Pathogenicity of hyphomycet fungi to aphids Aphis gossypii Glover and Myzus persicae (Sulzer) (Hemiptera: Aphididae)

The aphids Aphis gossypii and Myzus persicae are cosmopolitan, poliphagous and damage cultivated plants. The effects of the entomopathogenic fungi Beauveria bassiana (isolate IBCB 66), Metarhizium anisopliae (isolate IBCB 121), Paecilomyces fumosoroseus (isolate IBCB 141) and Lecanicillium (= Verticillium) lecanii (isolate JAB 02) on third instar nymphs of A. gossypii and M. persicae were evaluated in the laboratory at 25 degrees C, 70 +/- 10% RH and 12h photophase. The aphids were transferred to petri dishes with a foliar disk (cotton or pepper) with a layer of 1 cm tick of agar-water. The fungi were applied in a suspension containing 1.0 x 106 to 1.0 x 108 conidia/ml. In the control treatment 1 ml of sterilized water was added to the foliar disks. The mortality of aphids was evaluated daily. B. bassiana and M. anisopliae caused 100% mortality at the seventh day after inoculation, for both species. L. lecanii was the fungus that provided mortality later in the aphids and M. persicae was more susceptible to both fungi than A. gossypii.     

Fitness cost associated with carbosulfan resistance in Aphis gossypii Glover (Hemiptera: Aphididae)

In order to collect basic information for a resistance management program of Aphis gossypii Glover to carbosulfan, studies to evaluate fitness costs associated to this resistance were conducted under laboratory conditions. For this purpose, we studied the stability of carbosulfan resistance in A. gossypii populations with differing initial frequencies of resistance and compared life-history traits of carbosulfan-susceptible and resistant strains. The stability of resistance was followed in three populations with initial frequencies of 20, 50 and 80% of resistant individuals. The susceptibility to carbosulfan was monthly estimated by using the diagnostic concentration of 32 ppm. The biology of carbosulfan-susceptible and resistant strains was evaluated in cotton plants kept under controlled climatic conditions. The resistance to carbosulfan was unstable, that is, there was a significant increase in the susceptibility of different populations of A. gossypii to this insecticide in the absence of selection pressure. Comparison of biological traits between carbosulfan-susceptible and resistant strains showed that there is a fitness cost associated with resistance. The resistant strain showed lower fecundity, shorter reproductive period and lower longevity than the susceptible strain. The net reproductive rate (Ro) was 14.04 and 43.18 and the finite rate of increase (lambda) was 1.25 and 1.30 females/female/day for the resistant and susceptible strains respectively. Therefore, the instability of carbosulfan resistance in A. gossypii can be exploited in resistance management programs.     

Population growth of Aphis gossypii and Myzus persicae (Hemiptera: Aphididae) in the presence of Linepithema humile and Tapinoma sessile (Hymenoptera: Formicidae)

Invasive ant species can have dramatic impacts on native ants, through direct predation and by usurping common resources. Most invasive ants and many native ants use honeydew, produced by phloem-sucking hemipterans. Because colonies of invasive ants can become very large after establishment, these ants may facilitate greater hemipteran trophobiont population growth compared with their sympatric native ant counterparts. We examined the population growth of an aphid mutualist, Aphis gossypii, and a nonmutualist, Myzus persicae, exposed to two Dolichoderine ants, Linepithema humile, a globally widespread invasive species, and Tapinoma sessile, a widespread co-occurring native ant, in North America in an enemy-free laboratory study. L. humile worker foraging activity was at least twice that of T. sessile, and populations of the myrmecophile, A. gossypii, were greater when exposed to L. humile than T. sessile, possibly caused, in part, by more frequent encounters with L. humile. L. humile ignored M. persicae when A. gossypii was absent, whereas T. sessile preyed on it. Both ant species preyed on M. persicae when A. gossypii was also present. This suggested that both ants may assess nutritional gains from aphid species (i.e., honeydew versus body tissue), eliminating less productive aphids competing for host plant space. Through their impact on populations of hemipteran mutualists, we suggest that colonies of L. humile and perhaps other invasive ants may acquire more honeydew than native ants, thereby fueling colony growth that leads to numerical dominance and widespread success in introduced environments.     

Organophosphorus resistance in Aphis gossypii (Hemiptera: Aphididae) on chrysanthemum in the UK

The FAO standard dip-test was used to test resistance of glasshouse populations of Aphis gossypii from chrysanthemums to the organophosphorus insecticides heptenophos and diazinon. Compared with a susceptible population collected in 1981, resistance factors to diazinon of up to 538 were found in populations collected after 1984. Resistance to heptenophos was less than that to diazinon but some populations collected after 1984 were 34 times as resistant as the susceptible strain. Possible reasons for the sudden increase in resistance in A. gossypii and current prospects for control of resistant populations are discussed.     

