Showing papers on "Aphididae published in 1999"

The structure of an aphid–parasitoid community

Abstract: 1 A quantitative parasitoid web was constructed describing the trophic relationships between the community of aphids, parasitoids and secondary parasitoids in an abandoned field in southern England Root aphids were omitted and secondary parasitoids were associated with aphids rather than primary parasitoids All aphids, parasitoids and trophic links were expressed in the same units (m−2) Over a 2-year period, separate webs were constructed for every month that aphids and parasitoids were active in the field 2 Twenty-six species of plants were attacked by 25 species of aphid which were parasitized by 18 species of primary parasitoids The primary parasitoids were attacked by 28 species of secondary parasitoids, of which 18 directly attacked the still living aphid (hyperparasitoids) and 10 attacked the aphid after mummification (mummy parasitoids) The aphids were attended by three species of ants 3 Eleven webs were constructed for the months May to September 1994 and May to October 1995 Aphids and primary parasitoids were most abundant and diverse in June, and secondary parasitoids one month later 4 The ratios of the number of aphid species to the number of species of primary parasitoid and hyperparasitoid were relatively constant across webs, as was the ratio of the number of links involving hyperparasitoids and mummy parasitoids The ratio of the total number of links to the total number of species increased with web size 5 The relative abundance of the species in the different webs was well described by a Dirichlet distribution with a common parameter This implies a gamma distribution of aphid abundances in the field with few common and many rare species 6 Predator (ie parasitoid) overlap graphs were constructed to assess the potential for indirect interactions between aphids Mummy parasitoids were the most important group linking different aphids A quantitative overlap diagram was developed to illustrate the potential strengths of indirect linkages Common aphid species shared few strong, indirect links via primary parasitoids or hyperparasitoids, but could be strongly linked by mummy parasitoids Symmetrical links were uncommon, and rare species were potentially strongly influenced by the presence of common aphids with which they shared parasitoids 7 Ant-attended aphids were attacked by fewer species of primary parasitoids and hyperparasitoids than those species not attended by ants Species of mummy parasitoids attack, on average, approximately twice the number of host species than species of either primary parasitoids or hyperparasitoids

Ant-aphid mutualisms: the impact of honeydew production and honeydew sugar composition on ant preferences.

Abstract: The honeydew composition and production of four aphid species feeding on Tanacetum vulgare, and mutualistic relationships with the ant Lasius niger were studied. In honeydew of Metopeurum fuscoviride and Brachycaudus cardui, xylose, glucose, fructose, sucrose, maltose, melezitose, and raffinose were detected. The proportion of trisaccharides (melezitose, raffinose) ranged between 20% and 35%. No trisaccharides were found in honeydew of Aphis fabae, and honeydew of Macrosiphoniella tanacetaria consisted of only xylose, glucose and sucrose. M. fuscoviride produced by far the largest amounts of honeydew per time unit (880 μg/aphid per hour), followed by B. cardui (223 μg/aphid per hour), A. fabae (133 μg/aphid per hour) and M. tanacetaria (46 μg/aphid per hour). The qualitative and quantitative honeydew production of the aphid species corresponded well with the observed attendance by L. niger. L. niger workers preferred trisaccharides over disaccharides and monosaccharides when these sugars were offered in choice tests. The results are consistent with the ants' preference for M. fuscoviride, which produced the largest amount of honeydew including a considerable proportion of the trisaccharides melezitose and raffinose. The preference of L. niger for B. cardui over A. fabae, both producing similar amounts of honeydew, may be explained by the presence of trisaccharides and the higher total sugar concentration in B. cardui honeydew. M. tanacetaria, which produced only low quantities of honeydew with no trisaccharides was not attended at all by L. niger.

How nutritionally imbalanced is phloem sap for aphids

Abstract: Aphids harbour intracellular symbionts (Buchnera) that provide their host with amino acids present in low amounts in their diet, phloem sap. To find out the extent to which aphids depend on their symbionts for synthesis of individual essential amino acids, we have evaluated how well phloem sap amino acid composition matches the aphids’ needs. Amino acid compositions of the ingested phloem sap were compared to amino acids in aphid body proteins and also to available information about optimal diet composition for other plant feeding insects. Phloem sap data from severed stylets of two aphid species, Rhopalosiphum padi (L.) (Homoptera: Aphididae) feeding on wheat, and Uroleucon sonchi (L.) (Homoptera: Aphididae) feeding on Sonchus oleraceus (L.), together with published information on phloem sap compositions from other plant species were used.

