Table 1. The ratios of copies of plasmid-borne amino acid biosynthetic genes (leuABCD, trpEG) to chromosomal gene copies for Buchnera of different aphid species and strains.

Aphid host	Aphid clone/population	leuABCD	trpEG
A. pisum	12 United Kingdom clones	—	2.4—16.2*
	N. A. Moran lab clone 5A (Madison, WI)	0.6	4.8
Diuraphis noxia	P. Baumann lab clone (Lincoln, NE)	0.9†	1.8‡
	South Africa population	0.3	0.4
Rhopalosiphum maidis	N. A. Moran lab clone (Tucson)	—	0.3
S. graminum	Biotype B (K. A. Shufran lab clone)	—	0.5
	Biotype E (T. Mittler lab clone)	23.5†	14.5§
	Biotype E (P. Baumann lab clone)	1.4	2.1
	Biotype E (N. A. Moran lab clone)	1.9	1.5
	Biotype E (K. A. Shufran lab clone)	1.6	2.6
	Biotype G (K. A. Shufran lab clone)	0.5	2.4
	Biotype SC (K. A. Shufran lab clone)	—	0.5
Uroleucon ambrosiae	86 individuals, 15 U.S. populations	0.5—2.8¶	0.3—1.9¶

Unless otherwise noted, values are previously unpublished and were estimated by using real-time quantitative PCR as in ref. 25 (primer sequences are available upon request). The reason for the discrepancy among Buchnera (S. graminum) estimates is uncertain, although the concordance of the quantitative PCR estimates across biotypes provides support for their accuracy.

^*Ref. 27; calculated by using quantitative DNA hybridization

^†Ref. 26; calculated by using quantitative DNA hybridization

^‡Ref. 30; calculated by using quantitative DNA hybridization

^§Ref. 18; calculated by using quantitative DNA hybridization

^¶Ref. 25; calculated by using real-time quantitative PCR