A rapidly spreading deleterious aphid endosymbiont that uses horizontal as well as vertical transmission.

Endosymbiotic bacteria that live inside the cells of insects are typically only transmitted maternally and can spread by increasing host fitness and/or modifying reproduction in sexual hosts. Transinfections of Wolbachia endosymbionts are now being used to introduce useful phenotypes into sexual host populations, but there has been limited progress on applications using other endosymbionts and in asexual populations. Here, we develop a unique pathway to application in aphids by transferring the endosymbiont Rickettsiella viridis to the major crop pest Myzus persicae. Rickettsiella infection greatly reduced aphid fecundity, decreased heat tolerance, and modified aphid body color, from light to dark green. Despite inducing host fitness costs, Rickettsiella spread rapidly through caged aphid populations via plant-mediated horizontal transmission. The phenotypic effects of Rickettsiella were sensitive to temperature, with spread only occurring at 19 °C and not 25 °C. Body color modification was also lost at high temperatures despite Rickettsiella maintaining a high density. Rickettsiella shows the potential to spread through natural M. persicae populations by horizontal transmission and subsequent vertical transmission. Establishment of Rickettsiella in natural populations could reduce crop damage by modifying population age structure, reducing population growth and providing context-dependent effects on host fitness. Our results highlight the importance of plant-mediated horizontal transmission and interactions with temperature as drivers of endosymbiont spread in asexual insect populations.

Evaluation of potential resistance in seeds of different soybean cultivars to Helicoverpa armigera (Lepidoptera: Noctuidae) using demographic parameters and nutritional indices.

The use of resistant cultivars is a key component of any integrated pest management (IPM) program. Here, we assess the resistance status of 10 different soybean cultivar seeds according to their effects on demographic and nutritional indices of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) when incorporated into artificial diets. All experiments were conducted at 25 +/- 1 degrees C, 60 +/- 5% RH, and a photoperiod of 16:8 (L:D) h. Life table, reproduction, development, adult longevity, and nutritional indices of H. armigera were significantly affected by the cultivars examined. Mean developmental time of across all immature stages varied from 57 d on 'L17' to 32 d on 'Clark'. Efficiency of conversion of digested food (ECD) for old larvae ranged from 36.4% on 'Sari' to 14.8% on 'Sahar'. The adults that emerged from these larvae had very different rates of reproduction; the highest and lowest values for net reproductive rate (Ro) were 270 and 17 on Clark and L17, respectively. The most important demographic parameter, intrinsic rate of increase (rm), ranged from 0.114 on Sari to 0.09 on L17. H. armigera did not perform well on Sahar, L17, 'Gorgan3', and 'M4'. These cultivars show antibiosis resistance compared with other tested cultivars and are key candidates for field tests to determine usefulness in an IPM system.