Leaf Reflectance Spectra of Cereal Aphid-Damaged Wheat

Abstract: The efficiency of field monitoring for insect pests would be improved with knowledge of reflected solar radiation from crop canopies during insect outbreaks. The objectives of this greenhouse study were to characterize leaf reflectance spectra of wheat (Triticum aestivum L.) damaged by Russian wheat aphids (Diuraphis noxia Mordvilko) and greenbugs (Schizaphis graminum Rondani) and to determine those leaf reflectance wavelengths that were most responsive to crop stress imposed by these aphid pests. When the ligule was visible on second oldest leaf, wheat plants were infested with four wingless adult Russian wheat aphids, four wingless adult greenbugs, or left uninfested (four replicate plants per treatment). Plants and aphid populations were allowed to grow under greenhouse conditions for 3 wk, after which leaf-reflected radiation (from the adaxial surface across the 350-1075 nm range), dry weight, area, and chlorophyll concentrations were measured. When compared with the control, greenbug feeding damage caused general necrosis in oldest (first) leaves and dramatically lowered the dry weight, leaf area, and chlorophyll concentration of the second, third, and fourth leaves. Russian wheat aphid feeding resulted in a reduction in leaf dry weight and area in the third and fourth leaves, and a reduction in total chlorophyll concentration in all leaves. Leaf reflectance in the 625- to 635-nm and the 680- to 695-nm ranges, as well as the normalized total pigment to chlorophyll a ratio index (NPCI), were significantly correlated with total chlorophyll concentrations in both greenbug- and Russian wheat aphid-damaged plants. Thus, both of these wavelength ranges, as well as this reflectance index, were good indicators of chlorophyll loss and leaf senescence caused by the aphid feeding damage.

Induction and Systemic Release of Herbivore-Induced Plant Volatiles Mediating In-Flight Orientation of Aphidius ervi

Abstract: In-flight orientation of the braconid Aphidius ervi in response to volatiles released from broad bean plants infested by the pea aphid, Acyrthosiphon pisum, was studied in a no-choice wind-tunnel bioassay. The role of aphid infestation level and duration, systemic production of volatiles by “insect-free” parts of the plant, and the specificity of aphid-induced volatiles on the flight behavior of the foraging female parasitoids were investigated. The upper insect-free part of a three-leaved broad bean plant, which was basally infested by a population of 40 A. pisum, released synomones detectable by A. ervi females after at least 48–72 hr of infestation, resulting in both significant increases in oriented flights and landings on the source compared with uninfested control plants. This suggests that volatiles involved in host-location by A. ervi are systemically released by broad bean plants either in response to circulation of aphid saliva, circulation of saliva-induced bioactive elicitors, or circulation of the synomones themselves. Air entrainment extracts of volatiles collected from a broad bean plant infested by the nonhost Aphis fabae or an uninfested broad bean plant elicited few oriented flights and landing responses by female parasitoids. These extracts were significantly less attractive than extracts collected from a broad bean plant infested by the host A. pisum, indicating the specificity of synomones elicited by different aphid species on the same plant species.

Effect of temperature on development rate and fecundity of apterous Aphis gossypii Glover (Hom., Aphididae) reared on Gossypium hirsutum L.

Abstract: The developmental time, survival and reproduction of the cotton aphid, Aphis gossypii Glover (Hom., Aphididae), were evaluated on detached cotton leaves at five constant and two alternating temperatures (15, 20, 25, 30, 35, 25/30, and 30/35°C). The developmental periods of the immature stages ranged from 12.0 days at 15°C to 4.5 days at 30°C. A constant temperature of 35°C was lethal to the immature stages of A. gossypii. The lower developmental threshold for the cotton aphid was estimated at 6.2°C and it required 108.9 degree-days for a first instar to become adult. The average longevity of adult females was reduced from 39.7 days at 15°C to 12.6 days at 30/35°C. The average reproduction rate per female was 51.5 at 25/30°C and 20.9 at 30/35°C. Mean generation time of the population ranged from 10.4 days at 30°C to 24.5 days at 15°C. The largest per capita growth rate (r m = 0.413) occurred at 30°C, the smallest at 15°C (r m = 0.177). It was evident that temperatures over 30°C prolonged development, increased the mortality of the immature stages, shortened adult longevity, and reduced fecundity. The optimal range of temperature for population growth of A. gossypii on cotton was 25/30-30°C.

Positive effects of an arbuscular mycorrhizal fungus on aphid life history traits

Abstract: Two generations of two aphid species (Myzus ascalonicus and M. persicae) were reared on Plantago lanceolata plants, with and without root colonization by the arbuscular mycorrhizal fungus, Glomus intraradices. Life history traits of the aphids measured were nymphal development time, teneral adult weight, growth rate, total fecundity, adult longevity and duration of post-reproductive life. For both aphids in both generations, mycorrhizal colonization increased aphid weight and fecundity, while other traits were unaffected. The increases were consistent between generations. In a second experiment, M. persicae was reared on plants with and without the fungus, under varying N and P regimes. The results of N addition were inconclusive because there was high aphid mortality. However, under P supplementation, positive effects of the mycorrhiza on aphid growth were seen at low and medium P levels, while at high P levels these effects disappeared. The positive effects of mycorrhizal colonization reported here are contrary to the majority of previous studies with chewing insects, which have reported negative effects. A number of possible mechanisms for this apparent discrepancy are discussed.

