Evaluation of the Performance of Cecidochares connexa (Macquart) (Diptera: Tephritidae) as a Biological Control Agent Against the Devil Weed, Chromolaena odorata (L.) King & Robinson Under Shaded Conditions.

Date

12-2025

Abstract

The devil weed (Chromolaena odorata) problem in the Philippines has evolved from an alien species invasion to an agricultural pest, as the thickets it forms disrupt farm operations in plantation crops. In this study, the introduced biological control agent, the gall fly (Cecidochares connexa), was found to be ineffective under shaded growing conditions since the gall fly and the weed are adapted to open-field conditions in their native range. The effectiveness of control was evaluated by assessing the ability of gall fly damage to reduce the height, clump size, and reproductive rate of devil weed through field surveys, screenhouse experiments, and computer modelling. In the field survey, the gall fly infestation was lower (32.07 ± 8.56%) in weeds growing under coconut than in the open field (36.19 ± 29.71%), resulting in an insignificant reduction in plant height and an increase in the number of stems and branches of the weed. In the screenhouse experiment, gall fly infestation severity was higher under shaded conditions (33.33 ± 10.0%) than under full light (9.99 ±  4.94%). However, this level of infestation did not significantly affect most growth and reproductive parameters of the weed (i.e. number of stems, number of shoot tips, number of branches, branch order proportions, biomass accumulation, and number of flowers and seeds), and the weeds grew taller under shade, with a 170.00 ± 31.85% increase compared to 146.00 ± 23.70% under full light. The computer model built from the experimental data predicted that shading alone can suppress weed growth and reproduction. Without the gall fly infestation, the devil weed under shaded growing conditions will accumulate 32% less above-ground biomass and produce 38% fewer seeds.

Document Type

Dissertation

Degree

Doctor of Philosophy in Entomology

College

Graduate School (GS)

Adviser/Committee Chair

Celia dR. Medina

Committee Member

Luis Rey I. Velasco, Barbara L. Caoili, Ireneo B. Pangga

Language

English

Location

UPLB Main Library Special Collections Section (USCS)

En – AGROVOC descriptors

CHROMOLAENA ODORATA; TEPHRITIDAE; INFESTATION; BIOLOGICAL CONTROL AGENTS; BIOLOGICAL WEED CONTROL

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