Interspecific interaction between populations of prostephanus truncatus horn (Coleoptera: Bustrichidoe) and sitophilus zeamais motsh. (Coleoptera: Curculionidae).

In this work, interspecific competition was studied experimentally between two pests of stored maize, the larger grain borer, Prostephanus truncatus Horn and the maize weevil Sitophilus zeamais Motsch. The two species were reared in environmental chambers at 30°C and four relative humidities (RH) namely 55, 60, 70 and 75%. The two species were competed in varying population proportions (1:1; 4:1; 1:4). To measure competition between the species, single-species populations (controls) of both species were set up under similar environmental conditions. The initial numbers were 4, 10, 16 and 20 insects for each species. The insects were reared on loose maize grains. Competition between species was investigated by assessing adult production, mortality, developmental period and adult body size for single- and mixed-species populations. Adult production increased with RH (for all measured humidities) for both species but the increase was more marked for S. zeamais (about 300) than for P. truncatus (about 50%). In both species, adult production values were higher for single- than for mixed-species populations. Mortality rates showed an inverse relationship with density in both species. Changes in RH did not affect mortality in P. truncatus. The effect of RH on mortality was marginally significant for S. zeamais: there was a tendency for mortality, in this species, to decrease with increase in RH. Mortality rate was lower for single- than for mixed-species populations in bath species. At 55% RH P. truncates had a shorter median developmental period (about 38 days} than S. zeamais (about 40 days). At higher RH, developmental period was 35 days for both species. There were no significant differences in developmental period between single- and mixed-species populations for both species. Body size ranged between 3.26 and 3.32mm for P. truncates, and between 4.10 and 4.13mm for S. zeamais. There was no variance in body size among the four RH levels for both species. There were no notable differences in body size between single- and mixed-species populations. The study indicated that interspecific interaction between P. truncates and S. zeamais affected adult production and mortality in both species. There were significant differences in these attributes between single- and mixed-species populations. Developmental period and adult body size were not affected by interspecific interactions in both species.