Aphidophagous Coccinellids in Alfalfa, Small Grains, and Maize in Eastern South Dakota

In a 13-year study of aphidophagous coccinellids associated with alfalfa (Medicago sativa), maize (Zea mays), and small grain crops in eastern South Dakota, the following species were consistently associated with the crops: Hippodamia convergens, H. tredecimpunctata tibialis, H. parenthesis, Coleomegilla maculata lengi, Coccinella transversoguttata richardsoni, Cycloneda munda, and Adalia bipunctata. All species except A. bipunctata were associated with each of the three crops, while A. bipunctata occurred only in maize. Relative abundances of each species varied among crops and among years. Although only seven species were associated with the crops, additional species were captured on sticky traps stationed adjacent to sampled fields. The species diversity of immature coccinellids did not differ among crops but did differ among years. The diversity of adults differed among crops and years. The site from which samples were taken had no influence on the diversity of immatures or adults. Species relative abundances in alfalfa and small grains were more similar to each other than they were to relative abundances in maize

Paleogeodetic records of seismic and aseismic subduction from central Sumatran microatolls, Indonesia

We utilize coral microatolls in western Sumatra to document vertical deformation associated with subduction. Microatolls are very sensitive to fluctuations in sea level and thus act as natural tide gauges. They record not only the magnitude of vertical deformation associated with earthquakes (paleoseismic data), but also continuously track the long-term aseismic deformation that occurs during the intervals between earthquakes (paleogeodetic data). This paper focuses on the twentieth century paleogeodetic history of the equatorial region. Our coral paleogeodetic record of the 1935 event reveals a classical example of deformations produced by seismic rupture of a shallow subduction interface. The site closest to the trench rose 90 cm, whereas sites further east sank by as much as 35 cm. Our model reproduces these paleogeodetic data with a 2.3 m slip event on the interface 88 to 125 km from the trench axis. Our coral paleogeodetic data reveal slow submergence during the decades before and after the event in the areas of coseismic emergence. Likewise, interseismic emergence occurred before and after the 1935 event in areas of coseismic submergence. Among the interesting phenomenon we have discovered in the coral record is evidence of a large aseismic slip or “silent event” in 1962, 27 years after the 1935 event. Paleogeodetic deformation rates in the decades before, after, and between the 1935 and 1962 events have varied both temporally and spatially. During the 25 years following the 1935 event, submergence rates were dramatically greater than in prior decades. During the past four decades, however, rates have been lower than in the preceding decades, but are still higher than they were prior to 1935. These paleogeodetic records enable us to model the kinematics of the subduction interface throughout the twentieth century

Visual ecology of aphids – a critical review on the role of colours in host finding

We review the rich literature on behavioural responses of aphids (Hemiptera: Aphididae) to stimuli of different colours. Only in one species there are adequate physiological data on spectral sensitivity to explain behaviour crisply in mechanistic terms. Because of the great interest in aphid responses to coloured targets from an evolutionary, ecological and applied perspective, there is a substantial need to expand these studies to more species of aphids, and to quantify spectral properties of stimuli rigorously. We show that aphid responses to colours, at least for some species, are likely based on a specific colour opponency mechanism, with positive input from the green domain of the spectrum and negative input from the blue and/or UV region. We further demonstrate that the usual yellow preference of aphids encountered in field experiments is not a true colour preference but involves additional brightness effects. We discuss the implications for agriculture and sensory ecology, with special respect to the recent debate on autumn leaf colouration. We illustrate that recent evolutionary theories concerning aphid–tree interactions imply far-reaching assumptions on aphid responses to colours that are not likely to hold. Finally we also discuss the implications for developing and optimising strategies of aphid control and monitoring

Spillover of Agriculturally Subsidized Predators as a Potential Threat to Native Insect Herbivores in Fragmented Landscapes

