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.     

Spermatogenesis in the aphid Amphorophora tuberculata (Homoptera,Aphididae)

Spermatogenesis was studied in Amphorophora tuberculata Brown & Blackman, a species of aphid with n=2. Spermatogonia have 2=3 (AA+XO). In early prophase I the autosomal homologues are united terminally to form a tandem bivalent. No evidence could be found of synapsis or of the formation and terminalisation of chiasmata. The terminal connection of the autosomes is retained until late in prophase II. Sister chromatids separate, and autosomal half-bivalents move apart at anaphase I, but the division is incomplete, the X chromosome forming a thin chromatin bridge between the two autosomal half-bivalents. In prophase II the autosomal half-bivalents double back on themselves, so that non-sister chromatids become aligned in parallel. The X chromosome then becomes associated with one of the autosomal half-bivalents. Anaphase II separates the non-sister chromatids, and meiosis is thus post-reductional.     

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.     

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.     

Differential susceptibility of poplar hybrids to the aphid Chaitophorus leucomelas (Homoptera: Aphididae)

After its recent introduction to Chile, the aphid Chaitophorus leucomelas Koch is becoming a serious pest affecting commercial poplar, Populus spp., plantations. The pattern of natural infestation of C. leucomelas among poplar hybrids with different pedigrees and the aphid intrinsic rate of increase (r(m)), of C. leucomelas were assessed in the field. In most of the hybrids, aphid abundance peaked in March (late summer). Among 12 types of poplar crosses, [(P. trichocarpa Torr. & Gray x P. deltoides Bartram ex Marshall) x (P. trichocarpa x P. deltoides)] and [(P. trichocarpa x P. maximowiczii Henry) x P. maximowiczii] showed the highest and lowest aphid densities, respectively. A trend to find more aphids in branch bases was apparent. The intrinsic rate of C. leucomelas increase was higher in [(P. trichocarpa x P. deltoides) x P. deltoides] hybrids, and lower in [(P. trichocarpa x P. maximowiczii) x P. trichocarpa] hybrids. Aphid density and performance were higher in hybrids with P. deltoides parentage, whereas hybrids with P. maximowiczii parentage showed lower aphid densities and performance. Hybrids with P. nigra L. parentage, namely, [P. trichocarpa x P. nigra], also had high aphid density, but aphid performance was lower compared with hybrids with P. deltoides parentage. These results suggest that among poplar hybrids studied, susceptibility to C. leucomelas is inherited through P. deltoides, whereas resistance seems to be inherited through P. maximowiczii. Thus, P. maximowiczii hybrids are recommended for commercial or ornamental planting programs in zones where there is a high risk of aphid infestation.     

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.     

Studies on the morphometry of the green peach aphid, Myzus persicae (Sulzer) (Homoptera: Aphididae)

Aphids are one of the most important groups of phytophagous insects because of their polyphenism, host alternation, heteroecious behavior and reproductive habits. Laboratory culture of the aphid Myzus persicae on the host plant Brassica pekinensis Hubner was maintained seasonally for biometrical studies. The metric analysis revealed gradual developmental changes from the first instar nymph to the adult stage in size, shape, and a number of characters. The transitional changes were sufficiently distinct to allow differentiation of each of the life stages irrespective of the season. A key to the nymphal stages of the pest is provided.     

Effect of entomopathogenic Aspergillus strains against the pea aphid,Acyrthosiphon pisum (Hemiptera: Aphididae)

Aphids (Homoptera: Aphididae) are sap-sucking insect pests that feed on several plants of agronomical importance. Entomopathogenic fungi are valuable tools for potential aphid control. As part of a selection process, laboratory bioassays were carried with five different concentrations of Aspergillus clavatus (Desmazières), Aspergillus flavus (Link) and Metarhizium anisopliae ((Metschnikoff) Sorokin) spores against the pea aphid, Acyrthosiphon pisum (Harris). Aspergillus isolates induced higher mortalities than M. anisopliae, which is a well-known entomopathogen in the literature. Lethal concentrations (LC₅₀ and LC₉₀) were 1.23 × 10³ and 1.34 × 10⁷ spores/ml for A. flavus, 4.95 × 10² and 5.65 × 10⁷ spores/ml for A. clavatus, and 3.67 × 10³ and 9.71 × 10⁷ spores/ml for M. anisopliae 5 days after treatment. Mycelia development and sporulation on adult cadavers were observed 48 h after incubation. The intrinsic growth rate of A. pisum decreased with increased spore concentration for all fungal strains, suggesting an increase in pathogen fitness related to a consumption of host resources. In conclusion, Aspergillus species could be useful in aphid control as pest control agents despite their saprophytic lifestyle. This is also to our knowledge the first report of A. clavatus and A. flavus strains pathogenic to aphids.     

