Host Plant Resistance and Biological Control for Linden Aphids

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Figure 1.
Scanning electron micrographs of midvein on ventral leaf surface. A - Tilia platyphyllos, with erect pubescence concentrated on veins and scattered elsewhere (x 35.7); B - T. cordata, showing axillary tufts and reduced, recumbent pubescence on midvein (x 36.7); C - T. europea, showing lack of pubescence, except for axillary tufts (x 35.9)

Table 1.

Linden aphid populations and Trioxys spp. parasitism from 8 northern California sites, 1991-93.

Site¹	Tilia species	T. curvicaudus present?¹	Mean no. aphids	Mean % Trioxys² parasitism
Berkeley (Albina St)	platyphyllos	+	4.1	20.8
San Jose	platyphyllos	+	8.4	19.9
Pleasanton	cordata	+	9.0	4.9
Berkeley (Mathews St)	cordata	+	20.6	6.6
San Anselmo	platyphyllos	-	1.2	2.1
Napa	platyphyllos	-	22.3	1.0
Vallejo	cordata	-	35.4	4.1
San Rafael 1991-92¹	europea	-	141.9	2.2
San Rafael 1993¹	europea	+	156.9	2.2

↵¹ + = T. curvicaudus established; - = T. curvicaudus absent Introduced at San Rafael 1992, considered established 1993
↵² T. curvicaudus, T. pallidus and T. tenuicaudus