Amaranth Pigweed Beetle Damage Level Correlates to Environmental Temperature Regimes

Abstract

Pigweed beetle Hypolixus haerens Boheman has been cited as a major insect pest of grain amaranth worldwide. This study evaluated injury level of both foliar and stem damage pests on eight varieties of Amaranthus hypochondriacus (L.) during two seasons of production at Katumani (LM4) and Kiboko ((LM5). Stem damage by beetle H. haerens correlates to environmental temperature. The hotter zone of low midlands five (LM5) was drier (43.7 ± 15.9 mm, 28 ± 2°C) than the cooler zone of low midlands four (LM4), which was relatively wetter (57.1 ± 13.8 mm, 24 ± 2°C). Beetle stem tunnel length inversely correlated with yield. The stem damage levels at the cooler zone were lower by 35, 42 and 47% in comparison to those from the hotter zone (LM5). Insect foliar damage level did not reflect direct grain loss. No variety was found resistant to H. haerens stem injury from the eight accessions evaluated. The wetter and cooler zone (LM4) was found to influence lower stem damage and subsequently 5-9 times higher grain yield than the hotter zone. In conclusion, considerations of the environmental factors in each agro-ecological zone would lead to right time of insecticide spray for management of the pests of grain amaranth to prevent yield loss.