Resistance of Glycine species and various cultivated legumes to the soybean aphid (Homoptera: Aphididae)

The soybean aphid, Aphis glycines Matsumura, is a new pest of soybean, Glycine max (L.) Merr., in North America. It has become widespread on soybean in North America since it was first identified in the Midwest in 2000. Species of Rhamnus L. (buckthorn) are the primary hosts of A. glycines, and soybean is known as a secondary host. There is limited information about the secondary host range of A. glycines. Aphid colonization on various legume hosts was compared in choice experiments. Aphid colonization occurred on species in the genus Glycine Wild. No colonization occurred on Lablab purpureus (L.) Sweet, Lens culinaris Medik, Phaseolus vulgaris L., Pisum sativum L., or species of Vicia L. and Vigna Savi. Colonization was limited or aphids were transient on species of Medicago L., Phaseolus L., and Trifolium L. There were significant differences in aphid colonization among Medicago truncatula accessions with numbers ranging from 7 to 97 aphids per plant. Six Glycine soja Sieb. & Zucc. accessions were as resistant as G. max accessions to A. glycines; these may represent novel sources of A. glycines resistance not found in G. max. Antibiosis was found to play a large role in the expression of resistance in three of the G. soja accessions. Results of this study indicated that G. max and G. soja were the best secondary hosts of A. glycines; however, its secondary host range may include other leguminous species. Therefore, A. glycines did not seem to have a highly restricted monophagous secondary host range.     

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.     

Resistance to biotype 2 Russian wheat aphid (Homoptera: Aphididae) in two wheat lines

Biotype 2 of the Russian wheat aphid, Diuraphis noxia (Mordvilko), was identified in the United States in 2003 and is virulent to all commercially available cultivars of winter wheat, Triticum aestivum L., that are resistant to biotype 1. We compared the development and reproduction of biotype 2 D. noxia at 21.7 +/- 0.12 degrees C on 'Trego' (PI 612576), a susceptible commercial cultivar, and on lines CI 2401 and 03GD1378027 that represent putative resistance sources. CI 2401 is a pure wheat line originating in the former USSR (Tajikistan), whereas 03GD1378027 is a USDA-ARS breeding line originally developed from crosses with a South African line that carried a large rye translocation conferring D. noxia resistance. Both lines previously showed resistance to biotype 1 and are currently being used in the development of D. noxia-resistant wheat cultivars. Both solitary apterous virginoparae of biotype 2 and their progeny experienced a reduction in survival and prolonged developmental times on CI 2401 and 03GD1378027 compared with Trego, but the former lines did not differ significantly from each other with respect to either measure of aphid performance. Progeny developed faster than did their foundress mothers on CI 2401 and Trego, but not on 03GD1378027. Mean foundress fecundity did not differ between CI 2401 and 03GD1378027 but was reduced on these lines relative to Trego. Foundresses also were more often found off plants of CI 2401 and 03GD1378027 than Trego. Estimates of intrinsic rate of increase were higher on Trego than on either CI 2401 or 03GD1378027, the latter two lines yielding similar values. The negative impacts of CI 2401 and 03GD1378027 on development and reproduction of biotype 2 indicate that these lines represent sources of resistance effective against this biotype.     

Seasonal dynamics of cereal aphids on Russian wheat aphid (Homoptera: Aphididae) susceptible and resistant wheats

Field experiments were conducted in 1997 and 1998 to evaluate the impact of resistance to Russian wheat aphid, Diuraphis noxia (Mordvilko), on the cereal aphid complex in wheat. Two spring wheats were planted: the variety "Centennial" (Russian wheat aphid susceptible) and the advanced line IDO488 (Russian wheat aphid resistant). IDO488 incorporates the resistance found in PI 294994 into a Centennial background. Field plots were artificially infested with adult D. noxia and sampled weekly. The most abundant aphid species in 1997 were Metopolophium dirhodum (Walker), Sitobion avenae (F.), D. noxia, and Rhopalosiphum padi (L.). In 1998, the order of abundance was M. dirhodum, R. padi, S. avenae, and D. noxia. The resistant genotype had significantly fewer D. noxia than the susceptible one during both years. However, plant genotype had no significant effect on the other aphid species in either year. Both the initial density of D. noxia and plant growth stage, had a significant effect on D. noxia population development, but had no effect on the other aphid species. There was no interaction between D. noxia resistance and the population density of the other aphid species observed.     

