Helicoverpa assulta, the oriental tobacco budworm, is a moth of the family Noctuidae. H. assulta adults are migratory and are found all over the Old World Tropics including Asia, Africa, and Australia.
This species has a brown coloured pattern on their forewings while their hindwings are yellowish orange and have a brown margin which has a pale mark. The wingspan is about . H. assulta is closely related to Helicoverpa armigera and Helicoverpa zea.
The larvae feed on various Solanaceae species, including Lycopersicon, Nicotiana (Nicotiana tabacum), Physalis and Solanum. It also feeds on fruits of Physalis peruviana and Datura species. Because of its feeding behavior, H. assulta is considered a pest of economically viable crops including tomatoes, tobacco, and hot peppers. Due to the pest status, understanding how to control the moth’s behavior is a priority, but the species’ larval eating behavior and growing resistance to insecticide complicate pest control.
Geographic range
H. assulta is distributed across three continents: Asia, Africa and Australia. In Asia, populations of H. assulta are specifically found in China, Korea, Thailand, and Japan. Environmental conditions, like temperature and geographic locality, can impact the fecundity of the moth.
Food resources
H. assulta is a pest of red peppers (Capsicum frutescens ), tobacco (Nicotiatna tabacum), tomato, and onion. They prefer to eat red peppers over tobacco, but are still considered a pest to both. In order to develop and survive successfully, the moth must both have access to nutrient rich food, and be able to digest and uptake the nutrients.
Capsaicin
H. assulta is one of very few insects that can successfully feed on and damage plants, such as hot peppers, containing capsaicin. Studies show that long-term dietary exposure to capsaicin stimulates larger larvae. Furthermore, its unique tolerance to capsaicin may have allowed H. assulta to expand its host range.
Life Stages
Larvae
Hatching larvae feed on tender or new leaves near the site of oviposition. When it goes through instar, larvae feed on the fruit and flowers of the host, and can infest the host over the course of their development. Newly hatched larvae exhibit a great preference for tender tobacco leaves, followed by pepper and tomato leaves. The success of H. assulta is significantly dependent on its larval diet. Larvae that fed on tobacco had a significantly greater fecundity than those that fed on red peppers. The sex ratio differs slightly depending on the type of food the larvae feed on. Larvae who feed on mainly tobacco have a higher female ratio compared to those which feed on mainly pepper. The H. assulta also preferred tomato as a host plant. The preference for bush red pepper, tobacco, and tomato may be correlated to the semiochemicals or allelochemicals of the host.
Adult
As an adult, the moth prefers to feed on tomatoes during oviposition, followed by tobacco and pepper. Larval diets also impact the number of eggs laid. Adults that previously fed as larvae upon red peppers laid significantly more eggs compared to those that fed on tobacco. Feeding on red peppers also yielded shorter generation time, heavier pupae and lower larval and pupal mortality compared to feeding on tobacco.
Mating
Mating occurs during the early hours of the scotophase or the dark phase of a light-dark cycle. However, the mating peak in virgin females tends to advance with age. Unmated adults have also been observed to live longer than mated adults. Prior to mating, females protract and retract the terminal abdomen and vibrate the wings. Mating behavior of adult males includes antennal movement, wing elevation and vibration, extension of hairs, and tapping of the female ovipositor, leading to copulation. Studies also indicate that sex pheromone release is also mediated by PBAN. Female calling and sex pheromone release are also mediated by circadian rhythms entrained to light. This moth is highly sensitive to light intensity, which impacted their sexual behavior. Female calling is inhibited in high-intensity light (50.0 lux), and promoted in low-intensity light (0.5 lux).