Movement, toxicity, and persistence of imidacloprid in seedling Tabasco pepper infested with Myzus persicae (Hemiptera: Aphididae)

Application of imidacloprid to the soil in which Tabasco pepper, Capsicum frutescens L., seedlings were growing was highly effective against the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae). In just 48 h after the soil drench, aphid numbers on treated plants declined from 292.1 to 33.0 per plant, a reduction of 89%. By 72 and 96 h after the application, the reductions were 97 and 100%, respectively. Reductions in green peach aphid numbers also indicated that imidacloprid readily moved throughout the Tabasco pepper plant. Although, initial green peach aphid reductions at 24 and 48 h after imidacloprid application to soil, were greater on the lower leaves than on the upper leaves, by 72 h toxicity was high throughout the plant. At 48 h, overall green peach aphid reduction on seedlings grown in wet soil was significantly higher than that on plants growing in the drier soil. Regardless of soil moisture or leaf location, no live green peach aphids were detected on treated seedlings after 96 h. After the initial uptake period, toxicity to green peach aphid remained high for 5 wk. Under Tabasco pepper production conditions in Central America, the greatest need for aphid management is just after transplanting. Imidacloprid soil drenches before transplanting should offer the Tabasco pepper producer an extended period of aphid-free production.     

Life cycle variation of Myzus persicae (Hemiptera: Aphididae) in Greece

During the years 1995-1999 the life cycle category of 2797 clones of Myzus persicae (Sulzer) was examined. The clones originated from primary and secondary hosts from different localities of North and Central Greece and the island of Crete in the south. Four different overwintering life cycle strategies were found that have also been described for M. persicae and other heteroecious species previously. A geographical variation was found in the proportion of holocyclic clones from tobacco and other secondary hosts associated with the abundance of the primary host in the sampling regions. In Central Macedonia, around the main peach-growing regions, the proportion of holocyclic clones was mostly above 50% and in some cases reached 100%. In localities of East Macedonia, holocyclic clones were also frequent. On the other hand, further south or in north-eastern Greece, where peach is not common, the proportion of holocyclic clones varied between 0 and 33%. Fifty seven percent of examined anholocyclic clones produced males under short day conditions, suggesting that androcyclic clones in Greece represent an important factor of genetic variability. Intermediate clones were sampled from all host-plants but at low frequencies (3.6% of total examined clones and 6.9% of non-holocyclic ones). Moreover, a regional variation was found in different colour forms feeding on tobacco plants. Red clones were predominant in regions where aphids overwinter parthenogenetically on weeds or winter crops. However, almost all clones from the primary host were green. The ecological aspects of life cycle variation are discussed.     

Development of neonicotinoid resistance in the cotton aphid Aphis gossypii (Hemiptera: Aphididae) in Japan

A neonicotinoid-resistant Aphis gossypii Glover population was first detected from cucumber and sweet pepper crops in Miyazaki Prefecture, Japan, in April 2012. In this study, we determined the insecticide susceptibility of five field-collected populations of A. gossypii to seven neonicotinoids. Insecticide susceptibility was determined by performing bioassays and using the seedling-treatment method. Insecticide susceptibility of a susceptible population of A. gossypii, originally collected from a cucumber field in 2008, was also determined. High mortality (96.4–100 %) was observed in the susceptible population for the seven insecticides. In contrast, the mortality rate of the five field-collected populations collected in 2012 was low for five of the seven neonicotinoid insecticides tested: imidacloprid (26.7–65.5 %), dinotefuran (0–27.3 %), clothianidin (20.0–35.7 %), thiamethoxam (7.1–42.3 %), and nitenpyram (6.7–32.1 %). Mortality was 86.2–100 % for acetamiprid and 90.2–100 % for thiacloprid. The resistance ratio in comparison with the susceptible population was the highest for clothianidin (687-fold), lowest for thiacloprid (17-fold), and ranged from 43- to 253-fold for the other five neonicotinoids. Thus, the frequency of insecticide use needs to be reduced and other insecticides need to be employed in order to prevent the development of resistance to these two insecticides in the future.     

Resistance of potato cultivars to Myzus persicae (Sulz.) (Hemiptera: Aphididae)

Aphids are the most important vectors of viruses infecting potato (Solanum tuberosum). We focused on the response of the aphid vector Myzus persicae (Sulzer) to five commercial potatocultivars: ágata, Jaette Bintje, Mondial, Monalisa and Santè, by traditional antibiosis and antixenosis tests and by the EPG (Electrical Penetration Graph) technique, as a step forward to the design of effective management practices. Our aim was to identify plant factors involved in resistance of these cultivars against M. persicae, both at the surface and in deeper plant tissues. Results from the antixenosis test confirmed a strong preference of M. persicae for the Mondial cultivar. The antibiosis study indicated a lower population development of the aphid in 'Monalisa' when compared to 'ágata' and 'Jaette Bintje'. EPG assays indicated that 'Santè' inhibited the initial feeding process of M. persicae, whereas 'Monalisa' showed a physical-type of resistance as demonstrated by a very high number of short probes. The cultivar Mondial showed average values for all EPG variables analyzed. The behavior in 'Jaette Bintje' indicated this cultivar was an ideal host for aphid feeding and reproduction. Together, the EPG data revealed the existence of pre and post-phloematics factors in the cultivars under study, which have important implications on the efficiency of transmission and spread of virus in potato by M. persicae.     