Aphid Attraction and Preference for Soybean and Pepper Plants Infected with Potyviridae

Abstract: The progress of nonpersistently transmitted virus epidemics can be substantially altered by the degree of aphid attraction and preference for virus-infected plants. Our objective was to determine whether color or odor-mediated cues of plants infected with Potyviridae mediate aphid attraction. We found that Myzus persicae (Sulzer) and Rhopalosiphum maidis (Fitch) preferred alighting on intensely (highly saturated) yellow than on green (plant-like) or brown (soil-like) ceramic tiles, and expressed no preference for landing on leaves infected with soybean mosaic virus (SMV) or on chlorophyll-deficient soybean leaves. Furthermore, neither aphid species showed odor-mediated attraction to leaf extracts of SMV-infected leaves. Also, R. maidis remained longer on uninfected than on SMV-infected soybean plants before taking flight, although M. periscae exhibited no preference. Neither aphid species had a preference to remain on healthy or potato virus Y-infected plants. Therefore, we conclude that both aphid species when landing are equally likely to alight on healthy or SMV-infected soybean plants in the field, but R. maidis is likely to remain a shorter time on SMV-infected than on healthy plants before taking off. The fact that aphids leave the infected plant soon after probing increases the probability of finding another plant and making an infective probe before the vector loses its potential to inoculate the virus. These results could be used to increase the precision of existing simulations models, such as the one previously developed for SMV.

Physiological and Growth Tolerance in Wheat to Russian Wheat Aphid (Homoptera: Aphididae) Injury

Abstract: Plant tolerance to injury from insect herbivores has several advantages as a pest management approach. However, its use is limited because mechanisms conferring plant tolerance are not well understood. We hypothesize that plant physiological responses, specifically photosynthesis, substantially contribute to plant tolerance to arthropod injury. This hypothesis was tested on 3 wheat ( Triticum eastivum L.) lines that differed in their mode of resistance to the Russian wheat aphid, Diuraphis noxia (Mordvilko). The lines were ‘Arapahoe’ (a susceptible line), PI 137739 (an antibiotic line), and PI 262660 (a tolerant line). These lines were grown in a greenhouse, aphids were maintained on plants for 1 wk, and physiological responses of these lines were determined. Light curve and fluorescence data indicated that the primary mechanism for photosynthetic rate reduction in aphid-injured leaves is via interference of the photochemical efficiency at the initial stage of photosynthesis. Aphid-injured seedlings had lower light-saturation points, which suggested less efficient use of light energy compared with control seedlings. Immediately after aphid removal, aphid injury reduced chlorophyll fluorescence and photosynthetic rates in all lines, but PI 137739 (with antibiosis) had significantly greater photosynthetic rate reduction. Photosynthetic rates of the tolerant line, PI 262660, began recovering 3 d after aphid removal with complete photosynthetic recovery 7 d after aphid removal. This gradual photosynthetic compensation did not occur in the other 2 lines. PI 262660 also had greater leaf area and more dry matter when compared with the other cultivars. This study demonstrates that photosynthetic adjustments can significantly contribute to plant tolerance resulting from arthropod injury. Moreover, evidence here indicates that an active plant defense through antibiosis comes at the cost of reduced capacity for physiological tolerance and compensation.

Predators and mutualists influence the exclusion of aphid species from natural communities.

Abstract: We investigated why two species of aphids (Aphis jacobaeae and Brachycaudus cardui) were very rare in a study site despite their abundance in the surrounding area. The study site contained many common species of aphid and we tested the hypothesis that the community of aphid predators in the field excluded the missing species. Colonies of the two aphid species were artificially initiated in the experimental site and allocated to one of four treatments: control; ground predator exclusion; total predator exclusion, and provision of mutualist ants. Two measures of colony performance were analysed: longevity and cumulative aphid density. Colonies decline naturally in late summer but control colonies disappeared very quickly while colonies protected from all predators survived the longest. The performance of colonies protected from just ground predators was intermediate. We failed to persuade ants to tend A. jacobaeae. Colonies of B. cardui attended by ants performed better than controls and those with ground predators excluded, but not as well as those with all predators excluded. We conclude that the absence of the two species of aphid in the study site is influenced by the resident predator community, and by the availability of mutualists.

The spatial and temporal distribution of the grain aphid Sitobion avenae in winter wheat

Abstract: The spatial and temporal distribution of the grain aphid Sitobion avenae F. (Homoptera: Aphididae) was studied within a field of winter wheat during the summer of 1996. Sampling was done using four nested grids comprising 133 locations. Analysis by Taylor's power law gave results typical for insect populations. Analysis by SADIE (Spatial Analysis by Distance Indices) showed spatial pattern due to edge effects and sampling scale, and positive but mild spatial association, although spatial patterns were ephemeral. Reasons for these findings and the implications for integrated crop management are discussed.