Habitat loss and fragmentation can have strong negative impacts on populations of some native species. Spillover of generalist natural enemies from the surrounding landscape matrix is one mechanism potentially generating such effects, yet this has been rarely studied in insects. We examined the influence of habitat conversion to agriculture on the abundance and potential effects of predatory coccinellid beetles on native insect herbivores within 12 grassland remnants in central Nebraska (U.S.A.). Results of sweep sampling revealed that coccinellids were three to six times more abundant at native grassland sites embedded within cropland- dominated landscapes compared with control sites in grassland-dominated landscapes over the 3 years of the study. Exclusion experiments further demonstrated that predation intensity was strongly related to coccinellid abundances across sites and that coccinellids can dramatically reduce densities of a native aphid herbivore. In contrast to studies of specialized insect parasitoids, which have generally found reduced enemy pressure in fragmented landscapes, our results suggest that native herbivores may in some cases experience increased consumer pressure in landscapes with increasing habitat loss because of spillover of generalist predators from surrounding cropland habitats. La pérdida y fragmentación del hábitat puede tener fuertes impactos negativos sobre las poblaciones de algunas especies nativas. El excedente de enemigos generalistas naturales en la matriz circundante es uno de los mecanismos que potencialmente genera tales efectos, pero esto ha sido poco estudiado en insectos. Examinamos la influencia de la conversión de hábitat en agricultura sobre la abundancia y potenciales efectos de escarabajos coccinélidos depredadores sobre insectos herbívoros nativos en 12 remanentes de pastizales en Nebraska central (E. U. A.). Los resultados de muestreos de barrido revelaron que los coccinélidos fueron tres a seis veces más abundantes en sitios con pastizales nativos enclavados en paisajes dominados por cultivos en comparación con sitios control en paisajes dominados por pastizales durante los tres años del estudio. Experimentos de exclusión adicionalmente demostraron que la intensidad de depredación estaba muy relacionada con las abundancias de coccinélidos en todos los sitios y que los coccinélidos pueden reducir dramáticamente las densidades de un áfido herbívoro nativo. En contraste con estudios de insectos parasitoides especializados, que generalmente encuentran presión reducida de enemigos en paisajes fragmentados, nuestros resultados sugieren que, en algunos casos, los herbívoros nativos pueden experimentar mayor presión de consumo en paisajes con incremento en la pérdida de hábitat debido al excedente de depredadores generalistas en los hábitats agrícolas circundantes

Effects of temperature, feeding position and crop growth stage on the population dynamics of the rose grain aphid, Metopolophium dirhodum (Hemiptera: Aphididae)

The population dynamics of Metopolophium dirhodum were studied on winter wheat seedlings at constant (10-degrees-C, 15-degrees-C, 20-degrees-C, 25-degrees-C and 30-degrees-C) and fluctuating (12(night)-22(day)-degrees-C) temperatures, and during booting to early inflorescence, and anthesis to early milky ripe stage, at 19-degrees-C. The pre-reproductive development time was decreased by increasing the temperature from 10-degrees-C to 25-degrees-C. It was significantly shorter when the aphids were feeding during booting to early inflorescence than during anthesis to early milky ripe stage but was similar when the aphids were feeding on the flag, second or third leaves. The total number of nymphs produced/apterous adult was not significantly affected by temperature from 10-degrees-C to 25-degrees-C but adult reproductive lifespan was reduced by increasing temperature from 10-degrees-C and 12-22-degrees-C to 15-degrees-C, 20-degrees-C and 25-degrees-C. The daily intrinsic rate of increase changed from 0.11 to 0.25, and the cohort generation time decreased from 31 to 12 days, with increase of temperature from 10-degrees-C to 25-degrees-C. Reproductive rate was similar when the aphids were feeding on the flag, second or third leaves during booting to early inflorescence at 19-degrees-C. The reproductive rate was higher when the aphids fed from mid-inflorescence to mid-milky ripe stage than from mid-milky to early ripe stage. These results were compared with those from other studies. Predictions from a simulation model using development and reproductive rates from this study and literature were compared and the former rates resulted in a more accurate prediction of field observations in 1979, an outbreak year