Crop: Chilli, chickpeas, maize and tomato
Why is it a problem? Caterpillars can attack a wide range of crops. In Bhutan they cause greatest damage to chillis. Chilli damage is internal, mostly to the seed, so the main affect is aesthetic and the loss of hot seeds. Whole crops can be lost locally. Newly introduced chickpeas were heavily attacked in eastern Bhutan when being trialed during the early 1990s. Larvae also feed on maize cobs, but losses are rarely significant. It can be a troublesome pest of tomato.
Where and when is it a problem? Chilli pod-borer probably causes losses in all chilli growing regions, but reports of serious losses have been received from Punakha, Wangdi and Tashi Yangtse. Greatest damage to chilli is typically early in the year (spring), and is generally localized. Losses of around 10% are common, but almost total crop loss can occur within a farm.
Caterpillars can reach 4 cm and vary in colour. The first two larval stages are yellowish-white to red-brown. Later stages are usually greenish, but sometimes brown to black.
Adults are stoutly built, large (wingspan up to 4 cm), brown or yellowish-brown moths. They have a conspicuous black spot in the center of their forewings. Eggs are small (0.5 mm diameter), yellowish with longitudinal ridges. They are laid in small batches of single eggs on the leaves of flowering plants.
Caterpillars go straight into the pod leaving no visible entry point. Feeding concentrates on the developing seed and seed bearing parts, leaving the pericarp (flesh) untouched. In chillis larvae are totally inside the fruit leaving no visible entry points. In tomatoes and pulses the front half of the body is characteristically in the fruit and the rear sticking out.
Confusion with other pests: Chilli pod-borer is the only large caterpillar in chillies.
Lifecycle: In temperate areas egg-laying starts in March. The presence of adults at lights at night is a clear indication that it has started. Females can lay more than 1,000 eggs. Larvae hatch after three days and initially feed on leaves and flowers. While growing older the caterpillars prefer to bore into fruiting bodies. Larval development takes 2-3 weeks. Pupation normally takes place in the soil and the pupal stage takes two weeks. In temperate Bhutan 2-3 generations occur, but more are likely in the south. It overwinters as pupae. Moths live for three weeks.
Dispersal: Adults are excellent fliers.
When can damage be expected? In chillis damage is greatest in early planted (spring) crops. Serious outbreaks are unpredictable and can occur on one farm but not neighbouring ones, as observed in Punakha valley in May 2016.
Hosts: Larvae can feed on a wide range of hosts. In Bhutan it can be troublesome in chilli, tomatos, chickpeas, maize and other pulses.
The chilli pod-borer is difficult to manage as outbreaks are unpredictable, and the immature stages within chillies are difficult to detect in time.
Presence of the moths near light forms a clear indication of potential egg laying activities. Scouting for eggs is one reliable method for determining the need for spraying. Eggs are small so it will require some practice to easily find and recognize them.
Effect of variety
- Maintain proper spacing between the plants. In one study damage due to the chilli pod-borer was more when spacing was 20 x 5 cm compared to 40 x 20 cm.
- Mass trapping using pheromone traps was found effective in reducing moth populations in near Punakha. Install 2 pheromone traps/ langdo or 4-5 pheromone traps/acre as soon as flowering starts to monitor and mass-trap the adults. Contact NPPC for advice on procuring pheromone traps.
- Deep ploughing of fields one week before transplanting of chilli will expose pupae to predators and the elements.
- Flooding the field will kill the pupae.
- Collect and destroy infested chilli pods. This includes all dropped chilli pods and flowers.
- Use of chemicals has four drawbacks:
- chilli pod-borer can rapidly develop resistance;
- only young caterpillars are vulnerable as the older stages are protected by the flowers or fruits in which they are boring;
- indiscriminate spraying wipes out the natural control system; and
- chilli pod-borer attacks the flowering stage so for crops depending on cross-pollination (like pulses) insecticides interfere with fruit setting.
- Chemical application needs to be accurately timed to target the vulnerable stage. Looking for eggs is one reliable method for determining the need for spraying.
- Provided application are properly timed, the recommended chemical is Fenvalerate 4D dust (1 to 2 kg per acre) or Malathion 50 EC (2 ml/litre of water). Chlorpyrifos 20 EC @ of 4 ml/1 litre of water is recommended in severely infested fields.
Version: NPPC 2017. Chilli pod-borer V1.0. Bhutan Pest Factsheet. www.PestsofBhutan.nppc.gov.bt. Date produced: 14 April 2017. Contact; firstname.lastname@example.org
Image acknowledgements: NPPC & Wikiwand.com/Helicoverpa armigera