The occurrence of green semilooper, Chrysodeixis acuta Walker (Lepidoptera: Noctuidae) in onion was recorded for the first time from the Pune district of Maharashtra State of India. Weekly observations of the pest and its damage were made to assess the intensity of the caterpillar population and its impact to the onion crop. Early instar larvae of C. acuta feed by scraping the leaves, whereas the later instars make circular cuts in the leaves. The presence of large cuts and defoliation is a sign of infestation in onion. Since C. acuta is polyphagous, it may spread to onion crops in the region and cause significant damage to the crop. Therefore, further research is required to monitor its spread and ability to become a pest in onion.
Green semilooper, Chrysodeixis acuta Walker (Lepidoptera: Noctuidae), is a major soybean pest in India (Singh & Singh 1991). The pest also is called soybean semilooper and tomato semilooper. It is a polyphagous pest spread across the soybean growing states of India (Singh et al. 1987; Singh & Singh 1987, 1991; Gurule & Nikam 2013), Oman (Wiltshire 1984), Vietnam (Ronkay 1989), Japan (Hirashima 1989), Africa (Deiber 1985), the Canary Islands (Dufay 1970), and Australia (Neilsen et al. 1996).
Chrysodeixis acuta is a defoliator pest that damages a variety of other crops, including sorghum (Sorghum bicolor [L.] Moench; Poaceae); linseed (Linum usitatissimum L.; Linaceae); barley (Hordeum vulgare L.; Poaceae); tomato (Solanum lycopersicum L.; Solanaceae); cotton (Gossypium hirsutum L.; Malvaceae); banana (Musa paradisiaca L.; Musaceae); tobacco (Nicotiana tabacum L.; Solanaceae); and citrus (Citrus indica Tanaka; Rutaceae) during the vegetative stage, capable of defoliating plants to the point of significant crop loss (Sharma & Shukla 1993; Mishra et al. 1995; Meena & Sharma 2006; Patil et al. 2014; Shailesh & Patel 2014; Shashank et al. 2018).
The occurrence of C. acuta in onion (Allium cepa L.; Amaryllidaceae) was recorded for the first time in the state of Maharashtra, India. The incidence was observed in kharif onions planted during the 2017–2018 season (rainy season) while conducting surveillance for onion pests. Chrysodeixis acuta feeds on the leaves of onion; early instars scrape tissue from the leaves, and leaves often become transulent, showing caterpillars inside the circular leaves of the onion; later instars bore large feeding holes (Fig. 1).
The caterpillar is a glassy green in color with 3 pairs of abdominal legs (prolegs) that typically bend their body in a semi-loop while walking. The pupae, which is green at the beginning and later turns to brown, forms a white silken cocoon on the plants. Adult moths are brown, the forewing bears a dark brown pattern with 2 characteristic silver spots (Fig. 1). Black scales are on the median region with tiny silver spots on the median line of the forewing. This species also has a silvery figure of a faint 8 on each forewing, with the 2 halves separated, and the second half elongated. The wing span of the moth is 35 to 37 mm.
Once C. acuta was observed, a weekly observation was made in a 1 m2 area of 5 spots to record damage and caterpillar population. The plants, which had a circular cut on the leaves, scraped leaves, and the presence of larval fecal material, was taken as a sign of infestation. Percentage of plant damage and the number of larvae in each spot was recorded. The occurrence was observed from early Sep (36th standard meterological wk) and continued until late Oct (43rd standard meterological wk). Mean plant damage ranged from 1.0 to 4.1% damage, and was highduring mid- to early Oct (Fig. 2). A maximum of 4.1% plant damage was recorded in the 40th standard meterological wk. The caterpillar population ranged from 0.7 to 1.4 per m2 area. A maximum of 1.7 larvae per m2 were recorded during the 41st standard meterological wk. The correlation analysis between climate variables, including maximum temperature (°C, Tmax, r = 0.397), total weekly precipitation in mm (RF, r = 0.125), and caterpillar incidence revealed a non-significant positive correlation (p > 0.05). A non-significant adverse correlation was noted between minimum temperature (°C, Tmin, r = –0.456), % morning relative humidity (RH1, r = –0.521), % evening relative humidity (RH2, r = –0.234),and caterpillar population.
Although the C. acuta caused less than 5% damage to the onion, considering the nature of the damage caused and the characteristics of the pests (polyphagous), it appears to be a new issue for cultivation of the onion, because the pest is expanding its host range. Under favorable circumstances, caterpillars may cause significant defoliation in onion. As a matter of fact, whenever the soybean-onion cropping system is adopted, a fair amount of attention is needed because the magnitude of the occurrence is due more to pest pupal residuals remaining in the field. In addition, increasing onion-adjacent soybean also may favor the incidence of C. acuta. Further studies in this direction, therefore, are needed to determine the impact of the soybean-onion cropping system on C. acuta occurrence. In addition, seasonal pest biology, succession, seasonal dynamics, and host suitability also needs to be studied in order to determine an effective management approach.
The authors are thankful to the Head of the Division of Entomology, Indian Agricultural Research Institute, New Delhi, India, and to P. R. Shashank, Division of Entomology, IARI, New Delhi, India, for confirmation of insect species.