The efficacy of volatile essential oils obtained from somearomatic plants of benin against the maize weevil, Sitophiluszeamais Motschulsky (Coleoptera: Curculionidae)

In West Africa, high losses caused by insects are experienced in grains and legumes storage. The development of pest resistance, and human&environmental health issues caused by synthetic toxic insecticides used extensively, necessitate the development of alternative methods. From this point of view, in this thesis, as an alternative to toxic insecticides in controlling stored products pests, the contact & fumigant toxicity and repellency of the essential oils extracted-by hydrodistillation- from Cymbopogon citratus Stapf., Ocimum gratissimum L., and Eucalyptus camaldulensis Dehnh of Benin (Africa) origin, were investigated against 1-2 weeks old Sitophilus zeamais (Coleoptera: Curculionidae) Motschulsky adults at 25°C, and 65% ± 5% R.H. The highest mortality rates recorded in contact toxicity tests performed in PVC vials (40 ml) were 99±0.78% for Eucalyptus camaldulensis applied at 20 µl oil/20 g corn dose (no F1 adult development was recorded); 90±2.24% for Ocimum gratissimum applied at 50 µl oil/20 g corn dose (F1 adult number was 2.6±0.81) on 14 day after treatment, and 84.25±4.4% for Cymbopogon citratus applied at 50 µl oil/20 g corn dose (F1 adult number was 1.5±0.5). In fumigant toxicity tests performed in glass jars (1000 ml), mortality rate increased with increasing concentration of all three essential oils. The highest mortality rate was 96.88±2.1% for Eucalyptus camaldulensis at 100 µL oil/1000 ml jar; 90±5.4% for Cymbopogon citratus at 250µL oil/1000ml jar, and 10.83±2.94% for Ocimum gratissimum at 100µL oil/1000ml jar. In repellency tests performed in PVC Petri Dishes (9 cm2 arena), the highest repellency rates for Eucalyptus camaldulensis, Ocimum gratissimum and Cymbopogon citratus, each applied at 100 µl oil/4.5cm2 arena, were 45%, 85% and 72.5%, respectively. Our results show that all three oils can be effective against stored product pests in terms of contact&fumigant toxicity and repellency.