Comparative biology and life tables of sorghum aphid Melanaphis sorghi (Theobald) (Hemiptera: Aphididae) from Mexico, at different temperatures

Abstract

The sorghum aphid Melanaphis sorghi (Theobald, 1904) is the most critical pest in sorghum crops grown in the USA and Mexico. The cultivated area of sorghum was reduced by more than 30% between 2016 and 2019 in northern Mexico, Guanajuato, Morelos, and other regions. This study provides essential information to support an Integrated Pest Management of this insect. M. sorghi field colonies from Guanajuato, Mexico, were identified by morphometric criteria and reared on Sorghum bicolor var. UPM-219 leaf discs using a bioclimatic chamber under different temperatures: 5, 10, 15, 20, 25, 30, 35 and 40 °C. The highest mortality occurred in extreme temperatures: 40 °C (100%). The lowest temperature assessed (5 °C) shows no reproduction, but the pre-reproductive period spread to 62.5 days, allowing an average of 88.2 days of the insects' survival. At 20 °C, M. sorghi produced a supernumerary N5 stage that prolonged the development by 7.1 days, while at the highest temperature (40 °C), N1s died after 0.9 days. The most prolonged reproductive period was 33.2 days (0.6 nymphs/day) at 10 °C, in contrast to 4.1 days (0.4 nymphs/day) at 35 °C. The most extended post-reproductive period (22.4 days) was observed at 10 °C and the shortest (4.2 days) at 35 °C. The highest fertility average (79.06 nymphs) was reached at 25 °C. The heat units required for each generation were 158.9, while theoretical thermal thresholds were 2.0 and 40 °C. Population parameters show that 25 °C is the optimal temperature for this aphid, estimating Ro (79.06), Rm (0.44), T (10.01), DT (1.59), and λ (1.55).