Use of silicon as inductor of the resistance in potato to Myzus persicae (Sulzer) (Hemiptera: Aphididae)

The aphid Myzus persicae (Sulzer) is an important pest of potato and causes direct harm, due to the quantity of sap extracted and for being vector of important phytovirus. This work was carried out to evaluate the action of silicon as a resistance inducer of potato to M. persicae. Four treatments were tried: foliar fertilization with silicon acid at 1%; soil fertilization with 250 ml silicic acid solution at 1%; foliar fertilization with silicon acid at 1% + soil fertilization with 250 ml silicic acid solution at 1%; and a control. The treatments were applied thirty days after the explants emergence. Fifteen days after the application of the treatments, feeding preference and some biological aspects of the aphids were evaluated. After, the content of tannins and lignin present in the leaves and the activity of the enzymes peroxidase and phenylalanine ammonia-lyase were also determined. The silicon fertilization did not affect the preference of the aphids; however it reduced fecundity and the rate of population growth of the insects. The lignin percentage increased in the leaves of plants fertilized with silicon via soil and/or foliar and the percentage of tannins increased only in the leaves fertilized via soil plus foliar. The silicon acted as a resistance inducer to M. persicae in potato.     

Aspects of insecticide resistance in the melon and cotton aphid, Aphis gossypii (Hemiptera: Aphididae)

Strains of the aphid Aphis gossypii, taken from cucumber in UK glasshouses were tested for resistance to pirimicarb, diazinon and heptenophos. Compared to a susceptible strain, resistance factors to diazinon of up to 659 were found in populations collected between 1987 and 1989. Compared to the same susceptible strain, diazinon-resistant populations also showed a reduced response to heptenophos. All field populations tested against pirimicarb were resistant. Host plant preference tests showed that all strains (including stock cultures) tested could readily breed on cotton. However strains originally collected from chrysanthemum did not transfer to cucumber and likewise strains from cucumber would not colonise chrysanthemum. Polyacrylamide gel electrophoresis of four of the aphid strains showed differences in migration rates and intensity of staining of esterase bands. Intensity of staining was correlated with the degree of diazinon resistance.     

Control of Aphis gossypii and Myzus persicae (Hemiptera: Aphididae) by a flightless strain of Harmonia axyridis (Coleoptera: Coccinellidae) on green pepper plants in open fields

The cotton aphid Aphis gossypii Glover and the green peach aphid Myzus persicae (Sulzer) are economically important pests with a worldwide distribution. We evaluated the efficacy of releasing a flightless adult strain of the multicolored Asian lady beetle Harmonia axyridis (Pallas) as a control measure against these aphids on green pepper plants in open fields. Flightless H. axyridis adults were observed on the green pepper plants in the releasing plots throughout the experimental period and were found to be effective biocontrol agents, markedly decreasing the numbers of aphids. These results suggest that adults of this flightless strain of H. axyridis are effective in controlling aphids on green pepper plants in open fields.     

Economic thresholds for Aphis gossypii (Hemiptera: Aphididae) on Citrus clementina

Different levels of Aphis gossypii Glover were maintained on clementine trees by means of isolation inside mesh cages. Clementine yield loss was correlated with the number of aphids per square meter of canopy, obtaining the corresponding formula. Starting from this formula, the economic injury level (EIL) was calculated as follows: [218,333C + 11,130.6 VP0K]/[57.08 VP0K - 100C] = EIL (aphids/m2), where C = total insecticide cost per hectare, V = fruit price per kilogram, P0 = yield per hectare of a minimum pest level orchard, and K = reduction of injury due to treatment. Starting from the EIL, the economic threshold, the environmental EIL, and the environmental economic threshold were obtained. Formulae relating the number of aphids per square meter with other simpler indices expressing these thresholds (percentage of infested shoots, infested shoots per 0.25 m2 ring, index of infestation, percentage of occupied rings, and number of weekly captured aphids in a yellow trap) also were calculated.     

