Can climate change be a cause for the spread of the Sena caterpillar?

The recent destruction caused by the Sena Caterpillar’s return was very prominent. The Sena Caterpillar damaged maize crops from several districts in the country. However, the director (Technical) of the Ministry of Agriculture, Anura Wijetunga, says that this harvest season, the Sena caterpillar was only found in 10-15% of maize cultivation.

The Climate Fact Checks team investigated if Climate Change impacts the spread of pests like the Sena caterpillar, which is a significant burden on agriculture.

This article will help you understand,

• Whether climate change has an impact on the spread of Sena Caterpillar
• The causes for the spread of Sena Caterpillar
• The damage to agriculture done by the Sena caterpillar.

Life cycle, feeding preferences of Sena caterpillar

Spodoptera frugiperda, locally known as Sena caterpillar with the common name Fall Armyworm, is an insect pest belonging to the Spodoptera genera in the Noctudae family. It is native to tropical and subtropical regions of America and is a major invasive pest in Africa. It has a voracious appetite and feeds on more than 80 plant species, including maize, rice, sorghum, and sugarcane.  It is considered a sporadic pest due to its migratory behavior and can migrate long distances of over 500 km on prevailing winds. As a result, it causes damage to crops.

These caterpillars consume many different crops but prefer Maize and usually feed on the undersides of leaves resulting in semitransparent patches, or “windows,” on the leaves. The young spin silk threads around them, which disperses the caterpillar via wind. The leaf whorl is preferred in young plants, whereas the leaves around the cob silks are attractive in older plants. If the plant has already developed cobs, it eats its way through the protective leaf and bracts into the side of the cob, where it begins to feed on the developing kernels. Feeding is more active during the night.

 It can spread and reproduce quickly across large geographical areas, making it an incredibly successful invasive species and persist throughout the year. Fall Armyworm has four distinct stages and six stages of the life cycle: egg, larvae, pupae, and adult. The adult is the moth stage which emerges to restart the cycle. During the first 1- 3 days of the life cycle, 200-1000 eggs are generally laid on the underside of the leaves, typically near the base of the plant, close to the junction of the leaf and the stem, as egg masses by the female moth. The color of the eggs is white, and eggs are covered with a cotton-like protective scale structure rubbed off from the moth’s abdomen after laying when the egg reaches its hatching time, its color change to black.

The larval phase comes after hatching and can be identified as the caterpillars, which usually feed on the undersides of leaves. A light-colored upside-down “Y” mark can be observed in dark brownish color faces of mature caterpillars and lasts 14-22 days. After the caterpillars reach their maximum weight and length, the weight and length gradually reduce and produce an oval-shaped cover about 1.5 cm in length and reddish brown in color, turning into pupae and coming into the ground. If the soil is too hard, the caterpillar will cover itself in leaf debris before pupating. After approximately 8-9 days. At the end of the pupae stage, it gave birth to the adult moth. The forewings of male moths have light brown and grey color spots, and females have light-colored forewings that last for five days.

Damage done in Sri Lanka by the Sena caterpillar.

Asian countries, including Bangladesh, Myanmar, Sri Lanka, and Thailand, reported the Sena Caterpillar incidents by December 2018. As a result, this became the most common issue in the Sri Lankan agriculture sector during the last few years. There was massive damage to maize cultivation which has a high demand, mainly to produce value-added products, particularly in Moneragala, Badulla, Ampara, and Anuradhapura, where many maize cultivations are cultivated well. Furthermore, this would become a threat to many other crops as well. Other field crops, which the Sena caterpillar mostly damages, comprise rice, soybean, sugarcane, tobacco, and wheat.

In Sri Lanka, more than 100,000 hectares of maize have been cultivated during the Maha cultivation season, which begins in September and runs until March every year. However, according to the Department of Agriculture, the total of 4264 hectares of corn cultivated by farmers in Puskila, Ampara District, over 3/4 of the cultivation (3556 hectares) had already been destroyed by the Sena caterpillar in 2019. Then, thousands of acres of maize cultivation in Horiwila, Anuradhapura, were infested by the Crop-destroying Fall Armyworm caterpillars in 2020.

