Spotted stalk borer facts for kids

The spotted stalk borer or spotted stem borer is a type of moth known as Chilo partellus. It belongs to the Crambidae family. A scientist named Charles Swinhoe first described it in 1885. You can find this moth in countries like India, Pakistan, Iran, Ethiopia, Lesotho, Madagascar, Malawi, South Africa, Sudan, Tanzania, Uganda, and on Mayotte.

C. partellus is a harmful insect that probably came to Africa from India in the early 1900s. Since then, it has spread across many countries in eastern and southern Africa. It is now thought to be moving into western Africa too. This moth is originally from Asia and became common in eastern Africa in the 1930s. It is one of the most damaging pests for crops in Asia and Africa. It attacks almost all parts of a plant, except for the roots.

Where the Spotted Stalk Borer Lives

The spotted stalk borer has spread quickly over a large area. It is very good at settling in new places and causes a lot of damage wherever it appears. Generally, C. partellus prefers warmer areas and lower to middle elevations (below 1500 meters). However, they have now been found in higher places, like Ethiopia, at 2088 meters.

This moth is very invasive. It can take over areas where other native stemborer species, like Busseola fusca and Chilo orichalcociliellus, used to live. Temperature and humidity are very important for adult C. partellus to survive and settle in new environments.

What the Spotted Stalk Borer Eats

C. partellus is a generalist herbivore. This means it eats many different kinds of plants. It feeds on both cultivated crops and wild plants.

How the Spotted Stalk Borer Looks

Eggs are flat and oval-shaped. They are creamy white and about 0.8 mm long.

Larvae (which are like caterpillars) can be creamy white to yellowish-brown. They have four purple-brown stripes running along their bodies. These larvae also have dark brown spots on their backs, which gives them their "spotted" look. When fully grown, the larvae have a reddish-brown head. They also have a shiny, reddish-brown to dark brown plate on their upper body, called a prothoracic shield.

Pupae can be up to 15 mm long. They are slender and shiny. The pupae of C. partellus are light yellow-brown to dark red-brown.

Adults are small moths. Their wings are usually 7–17 mm long, and their wingspan (from one wingtip to the other) is 20–25 mm. The front wings of adult moths are yellowish-brown. They have darker patterns that form stripes. The back wings of male moths are a pale straw color, while female moths have white back wings.

Sometimes, other similar moths, like Chilo orichalcociliellus found in East Africa, can be mistaken for Chilo partellus.

Life Cycle of the Spotted Stalk Borer

Female moths lay their eggs in groups of 10 to 80. They place them on the top or bottom of plant leaves, usually near the main vein. These eggs hatch after 4 to 10 days.

Younger larvae (caterpillars) eat the tender, rolled-up leaves at the top of the plant. As they get older, the larvae tunnel into the plant stems. They feed and grow inside these tunnels for about 2 to 3 weeks. Once fully grown, they turn into pupae and stay inside the maize stem. After 1 to 2 weeks, the adult moths emerge from the pupae. They then mate and lay eggs on other maize plants, continuing to damage crops.

During dry seasons, larvae might enter a state called diapause. This is a period where their development stops for several months. They will only turn into pupae once the dry season ends and rain returns. Adult moths usually emerge from pupae in the late afternoon or early evening. They are active at night and rest on plants during the day.

The entire life cycle takes about 3 to 4 weeks. However, this can change depending on temperature, humidity, and other factors. If conditions are good, with warm temperatures, high humidity, enough water, and plenty of host plants, five or more generations can develop. C. partellus can reproduce and grow all year long.

What the Spotted Stalk Borer Does to Plants

This pest causes huge losses to crops. For example, it causes about US$334 million in damage to sorghum alone each year in dry, warm regions.

C. partellus attacks many types of grass. These include both cultivated crops and wild grasses. Some of the cultivated crops it attacks are maize (corn), sorghum, pearl millet, rice, and sugarcane. Wild plants it feeds on include elephant grass (Pennisetum purpureum), reeds (Phragmites), and vossia (Vossia cuspidata).

