Altered behavior and distribution of pea aphids, Acyrthosiphon pisum (Homoptera: Aphididae), infected with Pandora neoaphidis (Zygomycetes: Entomophthorales)

The distribution and mobility of infected aphid hosts can have a great effect on the ability of a pathogen to spread throughout a population. The distribution of dead and living pea aphids (Acyrthosiphon pisum) infected with Pandora neoaphidis was compared with that of their healthy conspecifics. Infected aphids were significantly more likely to be found on the undersides of alfalfa leaves and off of the plants than were healthy aphids. These two shifts in microhabitat location have potential costs and benefits for both the host and the pathogen.     

Prevalence of Pandora neoaphidis (Zygomycetes: Entomophthorales) infecting Nasonovia ribisnigri (Hemiptera: Aphididae) on lettuce crops in Argentina

Lettuce crops, Lactuca sativa, organically produced in La Plata, Argentina, were sampled in order to determine the prevalence of fungal diseased aphids. Nasonovia ribisnigri was the only aphid detected and its occurrence was highly variable. The fungal pathogen Pandora neoaphidis (Entomophthoromycotina: Entomophthorales) was the only pathogen detected. We recorded a maximum of 34.2 aphids per plant and the highest rate of fungal prevalence was 56.6% (n = 30) (aphids infected/total aphids). Infected aphids were observed in all sampling sites. No differences of infection rates were detected between the center and the edge of crops. Host density was an important factor determining infection. The majority of host population was comprised of nymphs which were the most infected in terms of individuals per habitat unit (lettuce plant), but considering the proportion of infected aphids per stage of development, the prevalence of infection in nymphs and adults was similar.     

Effect of fungicide application on activity of Neozygites fresenii (Entomophthorales: Neozygitacaea) and cotton aphid (Homoptera: Aphididae) suppression

The development of resistance in aphid populations highlights the importance of biological control as a pest management tactic. Four treatments were evaluated to determine the effects of pesticides on the population dynamics of Aphis gossypii Glover and Neozygites fresenii (Nowakowski) Batko: (1) weekly applications of the insecticide imidacloprid (Provado 1.6 F); (2) weekly applications of the fungicide chlorothalonil (Bravo 720); (3) applications of imidacloprid (Provado 1.6 F) when aphid densities exceeded 30 aphids per leaf, and (4) untreated control. Differences in aphid density among the four treatments were shown only to be significant during the 1997 growing season; however, aphid densities were greater in the chlorothalonil treatment than in the other treatments during each growing season. Percentage of N. fresenii-killed aphids was most often highest in the chlorothalonil treatment as well. The fungal epizootic caused by N. fresenii was delayed approximately 1 wk in the chlorothalonil treatment when compared with the other treatments. This delay allowed the aphids to temporarily escape suppression by the fungus and to continue to increase in density until the density-dependent effects of the epizootic overwhelmed the aphid population. N. fresenii also appeared to persist in the system when imidacloprid was in use and does appear responsible for initial aphid reductions. Treatment did not appear to have a large influence on yield outcome. Yield was variable from year to year and from location to location.     

Infectivity of Pandora neoaphidis (Zygomycetes: Entomophthorales) to Acyrthosiphon pisum (Hom., Aphididae) in response to varying temperature and photoperiod regimes

The infectivity of the pea aphid, Acyrthosiphon pisum , by the aphid-specific entomophthoralean fungus, Pandora neoaphidis , was studied in environmental chambers using computer simulated late-season temperature and photoperiod patterns and an excised fava bean leaf system. A complementary log-log (CLL) time–dose–mortality model was used to model time–dose trends in infectivity of A. pisum by P. neoaphidis as a function of time and dose, and calculate the LC₅₀. The likelihood ratio test based on the CLL model was used to test for differences in levels of aphid infectivity by P. neoaphidis over different photoperiod regimes. Differences in the LC₅₀ values from CLL modelling over different time periods were found among the two regimes of 11- and 16-h photophases at a constant temperature of 20°C, and two regimes at daily fluctuating temperatures from 5.4 to 18.9°C (with half-hourly changes of 0.56°C the mean temperature was 12.12°C). The LC₅₀ for the same time period was lower under the higher temperature conditions than under lower fluctuating temperature conditions. The likelihood test ratio statistics showed no significant difference in the slope parameter for three out of four treatments (two from the constant temperature of 20°C, and one from 5.4 to 18.9°C, irrespective of photophase conditions). This suggests that different temperatures and photophases may change the temporal characteristics of P. neoaphidis , and result in higher or lower infectivity to the pea aphid at certain dosage levels. However, changes in the photoperiod appear to be less important for the infectivity of P. neoaphidis to pea aphid than changes in temperature.     

