Gary H. Sewell

Changes in a lady beetle community following the establishment of three alien species

A number of recent studies indicated that establishment of exotic lady beetles (Coleoptera: Coccinellidae) may have adverse affects on native lady beetle species. In the present study, we analyzed changes in coccinellid community inhabiting potato crops in northern Maine over the past 31 years. Prior to 1980, lady beetle communities were comprised almost exclusively of the two native species, Coccinella transversoguttata Brown and Hippodamia tredecimpunctata(Say). Starting 1980, an exotic species Coccinella septempunctata L. became permanently established in potato crops and quickly started to dominate lady beetle community. Two other exotic species, Harmonia axyridis(Pallas) and Propylea quatordecimpunctata(L.) became prominent members of the lady beetle community in 1995 and 1996. Invasion by exotic species was followed by a significant decline in the abundance of C. transversoguttata and H. tredecimpunctata, and a significant increase in the overall diversity of lady beetle community. The abundance of aphid prey was substantially reduced after the establishment of H. axyridis. The observed trends demonstrate the profound effects that exotic natural enemies may have on target and non-target native species, and highlight the importance of their thorough evaluation before initiating biological control programs.

On-Soil Movement and Plant Colonization by Walking Wingless Morphs of Three Aphid Species (Homoptera: Aphididae) in Greenhouse Arenas

Abstract Potato aphid, Macrosiphum euphorbiae (Thomas); green peach aphid, Myzus persicae (Sulzer); and buckthorn aphid, Aphis nasturtii Kaltenbach are polyphagous herbivores that commonly colonize potato plants, Solanum tuberosum L., in the northeastern United States and Canada. Their movement influences spatial and temporal patterns of viral spread within potato fields. We investigated aphid movement between potato plants early in the season, with a particular focus on their ability to walk over bare soil. On average, aphids survived 1.16 ± 0.04 d (mean ± SE) on the surface of bare soil; all of them dying within 3 d. Wingless aphids did not leave potato plants that were adequate as a food supply. When forcibly removed from the host plant and released on the soil surface, all three species colonized the nearest plant within 1 h. However, when given no other choice, a significant proportion of aphids was fully capable of colonizing potato plants as far as 180 cm away from the point of release. Potato aphid, which is the largest, was the most mobile of the three species. The green peach aphid was intermediately mobile, and the buckthorn aphid was the least mobile species.

Differential Effects of Weather and Natural Enemies on Coexisting Aphid Populations

ABSTRACT Study of mechanisms responsible for regulating populations of living organisms is essential for a better comprehension of the structure of biological communities and evolutionary forces in nature. Aphids (Hemiptera: Sternorrhyncha) comprise a large and economically important group of phytophagous insects distributed worldwide. Previous studies determined that density-dependent mechanisms play an important role in regulating their populations. However, only a few of those studies identified specific factors responsible for the observed regulation. Time series data used in this study originated from the untreated control plots that were a part of potato (Solanum tuberosum L.) insecticide trials in northern Maine from 1971 to 2004. The data set contained information on population densities of three potato-colonizing aphid species (buckthorn aphid, Aphis nasturtii; potato aphid, Macrosiphum euphorbiae; and green peach aphid, Myzus persicae) and their natural enemies. We used path analysis to explore effects of weather and natural enemies on the intrinsic growth rates of aphid populations. Weather factors considered in our analyses contributed to the regulation of aphid populations, either directly or through natural enemies. However, direct weather effects were in most cases detectable only at P < 0.10. Potato aphids were negatively affected by both fungal disease and predators, although buckthorn aphids were negatively affected by predators only. Parasitoids did not have a noticeable effect on the growth of any of the three aphid species. Growth of green peach aphid populations was negatively influenced by interspecific interactions with the other two aphid species. Differential population regulation mechanisms detected in the current study might at least partially explain coexistence of three ecologically similar aphid species sharing the same host plant.

Aphid abundance and potato virus y transmission in imidacloprid-treated potatoes

Imidacloprid is a commonly used insecticide that is highly effective in controlling insect pests of potato. The relatively high cost of imidacloprid provides commercial growers with a strong incentive to reduce field application rates. In the present study, we investigated the impact of reduced imidacloprid rates on aphid abundance and potato virus Y transmission within potato fields. Infurrow applications of imidacloprid provided better aphid control even at a reduced rate when compared to threshold-based foliar applications, but did not suppress the spread of the non-persistently transmitted potato virus Y. Virus transmission was significantly decreased in foliar-sprayed plots, possibly because foliar applications incapacitated aphid vectors probing or feeding on infected plants. Despite these generally encouraging results, we still observed 2.3 to 2.7 fold increase in virus infection at foliar-treated plots at the end of the growing season.

