Population growth of Prostephanus truncatus (Horn) (Coleoptera: Bostrychidae) in a wide range of temperatures: Does the geographic origin of a strain affect its development and progeny production capacity?

Abstract: Laboratory studies were conducted to evaluate the population growth of adults
belonging to the larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae), an important pest of stored maize, towards a wide range of temperatures. Population growth and infestation levels of three different P. truncatus strains obtained from various geographic areas were compared to evaluate the optimal thermal requirements for reproduction, the infestation levels at lower and higher temperatures, and the effect of the origin of the population. For this purpose, groups of 10 adults per strain were introduced in climatic chambers at temperatures of 25, 30, 32, 35, 38 and 40 °C and 55 % relative humidity. The progeny production, the number and weight of damaged by insects’ kernels, and the frass in the vials was counted after 45 and 70 days, with different sets of vials for each developmental period.
The optimal growth rate of the studied strains in terms of both developmental period and
progeny production was observed at temperatures ranging between 25 to 32 °C. At the same
time, the population growth of the species appeared to be affected by the combination of
temperature and/or developmental period. Differences were observed between the strains, both in terms of their growth rate and the infestation they caused on the kernels over time. The results of the present study led us to the conclusion that P. truncatus has a different thermal response based on the origin of the strain. These data are necessary for the accurate prediction or elimination of future infestations, aiming at the immediate and early detection of the pest in areas where is likely to establish.