Factors affecting sporulation and germination of Pandora nouryi (Entomophthorales: Entomophthoraecae), a pathogen of Myzus persicae (Homoptera: Aphididae)

Pandora nouryi discharged large numbers of primary conidia between 8 and 25°C from cadavers on the surface of water-agar. At 8°C conidial discharge lasted for 120 h, but most conidia were produced within 48 h when temperature was >15°C. Saturated humidity alone was not enough to allow for sporulation to occur freely and where RH?<?95%, no conidia were discharged. Light did not affect the pattern of conidial production nor the total number of conidia. Germination percentages of conidia on the surface of water-agar were 40 and 66% at 8 and 30°C, respectively, and were significantly lower than that at 15–25°C where germination was >95%. Conidia on leaves germinated well when RH?>?74%, while no germination occurred when RH?<?100% on cover slips. All eight insecticides tested entirely inhibited conidial germination at recommended doses (R), in particular, both the organophosphorus pesticides Lorsben (chlorpyrifos) and the organochlorine pesticides Thiodan (endosulfan) completely inhibited conidial germination even at 0.2R dose.     

Host-dependent association and its implications on the relative abundance of blue alfalfa aphid and pea aphid (Homoptera: Aphididae) on alfalfa in Oklahoma

Field populations of blue alfalfa aphid and pea aphid on alfalfa were sampled during 1985 and 1986 to determine the association of co-occurrence, interspecific interactions and comparative temporal variations in the spatial dispersion patterns of these species in Oklahoma. Relative abundance of these species is discussed in the light of above analyses.Cole' s coefficient revealed a high degree of association between these species in terms of their occurrence on the same alfalfa stems in the field. Regression analyses indicated that the species populations tended to increase in concert on the same stems without evidence of competitive displacement. Spatial dispersion patterns of both species were highly aggregated at low population densities early in the season. Over time, both species tended to disperse and became less aggregated as numbers increased. It was concluded that magnitude of interspecific interactions between the blue alfalfa aphid and the pea aphid were not of a nature that they could be termed as competing species. On the contrary, a concept of an “ecospecies” is proposed for practical applications such as sampling plans and economic threshold determinations.     

Acceptance of low-saponin lines of alfalfa with varied phenolic concentrations by pea aphid (Homoptera: Aphididae)

This research aims to examine the effect of phenolics on pea aphid (Acyrthosiphon pisum) (Homoptera: Aphididae) development and feeding behaviour, on leaves of selected low-saponin lines of Radius alfalfa (Medicago sativa). There was a slight, negative correlation (Spearman rank correlation r _s = −0.80) between concentrations of saponins and phenols. Lines with higher concentrations of saponins had less phenolics. Levels of phenolics in low-saponin lines of alfalfa cv. Radius were related to their acceptance by the pea aphid. Our data revealed an inverse relationship between level of phenolics and the aphid abundance and its biology on studied alfalfa lines. Larval development of the pea aphid was longer, reproduction period was shorter, and the fecundity was lower on low-saponin lines with higher level of phenolics. There were observed some tendencies in the pea aphid feeding behaviour on these lines: prolonging the probing of the peripheral tissues (epidermis and mesophyll) and shortening the period of phloem sap ingestion. The better hosts for the pea aphid were low-saponin lines with low levels of phenolic compounds.     

Isolation of six microsatellite markers from the pea aphid,Acyrthosiphon pisum (Homoptera,Aphididae)

Using the magnetic particles method, we isolated six polymorphic microsatellite loci from the pea aphid, Acyrthosiphon pisum (Harris), which feeds on a wide range of legume species. The isolated loci were polymorphic, with three to six alleles in 40 aphids. Expected heterozygosities ranged from 0.12 to 0.65. These loci can be used to quantify clonal diversity and compare genetic population structure between sexual and asexual populations.     

