Survival and Fecundity of Single and Grouped Clonal Sorghum Aphids and a Novel Aphid-Marking Technique

Aphids have rapid intrinsic rates of increase because clonal females can reproduce parthenogenetically. Studies to investigate host plant resistance often measure life history characteristics of an individual on the test cultivar. However, aphid lifespan, fecundity, and intrinsic rate of increase could be influenced by the presence and feeding effects of multiple individuals, potentially overestimating antibiosis when a single individual is monitored. We compared life history traits of a single sorghum aphid, Melanaphis sorghi (Theobald, 1904) (Hemiptera: Aphididae) with life history parameters of groups of 10 females on susceptible sorghum (Sorghum bicolor (L.) Moench). There were no significant differences between single and grouped aphids for longevity (F = 3.67, P = 0.08), number of offspring produced (F = 0.31, P = 0.59), time spent reproducing (F = 3.74, P = 0.08), or the number of offspring per day (F = 0.93, P = 0.35). Demographic parameters [fecundity rate (Dm) and intrinsic rate of increase (rm)] were also not different. Overall, our results indicated that single aphids are suitable to investigate plant resistance, including antibiosis. When assessment requires using groups of aphids, it can be difficult to identify individuals. We investigated using non-toxic permanent markers (black, blue, green, and red) to put colored markings on the thorax of individuals. Survival and reproduction of marked individuals were similar to those of checks, and marks were readable for at least 2 weeks, demonstrating that permanent markers can be used when an experiment requires distinguishing among individuals or cohorts that are mixed.