How General are Aphid Responses to Elevated Atmospheric Co2

Abstract: We studied the impact of elevated CO2 on 2 aphid pest species, Myzus persicae and Brevicoryne brassicae (Homoptera: Aphididae), on a series of host plants in 3 independent studies each differing in experimental complexity. Measurements on individual aphids showed that host plant and aphid species significantly influenced the response to elevated CO2. These differences occurred not only in the level of responsiveness but also directionally. B. brassicae reared on Brassica oleracea produced significantly less offspring at elevated CO2, whereas the opposite was found for M. persicae on the same host. No response was found for M. persicae on Senecio vulgaris. When populations of B. brassicae and M. persicae were followed for a longer period, no differences were observed in population sizes. Comparisons between different experimental systems show that long-term population responses to elevated CO2 can not be reliably predicted from detailed measurements on individual aphids. The consequences of these findings for climate change research are discussed.

Seasonal Abundance of the Brown Citrus Aphid, Toxoptera Citricida, (Homoptera: Aphididae) And Its Natural Enemies In Puerto Rico

Abstract: Populations of the brown citrus aphid (BCA), Toxoptera citricida (Kirkaldy), and associated insects were monitored in citrus groves in western Puerto Rico in 1996 and 1997. Peak populations of the aphid were observed in spring and fall of both years. A total of 6,737 infested citrus terminals were examined and categorized by growth stage and BCA colony size. Natural enemies, primarily coccinellids, syrphids, chrysopids, and aphidiids, were recorded when present in BCA colonies and a list of species is presented. A complex of large coccinellid species was inferred to have the greatest potential for impact on BCA populations in Puerto Rico. Predation by syrphid larvae was another important source of BCA mortality. The parasitoid, Lysiphlebus testaceipes (Cresson), was abundant in some samples, but usually parasitized only a small percentage of aphids within colonies. The fungus, Verticillium lecanii (Zimm.), infected BCA colonies sporadically. The red imported fire ant, Solenopsis invicta Buren, was often observed harvesting honeydew from BCA colonies and interfering with natural enemies.

Effects of augmentative releases of eggs and larvae of the ladybird beetle, Adalia bipunctata, on the abundance of the rosy apple aphid, Dysaphis plantaginea, in organic apple orchards

Abstract: The impact of augmentative releases of larvae and eggs of the indigenous ladybird beetle Adalia bipunctata (L.) (Coleoptera: Coccinellidae) against the rosy apple aphid Dysaphis plantaginea Pass. (Homoptera: Aphididae), a major pest insect on apple trees, was assessed in field experiments in Switzerland, during 1997. In a first experiment, eggs and larvae were released on 3-year old apple trees infested with five aphids at four different predator-prey ratios (0:5, 1:5, 1:1, 5:1). In a second experiment, eggs and larvae were released at a predator-prey ratio of 5:1 on branches of apple trees naturally infested with aphids. In both experiments, the interaction with ants was taken into account and the releases were done at two different times in spring. The results showed that an augmentative release of larvae significantly prevented the build-up of colonies of D. plantaginea. Significant reductions in aphid numbers were recorded at the two highest predator-prey ratios, 1:1 and 5:1. Larvae were efficient just before flowering of apple trees at a time when growers normally have to spray their trees. On trees where ants were present the larvae of A. bipunctata were significantly less efficient. Effects of eggs of A. bipunctata, however, were less reliable. At the first date of release (5 April), they did not hatch, probably as a consequence of bad weather conditions.

Individual variation in oviposition preference, and its interaction with larval performance in an insect predator

Abstract: Individual female Episyrphus balteatus (DeGeer) (Diptera: Syrphidae) show different oviposition preferences when presented with two aphid prey species, Aphis sambuci L. and A. fabae (Scop). After larvae were reared on those aphids, some fitness components indicated that individual females were adapted to different host-use strategies, with preference for one aphid prey species entailing a trade-off in poorer performance on another. We interpret the pattern of significant interactions as suggesting that natural selection has responded to the nutritional value of prey.

