Bionomics of diamondback moth, Plutella xylostella (Linn.) on cabbage crop under laboratory condition

Introduction

The diamondback moth (DBM), Plutella xylostella, is globally distributed pest, which was reported from India in 1914 (Fletcher, 1914), but now widely distributed in 128 countries (Shelton, 2004). This has been reported to cause 52% yield loss on cabbage in India (Krishnamoorthy, 2004) [3] . Globally, this pest has been reported to cause more than 90% of production loss of crucifer crops (Talekar and Shelton, 1993;Furlong et al., 2013;Paudel et al., 2022) [7, 1, 5] . Like other brassicas, wide spectrum of pests attacked on cabbage plant. In cruciferous crops, 51 insect pests were listed throughout the world, out of which diamondback moth (DBM), Plutella xylostella (Linnaeus); cabbage butterfly, Pieris brassicae Linnaeus; cabbage semilooper, Trichoplusia ni Hubner; head borer, Hellula undalis Fabricius; tobacco caterpiller, Spodoptera litura (Fabricius); cabbage aphid, Brevicoryne brassicae Linn., and green peach aphid, Myzus persicae (Green) are the major productive constraints (Maison,1965) [4] . Diamondback moth is recorded as a major and oligophagous pest with the larvae feeding specially on the members of the family cruciferae, cabbage, Chinese cabbage, cauliflower, broccoli, knolkhol, radish, turnip and mustard. It has been recorded since 1746 (Harcourt, 1962) [2] . Among all the crucifer vegetables, cabbage and cauliflower are the most preferred host plants for diamondback moth due to the fact that both plants possess fleshy and succulent leaves having glucosides and glucosinolates which stimulate feeding and oviposition. Commercial considerations of this crop have, compelled the growers to go for more frequent and injudicious use of insecticides for better marketable yield (Tabashnik and Cushing, 1987) [6] . However, excessive use of insecticides has led to insecticidal resistance development, pest resurgence, residue hazards in foods and overall environmental contaminations. Various management strategies of cruciferous pests are completely based on chemical pesticides without giving much importance to the biopesticides, botanicals and cultural control. Studying bionomics is essential for effective pest management because it provides the foundational knowledge needed to create sustainable, precise, and ecologically sound control strategies. By understanding insect's life cycle, behavior, and interaction with its environment, which helps to develop targeted, non-chemical solutions that minimize crop damage and reduce reliance on broad-spectrum pesticides.

Materials and Methods

• Investigations on biology of diamondback moth were carried out in the laboratory of the Department of Entomology at Indira Gandhi Agricultural University, Raipur (C.G.) during year 2015-16 and 2016-17. • To maintain the culture of Plutella xylostella, the healthy larvae of DBM, diamondback moth were collected from unsprayed field and reared in glass jars (20 × 15 c.m.). • Fresh tender leaves of cabbage were served as food to the larvae and food was changed daily. The full grown larvae were transferred to fresh chimneys for pupation. • At every successive instar, the larvae were gently transferred to other clean jars containing fresh leaves. • After adult emergence, each pair male and female were released on cabbage plants raised earlier in the earthen pots. These pots were kept in cage of (50× 50 ×50 c.m.) for mating and egg laying.

The cotton swab soaked in 10% honey solution was provided as food to the adults. Freshly laid larvae were separated gently. Larvae and adults (ten in number) were anesthetized in 70% ethyl alcohol. Measurement was done with the help of graph paper, scale and eggs under a microscope fitted with an ocular micrometre.

Results

Investigations on bionomics of DBM were carried out in the laboratory condition by using cabbage plant leaves. The laboratory temperature during this period ranged between 25.12 0 C -38.9 0 C. The results are being presented in table 1, 2.

From maintained culture of Plutella xylostella, the freshly hatched larvae were lifted gently, transferred to Petri dishes (10 cm) and provided with fresh leaves daily till pupation.

Observations were recorded on number of instars, duration of instars, colour changes etc. Period from hatching to first moulting was recorded as developmental period. The time interval between inactivation and pupal formation was recorded as pre-pupal duration in days. Time of pupa formation till the emergence of moths was recorded as pupal period. The total duration (days) of adult male and female from emergence till death were computed.

Incubation period

The freshly laid eggs were yellow to pale green and oval shaped, length ranged from 0.46 -0.49 mm and breadth from 0.24 -0.26 mm. The mean incubation period was recorded 4.4 ± 0.22 days. The period of incubation of egg was 4 -6 days.

Larval period

The larvae passed through four instars. Their chewing resulted in irregular patches of damage, and the upper leaf epidermis often remained left intact.

The range for larval periods, 1 st , 2 nd , 3 rd and 4 th instars were recorded as 2-4, 2The larval head capsule was grey green and that of fourth instar was greenish brown in colour. The larval head capsule in first, second, third and fourth instars were recorded as (0.11±0.17), (0.21±0.31), (0.33±0.47) and (0.52±0.61) mm with range variation as 0.11-0.17, 0.21-0.31, 0.33-0.47 and 0.52-0.61mm, respectively.

Pupal period

The newly formed pupae were yellowish green in colour and it became brownish and gradually attained dark brown colour covered all around from silken thread by the time of adult emergence. The range of length and breadth of pupa recorded was 7.50-8.50 mm and 2.50-3.00 mm.

Adult stage

Diamondback moth is a small moth with long antennae. The colour of male and female was grayish. The adult moths had a line of three diamond shaped markings on middle of the back. Males were slightly smaller than that of females. The duration from egg to adult emergence was 19.2±2.21 days with range of 17-28 days. Total duration life span of adult male and female was completed in 30.4±0.98 and 34.17±1.16 days, respectively. The range of development period from egg to adult stage of male and female was observed as 24-36 days and 27-41 days, respectively. It confirmed that female were bigger than the male with higher longevity. The range of adult wingspan recorded in male and female both were 12.25 -13.00 mm and 12.75 -13.25 mm, respectively. Length of adult male ranged from 4.75 to 5.00 mm whereas in female, ranged from 4.75 to 5.25 mm. Adult emergence was calculated in per cent for male and female both were 65% and 35%, respectively. Adult emergence per cent was calculated as

References

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