Abstract
Aphidius ervi Haliday is a parasitoid of natural populations of both Acyrthosiphon pisum (Harris) on alfalfa and Sitobion avenae (Fabricius) on wheat in Chile. In this study the performance of the aphid parasitoid on both host species was evaluated. Regardless of origin, both females and males of A. ervi were significantly smaller when reared on S. avenae than on A. pisum. Males and females of A. ervi reared on S. avenae on wheat also took significantly longer to develop than when reared on A. pisum. There was no significant difference in the sex ratio of the parasitoid when reared on these two host aphids. Survival of parasitoids from the A. pisum - alfalfa system was significantly lower when reared on S. avenae relative to those reared on A. pisum, but no significant difference in survival on both hosts was detected in parasitoids from the S. avenae - wheat system. Behaviour of parasitoid females during oviposition, such as frequency of encounters, number of attacks and stabbings of host aphids, were significantly higher in the A. pisum - A. ervi interaction than in the S. avenae - A. ervi interaction, regardless of the origin of the parasitoid. Aphid defensive reactions such as kicking or production of cornicle secretion, were significantly higher in the A. pisum - A. ervi than the S. avenae - A. ervi interaction. The results are discussed in relation to the effect of host quality and host aphid body size on parasitoid development.
Highlights
Aphidiinae wasps (Hymenoptera: Braconidae) are soli tary, koinobiont endoparasitoids, which only parasitize aphids (Hemiptera: Aphididae)
Attacks and stabs by the parasitoid were higher on A. pisum than on S. avenae, when the origin o f the parasitoid was the A. pisum - alfalfa system, but not when it was the S. avenae wheat system (Table 1)
Regardless o f sex, total parasitoid development time was significantly higher on S. avenae than on A. pisum when parasitoid origin was the S. avenae - wheat system, but not when it was the A. pisum - alfalfa system (Table 2, MS origin = 0.055, F1,88 = 3.769, p = 0.055; MS host = 0.460, F1,88 = 31.847, p < 0.001; MS sex = 0.012, F ^ = 0.837, p = 0.363; MS origin x host = 0.142, F ^ = 9.826, p = 0.002; remaining interactions non-significant)
Summary
Aphidiinae wasps (Hymenoptera: Braconidae) are soli tary, koinobiont endoparasitoids, which only parasitize aphids (Hemiptera: Aphididae). Aphidius ervi Haliday is an oligophagous aphid parasitoid, variable in its preferences and performance on different aphid host species (Cameron et al, 1984; Pungerl, 1984; Starý et al, 1985; Powell & Wright, 1988; 1991; Christiansen Weniger & Hardie, 1997; Takada & Tada, 2000). Sitobion avenae (Fabricius) on cereals is a suitable host o f A. ervi, this parasitoid is of only minor importance as an aphid biocontrol agent o f aphids on cereals in Europe (Cameron et al, 1984) This situation is expected to improve if cereals are grown near perennial legume fields (Starý, 1978). In Chile, the intro duction o f this parasitoid from cereal hosts in France occurred nearly 25 years ago (Zúftiga, 1990), and it parasitizes here both A. pisum on alfalfa and S. avenae on wheat(Starýetal., 1993; Starý, 1993)
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