Seasonal occurrence of amaranth Lepidopteran defoliators and effect of attractants and amaranth lines in their management

Lepidopteran defoliators are the most important pests of cultivated amaranths causing severe losses in cultivated fields worldwide. Leaf‐webbers, whose larvae fold, web or glue amaranth leaves using their silken webs as they feed and leaf‐worms which cause windowing but do not glue or fold leaves are mainly reported. Sustainable management strategies for these pests are still lacking given the adverse effects of synthetic pesticides. Field experiments were conducted during two seasons at two different sites in Central Kenya, to assess amaranth lepidopteran pests and their natural enemies’ population dynamics, evaluate the efficacy of phenylacetaldehyde (PAA) floral lure as attractant and the effects of three amaranth lines (Abuk1, Abuk2 and Abuk8) on the pests’ abundance and damage. Abundance of leaf‐webbers (p = .537), leaf‐worms (p = 1) and their associated parasitoids (p = .083) did not differ between the dry and wet seasons. The parasitoids Atropha tricolor and Apanteles sp. caused parasitism of 6.2% and 33.3% on Spoladea recurvalis and Choristoneura sp., respectively. PAA incorporated traps attracted moths that were largely unrelated to the damaging larvae observed on the crops with only 0.5% of total trap catches being S. recurvalis. Sub‐sites in which PAA were incorporated had significantly higher number of leaf‐webber larvae on the crops compared to control sub‐sites (p = .014). Amaranth lines studied had significant (p = .007) effect on lepidopteran defoliators’ abundance and damage, with fewer leaf‐webbers and lower severity of damage recorded on Abuk2 compared to Abuk8. The implication of these findings for the control of lepidopteran defoliators in East Africa is discussed.