Ecological Dynamics of Two Seed Predators, Araecerus levipennis and Acanthoscelides macrophthalmus, on Leucaena leucocephala

Abstract

Two seed predators, Araecerus levipennis Jordan and Acanthoscelides macrophthalmus (Schaeffer), exist in the invasive tree Leucaena leucocephala (Lam.) de Wit. This study aimed to understand interactions among Ar. levipennis, A. macrophthalmus and L. leucocephala in the invaded ecosystem. Bagging treatments were used to differentiate niches between the two seed predators. Results indicated niche partitioning between these seed predators as a guild; Ar. levipennis preferred early-stage pods while A. macrophthalmus preferred late maturity stage pods. Logistic regression analysis of 401 pod samples with 64.3% single-species occupation showed negative effects between species occurrence and heterospecific abundance (Ar. levipennis from 67% to 35% and A. macrophthalmus from 50% to 0%), suggesting interspecific competition. Ar. levipennis demonstrated priority effects, preempting resources at early maturity stages and competitively excluding A. macrophthalmus. Furthermore, early-stage pods attacked by Ar. levipennis inhibited seed dispersal, triggering L. leucocephala to produce resin as a defence response. To understand the germination of predator-attacked seeds, damaged seeds were collected to test germination and seedling survival. Seeds damaged by Ar. levipennis and A. macrophthalmus effectively reduced germination and seedling survival in the laboratory, but field observations revealed that L. leucocephala compensates through prolific seed production. This is the first comprehensive study documenting Ar. levipennis as a seed predator in the L. leucocephala system, highlighting the complex interactions between invasive plants and their seed predators. These findings demonstrate that single-agent biocontrol is insufficient for effective management and highlight the necessity of biological control strategies that combine multiple control agents.