Host genotype–endosymbiont associations and their relationship with aphid parasitism at the field level

1. The relationship between endosymbionts and insects represent complex eco‐evolutionary interactions. Vertically transmitted endosymbionts can be a source of evolutionary novelty by conferring ecologically important traits to their insect hosts, such as protection against natural enemies. Host–endosymbiont associations could constitute an adaptive complex (holobiont) on which selective pressures present in the environment can act, being transferred to the next generation. 2. Although several laboratory‐based studies have confirmed host genotype × symbiont interactions, few studies have been directed at those associations in the natural populations and their ability to protect themselves from parasitism pressure at the field level. 3. A field‐based approach to study the aphid genotype–endosymbiont associations and its relationship with the total parasitism in the grain aphid Sitobion avenae was conducted. From the field study, experiments were carried out to study the defensive effect of the two most common facultative endosymbionts (Regiella insecticola and Hamiltonella defensa) present in S. avenae against one of the most important parasitoid species, Aphidius ervi. 4. Evidence is presented here of a high specificity of the aphid clone–endosymbiont associations in the field; however, the field and experimental results here do not support a relationship between the aphid clone–endosymbiont associations and a proxy of total parasitism in S. avenae. These findings highlight the importance of particular host clone–endosymbiont couplings as a key factor in gaining an understanding of the coevolutionary dynamics of endosymbionts in nature and their effect on the invasive potential of pest insects.     

Heavy-Light Chain Disulphide Bridge common to γA1 and a Genetic Variant of γA2 Immunoglobulins

IN a genetic, marker^{1, 2} from human γA2 immunoglobulin, it has recently been shown³ that the γA2 proteins belonging to the AM2(+) genetic variant lack the disulphide bond linking the heavy and light chains but that the other variants Am2(?) have the usual characteristics of other immunoglobulins. The fact that twenty out of twenty-two γA2 myeloma proteins (primarily from Caucasians) were Am2(+) explains previous reports that the H—L disulphide bond is absent in the γA2 molecules and that these molecules dissociate in acid. We have, however, found a third γA2 myeloma protein from a Caucasian (Rou) which failed to dissociate in the presence of acid and urea. It was typed by Dr Kunkel as an Am2(?) and the light chains are of the kappa type. The first two Am2(?) immunoglobulins identified³ were lambda type.     

The incidence and distribution of viruses infecting lettuce, cultivated Brassica and associated natural vegetation in Spain

A virus survey was conducted during the spring and autumn of 2001 and 2002 to determine the presence, prevalence and distribution in Spain of the viruses that are most commonly found infecting lettuce and Brassica worldwide. Crop plants showing virus symptoms from the principal lettuce and Brassica-growing regions of Spain, and some samples of the annual and perennial flora nearby, were tested by enzyme-linked immunosorbent assays using specific commercial antibodies against the following viruses: Alfalfa mosaic virus (AMV), Broad bean wilt virus 1 (BBWV-1), Beet western yellows virus (BWYV), Cauliflower mosaic virus (CaMV), Cucumber mosaic virus (CMV), Lettuce mosaic virus (LMV), Pea seed-borne mosaic virus (PSbMV), Turnip mosaic virus (TuMV) and Tomato spotted wilt virus (TSWV). Samples were also tested with a Potyvirus genus antibody. Virus incidence was much lower in spring than in autumn, especially in 2001. In spring 2002, CMV and LMV were the most prevalent viruses in lettuce, while CaMV was the most important virus present in Brassica crops grown in Navarra, followed by CMV and BWYV. In the autumn, the spectrum of viruses was different; potyviruses were widespread in lettuce grown in Madrid, but TSWV and BWYV were predominant in the Murcia region. The prevalent Potyvirus detected in lettuce fields was LMV, but none of the samples collected were positive for PSbMV or TuMV. In Brassica crops, TSWV was the most abundant in autumn-sown crops, especially in the Navarra region. All of the viruses present in lettuce and Brassica were also frequently detected in their associated natural vegetation at the same time, suggesting that they probably play an important role as virus reservoirs. Sonchus spp. were particularly common and were frequently infected with CMV, LMV and BWYV. Another common species, Chenopodium album, was often infected with TSWV and BWYV. Multiple infections were common, especially in non-crop plants, and the most common combination was BWYV and TSWV. The role of weeds in the epidemiology of viruses that infect lettuce and Brassica crops in Spain is discussed.