Biological response of Rhopalosiphum padi and Sipha flava (Hemiptera: Aphididae) changes over generations.

Multigenerational effects on biological aspects and on the life table of Rhopalosiphum padi (Linnaeus) (Hemiptera: Aphididae) and Sipha flava (Forbes) (Hemiptera: Aphididae) are not known. These studies can help further our understanding of the reasons for the conflicting results of the biological performance of aphids determined under laboratory conditions. Hence, the objective of the present work was to evaluate the biological aspects and life table of R. padi in brachiaria (Urochloa ruziziensis (R.Germ. & C.M.Evrard) Crins Poaceae) and S. flava in elephant grass (Pennisetum purpureum Schumach. Poaceae) during five consecutive generations, in the laboratory. The insects were observed daily under a stereoscopic microscope, recording: number of instars, duration and survival of each instar, duration and survival of the nymphal period, longevity of the adult, biological cycle (nymph + adult) and daily and total production of nymphs. During the five successive generations, the insects were subjected to the same climatic conditions and host plants. A joint analysis of the data obtained allowed us to record that the characteristics of the original infestation (first generation) influenced the results of research carried out in the laboratory with S. flava and R. padi, with significant differences in the biological parameters and life table of the aphids. Based on biological data, it was observed that S. flava showed greater adaptation, with faster development and greater fertility in the fifth generation, and R. padi was negatively affected, showing lower longevity, nymphal survival and fecundity in the second, fourth and fifth generations. Thus, the standardization of the generation used and the use of multigeneration studies are important tools for biological studies of these aphid species and the application of these studies to forage improvement programs.