Potential Weed Species as Alternate Hosts ofInsect Vectors of the Lethal Yellowing Disease(LYD) of Coconut Palms (Cocos nucifera L.) inNigeria

摘要

Weed species examined as alternate hosts implicated Panicum maximum Jacq as the most abundant host of vector insects of the lethal yellowing disease (LYD) of coconut palms. Ten weed species out of the 19 examined hosted leaf hoppers Cicadellidae and plant hoppers Flugoroidea. They were found in inner leaf sheaths and leaflets. The weed species in coconut LYD areas recorded abundance of Cicadellidae and Flugoroidea species with Panicum maximum 32.7%, Andropogon gayanus 23.6%, Sorghum arundinaceum 13.4%, Cyperus difformis 12.4% and Oryza barthii 11.2%. Weed species in coconut non-LYD areas recorded relatively low abundance with P. maximum 9.1%, A. gayanus 8.4%, Leptochloa filiforms 6.8%, and S. arundinaceun 2.8%. Eggs, nymphs and adult Cicadellidae and Flugoroidea species were excised from these weeds mainly grasses. The under-story canopies of coconut palms LYD temperature at 26 ± 2oC made the vegetation cool, conducive and environmentally friendly for mass breeding when compared with non LYD areas at 32 ± 2oC. The insects were found on the canopies of LYD coconut palms up to late in the evening (7:00 p.m.) and early in the morning (6:30 a.m.). Some of the Flugoroidea species were observed with the proboscis pointed down to the leaf surface with streak damages, an indication of feeding and nesting. Frequencies occurrence of Cicadellidae and Flugoroidea species proved that abundance of decaying palm logs, pruned fronds, spathes and inflorescence were reservoir for mass breeding. This development could predispose coconuts to series of infections and possible transmission of LYD to healthy coconut palms.