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FemaleCotesia flavipes Cameron andCotesia sesamiae (Cameron) were attracted to odors in a Y-tube olfactometer from uninfested maize (Zea mays L.), sorghum [Sorghum bicolor (L.)], and napier grass (Pennisetum purpureum Schumach). In dual choice tests,Cotesia flavipes showed a preference for maize over sorghum, while maize and napier grass were equally attractive. In contrast,Cotesia sesamiae preferred volatiles from sorghum and napier grass over those from maize. The two parasitoids were significantly more attracted to maize infested with the stemborers,Chilo partellus (Swinhoe),Chilo orichalcociliellus Strand,Sesamia calamistis Hampson, andBusseola fusca (Fuller), than uninfested maize. In dual choice tests,Cotesia flavipes andCotesia sesamiae were unable to discriminate between odors from plants infested by the different species of stemborers.

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The development of Dermestes maculatus (DeGeer) on four smoked fish substrates [Trigger fish (Balistes capriscus), Catfish (Synodontis sp.), African catfish (Clarias gariepinus) and Nile Tilapia (Oreochromis niloticus)] were investigated as completely randomized design under laboratory temperature of 30 o C, relative humidity of 65±5% and a light: darkness regimen of 12:12 hours. Females laid eggs within 24 hours of copulation. The numbers of eggs laid and the period between larval instars were not significantly different (P > 0.05). Mean total egg laying period varied from 18 days on B. capriscus to 30 days on Synodontis sp. with about 75% of eggs laid on days 13, 15, 15 and 17 for O. niloticus, B. Capriscus, C. gariepinus, and Synodontis sp., respectively. Hatching started 48 hours after copulation on all fish substrates. The mixed fish substrate (comprising all species) gave the longest (P < 0.05) developmental period of 42.75 days. Except C. gariepinus which recorded five larval instars, all others gave six instars. The total development period of D. maculatus from egg → larva → pre-pupa → pupa → adult emergence on the fish substrates decreased in the order Synodontis > O. niloticus > Mixed > C. gariepinus > B. capriscus.

SummaryThis paper describes a series of experiments conducted to determine why Sitophilus zeamaisMots. and Sitotroga cerealella (Oliv.) could not survive together in maize cultures in the laboratory. The effect of S. zeamais on different developmental stages of S. cerealella was investigated. The presence of adult S. zeamais slightly affected moth copulation, egg laying and moth eggs in a mixed culture, but large numbers of developing moths inside maize grains were killed by the adult weevil through feeding on the grains. The major cause of elimination of S. cerealella by S. zeamais from mixed cultures was therefore found to be damage to the immature moths in grain and such moth mortality increased as the developing moths became bigger in the grains. A weevil: grain ratio of approximately 1.4∶1 was found to be the critical weevil density at which the moth disappeared from the mixed cultures.