Extent and pattern of damage in wheat caused by three different species of storage insect pests

Abstract

We investigated the extent and pattern of damage in wheat caused by Tribolium castaneum Herbst (Coleoptera: Tenebrionidae), Trogoderma granarium Everts (Coleoptera: Dermestidae) and Rhyzopertha dominica F. (Coleoptera: Bostrichidae) over a period of 75 d. Damage parameters included numbers of damaged grains, their weight; numbers of undamaged grains, their weight; frass weight and percent weight loss. Results showed after 75 d, maximum damaged grains were 125.17 ± 22.88 by R. dominica followed 80.50 ± 6.91 by T. granarium and least were 20.00 ± 2.61 after 50 d by T. castaneum. For R. dominica and T. granarium damage to grains increased with time (P 0.05). Maximum percent weight loss was 7.02 ± 1.87 g by R. dominica followed by 2.89 ± 0.33 g by T. granarium and least 0.65 ± 0.08 g by T. castaneum. Maximum dead insects percentage was 82% after 25 d for R. dominica, 59.67 ± 3.44 for T. granarium after 50 d and 100.00 ± 0.00 for T. castenum after 50 or 75 d compared to other time periods (P < 0.05). Percent increase in population was recorded for T. granarium but not for other two species during 75 d period. Microphotography of damaged grains after 75 d to compare damage pattern showed R. dominica made circular holes (Fig. 1), T. granarium made irregular holes (Fig. 2) and T. castaneum made circular damage but it did not traverse grains (Fig. 3). Radius length of circular damage was more for T. castenum compared with for R. dominica (P < 0.05). Damage area was maximum by T. granarium followed by T. castenum and least by R. dominica while perimeter of damage was greatest by T. granarium followed by T. castenum and least by R. dominica (P < 0.05).