Laboratory studies on the biology of the corn leaf aphid, Rhopalosiphum maidis (Homoptera: Aphididae)

The biology of R. maidis has been shown to be affected considerably by the temperature, the host plant, and the physiological age of food plant. The optimum temperature was 30°C; here nymphal development was accelerated, the whole life-span was drastically shortened to less than half that at 15°, and natality rate/surviving female was increased with rather negligible deaths among progeny. Barley was the most favourable host studied under the specified experimental conditions, and young plants (3–5 days old) represented the best stage of plant growth. R. maidis may have about 50 generations/year when aphids were kept feeding continuously on 5-day old barley plants but this does, by no means, represent the actual number of generations under field conditions; it only indicates that almost half of these may be restricted to the summertime.

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Résumé La présente étude montre que la température, ainsi que l'espèce de la plante hôte et son âge physiologique influencent grandement la biologie de Rhopalosiphum maïdis.Quand ce puceron est élevé sur des pousses d'orge âgées de 5 jours, la température optimum est de 30°. Dans ces conditions, la maturation peut être acquise en un délai aussi court que 4,6 jours, tandis que la longévité est réduite à 16,8±1,3 jours contre 35,1±5,1 jours à 15°. Enfin, la natalité par femelle et par jour est accrue avec un taux de mortalité négligeable parmi la descendance.De quatre plantes testées, (orge, mil, fève et maïs) au même âge de croissance (7 jours) l'orge est le plus favorable. Rhopalosiphum maïdis peut avoir environ 50 générations par an quand il est élevé de façon continue sur des plants d'orge âgés de 5 jours; cela ne signifie pas que dans les conditions naturelles il en est ainsi, mais indique que presque la moitié de ce nombre de générations peut intervenir pendant l'été.

     

Enumerative and binomial sequential sampling plans for soybean aphid (Homoptera: Aphididae) in soybean

Since the discovery of the soybean aphid, Aphis glycines Matsumura, in midwestern U.S. soybean, Glycine max L., in 2000, the aphid has become a significant economic pest. Basic information about estimating population density within fields is unknown. Therefore, we developed two sampling plans to efficiently characterize A. glycines densities. Enumerative and binomial sequential plans were developed using 89 data sets collected from 10 commercial fields sampled during 2001-2003. Re-sampling software was used to validate the enumerative plan on whole plant counts, based on Taylor's power law parameters (a = 9.157 and b = 1.543). For research applications, the enumerative plan was modified to provide an actual precision level of 0.10 (SE/mean), which resulted in an average sample number of 310 individual plants. For integrated pest management (IPM) purposes, we developed an enumerative plan with an actual precision of 0.25, which resulted in an average sample number of 38 individual plants. For IPM applications, the binomial plan will likely be more practical. Binomial plans were developed using two tally thresholds at five action thresholds. Final analysis of the operating characteristic curve for each plan indicated that the tally threshold of > or = 40 aphids per plant, and an action threshold of 0.837 (84% of the plants infested) provided the most correct treat (4%) and no-treat (95%) decisions, with very low incorrect treat (0.5%) and no-treat (0.5%) decisions. A tally threshold of > or = 40 aphids per plant and action thresholds of 84% of plants infested is equivalent to a mean density of 250 aphids per plant, a recently recommended economic threshold. Using this threshold, the minimum required sample number for the binomial plan was 11 plants.     

