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Disruption of Nisotra basselae oviposition to improve pest management on Abelmoschus manihot in the Solomon Islands

Vaqalo, M., Furlong, M. J., Zalucki, M. P.
Acta horticulturae 2015 no.1102 pp. 151-156
Abelmoschus manihot, Chrysomelidae, adults, cabbage, cultural control, eggs, females, field experimentation, host plants, instars, integrated pest management, islands, larvae, leaves, mulches, oviposition, oviposition sites, pests, roots, soil, stems, traps, vegetable crops, Solomon Islands
Slippery cabbage, Abelmoschus manihot Medicus, is a leafy vegetable crop grown throughout the Pacific, especially in Melanesian countries where it is a popular leafy vegetable. The slippery cabbage flea beetle, Nisotra basselae (Bryant) (Coleoptera: Chrysomelidae) was first recorded in the Solomon Islands in 1981; it has since become a severe pest of A. manihot and it is present in most islands in the archipelago. Very little was known about the biology or ecology of the beetle prior to this study. Adult beetles defoliate the crop but immature development is completed below ground, where the three larval instars feed on A. manihot roots. In laboratory and field studies we found that following maturation the beetle feeds and mates on A. manihot leaves. Female beetles descend the plant stems at night and deposit their eggs in small clusters close to roots beneath the soil surface. In laboratory studies >95% of eggs were laid within 2 cm of the plant stem and in field studies a strong positive correlation between adult density on foliage and egg density on roots was detected. In field studies female beetles were collected in Tangle-foot traps at the base of plant stems, leading to a decline in adult density and suggesting a high degree of fidelity to individual host plants. Mechanical disruption of preferred oviposition sites with copra sacking significantly reduced egg densities on roots and adult densities on foliage when compared to standard practice (bare soil), the application of mulch or under-sowing with clover. Results are discussed in the context of ongoing work to develop cultural control based IPM strategies for N. basselae on A. manihot in the Solomon Islands.