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The fall armyworm Spodoptera frugiperda is a lepidpopteran pest that feeds in large numbers on leaves and stems of more than 80 plant species, causing major damage to economically important cultivated grasses such as maize, rice, sorghum, sugarcane but also other vegetable crops and cotton. It has been repeatedly intercepted at quarantine in Europe and was first reported from Africa in 2016 where it is causing significant damage to maize crops and has great potential for further spread and economic damage. Scientists generally say that this notorious pest is there to stay and therefore the need for stringent management practices to minimize economic damage, thus enhancing food security.
Detailed Description
Eggs
Eggs are spherical (0.75 mm diameter); they are green at the time of oviposition and later become light brown. Egg maturity takes 2-3 days (20-30°C). Eggs are usually laid in masses of approximately 150-200 eggs which are laid in two to four layers deep on the surface of the leaf. The egg mass is usually covered with a protective, felt-like layer of grey-pink scales (setae) from the female abdomen. Up to 1000 eggs may be laid by each female.
Larvae
Larvae are a light green to dark brown with longitudinal stripes. In the sixth instar, larvae are 3-4 cm long. Larvae have eight prolegs and a pair of prolegs on the last adbominal segment. On hatching they are green with black lines and spots, and as they grow they either remain green or become buff-brown and have black dorsal and spiracular lines. If crowded (by a high population density and food shortage) the final instar can be almost black in its armyworm phase.
Large larvae are characterized by an inverted Y-shape in yellow on the head, black dorsal pinaculae with long primary setae (two each side of each segment within the pale dorsal zone) and four black spots arranged in a square on the last abdominal segment. There are usually six larval instars, occasionally five.
Pupae
Pupae are shorter than mature larvae and usually they are shiny brown.
Adult Male
Male body length is 1.6 cm and wingspan 3.7 cm. The forewing is mottled (light brown, grey, straw) with a discal cell containing straw colour on three quarters of the area and dark brown on one quarter of the area.
Adult Female
Female body length is 1.7 cm and wingspan 3.8 cm. The forewing is mottled (dark brown, grey). Hindwings are straw colour with a dark brown margin.
Distribution
S. frugiperda is native to tropical and subtropical regions of the Americas. In 2016 it was reported for the first time from the African continent, in Nigeria, Sao Tomé, Benin and Togo (IITA, 2016; IPPC, 2016). It has now been confirmed in Ghana (CABI, 2017), Zimbabwe (FAO, 2017), Swaziland (IPPC, 2017), Kenya (Republic of Kenya Ministry of Agriculture, Livestock and Fisheries, 2017), Zambia (IPPC, 2017d) and Congo Democratic Republic (IPAPEL-FAO, 2017), and there are preliminary reports of the pest in Malawi, Mozambique, Namibia and South Africa (BBC, 2017).
Growth Stages
Flowering stage, Fruiting stage, Seedling stage, Vegetative growing stage – Almost any stage.
Symptoms
Seedlings are fed upon within the whorl. Larger larvae can cut the base of the plant. Mature plants suffer attack on reproductive structures. On tomato plants, buds and growing points may be eaten and fruits pierced. Maize leaves are eaten and the whorl (funnel) may be a mass of holes, ragged edges and larval frass. Young larvae skeletonize the leaf lamina. Early in the season, severe feeding damage to young plants can kill the growing point; a symptom called ‘dead heart’ in maize. Maize plants may have the cobs attacked by larvae boring through the kernels. At high densities, large larvae may act as armyworms and disperse in swarms, but they often remain in the locality on wild grasses, if available.
Biology and Ecology
Eggs are laid at night on the leaves of the host, stuck to the lower surface of the lower part of the lower leaves, in tight clusters of 100-300 and sometimes in two layers, usually covered with a protective layer of abdominal bristles. Hatching requires 2-10 days (usually 3-5). The young larvae feed deep in the whorl; the first two instars feed gregariously on the underside of the young leaves causing a characteristic skeletonizing or ‘windowing’ effect, and the growing point can be killed. Larger larvae become cannibalistic and thus one or two larvae per whorl is usual.
The rate of larval development through the six instars is controlled by a combination of diet and temperature conditions, and usually takes 14-21 days. Larger larvae are nocturnal unless they enter the armyworm phase when they swarm and disperse, seeking other food sources. Pupation takes place inside a loose cocoon in an earthen cell, or rarely between leaves on the host plant, and 9-13 days are required for development. Adults emerge at night, and they typically use their natural pre-oviposition period to fly for many kilometers before they settle to oviposit, sometimes migrating for long distances. On average, adults live for 12-14 days.
Detection and Inspection
Detection is facilitated by searching fields for leaf feeding damage and by pheromone traps.
Similarities to Other Species/Conditions
Larvae of S. frugiperda are distinct in their aggressive feeding behaviour and dark coloration. Adults of S. frugiperda can be confused with those of S. exempta and S. littoralis. In S. frugiperda the veins of the hindwing are brown and distinct, and in the male forewing the pale orbicular stigma has a pronounced pale ‘tail’ distally.
Prevention and Control
There are various management control options that has been identified, tried and tested and recommended for incorporation into the Integrated Pest Management (IPM) but in this particular bulletin, only chemical control is going to be dwelt on.
The following chemicals have been suggested. NB. These are only technically wise suggestions and NOT an order. Agricura does not condone the use of unregistered products for unregistered uses and therefore accepts no responsibility whatsoever for any crop damage injury or loss of any kind as a result of using a product on a crop for which it is not registered.
Emamectin benzoate + Lufenuron, Emamectin benzoate + Thiamethoxam, Avaunt/Steward, Lannate/Methomyl, Runner, Cartap hydrochloride, Acephate, Carbaryl 85wp , Tank mixture of Chlopyrifos + Fenvelerate or Lambda cyhalothin or Karate Zeon, Tank mixture of Belt + Decis forte, Delegate/Spinosad, Tracer/Spinosad, Ampligo (Zeon chemistry + chlorantraniliprole).
For more information contact us today:
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Acknowledgements:
IPPC, 2017. Occurrence of Fall Armyworm (Spodoptera frujiperda) in Mozambique. IPPC Official Pest Report No. MOZ-61. Rome, Italy: FAO.https://www.ipcc.int/