The effect of Fusarium verticillioides on oviposition behaviour and bionomics of lepidopteran and coleopteran pests attacking the stem and cobs of maize in West Africa

The effect of Fusarium verticillioides Sacc. (Nirenberg) in maize stem and grain on the oviposition behaviour and bionomics of lepidopteran and coleopteran pests in West Africa was studied in olfactometer, greenhouse, and field trials in Benin. In a choice experiment, the pyralid Eldana saccharina ( Walker) laid on average 31.9 eggs on inoculated maize stems vs. 9.2 and 7.8 on stems from plants, grown from hot-water or fungicide treated seeds, respectively. For the pyralid Mussidia nigrivenella (Ragonot) the values were 42.1 in the inoculation and 7.8 eggs in the fungicide treatment. The survival of E. saccharina larvae was significantly higher from the inoculation than the hot-water or fungicide treatments. Fecundity in the three treatments was 494, 307, and 268 eggs per female, respectively. In an olfactometer experiment, no significant differences were found in the time spent by the curculionid Sitophilus zeamais Motschulsky between the odor field with Fusarium-infected grain and with uninfected grain, but both were significantly different from the controls. Significant differences were obtained for the nitidulid Carpophilus dimidiatus ( Fabricius) with 50.5 and 35.8%, respectively, of the time spent in the Fusarium-infected and non-infected odor field. For both species, no differences were found between sexes. For S. zeamais, development time was significantly higher when reared on infected (37.2 days) than on non-infected grain (34.4 days), whereas fecundity, expressed as number of progenies during the first 4 weeks, was lower on the inoculated grain ( 11 vs. 16 offspring per female). For C. dimidiatus the situation was the reverse: development time was shorter and fecundity was higher on infected grain (32.4 vs. 34.4 days, and 18 vs. 13 offspring per female, respectively). It was concluded that the higher pest densities found in the stem and ear of field grown maize was due to a higher attraction to and higher immature survival and adult fecundity on F. verticillioides infected plants.