Evidence for a relationship between certain soil arthropods and acid scab development

Springtails and mites have been found consistently in acid scab lesions and studies have shown that these arthropods carryStreptomyces spp. both on and in their bodies. Tests with several soil-applied, systemic insecticides have shown significant control of acid scab despite having little effect on the acid scab pathogen in culture. Diazinon, a long residual insecticide, gave acid scab control as good as the best fungicides thus far tested as seed or soil treatments. This insecticide also was found to be almost nontoxic to the acid scab pathogen. We suggest that soil arthropods appear to be a factor in acid scab development and present circumstantial evidence suggestive of their involvement in all potato scab development.ResumenSe ha encontrada en forma consistente la ocurrencia de colémbolos y ácaros en las lesiones de la sarna ácida y los estudios han demostrado que estos artrópodos llevan elStreptomyces spp. tanto sobre, como dentro de sus cuerpos. Ensayos con varios insecticidas sistémicos aplicados al suelo han dado un control significativo de la sarna ácida a pesar de tener sólo un pequeño efecto contra el patógeno en cultivo. El Diazinon, un insecticida de suelo de largo efecto residual, produjo un control de la sarna ácida tan bueno como el mejor de los fungicidas que haya sido probado como tratamiento de semilla ó del suelo. Este insecticida casi no fue tóxico para el patógeno de la sarna ácida. Sugerimos que los artrópodos del suelo constituyen un factor en el desarrollo de la sarna ácida y la evidencia circunstancial que se presenta sugiere que ellos están involucrados en todo desarrollo de sarna ácida.

Reeves kingpin: A high-yielding mid-season potato variety suitable for fry processing

Reeves Kingpin is a mid-season processing potato variety developed and selected at the University of Maine’s Aroostook Research Farm in Presque Isle, Maine. Its main attribute is its high-yielding potential, giving an average yield of 47 mt/ha. Reeves Kingpin is suitable for processing into french fries due to its large tubers, high specific gravity, and acceptable fry color. The average specific gravity of Reeves Kingpin is 1.085 which is comparable or better than ‘Russet Burbank’ and ‘Shepody’. Reeves Kingpin has received good baking scores, which may qualify it for fresh market; however, its tuber appearance generally does not meet fresh market standard. The tubers have netted to lightly russeted skin and are long and blocky in shape. The tubers rarely exhibit the pointed and knobby characteristics of Russet Burbank. The incidence of misshapen tubers, sunburn, and growth cracks can be high under some conditions; however, hollow heart, internal heat necrosis, and vascular discoloration are not usually a problem. Tubers of Reeves Kingpin are relatively tolerant to shatter and black spot bruise. The plants of Reeves Kingpin are relatively taller, with greener leaves, more flowers, and moderate to heavy fruit set compared to Russet Burbank. The late-season vigor of Reeves Kingpin is an advantage compared to Shepody, but its haulms can be hard to kill prior to harvest, particularly if over-fertilized. Reeves Kingpin is resistant to tuber net necrosis and moderately resistant to verticillium wilt and early blight. However, it is susceptible to golden cyst nematode, late blight, bacterial ring rot, and corky ring spot virus and moderately susceptible to common scab.ResumenReeves Kingpin es una variedad de papa para procesamiento de madurez medianamente temprana, desarrollada y seleccionada en la Granja Experimental Aroostook de la Universidad de Maine en la Isla Presque, Maine. Su mayor atributo es el tener un alto rendimiento potencial con un promedio de 47 t/ha. Reeves Kingpin es apropiada para papa frita por tener tubérculos grandes, gravedad específica alta y color de fritura aceptable. Tiene un promedio de gravedad específica de 1.085, comparable o mejor que Russet Burbank y Shepody. Reeves Kingpin tiene buen puntaje de papa para horneado que la calificaría para su mercadeo en fresco, a pesar de que la apariencia del tubérculo no alcanza los estándares exigidos para este fin. Los tubérculos tiene la piel reticulada a ligeramente rosada, son alargados, de forma cúbica y rara vez exhiben las características de aguzados y nudosos propios de Russet Burbank. La incidencia de tubérculos deformes, rajaduras de crecimiento y por rayos solares, pueden ser altas bajo determinadas condiciones, pero generalmente no presentan problemas de corazón vacío, necrosis interna por calor y descoloramiento vascular. Los tubérculos de Reeves Kingpin son relativamente tolerantes a las rajaduras y magulladuras por mancha negra. Las plantas de Reeves Kingpin son relativamente altas con hojas más oscuras, mayor número de flores y fructificación moderada a alta en comparación con Russet Burbank. El vigor tardío de Reeves Kingpin es una ventaja cuando se compara con Shepody, pero sus rastrojos pueden ser difíciles de destruir antes de la cosecha, particularmente si las plantas han sido sobre fertilizadas. Reeves Kingpin es resistente a la necrosis en red del tubérculo y moderadamente resistente a la marchitez por Verticillium y tizón temprano, pero es susceptible al nematodo dorado, tizón tardío, pudrición bacteriana en anillo y al virus de la mancha corchosa en anillo y moderadamente susceptible a la sarna común.

Scientific Note: Adult red-headed flea beetle found feeding on potato in Maine (Coleoptera: Chrysomelidae)

Here we present the first record of Sphyrion lumpi (Copepoda), a mesoparasitic species found on macrourid Coelorinchus marinii from Southern Brazilian continental slope.