Laboratory and Field Evaluation of Hyphomycete Insect Pathogenic Fungi for Control of Brown Citrus Aphid (Homoptera: Aphididae)

Abstract: Single- and multiple-dose bioassays and field trials were conducted to evaluate the efficacy of various isolates of entomopathogenic fungi against the brown citrus aphid, Toxoptera citricida (Kirkaldy). Single-dose bioassays demonstrated that brown citrus aphid is susceptible to several isolates of Beauveria bassiana (Balsamo) Vuillemin, Paecilomyces fumosoroseus (Wize) Brown & Smith, and Metarhizium anisopliae (Metschnikoff) Sorokin. Overt mycosis ranged from 23.1% ( M. anisopliae ARSEF 759) to 78.0% ( B. bassiana SARC 6000). In multiple-dose bioassays, good dose–-response was obtained with 3 B. bassiana isolates. The 6-d LD50 values for these isolates ranged from 119 to 995 conidia per square millimeter. There was a strong correlation (slopes >1.30) between rapid rise in mortality and dosage increase for all 3 isolates. Replicated field trials of the B. bassiana (strain GHA)-based mycoinsecticide Mycotrol ES provided relatively rapid kill at the application rates. The 5-d Abbott percentage efficacies of Mycotrol ES were, respectively, 79.8 and 94.4% at the half and full rates (2.5 × 1013 and 5 × 1013 conidia per hectare). Proportions of overt mycosis ranged from 0.67 at the half rate to 0.80 at the full rate. Mycotrol ES could be an important component of integrated brown citrus aphid management in the future.

Development and Fecundity of Aphis Gossypii Glover (Homoptera: Aphididae) on Three Malvaceae Hosts

Abstract: Aphis gossypii Glover (Homoptera, Aphididae) obtained from cotton fields near Adana in the east Mediterranean region of Turkey were colonized on Gossypium hirsutum L. 'Cukurova 1518' in a climatic room. The effect of host transfer from cotton to common mallow, Malva sylvestris L., and okra, Abelmoschus esculentus (L.) Moench 'Bamya 501', on performance of A. gossypii was studied at constant 25 ± 1°C, 60 ± 5 % relative humidity and 16 h of artificial light (5000 lux) in temperature cabinets. Three subsequent generations of A. gossypii from cotton were additionally tested on okra. Fecundity tables were constructed to compare the performance of the cotton aphid on the three different Malvaceae hosts. Developmental time (6.0 days) was longer and fecundity reduced (4.5 nymphs/aphid) on okra compared to common mallow (5.6 days and 62.8 nymphs/aphid) and cotton (5.5 days and 37.9 nymphs/aphid). The highest age-specific number of nymphs (m x ) occurred on common mallow at an age of nine days with 6.8 nymphs/aphid, and the lowest on okra with only 1.2 nymphs/aphid at the ninth day. A. gossypii on cotton produced a maximum age-specific number of nymphs at day ten with 3.4 nymphs/aphid. Generation times (T O ) were similar for all three host plants, however, the mean number of aphids laid during an individual's lifetime (Ro) varied largely between 4.2 aphids/aphid on okra to 65.7 nymphs/aphid on common mallow. The significantly lowest intrinsic rate of increase (r m ) (0.129 aphids/aphid/day) was calculated for A. gossypii on okra. Even after three subsequent generations on okra, the performance did not improve, indicating that genetically distinct host races exist in A. gossypii. On common mallow an r m - value of 0.397 aphids/aphid/day occurred, whilst on cotton the intrinsic rate of increase was significantly lower with 0.338

Examination of the effect of aphid vector population composition on the spatial dynamics of citrus tristeza virus spread by stochastic modeling.

Abstract: Aphid vector species population composition is known to affect the spatial patterns of citrus tristeza virus (CTV) and the changes in these patterns over time. However, the biological processes that are associated with virus spread have not been well defined. The spatiotemporal dynamics of CTV were examined using data collected from research plots in the Dominican Republic and Costa Rica, where the brown citrus aphid (BCA), Toxoptera citricida, was the predominant species, and in Florida, where the BCA was absent and the melon aphid, Aphis gossypii, was the predominant vector. Data were analyzed using a spatiotemporal stochastic model for disease spread, and parameter values were evaluated using Markov chain Monte Carlo stochastic integration methods. Where the melon aphid was the dominant species, the model parameter likelihood values supported the hypothesis that the disease was spread through a combination of random background transmission (transmission originating from inoculum sources outsid...

Numerical response of ladybird beetles (Col., Coccinellidae) to aphid prey (Hom., Aphididae) in a field bean in north-east India

Abstract: Two predaceous species of Coccinellidae, Menochilus sexmaculatus and Coccinella transversalis, occurred abundantly in bean crops infested with the aphid, Aphis craccivora Koch in north-east India. The number of eggs and adults of the two coccinellids increased in response to the increase in the population of aphid prey. Reproductive numerical responses were found to be synchronous to prey density whereas aggregative numerical responses appeared asynchronous in the later part of the aphid cycle on beans. Menochilus sexmaculatus oviposited smaller clusters of eggs at lower density of aphids than C. transversalis which laid larger clusters and showed greater numerical response at higher densities of aphids. Within a species cluster the size of the eggs seems to be directly related to aphid density. The two coccinellid species of this study seem to be efficient predators of A. craccivora in terms of their reproductive and aggregative numerical responses.

