Study of developmental stages and morphometrics of Parthenium beetle in Bastar plateau agro-climatic zone of Chhattisgarh

Ranjan Lal¹, S. K. Prasad^2*

^1,2School of Studies in Life Science, Pt. Ravishankar Shukla University, Raipur-492010, Chhattisgarh, India

Abstract:

Parthenium hysterophorus (Gajar ghas or Congress grass) is one of the most aggressive, invasive weeds which threaten natural and agricultural ecosystems. Mexican beetle (Zygogramma bicolorata) is one of the most popular, sustainable, and environment-friendly agents for the management of this harmful weeds. Therefore, the present study was carried out to investigate the developmental stages and morphometrics of Zygogramma bicolorata in Bastar plateau agro-climatic zone of Chhattisgarh. Results (1. Developmental stages: laid egg about 785-1300, grub hatched after 3-4 days and total life Spain was 58-86 days. 2. Morphometric parameters: an average single egg had 1.18-1.24 mm length, 0.4-0.46 mm width, 0.14-0.18 mg weight following length, width and weight of larva, pupa and adult male and female) obtained in the present study might be helpful in mass rearing of Zygogramma bicolorata and for the biological control of parthenium weed in Bastar plateau agro-climatic zone of Chhattisgarh.

Keywords: Parthenium beetle, Developmental stages, Morphometry, Bastar plateau agro-climatic zone, Chhattisgarh

1.     Introduction:

Parthenium hysterophorus is a dangerous weed belonging to the aster family, Asteraceae. Parthenium is a dominant, aggressive, and exotic weed commonly called Gajar ghas, Carrot grass, (Tower and Rao, 1992). It is an annual herbaceous plant with short life cycle. It is a pernicious, noxious, and invasive weed with a huge negative impact on agricultural and natural ecosystems, including human health (Shrestha et al., 2019). This weed secrets sesquiterpene lactones which inhibits the growth of other adjacent plant species and causes serious human health problems such as hay fever, asthma, and allergic dermatitis (Das et al., 2007; McFadyen, 1995). In addition, the weed changes the soil's physical and chemical properties and reduces agricultural field’s fertility. In a recent study, P. hysterophorus has shown enhanced growth, development, and adaptability under increased CO₂ levels which may further exacerbate its spread (Nguyen et al., 2017; Singh et al., 2018). It can only be managed effectively by developing an integrated approach involving many options in combination.

At present Parthenium has invaded about 35 million hectares in India, which is a nuisance on roadsides, railway tracks, barren lands, wastelands, industrial areas, on the sides of open drainage systems, irrigation canals, besides invading crops, orchards and forest area. A single plant can produce about 5,000 to 25,000 seeds.  As it matures, the plant develops many branches on its upper half and eventually grows up to 2 meters (McFadyen, 1995). Its leaves are pale green and covered with small hairs. Flower is small and creamy white. Each flower contains 4 to five, 1-2 mm long flattened and triangular dark brown to black seeds (Trounce, 1998). Parthenium completes seed-to-seed life within 80 days (Gupta, 2000). Besides a threat to biodiversity and loss of crop productivity it is notorious for causing allergic reactions (Kologi et al., 1997). The high dominance of Parthenium is attributed to its fast growth rate, high reproductive potential and adaptive nature interference by allelopathy (Koli and Rani, 1994).

The Mexican beetle, Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae), an effective bio-control agent of P. hysterophorus, was introduced in 1983 from Mexico to Bangalore. Both adults and larvae of Z. bicolorata can feed on leaves, terminal buds, and leaf blades of parthenium. Since the first release in the field in 1984 at Bangalore, the beetles became established in most parts of South India and many parts of Central and North India. In many states of India, beetles have been established and contributed to control parthenium very effectively and economically without causing hazards to the existing ecosystem (Anonymous, 2010; Afaq et al., 2024). Adults and grubs of this beetle defoliate the plant completely feeding from the margin of the leaf. However, the hard midrib and veins in old leaves may be left uneaten completely and defoliated plants may die gradually. Different control approaches have been used for the management of Parthenium, although manual and chemical methods are effective strategies to control the weed in agricultural fields, these are not economical in pastures and large natural areas or wastelands (Krishnamurthy et al., 1977). Biological control of Parthenium weed is considered to be the most cost-effective, environmentally safe, and ecologically viable method (Dhileepan et al., 2000). Therefore, the present study was carried out to investigate the developmental stages and morphometrics of Zygogramma bicolorata in Bastar plateau agro-climatic zone (19.0861⁰ N, 82.0188⁰ E and Altitude-554.2 m) of Chhattisgarh.

2.     Materials and methods

Collection and rearing of Zygogramma bicolorata   

The beetles (Zygogramma bicolorata) were collected on Parthenium plants in its natural environment conditions from Jagdalpur which comes under Bastar plateau agro-climatic zone of Chhattisgarh. The adult beetles were collected during the months of May and June, as the beetles were emerging after diapause during these months and reared under the laboratory conditions (at room temperature) at School of studies in Life Science, Pt. Ravishankar Shukla University, Raipur, Chhattisgarh. Collected male and female beetles were placed in a plastic beaker (10 cm in length and 8cm in width) for mating having fresh parthenium leaves with few flowers (Fig.1) and the open side of the beaker was covered with a muslin cloth with a tight rubber band (Fig.2). Parthenium leaves were changed daily. Female beetles were laid eggs on both muslin cloth and leaves (both upper and lower side). Eggs were separated and transferred in 9 cm Petri plate with the help of camel hair brush. Fifty eggs were carried out for further study.

