Overview
- What is Helicoverpa armigera?
- What is the impact of Helicoverpa armigera?
- How do I know if I have a Helicoverpa armigera problem?
- How do I get rid of Helicoverpa armigera?
- Summary
The cotton bollworm (Helicoverpa armigera), also known as the old world bollworm, is a species of moth that causes significant agricultural damage in outdoor and greenhouse settings. It has a broad global distribution and is found in Africa, Europe, Asia, Australia, and South America, including Brazil. A relative of this species commonly called the corn earworm (Helicoverpa zea) is a pest in the United States that feeds on many host plants causing significant economic damage. H. armigera attack many plants and can particularly damage soybean, cotton, corn (maize), tomatoes, pigeon peas, and chickpeas. The larval form causes damage to plants by directly feeding different plant parts, while adults are able to fly over long distances, allowing them to spread out over wide areas. In this article, we will discuss how to identify and control this pest using integrated pest management that includes cultural, mechanical, and biological control methods.
What is Helicoverpa armigera?
Adult H. armigera moths are light brown with dark markings and have a 3.5 to 4 cm wingspan. Males can appear greenish-grey, while females are typically orange-brown. H. armigera larvae occur in various colours depending on the stage of development. Less developed larvae (first and second instar larvae) are yellowish-white to reddish-brown, while fully grown larvae are typically 3 to 4 cm long with brown heads and light and dark bands along the body. Larvae can also appear in black, pinkish or reddish brown, and green. The pupae (cocoons) of the cotton bollworm are found in the soil or on host plants and are brown and measure between 1.4 and 1.8 centimetres. Eggs are round or pomegranate-shaped and yellow-white when laid but become darker closer to hatching.
Lifecycle
Like other insect pests, H. armigera completes its life cycle faster in warmer seasons and climates than colder ones. This means that its numbers can increase more quickly in warmer environments, leading to the production of up to eleven generations per year in favourable conditions. Adults emerge from cocoons as early as March and as late as June and live for around ten days, during which females can lay thousands of eggs on various parts of the host plant. The eggs take between three and eleven days to hatch. Larvae feed on the host plant for 19 to 36 days and progress through seven developmental stages (instars). When fully grown, they drop to the soil or remain on the host plant and form a cocoon. How long it stays in this stage depends on the climate and season. H. armigera overwinters in soil in its cocoon stage, and adult moths emerge the following spring and restart the cycle. The entire lifecycle can take four to twelve weeks, not including the overwintering stage.
What is the Impact of H. armigera?
H. armigera larvae feed directly on many parts of host plants, including leaves, buds, flowers, bolls, seeds, and fruit. This leads to a significant loss of yield. Furthermore, this pest has a preference for high-value crops like cotton, tomato, and sweetcorn. Their ability to rapidly migrate and multiply means they cause significant economic damage to affected areas. For example, by searching Google Scholar or PubMed, you can find studies describing how this pest inflicted billions of dollars in damage to Brazilian soybean and cotton harvests in 2012 and 2013. The cost of control measures to deal with this pest can also put a significant strain on countries with a significant H. armigera problem. Adult moths do not cause damage to plants. However, a higher number of adults may indicate large numbers of larvae.
How do I know if I have a H. armigera problem?
H. armigera larvae are easier to see when they feed on leaves, flowers, and the outside of fruits. However, they also bore (tunnel) inside plants to feed on internal tissues, making them more challenging to spot. It is possible to spot holes created by this pest, but plants often need to be cut open to identify H. armigera. Symptoms of this pest vary by host plant. For instance, it preferentially targets young tomatoes and cotton bolls, causing them to drop off the plant. In pea plants larvae can penetrate the pod and feed on peas directly. It can also eat into peppers. Larvae that hatch from eggs laid in corn silk bore into the ear and feed on kernels.
How do I get rid of H. armigera?
Fortunately, several effective methods exist for dealing with H. armigera and reducing its impact on crop yield. Integrated pest management is an approach that includes implementing various biological, chemical, physical and crop specific (cultural) techniques, which you can learn more about in this blog.
Monitoring
This pest can attack plants in the early stages of growth, emphasising the importance of early and vigilant monitoring for larvae and signs of damage. As described above, larvae can be found in different parts of the host plant.
Cultural control
Cultural control involves different farming techniques to reduce pest populations and prevent damage.
- Many pests can live on or in dead plant material, so it is crucial to keep growing areas clear to help keep numbers down.
- Pupae busting is a pest control method that consists of the cultivation of the soil after harvest. This practice disrupts the development of insect pupae in the soil, preventing them from maturing into adult pests and reducing the number of future generations.
- Trap cropping involves intentionally planting crops that pests prefer to keep them away from cash crops. Trap crops can be planted at the perimeter of growing areas or among cash crops.
Mechanical control
Mechanical control can involve using:
- Physical methods like traps, barriers, or manual removal to reduce pest populations and prevent crop damage.
- Pheromones, a type of semiochemicals, can be used to attract and trap pests.
- Handpicking and destroying infested fruit can also reduce pest numbers.
Biological control
Biological control methods use products derived from nature to provide an alternative to harsh broad spectrum insecticides, which damage the environment and human health.
Microbials
These are species of bacteria, fungi, and viruses that infect and kill pests. Different types of viruses, such as Baculovirus and Nucleopolyhedrovirus, can target and kill H. armigera in its larval stage. The fungal species Isaria fumosorosea also causes lethal infections in H. armigera.
Macrobials
Macrobials are beneficial insects, mites, and nematodes, that are used to control pest populations. Trichogramma pretiosum is a parasitic wasp that kills H. armigera by laying its eggs inside the pest’s eggs. The Trichogramma larvae then consume the contents of the Helicoverpa eggs, preventing them from developing and hatching.
Summary
H. armigera poses a significant threat to agriculture in Brazil and globally due to its wide host range and ability to proliferate and migrate rapidly. Effective management of this pest requires a multifaceted approach, including vigilant monitoring, cultural and mechanical control methods, and biological agents. By understanding the lifecycle and behaviour of H. armigera, farmers can implement strategies to mitigate its impact and protect valuable crops.
Search for specific pests, such as the fall armyworm (Spodoptera frugiperda) and corn earworm (Helicoverpa zea), using the CABI Bioprotection Portal to receive a list of effective biological solutions. Visit our resource page to find articles describing how to manage lepidopteran pests that commonly affect soybeans in Brazil and many others.