Acceptability of different species of Brassicaceae as hosts for the cabbage aphid

Abstract: The probing and feeding behaviour of the cabbage aphid, Brevicoryne brassicae (L.), (Homoptera, Aphididae) was studied on several plant species that represented various levels of acceptability: Sinapis alba L. (a permanent host plant), Capsella bursa-pastoris (L.) Med., Thlaspi arvense L. Lunaria annua L., Erysimum cheiranthoides L. (accidental host plants), Vicia faba L. (a non-host plant), using the electrical penetration graph technique (EPG). B. brassicae on V. faba did not show any patterns related to penetration of phloem vessels. Stylet penetration was deterred on L. annua and E. cheiranthoides where non-penetration prevailed, the periods of sap ingestion were short or did not occur, the percentage of time spent in the phloem was consistently low (5–6%) and El salivation predominated. The pathway activities were not suppressed on C. bursa-pastoris and T. arvense and the aphids spent an average of 3 h in the phloem during the 8-h experiment. However, a considerable delay between finding and accepting the phloem and a substantial proportion of El salivation (20–30% of all phloem activities) indicated a deterrent factor in the sieve elements of these plants. Aphid probing and sap ingestion were rarely interrupted on S. alba. The results of this study suggest that the deterrent agents vary in activity and may hinder stylet penetration at different levels (epidermis, parenchymatous tissues and/or phloem elements), depending on the plant species.

Effects of Host Plant and Temperature on the Biology of Toxoptera citricida (Homoptera: Aphididae)

Abstract: Development reproduction, and population growth parameters of the brown citrus aphid. Toxoptera citricida (Kirkaldy), were evaluated at 25 degrees C on 5 citrus-related host plants ('Carizo','sour orange'. 'Duncan grapefruit', 'Pineapple sweet orange', and 'Mexican lime'), and at 3 temperatures (20, 25, and 30 degrees C ) on 'sour orange'. Brown citrus aphids had faster nymphal developmental times on 'Carrizo' and 'sweet orange' (6.7 d) compared with the other host plants (7.5-7.6 d). Aphids reared on 'Carrizo' had the highest fecundity (67.5 offspring/aphid) and daily reproduction (3.8 offspring/aphid/d). The net reproductive rate (62.6 offspring/aphid/generation) on 'Carrizo' was 21%, 49%, 53%, and 77% higher and the population doubling time (1.8 d) was 2%, 13%, 14%, and 20% faster compared with on 'sweet orange', 'sour orange', grapefruit, and 'Mexican lime', respectively. Development of nymphs was completed in either 4 or 5 instars. The brown citrus aphid had longer nymphal developmental times and adult reproductive periods at 20 degrees C (9.0 and 22.2 d, respectively) compared with at 25 degrees C (7.5 and 15.2 d) and 30 degrees C (6.3 and 11.2 d). The moderate temperature (25 degrees C) was optimal for the brown citrus aphid population growth and intrinsic rate of increase (0.33) was highest. Fecundity of brown citrus aphids reared at 30 degrees C in Florida (our data) was approximately equal to 10 times greater, and r(m) was twice as large as those reared under similar conditions in Japan (data from Komazaki 1982). It was concluded that brown citrus aphid populations in Florida could tolerate higher temperatures than the populations in Japan, and that different populations of brown citrus aphids may have greater genetic variation than was previously thought.

Responses to aphid sex pheromones by the pea aphid parasitoids Aphidius ervi and Aphidius eadyi

Abstract: Aphidius ervi and Aphidius eadyi, two parasitoids of the pea aphid Acyrthosiphon pisum, were attracted to components of the aphid sex pheromone in laboratory bioassays. Pre-test experience with host aphids in the presence of aphid sex pheromone did not affect the response of A. ervi to pheromone in a 4-way olfactometer, compared with that of naive parasitoids. Aphidius ervi females exposed only to the pheromone prior to testing did not respond in the olfactometer, suggesting habituation to the foraging cue by the parasitoid. In a wind tunnel, aphid sex pheromone increased the attraction of A. ervi to the plant-host complex (Vicia faba/A. pisum), suggesting an additive effect when two different foraging cues are present simultaneously.

Polymerase Chain Reaction Techniques for Distinguishing Three Species and Two Strains of Aphelinus(Hymenoptera: Aphelinidae) from Diuraphis noxiaand Schizaphis graminum(Homoptera: Aphididae)

Abstract: Ribosomal DNA sequences for the internal transcribed spacer 2 (ITS2) were cloned and sequenced from Aphelinus albipodus Hayat & Fatima, A. varipes (Foerster), and 2 strains of A. asychis Walker, all endoparasitoids that have been released against the Russian wheat aphid, Diuraphis noxia (Mordvilko). The polymerase chain reaction (PCR) using primers designed on the basis of these rDNA sequences, followed by agarose gel electrophoresis, successfully distinguishes all 4 Aphelinus populations from each other and from the Russian wheat aphid and another economically important cereal aphid, the greenbug, Schizaphis graminum (Rondani). Two additional strains of A. asychis and 4 postrelease populations of A. albipodus are also correctly identified to species with these primers. An additional strain of A. varipes was not separable from A. albipodus, but on microscopic analysis it proved to be morphologically anomalous. Using this technique, A. asychis DNA is detectable in a parasitized Russian wheat aphid 24 h after parasitization. The sensitivity is 10 -3 adult wasp DNA equivalent.