Demography of soybean aphid (Homoptera: Aphididae) at summer temperatures

Soybean aphid, Aphis glycines Matsumura, is now widely established in soybean, Glycine max L., production areas of the northern United States and southern Canada and is becoming an important economic pest. Temperature effect on soybean aphid fecundity and survivorship is not well understood. We determined the optimal temperature for soybean aphid growth and reproduction on soybean under controlled conditions. We constructed life tables for soybean aphid at 20, 25, 30, and 35 degrees C with a photoperiod of 16:8 (L:D) h. Population growth rates were greatest at 25 degrees C. As temperature increased, net fecundity, gross fecundity, generation time, and life expectancy decreased. The prereproductive period did not differ between 20 and 30 degrees C; however, at 30 degrees C aphids required more degree-days (base 8.6 degrees C) to develop. Nymphs exposed to 35 degrees C did not complete development, and all individuals died within 11 d. Reproductive periods were significantly different at all temperatures, with aphids reproducing longer and producing more progeny at 20 and 25 degrees C than at 30 or 35 degrees C. Using a modification of the nonlinear Logan model, we estimated upper and optimal developmental thresholds to be 34.9 and 27.8 degrees C, respectively. At 25 degrees C, aphid populations doubled in 1.5 d; at 20 and 30 degrees C, populations doubled in 1.9 d.     

Particle film affects black pecan aphid (Homoptera: Aphididae) on pecan

Three species of aphids attack pecan foliage, Carya illinoensis (Wang.) K. Koch, and cause economic damage. We tested a kaolin-based particle film against one of these aphid species, black pecan aphid, Melanocallis caryaefoliae (Davis). Effect of particle film on host selection, adult mortality, and production of nymphs by M. caryaefoliae was tested on seedling pecans in the laboratory. Fewer M. caryaefoliae adults selected treated foliage compared with untreated foliage. A higher percentage of adults that did select treated foliage were recovered from upper leaf surfaces compared with the percentage of adults recovered from upper leaf surfaces of untreated leaves. Observations with a microscope revealed an accumulation of particle film on aphid body parts, especially on tarsi, and strongly suggests that aphid mobility was restricted. Adult mortality was higher on treated foliage and led to an overall decrease in production of nymphs on those seedlings. In addition, we measured spectral properties of treated seedling pecan foliage. Light reflectance by treated foliage was increased and absorptance decreased compared with control foliage whereas transmittance of light through control and particle film-treated leaves was similar. We did not detect any phytotoxic effect on pecan due to application of particle film.     

Development of soybean aphid (Homoptera: Aphididae) on its primary overwintering host, Rhamnus cathartica

Thermally dependent development of soybean aphid (Aphis glycines Matsumura) and common buckthorn (Rhamnus cathartica L.) were examined in growth chambers in spring 2005. Models based on ambient air temperatures for all development events were developed. Adjusted models were developed to account for heat units acquired because of solar radiation. These models were tested at field sites in Guelph and Ridgetown, Ontario, Canada. It was found that egg hatch of aphids and bud swell of buckthorn coincided at low temperatures in growth chambers and in the field. Development thresholds of 9 and 10 degrees C were acquired for bud swell and egg hatch, respectively. Models based on ambient air temperatures were poor predictors of bud swell and egg hatch in the field, but models adjusted for solar radiation predicted these events just 1-4 d before they were observed at both sites. The results obtained have broad application for predicting aphid hatch on a regional basis.     

Photosynthetic responses of soybean to soybean aphid (Homoptera: Aphididae) injury

The soybean aphid, Aphis glycines Matsumara, was discovered in the United States in the summer of 2000. Since that initial discovery, the aphid has spread across northern soybean production regions. In 2001, we examined the physiological responses of soybeans to low aphids densities (fewer than 50 aphids/leaf). In this study, we determined photosynthetic rates, leaf fluorescence responses, and photosynthetic responses to variable carbon dioxide and light levels. In addition, analyses for chlorophyll content and stable carbon isotope ratios were used to differentiate potential differences in stomatal versus mesophyll limitations to photosynthesis. We observed rate reductions of up to 50% on infested leaflets, including lealets with no apparent symptoms of aphid injury (such as chlorosis). Differences in fluorescence data indicated that photoelectron transport was not impaired. These results indicate that substantial physiological impact on soybean is possible even at low aphid densities. Also, the conventional view of aphid injury acting through reductions in chlorophyll content and light-harvesting reactions of photosynthesis is not supported by our findings in this system.     

