Sexual Reproduction Capabilities of Greenbugs (Homoptera: Aphididae)1

Sexual reproduction capabilities of greenbugs, Schizaphis graminum (Ron dani), were studied using 180 field collected samples, 91 laboratory clones and 8 biotypes exposed to a photoperiod of 11:13 (L:D) h at 20:18?C. The clones of biotypes C, E, and I produced large quantities of sexual morphs and viable progeny under these conditions. Biotypes G and F developed slowly and produced few viable eggs. Biotypes B, H, and J did not produce any sexual morphs. Field samples collected in May and moved directly to a long scotophase did not produce sexual forms. For other samples and laboratory clones with extended exposure to a 15:9 (L:D) h photoperiod, 73% produced males, 65% produced oviparae; and 67% of the oviparae produced black eggs considered to be viable. Prolonged cold treatment at 0?C beyond the standard seven weeks did not affect eclosion or nymphal survival. Hatching percentages ranged from 17 to 26%. Survival of fundatrices ranged from 5 to 52%. Our results suggest that holocycly may be lost entirely for some greenbug biotypes and is not readily induced in all individuals of any population. Understanding the holocyclic capabilities of greenbugs, Schizaphis graminum (Rondani), is important in predicting biotype shifts in the field, in laboratory genetic studies, or in determining the vulnerability of new resistance sources used in plant breeding programs. The greenbug holocycle was reviewed by Puterka and Peters (1990). They observed hatching of eggs resulting from controlled mat ings of greenbug biotypes C, E, F and G, but not from biotypes B and H. Greenbug biotypes are characterized by their ability to differentially damage various sources of resistance in small grains and sorghum. All members of a biotype share the phenotypic expression for damaging specific resistant germ plasm, however, their capability to damage additional hosts is unknown. There fore, it is essential to begin test populations of a biotype with a single individual to avoid variability at other loci. Puterka and Peters (1989) assigned genotypes to biotypes C, E, and F for virulence to wheat genes Gb2 and Gb3. The genotypes of these aphids may be changed either by mutation or by recombination during sexual reproduction leading to changes in responses to plant cultivars with these or other resistance genes. Our objectives were to determine the potential ability of greenbugs from field samples or laboratory produced clones to produce sexual morphs and viable eggs which could give rise to additional diversity within the species.