Learn about how to control pests of soyabean!
It has been found that no information on the insect pests of soybean, has been considered as a wonder crop in India. Because the soybean incorporates in itself the characteristics of pulses, oil seeds and vegetables. Thus meeting the important basic requirements of oil, protein and vegetables needed by man. Despite numerous insects found on soybean only a small number of them are economically important.
Hence, in this article an attempt has been made to describe some 8 important insect pests of soybean. The other insect pests viz. Spodoptera, Heliothis, Diacrisia and Stomopteryx etc. are equally injurious to soybean crop.
1. Girdle Beetle:
Oberea Brevis Swed. (Coleoptera- Lamiidae):
The beetle is distributed throughout in the various parts of India. Besides soybean, it is also a pest of cowpea (Vigna sinensis L.) and bitter gourd Luffa cylinderica etc. As a result of girdle formation, the leaf withered at the distal ends and dries up ultimately. The girdled part also dries up in course of time and breaks off.
Before egg laying, a female constructs two parallel rings or girdles on the petiole, stem or base of any one of the trifoliate leaves, usually the central one. A female lays singly about 8-72 elongate and yellowish egg in the pith of the stem, petiole or stalk of a leaflet. Haching takes place in about 4-8 days.
The larva which is yellowish white, smooth and apodous, with a swollen prothoracic segment gradually tunnels towards the main stem and hollows it upto the base of the plant. Only one grub lives in a plant at any one time. A full grown larva measures about 19-22 mm. in length. A large number of larvae undergo diapause until the rains of the following year.
Larva completes its development in about 32-62 days in non diapausing cases. In the diapausing cases, larval period lasts for about 248-308 days. In such cases, initiation of larval activity and consequently pupation depends upon the showers of rains in June-July when adults emerge in 8-11 days. Freshly developed adult is yellowish red or brown on the head, thorax and bases of elytra and lives for a few days in the tunnel itself. It comes out only when become black in colour.
2. Stemfly:
Melanagromyza Phaseoli (Tryon) (Diptera- Agromyzidae):
The stemfly is a serious pest of soybean infesting about 95 percent plants in the Kharif (July-October) and up 60 percent plants in the Rabi (November -April) season. It is worldwide in distribution.
Life History:
A female stemfly makes several punctures in the upper surface of the soybean leaf with the help of its ovipositor and lays about 14-64 eggs on the underside of the leaf below the epidermis. Incubation period lasts for 2-3 days. The maggot enters into the stem immediately and make zigzag galleries upto the ground level.
The maggot is yellow in colour and takes 7-12 days for full development after which it drills a small hole into the stem for future imago to escape. Only one maggot develops at a time in a stem, though 2-3 pupae may also be found at some distance from each other. The adult fly emerges in 5-9 days. There are 8-9 generations in a year.
3. Seed-Corn Maggot:
Hylemyia Cilicrura (Rond.) (Diptera- Anthomyiidae):
The seed-corn maggot attacks soybean seeds. As a result of attack by the seed-corn maggots, soybean seeds fail to germinate, while germinating seeds fail to unfold cotyledons above the soil and dies prematurely. Besides soybean, the soybean seed corn maggot infests pea, potato, cucurbits, tobacco, cereals, cruciferous vegetation etc. It is distributed throughout the world.
The adults of the seed-corn maggot, generally prefers germinating seeds. The female lays eggs on or near to the seeds in the soil. The eggs are elongate, white in colour which hatch in about 4-5 days in the form of small, dirty whitish maggots. The maggots feed either alone or in groups of 2-3 inside the moist swollen seeds. They are full grown in 11-14 days. Pupation takes place in the soil. The pupae are red-brown in colour and elongate. The adult flies emerge in about 7-11 days. There are several generations in a year.
4. Brown-Striped Semilooper:
Mods Undata Fabr. (Lepidoptera- Noctuidae):
The pest is distributed in several parts of the world. Extensive damage to soybean foliage is caused by the larvae during monsoon (August- September) season, as result of which the yield is drastically reduced. The larva is slender, elongate and brownish in colour with beautiful longitudinal stripes of pink, brown and red in colour which gives almost velvety appearance to the larva.
The adult moth which is large-sized-stout and brown in colour, starts oviposition after 3-5 days of emergence and continues for about 3-8 days. The total number of eggs laid by a female moth varies from 49-204. The egg is greenish in colour and spherical in outline. Hatching takes place in 3-5 days in favourable conditions. The newly hatched larva is pale green with a pink brown head and a few setae or bristles on the body.
It undergoes 6 moultings before pupation. The full grown larva measures about 41-53 mm. in length. The larval period lasts about 17-22 days after which pupation takes place within a silken cocoon, with which are attached dry leaves and soil particles. The adult emerges in about 8-17 days from the pupa. The latter is ashy dark brown in colour. The life cycle from egg to adult requires 31- 35 days during monsoon (September) and 38-43 days in the post monsoon (October — December) season.
5. Greasy Green Caterpillar:
Lamprosema Indicata Fabr. (Lepidoptera- Pyralididae):
The larva is also known as “leaf folder”. The larva has the habit of folding the soybean leaves either from the tip inwards or along the mid-rib and securing the folds with the help of white resinous gum exuded by the larvae. Webbing together of several leaves is also not uncommon. The pest is distributed throughout the country but it is more common in South India.
