy and are cream coloured, measuring about 1.5mm in length. By the second instar, they will have developed into a light green, and then a rose or brown by the last instars. The more they develop the more pronounced their stripes will be that run lengthwise down their body, and also black spots that are dispersed over the body. Fully mature larvae can reach to be 44mm long. The pupae are slightly smaller, about 31mm in length and start off as a rust brown colour, turning dark brown close to the time the adults are ready to emerge.
The bollworm is fairly common in most areas of the Western Hemisphere, especially in the southern states. While they prefer corn, they will also feed on a number of other plants such as alfalfa, tobacco, cotton, peanut, sorghum, strawberry, soybean, sweet potato, and sweet pepper. The young larvae will cause damage to host plants by feeding on the outer layers of plant terminals. Older larvae will cause the most significant injury to plants, feeding on buds, squares, bolls, and blooms. They can burrow themselves into the plant and hollow out the bolls, which can also introduce pathogens to the plant. Even in low populations, this pest can cause a noticeable amount of damage.
Bollworm Complex Management and Control Methods
To assist in the suppression of bollworms in your crops, some cultural control methods you should consider: wherever possible, practice crop rotation with plants that are not desirable to the bollworm. Practice skip row irrigation or drip irrigation to avoid an excessive amount of irrigation. This can help decrease the chances of creating a favorable microclimate for this pest to build-up in. In infested cotton fields, you can plant sorghum or maize in-between rows to encourage the presence of aphids, who will feed on the bollworms. Placing bird perches in fields approximately 25 hectares away from each other can promote carnivorous birds such as Drongo and Myna to feed on the bollworm larvae. If you are protecting cotton crops, there is transgenic cotton available that can help keep the bollworm population to a minimum. It is important to note that having satisfactory control is often dependent on using an integrated management system that includes the use of both cultural and chemical methods.
Before treatment, you should check bollworm population levels to ensure there are approximately 20 larvae for every 100 plants. In this case, you can use chemicals such as chlorantraniliprole, flubendiamide, methomyl. Bacillus thuringiensis has proven to have successful results. Pyrethroids can also be effective when targeting adults or young larvae. Be sure to carefully read the label for cautions and proper application. It is extremely 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 Bollworm Complex Names