Arthropod Fauna of Brassica Napus and Brassica Juncea from Southern Punjab (Pakistan)

Abstract

Cultivation of oilseed brassicas in the Indian Sub-continent date back from 2000 to 1500 B.C. These crops are an important source of edible oil, with current local production of edible oil in Pakistan accounting for 31% with the remaining 69% met through imports. Damage due to insect pests is a major constraint to production of these crops. In Pakistan 70–80% losses in yield have been reportedly due to aphids in these crops in other parts of country (Rustamani et al., 1988). We have been surveying these crops since the mid 1990s. Insect pests and natural enemies were recorded on a weekly basis from the end of November to the end of March at Multan, Bahawalpur and Dera Ghazi Khan are 100 km away from Multan. Populations of aphids were recorded by beating the top 10 cm of the central inflorescence of plants gently 10 times with a 15 cm stick (of pencil thickness). Aphids were collected on a piece of white sheet and counted. Populations of predators were noted on a per plant basis. No arthropods other than insects were observed during the study. Specimens occasionally sampled from time to time have been deposited in the Canola Laboratory at the University College of Agriculture, Bahauddin Zakariya University, Multan (Pakistan). Cabbage aphid, Brevicoryne brassicae (L.) and turnip aphid, Lipaphis erysimi (Kaltenbach) were continuously observed as the most abundant among all insects observed. Only a few plants of B. napus were found to be infested by Myzus persicae (Sulzer) during 2003 at Multan. Population of the cabbage aphid were always greater in abundance than that of turnip aphid on B. napus and B. juncea. Other insects recorded were the sawfly, Athalia lugens (Klug) (Hymenoptera: Tenthredinidae), Spodoptera litura L., Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) and the whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). A. lugens feeds upon the leaves by making holes. No insect other than B. brassicae and L. erysimi were observed to cause economic damage on crops sown timely, i.e., last week of October and onward. However, S. litura and B. tabaci severely damaged the crops sown early, i.e., mid-October in years when outbreaks occurred on cotton. Cotton is an important source to these two species of insects, and both of these insects are a threat to very early sown oilseed