Plasmid-encoded anthranilate synthase (TrpEG) in Buchnera aphidicola from aphids of the family pemphigidae.

Abstract: Aphids are dependent on an intracellular symbiont (Buchnera aphidicola, Proteobacteria) for normal growth and reproduction (7, 19, 45). The bacteria reside in specialized cells in the aphid hemocele and are transmitted maternally through infection of eggs or embryos (11, 26). Phylogenetic studies have revealed two major characteristics of the evolutionary history of the association (37, 39); (i) the symbiosis had a single origin, dated about 150 million to 250 million years ago; and (ii) host and symbiont lineages have since diverged strictly in parallel. The association, like other symbioses in insects feeding on restricted and unbalanced diets, is thought to have a nutritional basis (5–7, 20). Aphids feed on plant phloem sap, a diet rich in carbohydrates but deficient in nitrogenous compounds, including most essential amino acids (16, 18, 27, 41). Buchnera has been proposed as the source of essential amino acids for the aphid (14), which has been supported by evidence from nutritional and physiological studies (17, 20–22, 45) and, more recently, by the finding of genetic modifications in the tryptophan and leucine biosynthetic pathways in Buchnera from several aphid species. In both cases, genes encoding key enzymes in the respective pathways were found to be amplified and relocated to plasmids (10, 30). Lai et al. (30) found that the genes for the two subunits of anthranilate synthase (trpE and trpG), the first enzyme in the pathway leading to tryptophan, are contained on a low-copy-number plasmid in Buchnera from the aphid Schizaphis graminum (Aphididae). The plasmid consisted of four identical tandem repeats of a 3.6-kb trpEG-containing unit. trpEG was amplified about 16-fold over the remaining genes of the pathway, which reside in a single locus [trpDC(F)BA] on the Buchnera chromosome (38). trpEG-encoding plasmids have since been found in Buchnera from various species of the Aphididae (4, 32, 42, 43), and their overall similarity suggests that the amplification is ancestral to this lineage (32). The Aphididae is the largest and evolutionarily most successful family of aphids. Many of its species have high growth and reproductive rates, and it includes a number of major agricultural pests (8). In contrast, Buchnera from the aphid Schlechtendalia chinensis, a member of the distantly related family Pemphigidae, was found to carry all the genes of the tryptophan pathway on the chromosome, organized into two single-copy linkage groups [trpEG and trpDC(F)BA] (31). This difference in organization, which is assumed to reflect a difference in the capacity to overproduce tryptophan, has been linked to potentially varying requirements for the amino acid by aphid hosts. S. chinensis has a long development time and a low reproductive rate, and its demand for tryptophan may therefore be lower than in the highly prolific aphids of the Aphididae (5–7, 9, 31). Here we report on the finding and molecular characterization of trpEG-containing plasmids in Buchnera from the aphids Tetraneura caerulescens and Pemphigus spyrothecae, both belonging to the Pemphigidae. We propose a scenario for the evolution of trp in Buchnera in which there was a single ancestral transfer of trpEG to a RepA/C-like replicon followed by independent events of replicon replacement and back-transfer of trpEG to the chromosome in different lineages.

Population dynamics of three coccinellids in flue-cured tobacco and functional response of Hippodamia convergens (Coleoptera : Coccinellidae) feeding on tobacco aphids (Homoptera : Aphididae)

Abstract: The seasonal abundance of 3 species of coccinellids was observed on flue-cured tobacco, Nicotiana tabacum L., during 1997 and 1998 in Tift County, GA. The most abundant coccinellid during both seasons was the convergent lady beetle, Hippodamia convergens Guerin-Meneville, which was present from mid-May, when tobacco aphids, Myzus nicotianae Blackman, colonized the crop, until late July when sampling ended. The sevenspotted lady beetle, Coccinella septempunctata L., and the multicolored Asian lady beetle, Harmonia axyridis (Pallas), were also observed. C. septempunctata was most abundant early in the season and maintained low population levels during June and July. Conversely, H. axyridis was absent in tobacco until late May and remained abundant until sampling was discontinued. Populations of H. convergens, H. axyridis, and C. septempunctata were linearly related to tobacco aphid populations during 1998. In functional response experiments, 4th-instar larvae and adult H. convergens exhibited a type II functional response to aphid density. Fourth-instar larvae had a higher search rate and a longer handling time than adult H. convergens. Two other coccinellid species were observed at low population densities on flue-cured tobacco, Coleomegilla maculata (Mulsant) and Cycloneda munda (Say). Collectively, coccinellids may be important biological control agents of tobacco aphids on Georgia flue-cured tobacco.

