Arrival of Fall Armyworm (FAW) in Manipur : A concern
Mohd Mustaque Ahmed
Recently there was news about the recent infestation of FAW (Fall Armyworm) in Manipur. The worm is commonly known as American wormand it is a moth like other caterpillars. It was originated from American countries. Escaping from there it landed in African countries in the year 2016. Then onwards it started showing its impact in the production of corns in Africa and now in Europe and Asian countries.
In India, the first of its report came from Karnataka and southern states then from western states and eastern states. Now, it’s the turn of Manipur and it is likely that the other northeastern states are also infested by this worm. The journey of fall armyworm is given from the year 2015 to 2019 (Table 1). The maize (Chujak) is its host plant and it is third most important food plant in India. Food and Agriculture Organization (FAO) of United Nations has already declared FAW (Spodopterafrugiperda) as a food security threat in the African continent. Although there is great loss in terms of thousands of million dollars in African countries, the impact of armyworm in India and its states is yet to assess.
Once infested by this moth there is great loss always in the crops.
RicBessin of University of Kentucky wrote, “fall armyworm feeds during the day and night, but are usually most active in the morning or late afternoon. The most common damage is to late pre-tassel corn”.
It travels long distances during summer. Maize is one of the breakfast foods in Manipur. It can be recalled that the estimated production of maize in India in the year 2011-12 was 21,000 matrictonnes(MT) while Manipur’s share was 9.10 thousand tonnes.
How is this moth recognized?: A search of moth infestation in ten plants in ten locations or twenty plants in five locations is considered to be adequate to assess the proportion of plants infested. Moth population can be sampled by using backlight traps and pheromone traps.
Life stages of Fall Armyworm (FAW):The followingstages of fall armyworm (pic.3) are accepted.
(i) Adult stage: It has a length of 6cm to 20 cm (fpic.2). Male: The forewing is shaded gray and brown with triangular white spots at the tip and near the center of the wing. Female: The forewings are less distinctly marked, ranging from a uniform grayish brown to a fine mottling of gray and brown. Adults are nocturnal and most active during warm and humid evenings. The adult stage extends up to twenty one days but the average is 10 days.
(ii) Pre-Oviposition stage: The pre-ovipositionstage is of three to four days and the female deposits eggs during the first four to five days of life cycle.
(iii) Egg stage: Egg masses are laid in fluffy masses on crowns of seedlings and on leaves of older plants. The total egg production per female averaged about 1500 with a maximum of over 2000.The most of the eggs are deposited in a single layer attached to foliage. A layer of egg scales are attached over the eggs appearing moldy appearance. The egg is dome shaped and it curves upward to a broadly rounded point at the apex. The egg stage is only two to three days during the summer months. In 5 to 10 days tiny caterpillars are hatched and feed for several weeks.
(iv) Larvae stage: There are six instars of fall armyworm. Head capsule widths are ranged from 0.35 to 2.6mm and it attains lengths ranged from 1.7 to 34.2mm.The face of the mature larva is marked with a white inverted “Y”. The stage is around 10 to 22 days and It varies season to season. First larvae stay close to the ground, feeding on grasses and other low growing plants. Then, larvae have cannibalistic behavior for e.g. it causes damage by consuming foliage of corn, cabbage, and beans. There is impact particularly in the corn plants by younger larvae to older larvae when eating on young leaf tissue to extensive defoliation respectively. Thus the damage is from mild stage that is holes of leaves to often leaving behind stalks of corn plants/a ragged/torn appearance. The plants are just skeletonizing due to their eating behavior. Larvae (Pic.1) will burrow into the growing points, destroying growth potential of plants. They sometimes burrow into the ear and feeding on kernels of corn. Total devastation of corns is due to this critical stage of FAW.
(v) Pupal stage: The pupation takes place inside the soil. The pupa is reddish brown in colour and measures 14 to 18 mm in length and 4.5mm in width. It is of 7 to 13 days period and this duration may differ from country to country.
Fall Army worms (FAW) are produced three to four times in a season. Generation after generation of worms is coming out of gardens for e.g. in coastal areas of North Florida the moths are abundant from April to December but some are found even during the winter months.
Some species of army worms will lay up to six times. Army worms overwinter as eggs and pupae beneath the soil while in warm climates they may be active entire year.
They move from one place to new areas en mass as its name suggests, an army on the march. The invasion of armyworm occurs after a cool wet spring. They lay eggs under the cover of darkness.
John L.Capnera of University of Florida wrote, “the lifecycle of armyworm is completed in about 30 days during the summer, but 60 days in the spring and autumn, and 80-90 days during the winter”.
Natural enemies: Numerous species of parasitoids affect fall armyworm. Some of the predators are ground beetles, the striped earwig, the spine soldier bug and the insidious flower bug. Some other predator vertebrates are birds, skunks and rodents. It is also reported that fungi, nematodes, protozoa, viruses etc are natural enemies of armyworms.
Control measures:The following control measures can be taken up to prevent FAW.
§ Biological Control: The most feasiblepathogen till date is Bacillus thuringiensis.
§ Cultural techniques: The employing of early planting and/or early maturing varieties is the most important cultural practice.
§ Insecticides: It is applied during vegetative and the silking stage. The insecticides may be applied in the irrigation water if sprinkler is used. Liquid insecticides should be applied to larvae less than 1 ½º only. The application of exact chemicals, dose and mode of application may be consulted with the nearest department of agriculture.
§ Resistant Plants: The resistant varieties of maize are yet to recognize since the fall armyworm is of only recent infestation.
§ Weed management: Weedy grasses should be burned down with a herbicide at least seven days before corn emergence. Herbicides applied to weedy grasses after corn emerges should be tank mixed with an insecticide.
Any suspect of the presence of this moth in the fields/home gardens one should inform to the nearest agriculture department. Therefore, the farmers should keep vigil of their plants (Chujak) in the fields and gardens.
The author is PhD student at Dept. of Botany, University of Science & Technology, Meghalaya, Ri-Bhoi, Baridua-793101