Effectiveness of Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) on Parthenium weed (Parthenium hysterophorus) under greenhouse condition in Ethiopia

Background Parthenium is an invasive annual weed that affects crop production, rangelands, grasslands, animals, the environment, and human health. Since its introduction into Ethiopia, different management options such as uprooting, slashing, burning, plowing, and applying synthetic herbicides have been practiced. However, these options are not sustainable in weed management. However, Zygogramma bicolorata is known to be used in different countries. Although many countries use it under field conditions, its population-based efficacy has not been well studied in Ethiopia. This study aimed to determine the effectiveness of Z. bicolorata populations on parthenium plants under greenhouse conditions. Methods This experiment was conducted at the Ambo Agricultural Research Center. Different numbers of Z. bicolorata per plant were used as treatments and were laid out in a completely randomized design with three replications. The numbers of damaged leaves, eggs, and larvae were recorded daily until the leaves were completely defoliated. The collected data and the correlation between beetle population and leaf defoliation were analyzed using SAS. Results The result revealed that all beetle populations caused damage to weed plants. A higher population of beetles completely defoliated the leaves within 12 days. However, lower numbers required 21 days to completely defoliate the weed. In contrast, a higher number of eggs (328.67) and larvae (272.33) were obtained from plants that received 20 pairs of beetles. The beetle population and exposure time were positively correlated, and the effectiveness of the bioagent was greater following the emergence of larvae. Conclusions Z. bicolorata can manage parthenium weeds, even with a lower population. However, more than 15 pairs of beetles could be suggested to manage weeds in a shorter time, and further study is needed under field conditions by considering the different agroecologies of the country.