After hatching larva were transferred to plastic rearing cages and provided with fresh Parthenium leaves as food. A continuous supply of parthenium leaves was given to the larvae to preserve the culture of Z. bicolorata. The larvae molted three times and the instars were judged with the help of exuvia of the larva that was observed daily in the morning hours. Along with recording the incubation period and the period between the instars, the measurements of the eggs and the larvae were studied under ocular and stage micrometres. Pupation cages (plastic rearing boxes) filled with sandy soil allow pupation. They were entered inside the soil and pupated. Newly emerged adults of beetles were transferred into plastic rearing cages with parthenium leaves and complete developmental stages (life cycle) were observed. Morphometric observation was done for length, width and weight of the first to fourth instars larva, pupa, and adults (male and female). The size of an adult male was smaller than the adult female. Morphometric data were recorded.                     

3.     Results and discussion

Developmental stages (Life cycle) of Parthenium beetle, Zygogramma bicolora were completed in 4 life stages i.e. egg, larva, pupa, and adult. Details of different developmental stages and their morphometrics are as below and data are presented in Figure-3; Table-1 and 2.

Egg – Eggs were yellow to orange in color, elongated cylindrical in shape. Female laid egg on both upper and lower surface of leaf and stem, flower bud, muslin cloths and beaker also. An average length of egg was 1.18-1.24 mm, width was 0.4-0.46 mm, weight was 0.14-0.18 mg and incubation period were 3 to 4 days.

First instar larva - The first instar newly hatched larva was pale yellow which turned into creamy white as it grew. First instar larvae were fleshy and have a faint line on the dorsal surface of the body but segments of the body were not recognized. Early instars larva was 1.12 -1.52 mm in length, 1.05-1.29 mm in width and 0.16-0.29 mg in weight. The total period of early instar grub was 2-3 days.

Second instar larva -1st instar larva molted to 2nd instar.  1st and the 2nd instar grubs were almost similar in color, and form. The grub of this instar showed 2.78-3.32 mm in length, 1.06 -1.32 mm in width and the average weight was recorded as 1.6-3.56 mg and the duration of 2nd instar grub was 3-4 days.  The segments (thoracic and abdominal) were distinguishable in the 2nd instar grub.

Third instar larva – The 2nd instar larva molted to form the 3rd instar, which could be easily distinguished from early instars by their spiracles. Nine pairs of spiracles were found on the thoracic and abdominal portion of the 3rd instar larva. Six black spots or beads were arranged in two separate rows having three spots in each row. Length was 4.2-5.4 mm, width was 2.7-3.1 mm and the duration of 3rd instar grub was 3-4 days and the average weight was recorded as 7.18-16. 22 mg.

Fourth instar larva – The fourth instar larva of Zygogramma bicolorata looked like a third instar larva which was measured 7.2-8.1 mm in length, 3.2-3.8 mm in width and the duration of 4^th instar grub was 4-6 days and the average weight was recorded as 15.00-28.30 mg.

Pupa - Pre-pupation period was 1-2 days.  After pre-pupa and entering the soil for pupation it was turned transparent creamish white to light yellow in color. Pupa was 5.4-6.2 mm in length 3.2-3.6 mm in width and average weight was 23.86 -32.75 mg. Total pupation period was 9-11 days. Pupa were buried in the soil at 1.0 to 3.0 cm depth.

Adult - The adults were emerged from the soil after pupation. The adult has an oval shape with a convex and seriated dorsal surface and is completely white with a deep yellow notum; the color of the adult changes over time. The color of the head changes to black. The pronotum changed to ground color and possessed a median hat-shaped black marking not covering the lateral and anterolateral corners. Hind wings were transparent and folded beneath the elytra. Elytra included the following markings: a stripe adjacent to the sutural line, two elongate spots arranged longitudinally, a hook-like elongate marking, and two smaller, posterior-lateral spots; sutural line with a black stripe broader in the anterior half. The attractive insects bear an undulating dark brown or blackish line on the elytra that runs longitudinally over an off-white background. The pattern of longitudinal marking on the elytra was non-uniform. A prominent blackish elongated spot was observed at the base of each elytron. Adult male and female beetles measured 5.4-5.8 mm, 5.6-7.1 mm in length and 3.5-3.8 mm, 3.9-4.2 mm in width. Total period of adult male and female beetles was 33-36, 38-52 days, and the average weight was recorded as 22.50 -28.40 mg, 32.60-54.40 mg.

Parthenium weed has been observed as a major threat to environment and agriculture for the last few decades in India. It has harmed crop production, soil properties and plant diversity. Still, now there is a lack of proper management tools to prevent the propagation of this harmful weed. Therefore, study of developmental stages and morphometrics of Parthenium beetle, Zygogramma bicolorata would help in mass rearing of this beetle and for the biological control of parthenium weed in Bastar plateau agro-climatic zone of Chhattisgarh.

Fig. 3. Developmental stages (life cycle) of Zygogramma bicolorata

Table-1. Development stages of Zygogramma bicolorata in Bastar plateau agro-climatic zone of Chhattisgarh under laboratory condition. ( ⃰ Value = Mean ± SE)

Table-2. Morphometry of different life stages of Zygogramma bicolorata in Bastar plateau agro-climatic zone of Chhattisgarh under laboratory condition.

Acknowledgement

The authors are grateful to the CSIR-UGC, New Delhi, NET / JRF to Ranjan Lal for the financial support.

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