Insecticidal activities of neem (Azadirachta indica A. Juss) seeds under laboratory and field conditions as affected by different storage durations

摘要

Neem seed water extract is found to be very potent in combating various pests of storage and fieldcrops in Sudan, and recommended for use in small holding farms. Two laboratory tests onTrogodarma granariun and a field experiment on okra crop were carried out to compare theinsecticidal activities of several water extracts prepared from neem seeds stored at differentdurations (1-5 years) under room conditions. Such field study also compared extracts of corticatedwith decorticated seeds. The laboratory tests showed that neem seeds stored at 2, 3 and 4 yearswere better than the seeds stored at 1 or 5 years, in controlling the studied pest. The newest seeds(1year) seemed to exert more repellent effect than older seeds, while diminishing of neem activitiesappeared to start after four years of storage when applied under shade. On the other hand, fieldresults reflected that all evaluated neem seeds of three storage periods (ca. 1, 2 and 3 years)significantly suppressed pests’ populations, increased marketable yields and saved the prevailingpredators. They all, except the oldest seeds (3 years), showed comparable or even betterperformance than the commercial insecticide used. Thus, declining of seeds activities under fieldsituation was recorded with seeds of three years old. However, field results also proved thesuperiority of corticated neem seeds over that of decorticated. It is concluded that, neem seedsstored in jute sacks under shade, can remain as potent as new seeds for up to four and two years,regarding their uses for pests control either in storage or field crops, respectively. Corticated neemseeds were recommended for pests control instead of decorticated ones.