Effect of intercropping of maize, bean, cabbage and toxicants on the population levels of some insect pests and associated predators in sugar beet plantations

Experiments were carried out at El-Riad district, Kafr El-Sheikh Governorate in two successive growing seasons (2009/10 and 2010/11) to study the effect of intercropping of faba bean, maize and cabbage with sugar beet on the population density of Empoasca spp. (nymphs and adults), Aphis spp. (nymphs and adults), Bemisia tabaci (adults), Pegomyia mixta (eggs and larvae), Cassida vittata (larvae, pupae and adults) and predators in sugar beet plantations compared with the non-intercropped plants and the resulting yield. The toxicity of certain compounds: fenitrothion, super misrona, sour orange oil, acidless orange oil, and Bermectine in reducing the population density of P. mixta and C. vittata larvae infesting sugar beet was evaluated. The rate of infestation was higher in the sole sugar beet plants than in those intercropped with faba bean, maize and cabbage plants which caused reduction of sucking pests and P. mixta eggs in the two seasons. The intercropping of faba bean plants led to higher infestation rate of P. mixta larvae in the two seasons and C. vittata (larvae, pupae and adults) in the first season. The intercropping with maize led to a higher population density of Chrysoperla carnea, Paederus alfierii and Scymnus spp. in the two seasons. Low population density of true spiders was observed in sole sugar beet (control) when compared with faba bean, maize and cabbage plants intercropped in the two seasons. Concerning the obtained root yield, the intercropping with maize and cabbage plants reduced the resultant yield of sugar beet roots in the two seasons. Bermectine and fenitrothion were the most effective toxicants followed by super misrona and then, sour orange that induced the lowest reduction in P. mixta larvae. Also, fenitrothion and Bermectine were the most potent compounds in reducing the population density of C. vittata larvae followed by super misrona and then, plant oil extracts. Concerning the side effects of these compounds on predators, sour orange oil and acidless orange oil had slight effects, whereas Bermectine and super misrona caused a moderate effect against predators. However, fenitrothion was the most highest toxic compound against predators.