Experimental epizootiology of Zoophthora anhuiensis (Entomophthorales) against Myzus persicae (Homoptera: Aphididae) with a description of a modified Gompertz model for aphid epizootics

Epizootiological features of Zoophthora anhuiensis, a fungal pathogen specific to aphids in southern China, were studied in six aptera colonies of Myzus persicae at 16 regimes of temperature (T = 10, 15, 20 and 25 degrees C) and relative humidity (H = 90%, 95%, 98% and 100% RH) with initially infected proportion (Ip) of 0.5 in experiment (Expt) 1 or at a fixed regime of 15 degrees C and 100% RH with a variable Ip of 0.17-1.00 in Expt 2. Mycosis-caused mortalities (Mp) varied with aphid densities (D) over time after colony initiation (t) were well fitted to a Gompertz growth model modified to include the variables T, H, Ip and D in the form of Mp = 91.72exp[-5.282exp[-(0.0095T + 0.0128H/T-0.5407D2/H)t]] for Expt 1 (r2 = 0.94) or Mp = 95.49exp[-4.314exp[-(0.1479Ip + 0.1636/D)t]] for Expt 2 (r2 = 0.97). These variables were effective in determining the rate of epizootic development in the M. persicae colonies. Based on the observed and fitted results, Z. anhuiensis was most adaptive to cool climate or season and epizootiologically was subject to a minimal effect of RH at an optimum of approximately 15 degrees C. However, the humidity became determinant for epizootic progress at higher temperatures. Interactive effects of the variables and application of the fitted models for predicting epizootic development in field situations are discussed.     

The life stages of Entomophthora virulenta (Entomophthorales: Entomophthoraceae)

An illustrated scheme of the life cycle of Entomophthora virulenta shows that an alternation of the conidal and resting spore stages is involved. The resting spores are azygospores; chlamydospores are also present.     

Lack of kin discrimination in the eusocial aphid pseudoregmabambucicola (Homoptera: Aphididae)

The significance of kin discrimination for the evolution of sociality is theoretically important. The behavioural response ofPseudoregma bambucicola soldiers to aphids from other colonies was studied to examine the possibility of context-specific kin discrimination. When non-kin aphids were artificially introduced into experimental colonies, they were never killed or removed by soldiers. Field experiments revealed that the soldiers frequently attacked distantly related species such asAstegopteryx bambucifoliae andCeratoglyphina styracicola, but rarely conspecific aphids or congeneric species such asP. koshunensis andP. alexanderi. Another experiment showed that the soldiers showed altruistic defence even when coexisting with non-kin reproductives. These results agree with and extend the results from previous studies of kin discrimination in social aphids. The absence of kin discrimination suggests that some other factors besides higher genetic relatedness may play a prominent role in the evolutionary maintenance of soldier behaviour in aphids.     

Evaluation of four co-occurring ladybirds for use as biocontrol agents of the pea aphid,Acyrthosiphon pisum (Homoptera: Aphididae)

The potential of four co-occurring ladybirds, Coccinella septempunctata (L.), Coccinella transversalis (F.), Cheilomenes sexmaculata (F.), and Propylea dissecta (Mulsant), as predators of the pea aphid, Acyrthosiphon pisum (Harris) was investigated. Larger ladybirds were more voracious while smaller ones had higher consumption indices and were more efficient converters of food.     

Biotypic variation among north American Russian wheat aphid (Homoptera: Aphididae) populations

The Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae), has been a major economic pest of small grains in the western United States since its introduction in 1986. Recently, a new Russian wheat aphid biotype was discovered in southeastern Colorado that damaged previously resistant wheat, Triticum aestivum L. Biotype development jeopardizes the durability of plant resistance, which has been a cornerstone for Russian wheat aphid management. Our objective was to assess the relative amount of biotypic diversity among Russian wheat aphid populations collected from cultivated wheat and barley, Hordeum vulgare L. We conducted field surveys from May through June 2002 and August 2003 from seven counties within Texas, Kansas, Nebraska, and Wyoming. Based upon a foliar chlorosis damage rating, three new Russian wheat aphid biotypes were identified, one of which was virulent to all characterized sources of Russian wheat aphid resistance. The future success of Russian wheat aphid resistance breeding programs will depend upon the continual monitoring of extant biotypic diversity and determination of the ecological and genetic factors underlying the development of Russian wheat aphid biotypes.     

First record of Entomophaga maimaiga (Entomophthorales: Entomophthoraceae) in Slovakia

The entomopathogenic fungus Entomophaga maimaiga was found for the first time in Slovakia in 2013. Late instar larvae of gypsy moth, Lymantria dispar, from two sites with different population densities were dissected to evaluate the presence of pathogens. The presence of conidia and resting spores of E. maimaiga in gypsy moth cadavers was confirmed from both sites.