Richard H. Storch

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.

Effect of time of inoculation with potato leafroll virus on development of net necrosis and stem-end browning in potato tubers

The Green Mountain cultivar was used in field tests to determine the effects of inoculating potato plants at various times with the potato leafroll virus (PLRV) on development of internal necrosis of tuber tissue. Viruliferous apterae of the green peach aphid,Myzus persicae (Sulz.), were placed on each stem in all hills to be inoculated in each 3.0 m single-row plot. Planting and inoculation dates were varied in all field experiments and, in one, several vine-killing dates were also included. All harvested tubers were stored for approximately four months at 10°C to enhance development of internal necrosis prior to examination. Similar but smaller greenhouse studies involving both apterous and alate green peach aphids were also conducted using Green Mountain, Irish Cobbler, and Russet Burbank cultivars. All results showed that as inoculation was delayed relative to plant development, more net necrosis (NN) occurred. Conversely, when plants were inoculated early, stem-end browning (SEB) rather than NN predominated. A high percentage of naturally occurring SEB tubers (cv. Russet Burbank) were found by ELISA to contain PLRV. Plants produced by these tubers only rarely developed leafroll symptoms. These findings suggest a previously unsuspected causal relationship between SEB and PLRV. Implications of this apparent relationship on the epidemiology of potato leafroll in Maine are discussed.ResumenLa variedad de papa Green Mountain fué usada en los experimentos para demostrar los efectos de la inoculación, en diferentes fechas, del virus enrollador de la hoja de la papa (PLRV) sobre el desarrollo de necrosis interna en tejido del tubérculo. Contaminados áfidos apteros del durazno verde,Myzus persicae (Sulz.), fueron colcocados sobre el tallo que iba a ser inoculado in cada una de las parceles de 3.0 metros. Las fechas de plantación e inoculación fueron cambiadas en todas los experimentos y en uno, las fechas de varias vine-killing fueron también incluidas. Todos los tubérculos cosechados fueron almacenados por aproximadamente cuatro meses a una temperatura de 10°C para acrecentar el desarrollo de la necrosis interna antes de ser examinado. Estudios similares pero en escala más pegueña en invernaderos, fueron hechos involucrando áfidos del durazno verde, con alas y sin alas, en estos experimentos fueron usadas las variedades de papa Green Mountain, Irish Cobbler y Russet Burbank. Todos los resultados demostraron que cuando la inoculación fué retardada en relación al desarrollo de la planta, más necrosis en red apareció (NN). Reciprocamente, cuando las plantas fueron tempranamente inoculadas, “stem-end browning” (SEB) predominó en vez de la necrosis en red (NN). Usando la téchnica ELISA se encontró, que un alto porcentaje de tubérculos que tenían SEB natural (sin inoculación) cv. Russet Burbank, contenían PLRV. Plantas preducidas por estos tubérculos raramente desarrollan sintomas de hojas enrolladas. Estos resultados sugieren una relación entre SEB y PLRV no pospechada anteriormente. Las implicaciones de esta relación aparente, en la epidemiología de la hoja enrollada de la papa, en Maine, son discutidas.

Effect of time and date of inoculation, plant age, and temperature on translocation of potato leafroll virus into potato tubers

Movement of potato leafroll virus (PLRV) to tubers following placement of viruliferous aphids on foliage was studied on the medium-maturing cultivar, Katahdin and the late-maturing cultivar, Russet Burbank. Inoculation was begun on August 20 and continued at three-day intervals until mid-September. There was no trend of increasing or decreasing numbers of leafroll-infected tubers from early to late inoculation. Several variables were examined to determine their effects on the incidence of PLRV-infected tubers. Multiple regression analyses showed that inoculation date, maximum daily temperature, minimum daily temperature, plant age, and length of time from inoculation to harvest explained 38% of PLR incidence in tubers of cv. Katahdin. Length of time from inoculation to harvest and minimum daily temperature explained 40% of PLR incidence in tubers of the cv. Russet Burbank.

Citrus limonoid effects on Colorado potato beetle larval survival and development

The effects of citrus limonoids, applied topically to potato (Solanum tuberosum L. var. ‘Katahdin’) foliage, on Colorado potato beetle (Leptinotarsa decemlineata (Say) (Chrysomelidae) larval development, growth, and survival were quantified in laboratory assays and a small‐plot field test. In laboratory assays, survival, development rate, and body weight decreased with increasing limonoid concentration, however these measures of larval response did not significantly differ among varying periods of limonoid exposure (three, six, or nine days). Significant limonoid application concentration and frequency effects on survival, development rate, and defoliation were observed in the field test. These results indicate the potential utility of lethal and non‐lethal effects of citrus limonoids for management of the Colorado potato beetle.

