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Department of Entomology, S.V. Agricultural College, ANGRAU, Tirupati-517502.
A study was carried out at the Department of Entomology, S.V. Agricultural College, Tirupati on the larval taxonomy of pod borer complex in field bean during rabi 2020-21. Four lepidopteran larvae viz., Maruca vitrata (Geyer), Spodoptera litura (Fabricius), Lampides boeticus (Linnaeus) and Etiella zinckenella (Treitscke) were collected from field bean crop and identified. All these lepidopteran larvae were identified and described based on the morphological characters and chaetotaxy of thoracic and abdominal segments, especially 3rd abdominal segment and arrangement of crochets on the ventral prolegs. The measurements viz., total length and width of the larva, length and width of head capsule, width across the compound eyes, length and width of thorax as well as abdomen were taken.
KEYWORDS: chaetotaxy, crochets, field bean, pod borer.
Field bean [Lablab purpureus (L.)] is an important pulse-cum-vegetable crop in India. It is cultivated for its tender and mature pods, seeds and fodder. The young and immature green pods are cooked as vegetable (Gowda, 2006). It has rich in nutritive value, the protein content of field bean varies from 20 to 28 per cent (Schaaffhausen, 1963). It is one of the oldest legume crops known to be cultivated in dry and semi-arid regions of Asia, Africa and America (Ayyangar and Nambiar, 1935). In India, it is popularly grown in South, East and North east parts of the country. In Andhra Pradesh, field bean is grown in an area of 12.02 thousand hectares with 139,320 tonnes of total production and 16.90 M.t ha-1 of total productivity (National Horticulture Board, 2019-20). The productivity of field bean is low as compared to cereals. One of the main reasons for the low yield of the crop is attack by many insect-pests at various stages of the crop (Krishna et al., 2019).The crop has been recorded to harbour a large number of insect-pests of which Helicoverpa armigera (Hubner), Adisura atkinsoni (Moore), M. vitrata,
The knowledge on biology and accurate identification of a pest allows formulation of the management strategies effectively. Larval stages of these lepidopterous pests are economically significant as they are the damaging stage of the insect. The destructive larval stage poses considerable difficulties in their identification. The intensive studies on chaetotaxy of different lepidopterous larvae are necessary to formulate a comprehensive account on external morphological features and to provide standard identification features which will be helpful for easy identification of larvae to the researchers and the students.
The lepidopteran larvae of pod borer complex were (third instar larvae) collected from the field during rabi 2020-21, taken to the laboratory and reared upto final instar on natural diet. Some of the larvae were reared for emergence of adults. The collected larvae were killed with
K.A.A.D mixture (kerosene-1 part, 95% ethyl alcohol-7 parts, dioxan-1 part and glacial acetic acid-2 parts). The killed larvae were immersed in 10 per cent solution of potassium hydroxide for maceration overnight, washed in water and passed through different grades of alcohol viz., 60, 80, 95 per cent consecutively for about 10-15 minutes to facilitate dehydration. The digested soft tissues were removed with the help of a pair of blunt needles and the specimens were transferred to clove oil for clearing. A 1:1 mixture of phenol + xylol was used to retain the specimens until the slides are prepared with Canada balsam permanently. The photographs of head capsule, thorax, abdominal segments, depicting the setal formula, crochets were taken with the help of photographic attachment in Olympus trinocular stereo zoom microscope. The measurements viz., width and length of the head capsule, thorax as well as abdomen of the identified larvae were taken with an Olympus trinocular stereo zoom microscope.
In the present study, four species of pod borers belonging to four genera of the order Lepidoptera viz., spotted pod borer [Maruca vitrata (Geyer)], tobacco caterpillar [Spodoptera litura (Fabricius)], blue butterfly [Lampides boeticus (Linnaeus)] and pea pod borer [Etiella zinckenella (Trieitscke)] were collected, identified and described. The list of identified lepidopteran pod borer complex was given here under.
Family: Pyralidae Order: Lepidoptera
(Figure 1 and Plate 1)
Colouration and External Morphology: Larva is cream coloured with stout dark hairs distributed on dark brown warts of the body and hence commonly is called as spotted pod borer. The larvae were broad at the head region and tapering towards caudal end. Six rows of black spots were present on the dorsal side of the body.
Head: Head sclerotized and projected ventrad (hypognathous) with inverted “Y” shaped epicranial suture. Lateral ocelli were six in number adjacent to the base of mandibles. Antennae short, three segmented. Mandibles well developed and prominent. A distinct protruding spinneret present on the labium. Adfrontal area present and distinct.
Thorax: Thorax three segmented with three pairs of four segmented true legs. The fourth segment bears a single curved claw with a distinct arolium. One pair of spiracles present on prothorax at the junction of pro and mesothorax and another pair at the junction of meso and metathorax.
Chaetotaxy of prothorax and mesothorax Prothorax: Prothorax bears sclerotized prothoracic
shield which extends upto the ventral margin of SD2.
Dorsal seta D2 is longer than dorsal seta D1. Anterior dorsal setae XD1 and XD2 are distinct. Subdorsal setae SD1 and SD2 are present. Lateral setae L1, L2 and L3
distinct and are present nearer to the spiracle. Subventral setae SV1 and SV2 present and SV1 is longer than SV2.
Mesothorax: Dorsal setae D1 and D2, Subdorsal setae SD1 and SD2 present and observable on respective pinaculi. Lateral setae L1, L2 and L3 are present. Subventral seta SV1 and ventral seta V1 are prominent.
Abdomen: Ten segmented. Abdominal legs fleshy, paired, non-segmented which are called prolegs exists on 3rd, 4th, 5th, 6th and on last segments. Eight pairs of spiracles present on 1st to 8th abdominal segments.
Chaetotaxy of 3rd abdominal segment: Dorsal setae D1 and D2 distinct. Subdorsal seta SD1 is long and present above the spiracle. Lateral setae L1 and L2 are prominent. Subventral seta SV1 is distinct.
Crochets: Crochets on abdominal prolegs are triordinal meso penellipse.
Adult: The moth is light pale brownish yellow and stout. The forewings are light brown with a white cross band The hind wings are white in colour with brown markings at the lateral edge.
Measurements (average of 10 third instar larvae): Total length of the larva 13.76 mm, total width (maximum width) of the larva 2.11 mm, length of the head capsule
2.17 mm, width (maximum width) of the head capsule
1.87 mm, width across the compound eyes 1.56 mm, length of the thorax 5.62 mm, width (maximum width) of the thorax 1.96 mm, length of the abdomen 7.70 mm, width (maximum width) of the abdomen 2.11 mm.
Family: Noctuidae Order: Lepidoptera
(Figure 2 and Plate 2)
Colouration and External Morphology: Caterpillar is stout, cylindrical and brownish with dorsal, subdorsal, sub spiracular and supra spiracular stripes of different colours. The general colour of the larvae is brown or sometimes greenish. Larvae often have a bright yellow or orange middorsal line, but also possess a less conspicuous subdorsal line marked by yellow or orange spots or dashes. The spiracular line often has a yellowish or orange-pink reticulate colouration with more intense orange or yellow accents.