Life Table Study of Brown Citrus Aphid (Homoptera: Aphididae) at Different Temperatures

Abstract: The development, survivorship, and reproduction of brown citrus aphid, Toxoptera citricida (Kirkaldy), were evaluated at 8 constant temperatures (8, 10, 15, 20, 25, 28, 30, and 32°C). The developmental periods of immature stages ranged from 63.1 d at 8°C to 5.5 d at 30°C. The lower developmental threshold for the brown citrus aphid immature was estimated at 6.27°C. The upper temperature threshold of 31.17°C for development of nymph was determined from a nonlinear biophysical model. The percentage of survivorship of immature stages varied from 81 to 97% within the temperature range of 8–30°C. However, survivorship was reduced to 29% at 32°C. The average longevity of adult females ranged from 60.0 d at 10°C to 6.5 d at 32°C. The average progeny per female was 52.5 at 20°C and 7.5 at 32°C. The largest rm (0.3765) occurred at 28°C. Populations reared at 10 and 32°C had the smallest rm values of 0.0588 and 0.0960, respectively. The mean generation time of the population ranged from 51 d at 10°C to 8 d at 32°C. The optimal range of temperature for T. citricida population growth was 20–30°C. Several mathematical functions were used to quantify brown citrus aphid development, survivorship, reproduction and lifetable parameters in relation to temperatures.

Insect growth regulating and antifeedant effects of neem extracts and azadirachtin on two aphid species of ornamental plants

Abstract: Leaf disc choice test bioassay demonstrated that formulated neem seed extracts were highly deterrent and growth regulatory to rose aphid,Microsiphum rosae (L.) and Chrysanthemum aphid,Macrosiphoniella sanbornii (Gillete). Effective concentrations to produce 50% feeding deterrence was 0.80 and 0.84% respectively for 2nd instar nymphs irrespective of bioassay duration. The disruption of aphid feeding was related to the presence of azadirachtin concentration in the extract. The toxicity on contact from the leaf surface or via topical application due to azadirachtin was significantly different and topical treatment was at least 7 times more effective for both species. Thus growth regulatory effects of azadirachtin were influenced by the host plant and the stage of treatment. Field evaluation with formulated neem extracts revealed the effect to be more of growth regulatory nature thereby showing that azadirachtin is a physiological toxin for aphid species. Neem seed extracts reduced the population of aphid on respective host plants significantly, EC50 values being 0.88 and 0.96% forM. rosae andM. sanbornii respectively.

Relative susceptibility of cereals and pasture grasses to the yellow sugarcane aphid (Homoptera: Aphididae).

Abstract: Yellow sugarcane aphid, Sipha flava (Forbes), is an important pest of small grains, Sorghum bicolor (L.) Moench, Saccharum officinarum L., and numerous pasture grass species. Because of the importance of pasture grasses to the economy of the southern states and recent history of the aphid damaging many important pasture grasses, we studied the survival and re- production of yellow sugarcane aphids on numerous cool- and warm-season grasses, legumes, and forbs to establish the relative susceptibility of the host plants. Yellow sugarcane aphid survived on 21 of 21 warm-season grass spe- cies, 32 of 32 cool-season grass species, 3 of 19 legume species, and 1 of 4 species of forbs. However, final aphid means of some plant species were lower than the initial infestation. Based on aphid population development, Bromus mollis L., B. biebersteinii Roemer & Schultes, B. marginatus Nees ex Steudel, Agropyron dasystachyum (Hooker) Scribner, and A. intermedium (Host) Beau- vois were the best hosts among the cool-season grasses. Echinochloa frumen- tacea (Link) W.F. Wight, S. bicolor, and Pennisetum orientale (Wild) L.C. Rich were the best warm-season grass hosts. Legumes and forbs were essentially nonhosts of the yellow sugarcane aphid. In a separate but related test, we determined the intrinsic rate of increase values (rm) of the aphid on eight species of grasses, Hordeum vulgare L., Triticum aestivum L., and S. bicolor. The rm values for the aphid were significantly higher on Bothrichloa caucasica (Trinius) Hubb, Dichanthium sp. Willemet, S. bicolor, and Digitaria ciliaris (Retzius) Koeler than on the other entries. Higher rm values were related to shorter prereproductive time, greater aphid fecundity, and increased longev- ity. The aphid had the lowest rm values on Sorghum halepense (L.) Persoon, Panicum virgatum L., and Andropogon gerardii Vitman.