Host-correlated morphological variation of Myzus persicae (Hemiptera: Aphididae) populations in Greece

Morphological variation in nine characters of 157 clones of Myzus persicae (Sulzer) was examined by multivariate analysis. The clones were collected from peach, Prunus persica, the primary host and the secondary hosts tobacco, Nicotiana tabacum, cabbage, Brassica oleracea, sugarbeet, Beta vulgaris and pepper Capsicum annuum. The 156 clones originated from various regions of Greece, both in the north, where a large part of the population has an annual bisexual generation on peach, and in more southerly regions, where populations are predominantly unisexual. One clone was collected from tobacco in Caserta, Italy. All clones were laboratory-reared on potato. Canonical variate analysis, hierarchical cluster analysis and a non-parametric classification tree method both revealed morphological differences associated with the host-plant on which they were collected. The scores of the first two canonical variates separated the tobacco-feeding clones from those originating from other secondary host-plants. However, in tobacco-growing areas the tobacco-feeding form predominated in spring populations on peach, and was sometimes found on other secondary hosts. In addition, using cluster analysis, the clones from tobacco which were sampled in the most southeasterly region showed a relatively large phenotypic distance from those collected further north and west. Moreover, clonal phenotypes were affected both by host plant and by long-term parthenogenetic rearing. However, in spite of these effects, the tobacco form was generally distinguishable from aphids originating from other hosts, indicating that the difference must have a genetic basis. In separate analyses of the clones originating from secondary hosts no association was found between morphology and either life cycle category or colour. Discriminant analysis showed that 89% of 1723 specimens could be correctly classified into the two groups.     

PCR detection of pirimicarb resistance in Australian field isolates of Aphis gossypii Glover (Aphididae: Hemiptera)

Aphis gossypii Glover (cotton aphid) is a major secondary pest of Australian cotton that readily develops resistance to the carbamate insecticide pirimicarb (Pirimor®) and to organophosphates generally. To test the pirimicarb resistance status of Australian strains of A . gossypii , a polymerase chain reaction (PCR) assay followed by restriction enzyme assay (REA) was designed to identify the Ace I polymorphism S431F known to be responsible for resistance. The method was tested against reference and 33 field strains collected over two consecutive seasons. Both methods confirmed pirimicarb resistance in two field strains, one from each cotton season, giving credence to the molecular technique described. The PCR assay proved specific for the Ace I gene. This PCR REA assay has the potential to replace bioassay for the routine pirimicarb resistance monitoring in A . gossypii. With the molecular assay providing results in 48 h, compared with 4–8 weeks for bioassay, such an assay could be used before insecticide control.     

Morphological discrimination of Aphis gossypii (Hemiptera: Aphididae) populations feeding on Compositae

Aphis gossypii Glover is a polyphagous aphid pest with a worldwide distribution. However, there is evidence that on a global scale the name A. gossypii is being applied to a number of forms with different life cycles and/or host-plant associations. Morphometric variation of A. gossypii samples from crops and non-cultivated plants in many parts of the world was examined, to determine whether this variation is correlated with the hosts from which the aphids originated. Samples of A. gossypii were collected from Cucurbitaceae and Malvaceae in Europe, and from Compositae in various parts of the world. Morphometric data for 13 parameters measured from 97 clonal lineages (728 specimens) and 27 field-collected samples (313 specimens) were analysed by a series of canonical variates analyses, using the field sample/clonal lineage as grouping factor. Clonal lineages were reared on a common host in controlled conditions to standardize the effect of host and environment on morphology. The analyses provided a clear morphometric separation of the aphids originating from Compositae and those collected on Cucurbitaceae and Malvaceae, regardless of the geographical origin of the aphids and the host plant on which they were reared. This indicates that within A. gossypii there are two widely distributed host races or subspecies with different plant family associations. The taxonomic implications are discussed.     

不同地理种群烟蚜形态特征差异分析

烟蚜Myzus persicae是一种世界性的重要农业害虫。为探讨我国不同地理种群烟蚜形态特征变异情况, 本研究测量了我国18个地理种群烟蚜的体长、 体宽、 头宽、 各足腿节长、 各足胫节长等18个形态性状度量特征和Q值, 并进行方差分析和基于欧氏距离与地理距离和海拔差距的Mantel Test, 利用各形态特征与体长的比值构成的比例特征进行系统聚类和主成分分析。结果表明： 部分地理种群烟蚜的形态性状差异显著。系统聚类和主成分分析表明, 18个烟蚜地理种群中贵州贞丰种群（ZF-GZ）与其他种群相比差异最大, 陕西南泥湾（NNW-SX）、 湖南慈利（CL-HN）、 安徽谯城（QC-AH）和重庆武隆（WL-CQ）种群差异最小, 其他种群间的差异程度介于这两者之间。Mantel Test显示欧氏距离与地理距离、 海拔高度差距都不具有相关性。烟蚜种群的形态分化不符合地理隔离模式, 地理气候条件对种群形态有一定影响, 种群形态差异的形成是多种因素综合作用的结果, 但具体作用机制尚不明确。