ASSESSMENT OF NATURAL ENEMY RICHNESS, DOMINANCE, DENSITY AND FUNCTION IN LEPIDOPTEROUS LARVAL PESTS ATTACKING Amaranthus hybridus L. IN ZARIA, NIGERIA

Abstract

This study evaluated the richness and dominance of larval pests and natural enemies, plant infestation, pest and parasitoid density and larval parasitism in Amaranthus hybridus L., as cultivated and volunteer hosts, in Zaria, Nigeria. Field inspections were carried out between June and September, 2018 in seven to 15 farmers’ fields and their fringes. Recovered larvae were maintained in the laboratory till adult insect emergence. Of the three lepidopterous larval pests found, the Beet web worm, Hymenia recurvalis (Fabricius) was the major pests (dominance (79%/92%) and frequency (69%/81%)), while the Leaf webber, Psara basalis Walker and the Leaf roller, Sylepta derogata (Fabricius) were minor pests (dominance (3%-12%) and frequency (25%-31%)). In all, five parasitoids (Apanteles sp., Bracon sp., Braunsia sp., Tetrastichus stictococci Silv. and Scelioninae) and one predator species (Scymnus loewii Mulsant) were recovered. In particular, Apanteles sp., Bracon sp. and S. loewii were common in both cultivated and volunteer hosts. Apanteles sp. was the most active parasitoid in both host types (dominance (61%-84%) and frequency (57%-78%)). Plant infestation rate was generally moderate to high (25%-43%) in A. hybridus. Although larval pest (16-23) and parasitoid abundance (4-8) per farmers’ field/fringe varied significantly between host types, their densities (3-4 and ≤1, respectively) per plant were significantly similar. Larval parasitism of Apanteles sp. (7%-12%) and the total seasonal rate (11%-18%) were low in A. hybridus. In conclusion, H. recurvalis is clearly the major lepidopterous larval pest of A. hybridus in this locality. Lepidopterous pests habour a few natural enemies in both cultivated and volunteer hosts. Apanteles sp. is the most dominant parasitoid species, but total parasitism per species or the seasonal rate is low and insufficient.