Seven native coccinellid species inhabited alfalfa, corn, and small grain fields in eastern South Dakota prior to invasion and establishment of Coccinella septempunctata L. Six species occurred in all crops, however, Adalia bipunctata (L.) occurred only in corn. The structure of native coccinellid communities differed significantly for years prior to compared with years after establishment of C. septempunctata in fields of the three agricultural crops. Differences in community structure were accounted for mainly by reduced abundance of two species, C. transversoguttata richardsoni Brown and Adalia bipunctata (L.). Annual abundance of C. transversoguttata richardsoni averaged 20-32 times lower during post-invasion years than in years prior to invasion, depending on crop; while annual abundance of A. bipunctata averaged 20 times lower in corn after invasion. Addition of C. septempunctata to the community did not result in a significant increase in total abundance of coccinellids in the crops. Coccinellid abundance in agricultural crops may be limited by the total abundance of prey or by the availability of other requisites in the landscape as a whole. Therefore, introduction of a new species, while resulting in reductions in native species populations, may not increase total coccinellid abundance, and may therefore have no net effect on biological control of aphid pests.

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Grain yield loss caused by bird cherry‐oat aphid (Rhopalosiphum padi L.) infestation and barley yellow dwarf virus (BYDV) infection may result from direct damage to the winter wheat (Triticum aestivum L.) crop as well as from reduced crop tolerance to stress environments. This greenhouse study measured the effects of R. padi infestation, BYDV infection, or a combination of R. padi plus BYDV on plant height, date of anthesis, yield, and yield components of four winter wheat varieties (‘Roughrider’, ‘Norstar’, ‘TAM 107’, and ‘Vona’) in the absence of additional environmental stresses. Treatments were applied at the two‐leaf growth stage. Early in the pre‐vernalization growth period, R. padi treatment (alone or in combination with BYDV) reduced plant height to about 55 to 60% of the control plant height while BYDY treated plants were about 90% of control. During the post‐vernalization growth period, plant heights attained about 90% of control in the R. padi treatment, to about 80% of control in the BYDV treatment and to about 70% of control in the R. padi+ BYDV treatment. Dates of anthesis were later in the R. padi+BYDV treatments than in the R. padi treatments for Norstar, Roughrider, and Vona but not for TAM 107. Individual kernel weights in the BYDV and R. padi+BYDV treatments were less than control or R. padi treatments for Norstar, TAM 107, and Vona but not for Roughrider. Control or R. padi‐treated plants had a greater number of fertile heads than plants given the BYDV or R. padi+BYDV treatments. Grain yield was strongly associated with kernel number per plant. The number of kernels per plant was reduced 19% by the R. padi treatment, 36% by the BYDV treatment, and 50% by the R. padi+BYDV treatment. Grain yield was reduced 21% by the R. padi treatment, 46% by the BYDV treatment, and 58% by the R. padi+BYDV treatment. With the exception of date of anthesis and individual kernel weight, there were no significant treatment by variety interactions for plant height, grain yield, and yield components. We conclude that R. padi infestation and BYDV infection caused significant yield reductions and that the varieties tested had little difference in their responses to these treatments in the absence of additional environmental stress.

on the extent of the insect infestation (Kieckhefer et al., 1995), the timing of the infestation during the growing There is little information available that describes the effects of season (Kieckhefer and Gellner, 1988), the growth stage bird cherry-oat aphids (Rhopalosiphum padi L.) and Barley yellow of the plant at infestation (Pike and Schaffner, 1985), dwarf virus (BYDV) on cereal plant root systems. This 2-yr field experiment was conducted to determine how spring wheat (Triticum and whether the R. padi transmit BYDV to the crop aestivum L.) root characteristics, shoot characteristics, and grain yield (McPherson et al., 1986). BYDV is a phloem-restricted respond to R. padi infestation, BYDV infection, or a combination of Luteovirus obligately vectored by several species of R. padi plus BYDV. Treatments were applied at the 2-to 3-leaf stage.aphids (Kolb et al., 1991). Symptoms of BYDV infection When measured at anthesis, plants that received R. padi treatments include leaf discoloration (yellow or red), leaf necrosis, (300 aphid days) had about a 30% greater total root length (as meastunting, and delay or lack of heading (Comeau, 1987; sured with a minirhizotron) than control plants. Plants that received Hewings and D'Arcy, 1986; Riedell et al., 1999). BYDV BYDV as well as those that received R. padi plus BYDV had about is considered to be one of the most economically impora 40% decrease in total root length when compared with the control.

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