Biology of Zygogramma Bicolorata Pallister on Parthenium hysterophorus Linn. under Laboratory Conditions

Parthenium hysterophorus Linn. is one of the most aggressive, invasive weeds threatening natural and agricultural ecosystems in the world including Nepal. Augmentative release of host-specific, leaf feeding beetle, Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) is one of the sustainable management approaches of parthenium weed. Successful mass rearing program requires knowledge on biology of Z. bicolorata for augmentative release. Thus, life cycle and biology of Z. bicolorata were studied in lab at 26±2 °C temperature and 70±10% relative humidity at NARC, Lalitpur, Nepal during March to September, 2016. The average incubation, larval and pupal periods of the insect were 4.33, 12.20, and 11.00 days, respectively. A single female could lay 1,837 eggs in 58.80 days oviposition period with 73.01% egg hatchability. The insect completed its life cycle in 108.40 and 105.50 days with adult longevity of 91.90 and 75.00 days for females and males, respectively. The average length of egg, pupa, adult female and male was 1.19 mm, 5.90 mm, 6.58 mm and 5.32 mm and breadth 0.51 mm, 3.74 mm, 3.94 mm and 3.20 mm, respectively. The average lengths of the first, second, third and fourth instar larvae were found 1.30 mm, 3.02 mm, 4.96 mm and 8.08 mm and breadth of 0.44 mm, 1.13 mm, 2.02 mm and 3.16 mm, respectively. These findings will help in mass multiplication of Z. bicolorata for biological control of parthenium weed.

Impact of Zygogramma bicolorata on vegetative and reproductive performance of Parthenium hysterophorus in Nepal

Parthenium hysterophorus Linn. is one of the most aggressive, invasive weeds threatening natural and agricultural ecosystems in Nepal. Leaf feeding beetle, Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae), is regarded as a potential candidate for biological control of Parthenium weed. Considering the fact effectiveness of Z. bicolorata against P. hysterophorus was evaluted in Nepal. Z. bicolorata caused 98.25 % defoliation of P. hysterophorus reducing 38.88 % plant height, 27.29 % plant width, 26.25 % root length, 12.33 % leaves, 40.58 % shoot biomass and 36.59 % root biomass in the period of 90 days. The flower production and soil seed bank were reduced by 50.22 % and 40.29 %, respectively. Z. bicolorata was an efficient bio-control agent with a significant negative effect on the vegetative and reproductive performance of the noxious weed P. hysterophorus.

Evaluation of host-specificity of Zygogramma bicolorata Pallister (Coleoptra: Chrysomelidae) for the biological control of Parthenium hysterophorus L. (Asteraceae: Heliantheae) in Nepal

Host-specificity test of Zygogramma bicolorata Pallister (Coleoptra: Chrysomelidae) was conducted in the field and laboratory of National Entomology Research Center, Khumaltar, Lalitpur, Nepal during April to September, 2017. Multiple-choice and no-choice tests were conducted on Agerataum houstoniamum Mill., Bidens pilosa L., Chrysanthemum indicum L., Dahlia pinnata Cav, Guizotia abyssinica L., Helianthus annuus L., Lactuca sativa L., Parthenium hysterophorus L., Perilla frutescence L., Xanthium strumarium L., Zinnia elegans Jacq. and Jasminum officinale L. Among tested plant species, P. hysterophorus was only a preferred host of Z. bicolorata on which both larvae and adults fed. Ovipostion, larval development, pupation and adult emergence of Z. bicolorata occurred successfully on P. hysterophorus completing its life cycle. Larvae consumed H. anuus but could not pupate, and adults fed on it when starved for 5 days in no-choice test. Both adults and larvae of Z. bicolorata consumed X. strumarium and completed larval and pupal developments, but adults did not oviposit. Adult longevity was significantly reduced after feeding on H. annus (19.00 days) and X. strumarium (29.33 days) compared to P. hysterophorus (83.33 days).