THE EFFECT OF PHOTOPERIOD ON COCCINELLA TRANSVERSOGUTTATA (COLEOPTERA: COCCINELLIDAE)

Diapause in Coccinella transversoguttata can be inhibited by exposing adult females to photoperiod regimens of LD 16: 8 or 14: 10 hours. The photoperiod regimen to which the immature instars are exposed has little effect on the diapause status of the adult female.

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.

FUNGI ASSOCIATED WITH COLLEMBOLA AND MITES ISOLATED FROM SCABBY POTATOES

Collembola and mites from the lesions of tubers infected with the acid scab organism were tested for the presence of fungal potato pathogens.Streptomyces spp. were found on and in the bodies of these arthropods.Verticillium albo-atrum was present on the external surface and in the body of the Collembola. Various other soil-inhabiting fungi which are not known to be potato pathogens and which were found on and in the bodies of these arthropods are noted.ResumenLa presencia de hongos patógenos de la papa fue determinada en Collembola y acaros obtenidos de las lesiones de tubérculos infectados con el tupo acidofílico del organismo causante de la sarna común. Streptomyces spp. se halló sobre y dentro del cuerpo de estos artrópodos. Verticillium albo-atrum estuvo présente en la superficie y en el cuerpo de Collembola. Otros hongos habitantes del suelo que no se conocen como patógenos de papa fueron hallados sobre y dentro de los cuerpos de estos artrópodos.

The extraction and partial purification of a rhamnosidase from Colorado potato beetle larvae (Leptinotarsa decemlineata (Say))

An enzyme which hydrolyzed a terminal rhamnose moiety from α-chaconine was extracted and partially purified from Colorado potato beetle (CPB) (Leptinotarsa decemlineata) larvae. This ammonium sulfate precipitated enzyme fraction resulted in nearly 97% metabolism of α-chaconine after a 144 hour incubation period at 42 C as determined by high performance liquid Chromatographic (HPLC) analysis. Approximately 81% of the metabolized α-chaconine was detected asβ2-chaconine. The isolated enzyme fraction from CPB larvae exhibited no metabolism of α-solanine. Metabolism was also followed over time by thin layer chromatography (tlc).CompendioUna enzima que hidroliza la porción terminal de la rhamnosa de α-chaconina fue extraída de larvas del escarabajo de la papa de Colorado (CPB) (Leptinotarsa decemlineata) y purificada parcialmente. Esta fracción de enzima, precipitada con sulfato de amonio, dió lugar a casi 97% de metabolismo de α-chaconina después de un período de incubación de 144 horas a 42°C lo que fue determinado por cromatografía líquida de gran precisión (HPLC). Aproximadamente el 81% de la α-chaconina metabolizada fue detectada como β2-chaconina. La fracción de enzima aislada de las larvas del CPB no exhibió ningún metabolismo de α-solanina. Durante todo el tiempo se siguió también el metabolismo por medio de cromatografía de capa delgada (tlc).

Testing for mild leafroll in Maine

Field and greenhouse readings in Maine together with test plot readings in Florida showed the incidence of potato leafroll virus infection in 10 Kennebec seed lots from south, central and northern Aroostook County to be about 1.2%. When the seed lots were indexed by aphid transmission of the virus toPhysalis floridana Rydb. in January and July the incidence of leafroll was found to be 2% and 10% respectively. SinceP. floridana detects mild strains as well as those capable of causing visible symptoms on potato, these results indicate that mild strains are present in the Kennebec variety being grown for seed in Aroostook County. The authors indicate, however, that leafroll symptom expression inP. floridana, in many instances, was not definitive and they suggest that their data may reflect an inaccurate estimate of the prevalence of mild strains of leafroll in Maine.ResumenLas lecturas de campo e invernadero en Maine juntamente con las lecturas de parcelas de terreno en Florida mostraron incidencia de infección de virus de enrollamiento en papa de cerca 1.2% en 10 lotes de semilla Kennebec del sur, centro y norte del Estado de Aroostook. Cuando los lotes de semilla fueron probados por transmisión del virus por medio de áfidos aPhysalis floridana Rydb. en enero y julio la incidencia del enrollamiento resultó ser de 2% y 10% respectivamente. Sabiendo queP. floridana detecta “strains” suaves así como aquellos capaces de casuar síntomas visibles en papa, estos resultados indican que “strains” suaves están presentes en la variedad Kennebec que se cultiva para semilla en el Estado de Aroostook. Los autores indican sin embargo, que la expresión de síntomas de enrollamiento enP. floridana, en muchos casos, no fue definitiva y sugieron que sus datos pueden reflejar un estimado inexacto de la prevalencia de “strains” suaves de enrollamiento en Maine.

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.