According to its feeding behavior, the damage can be identified. The fall armyworm reaches the protective region of the whorl, where it does the most damage, resulting in ragged holes in the leaves. Feeding on young plants can kill the growing point, resulting in no new leaves or cobs. Often only 1 or 2 caterpillars are found in each whorl, as they become cannibalistic when larger and will eat each other to reduce competition for food. Large quantities of frass resemble sawdust; the plant’s growth may reduce.

How the Sena caterpillar is controlled

In addition, there is no doubt that as this pest was not reported in Sri Lanka before the year 2017, studies carried out on this pest’s feeding habit, lifecycle, and eco-friendly control measures in Sri Lankan context are rare. However, several botanical extracts from plants such as Ginger, Margosa, Lemon grass, Chickweed, and high mallow have shown promising results in controlling the FAW. Furthermore, compounds such as chlorpyrifos, Larvin 5, and monocrotophos have also shown promising results against controlling the Sena caterpillar. Recently, prof. Rohan Rajapaksa has emphasized several strategies to control this pest.

Short-Term Strategies include destroying FAW eggs found on leaves and developing whorl by hand. This requires training to detect the eggs and destroy them immediately on the ground farmers and all other responsible officers. The only opportunity to destroy the mature eggs is by applying a Department of Agriculture-approved chemical pesticide, using a knapsack sprayer or power sprayer at the recommended dilution. When the larvae are small, proper timing and spraying of pesticides are critical for the elimination of this pest.

 Mid-term and long-term strategies contain early detection of the pest, stopping its spread, initiation of research programs to import tolerant varieties, and granting permission to import such tolerant varieties. However, these should be controversial.

Recent studies have shown that synthetic insecticides have caused more than 90% larval mortality. Furthermore, the use of higher doses of chemical insecticides contributes to environmental pollution and disturbs the balance of the ecosystem. A team of experts from the African nation of Rwanda visited Sri Lankan farmlands to offer a solution to the damages caused by the Fall Army Worm in 2021; however, no one knows what sort of pesticides these Rwandan Experts have recommended. However, it is essential to highlight the importance of discovering eco-friendly control measures to control FAW soon.

Has Climate Change increased the spread of the Sena caterpillar?

One of the biggest threats in the world of agriculture is climate change which is likely to result in crop failure. Studies have revealed that the impact and consequences of climate change on agriculture tend to be more severe for countries like Sri Lanka with higher initial temperatures, areas with marginal or already degraded lands, and lower levels of development with little adaptation capacity. These changes may also affect insect pest occurrence. Increased temperature can affect insect survival, growth, geographic range, and population size.

Temperature and rainfall have a powerful influence on insect pests’ development, reproduction, and survival. As a result, these organisms will likely be affected by any changes in climate. Besides, several types of pests arise in Sri Lanka and worldwide due to climate change and attack valuable crops.

FAW can also breed continuously in areas with suitable climates. Also, it is a well-known sporadic and long-distance migratory pest, with adult moths able to fly over 100 km in a single night. Because the FAW has a wide distribution, it is subjected to much climatic diversity, namely, temperature, moisture, and soil type. These adaptations can be directly related to the connection between climate change and the spread of this pest.

Moreover, insect pest responses to environmental change are crucial for understanding how agroecosystems will respond to climate change. Population abundances of pests, beneficial insects, competitors, and symbionts may undergo substantive changes with a changing climate, including FAW. These changes can cause positive, negative, and neutral interactions to become more or less intense, and their abundance may increase with a changing climate. It may become more invasive and impact a more comprehensive number of species within its realized niche.

With the emerging threat of FAW in the past three years, finding eco-friendly control measures is of great importance to Sri Lanka. It is also important to investigate possible threats of damaging other crops by this caterpillar and observation of the life cycle of this pest to check its life cycle duration and characteristics under tropical and climate change in Sri Lanka.

(With Inputs from Nuwandhara Mudalige )