When an insect finds a host plant, it goes through several steps. These include finding the plant, feeding on it, using the food for energy, growing, surviving, laying eggs, and more. If a plant does not meet these needs, the insect will find it unsuitable. So, how much an insect settles on a plant depends on how the insect reacts to different plant features.

Several things can make insect pest problems worse. For example, creating an environment that helps insects grow and reproduce can increase their numbers. On the other hand, using too many chemicals (like insecticides) or unbalanced fertilizers can also cause problems.

Damage to plants can start about two weeks after the seedlings appear. The first sign is small, irregular holes in the leaves. These are caused by young larvae eating the rolled-up leaves. Later, these holes can turn into longer marks on the leaves. Infested plants look torn and unhealthy. Older larvae leave the rolled leaves and bore into the stem. They reach the growing point of the plant. Here, the larvae cut the plant, causing a symptom called "deadheart". This means the central part of the plant dies.

So, the damage from this pest includes eating and destroying leaves. It also creates many tunnels in stems and maize cobs. This stops nutrients from flowing through the plant. The plant can even die if the growing point is damaged.

How Plants Defend Themselves

Studies show that some plants can defend themselves against C. partellus. For example, some types of maize have learned to react when C. partellus lays eggs on them. They release special smells that attract tiny wasps. These wasps are natural enemies of C. partellus and can kill them. Scientists think this plant defense could be used to help manage the pest. However, more research is needed to understand how this works fully.

Also, some plants might produce bad-tasting chemicals when C. partellus larvae eat their leaves. This makes the plants less appealing to the pests. This could be another way to control C. partellus.

How to Manage Spotted Stalk Borers

There are several ways to reduce the number of C. partellus pests. These methods include:

Finding the Pests: You can spot C. partellus infestations by walking through fields. Look for plants that look unhealthy or have "deadhearts." You can also cut open infested stems to find caterpillars and pupae. It's a good idea to let them grow into adult moths to be sure they are C. partellus.

Farming Practices:

• Intercropping: Planting maize together with non-host crops like cassava can help reduce the C. partellus population.
• Trap Plants: You can use "trap plants" like Napier grass (Pennisetum purpureum). These plants attract adult female moths away from the main crop. More eggs are laid on the trap plant, but the larvae don't grow well there. This method is called "push-pull".
• Destroying Plant Leftovers: Make sure to destroy all parts of infested maize plants after harvest. This kills any remaining larvae and reduces the chance of new infestations.

Biological Control: Two types of parasitic wasps, Cotesia flavipes and Xanthopimpla stemmator, can attack and kill C. partellus. These wasps lay their eggs inside C. partellus (C. flavipes lays eggs on the larvae, and X. stemmator lays eggs on the pupae). When the wasp eggs hatch, the young wasps eat the pest from the inside. Then, they come out and spin cocoons. By protecting the habitats of these helpful wasps, we can help reduce C. partellus numbers.

Chemical Control: Applying special granules or dust to the rolled-up leaves early in the plant's growth can kill young larvae. However, this method is not very effective once the larvae have bored into the stem. Also, studies show that using nitrogen fertilizer can help control C. partellus on maize crops.

Climate Change and the Borer

Climate change might be one reason why this pest is moving to higher places. This means it is spreading to new areas. A study showed that temperature and humidity greatly affect how fast C. partellus develops.

The study found that eggs took longer to hatch in colder temperatures. Larvae developed faster in warmer temperatures because they were more active and ate more. Pupae also developed faster in warmer temperatures. This means that higher temperatures lead to a shorter time from egg to adult. Also, eggs hatched faster in higher humidity. This suggests that humidity changes how temperature affects the egg period. In general, higher temperatures also mean a shorter life cycle for the pest. This means the adult moths don't live as long when it's hotter.