New species of the aphid tribe Macrosiphini (Homoptera,Aphididae, Aphidinae) from Kazakhstan

Two new species of the genera Uroleucon Mordvilko, 1914 and Pleotrichophorus Börner, 1930 are described from Kazakhstan. Uroleucon dzhungaricum sp. n. feeding on Senecio nemorensis L. (Asteraceae) in the Dzhungar Ala Tau is closely related to U. minor (Börner, 1940). Both these species differ from the closely related U. solidaginis (Fabricius, 1794) in a smaller length ratio between the processus terminalis and the 3rd antennal segment (0.8–1.0 versus 1.0–1.5). The new species differs from U. minor (Born.) in a greater number of the secondary rhinaria on the 3rd antennal segment of the apterous viviparous females (21–37 versus 15–21), in a fewer number of hairs on the cauda (10–16 and 15–23), and in the host plant. Pleotrichophorus ugamicus Kadyrbekov, sp. n. feeding on Artemisia santolinifolia Turcz. is described from the Sairam-Ugam Natural Park (Southern Kazakhstan). The new species is similar to P. glandulosus (Kaltenbach, 1846) and P. achilleae Holman, 1965. Pleotrichophorus ugamicus sp. n. differs from these species in the length ratio of the processus terminalis to the base of the 6th antennal segment (4.1–5.0 versus 5.0–9.0 and 5.1–6.2), in that of the ultimate rostral segment to the 2nd segment of the hind tarsus (0.68–0.76 versus 0.80–0.97 and 0.80–0.90), and in the host plant. This species differs from P. glandulosus in the ratio of the length of dorsal hairs on tergites I–V to the basal diameter of the 3rd antennal segment (1.0–1.2 and 1.4–1.7). In addition, the new species differs from P. achilleae in the length ratio of the 3rd antennal segment to the 6th segment (0.56–0.66 versus 0.70–0.87) and to the processus terminalis (0.67-0.82 versus 1.39–1.80), as well as in the shape of the dorsal hairs. A key to the Palaearctic species of the genus Pleotrichophorus is presented.     

Induced life cycle transition from holocycly to anholocycly of the Russian wheat aphid (Homoptera: Aphididae)

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko),exists with holocyclic life cycle in Tacheng, Xinjiang in Northwest China. It produces males and oviparae to mate and oviposit for overwintering by eggs. Under laboratory conditions with 14 h/d photophase and temperature not lower than 15℃, RWA occurred in parthenogenesis and produced no males. The laboratory popu-lations of Russian wheat aphid, which were kept under natural conditions in fall by 15th, 49th and 81st generation while wild populations produced males and oviparae for mating, produced males and oviparae with their number decreased gradually, but viviparae and nymphs increased sequen-tially. As a result, it produced a small amount of oviparae and no males emerged in fields by 49 generations' reproduction in laboratory. After development of 81 generations, oviparae happened occasionally and no eggs occurred for overwintering instead of viviparae and nymphs. A hypothesis of RWA disastrous process was proposed. The life cycle of RWA can be changed from holocycly to anholocycly in its long-term spread and evolution. Anholocycly is more dangerous than holocycly to small grains for its strong adaptability and dispersal ability.     

Action of beta radiation on the black bean aphid Aphis fabae Scop. (Aphididae, Homoptera)

A study was made of the effect of direct single exposure to beta-radiation of 0.5, 5, 10, 20, 30, and 50 Gy on development and reproduction of Aphis fabae Scop. (Aphididae, Homoptera). The numbers of bean aphid are prognosticated with regard to the radiation dose applied.     

Effect of synthetic aphid alarm pheromone (E) -beta-farnesene on development and reproduction of Aphis gossypii (Homoptera: Aphididae)

The synthetic aphid alarm pheromone (E)-beta-farnesene (EBF) is released by aphids in response to predation or other disturbances that occur in the colony. This is presumed to benefit the population by allowing increased survival of related individuals taking successful evasive action after perception of the pheromone. The effect of pheromone perception by aphids in the absence of real threats was investigated to determine the baseline effect of this communication on aphid survival, development, and fecundity in the laboratory. All four nymphal stages of cotton aphid, Aphis gossypii Glover (Homoptera: Aphididae), were stimulated with EBF. No significant difference in survival rates was observed in the aphids stimulated with EBF compared with the untreated control. Developmental times of the aphids were significantly prolonged in first and third instars when they were stimulated with EBF. Significantly lower fecundity and lighter weight of adult aphids were observed in aphids stimulated with EBF at as first instars compared with untreated controls and other instars. Results indicate that exposure of the first instar of A. gossipii to the synthetic alarm pheromone adversely affects subsequent development and fecundity of the population. This reduces aphid fitness that must be compensated by increased survival from predation for the pheromone to confer a selective advantage to the species.