Nahan (Himachal Pradesh): The department of Botany degree college Paonta Sahib has claimed to sight the biocontrol insect beetle feeding the annual Asteraceae weed Parthenium hysterophorus (Congress grass / Gajar Ghas) in the valley. The Parthenium weed was first detected in 1956 in Pune. It then spreaded to all parts of the country, reaching even up to hills by the anthropogenic reasons. Problems of management of this weed were compounded due to its capacity to germinate throughout the year in a wide range of environment and soil, huge seed production, light weight of seeds and wide spread occurrence, said Prof Jaswant Saini of degree college Paonta sahib.
Parthenium is known to cause diseases like asthma, allergy and skin disorders. Air borne pollen may cause severe allergic rhinitis in some people. The adults and larvae are capable of feeding on the Parthenium leaves thus checking the plant growth and flower production. This year it is seen that feeding by Z. bicolorata caused damage to meristems, resulting in shorter height of the primary stem and changed branching pattern. Prof. Jaswant Singh Saini, Department of Botany, Govt Degree Collage Paonta Sahib told that the biocontrol insect Zygogramma bicolorata Pallister (Coleoptera) also known as Parthenium beetle or Mexican beetle feeding the annual in Valley. Immature are cut by the beetles in an effort to chew the soft tissues beneath the flowers.
Completely defoliated plants start to show die-back symptoms and gradually get killed. The negative effects of defoliation on flower production, leaf production, and plant biomass were more significant when defoliated at flowering stage than at early stages of plant growth. Here it is reported that many plants are flowerless due to attack of Mexican Beetle. It is also seen that this insect eats up the leaves of the Parthenium and does not harm any other crop in the area.