The adult is a delicate, slender, creamy-yellow to light-brown moth with long legs. Its wings are marked with wavy irregular brown lines. A female moth lays from 54-150 eggs singly on the underside of the leaves of soybean. The egg is creamy white and flat in form. Hatching takes place in about 7-8 days. The larva is whitish green, with light brown head and a prothoracic shield of the same colour. It rolls up the leaf and grows by feeding on the chlorophyll matter only without making perforations in the leaf.
As a result of chlorophyll loss, the yield is also affected. The larva is full grown in about 21-23 days, greasy green in appearance with light brown head and prothoracic plate. Pupation takes place in the folds of the leaves or in the fallen leaves on the ground surface. The pupal period lasts about 9-19 days. The total life cycle from egg to adult is completed in about 42-45 days.
6. Curious Form Looper Larva:
Scopula Remotata Guen. (Lepidoptera- Geometridae):
The pest is distributed throughout India. The larva of the moth appears on soybean in the second week of September to make small sieve like network of holes in the leaves. Due to their curious form and mimicry in respect of colour and appearance, they are difficult to detect. It is the larval stage which causes a lot of damage to the soybean. The adult is a medium sized, dirty-white moth, with numerous small black dots scattered on the wings.
The fecundity of a female moth ranges from about 28-323 eggs. The average number of eggs is about 123. Each egg is oval, yellowish green, changing to pink within a few hours, – a sign of fertility which ranges between 72-100 percent. The incubation period varies from 4- 11 days and a freshly hatched larva is light brown, slender and elongate in form. The larvae of all instars are capable of twisting their body into various curious forms.
They moult 5 times before changing into pupae. The full grown larva which turns green, measures about 22-24 mm. in length, which is attained in about 18-26 days in October – November and in 40-53 days in December – January. The pupa is formed in the folds of leaves. The adult moth emerges in about 8-15 days in October – November and about 15-19 days in December to January. The whole life cycle is completed in about 35-42 days in October to November and in about 59-77 days in December to January.
7. Black Spiny Caterpillar:
Syntomis Fortunei Orza (Lepidoptera- Syntomidae):
The adults of Syntomis fortunei are easily recognized by their diurnal flight activity in the soybean fields, general black colour of the body and the wings. The body also bears three transverse orange colour bands on the back of the head and the abdominal segments, while the wings are transparent and covered with several white specks.
Life History:
The fecundity of a female moth ranges from 357-548 eggs. Each egg is pale greenish in colour, spherical in shape and is laid singly or in groups. The incubation period lasts from 4-9 days. The freshly emerged larva is pink brown to black in colour with a prothoracic plate of the same colour. There are 6-7 moults before pupation. The larval period requires about 53-61 days. The full grown larva measures about 20-22 mm. in length. The pupal period requires 12-18 days after which the moth emerges.
8. Brown Coreid Bug:
Riptortus Linearis Fabr. (Heteroptera- Coreidae):
The adults appear in early September and continues through October when their activity probably synchronized with the development of the pods, and maturation of soybean. It is distributed in several parts of the world. The pest also infests rice and a wide range of plants of Graminae, Leguminacae, Solanaceae and Convolvulace.
The adult bug is brown in colour and elongate in form with flattened hind femora bearing tooth like projections on the inner side. A female bug lays about 5-28 eggs in 11-19 days of its life. During this period the food of the bugs consist of both the leaves and green pods. The egg is brown in colour, round in shape and dorsally depressed.
The incubation period lasts for about 6-10 days. The young nymph is dark brown in colour and is almost antlike in appearance and moults 5 times before becoming adult. The nymphal period is about 15-20 days. The total life cycle from egg to the adult is completed in about 21-25 days.
Control of the Pests of Soybean:
(1) It was found that an application of lindane granules in the soil at the rate of 2.0 kg a.i. / ha. followed by two-four spray treatments in the beginning (21-30 days of germination) with monocrotophos (nuvacron) 0.04%, endosulfan (Thiodan 0.07%) or dimethoate (Rogor 0.03%) will give healthy crop. Other granules like phorate (Thimet) at the rate of 2.0 kg and 1.0 kg a.i. / ha can also be used in the place of lindane granules.
(2) Lindane dust at the rate of 0.5 kg. or 1.0 kg a.i./ha in the soil furrows before sowing followed by 2-4 sprays of ethyl parathion 46.7 EC at 0.02% proved to be the best checking the general infestation of insects on soybean including the stemfly. Thimet (phorate) 10% granules @ 10 kg/ha or disystone 5% granules @ 20 kg/ha in the soil before sowing or spraying thiodan 35 EC @ 1 litre/ha or phosphamidon @ 250 ml/ha mixed in 1000 litres of water control the pests.
(3) The infestation of soybean by the gridle beetle, Oberea brevis can be effectively checked by sprays of endosulfan 35 EC, methyl demeton 30 EC and dimethoate (Rogor) 30 EC in 0.05, 0.03 and 0.03 percent concentrations. Endosulfan is significantly more effective than monocrotophos 40 EC.
(4) The seed corn maggot, Hylemyia cilicrura can be controlled by the furrow application of phorate (Thimet) 10 gm. at the rate of 2.0 kg / ha. and dimethoate (Rogor) 5 gm., (1.0 kg a.i./ha.). The latter insectides proved no better than check (untreated). Further, carbaryl (Sevin) is very powerful insecticide for the control of many pests of soybean but it causes phytotoxicity and therefore should not be used.