Hoverfly oviposition response to aphids in broccoli fields

The oviposition response of predacious hoverflies (Diptera: Syrphidae) to Brevicoryne brassicae L. and Myzus persicae (Sulzer) (Homoptera: Aphididae) in commercial broccoli, Brassica oleracea var. italica L., Plenck (Brassicaceae), fields was investigated at two sites over the course of a growing season. The hoverfly oviposition responses to these aphid species on different parts of the broccoli plant canopy were also examined. There were no hoverfly eggs on broccoli plants without aphids, egg numbers were very low on plants with fewer than 50 aphids, and no peak in oviposition relative to aphid numbers was observed. Within individual plants that were colonized by aphids, there was some oviposition on individual leaves without aphids, and no hoverfly eggs were seen on leaves that had more than 400 aphids. Leaves in the broccoli plant canopy, and the datasets associated with them, were divided into three sections vertically, ‘upper’, ‘middle’, and ‘lower’. Brevicoryne brassicae was more abundant in the upper and middle canopy sections, while M. persicae was found mostly in the lower section. The rate of hoverfly oviposition per aphid was higher in the upper section than in the two other sections. Modeling of the oviposition response using logistic regression showed that the presence of hoverfly eggs was positively correlated with numbers of each aphid species and sampling date.     

Direct and Indirect Impacts of Infestation of Tomato Plant by Myzus persicae (Hemiptera: Aphididae) on Bemisia tabaci (Hemiptera: Aleyrodidae)

The impacts of infestation by the green peach aphid (Myzus persicae) on sweetpotato whitefly (Bemisia tabaci) settling on tomato were determined in seven separate experiments with whole plants and with detached leaves through manipulation of four factors: durations of aphid infestation, density of aphids, intervals between aphid removal after different durations of infestation and the time of whitefly release, and leaf positions on the plants. The results demonstrated that B. tabaci preferred to settle on the plant leaves that had not been infested by aphids when they had a choice. The plant leaves on which aphids were still present (direct effect) had fewer whiteflies than those previously infested by aphids (indirect effect). The whiteflies were able to settle on the plant which aphids had previously infested, and also could settle on leaves with aphids if no uninfested plants were available. Tests of direct factors revealed that duration of aphid infestation had a stronger effect on whitefly landing preference than aphid density; whitefly preference was the least when 20 aphids fed on the leaves for 72 h. Tests of indirect effects revealed that the major factor that affected whitefly preference for a host plant was the interval between the time of aphid removal after infestation and the time of whitefly release. The importance of the four factors that affected the induced plant defense against whiteflies can be arranged in the following order: time intervals between aphid removal and whitefly release > durations of aphid infestation > density of aphids > leaf positions on the plants. In conclusion, the density of aphid infestation and time for which they were feeding influenced the production of induced compounds by tomatoes, the whitefly responses to the plants, and reduced interspecific competition.     

The effect of leaf excision on the performance of Myzus persicae and Brevicoryne brassicae in relation to the nutrient treatment of the plants

Two groups of brussels sprout plants of one variety given different fertilizer treatments proved ‘resistant’ and ‘susceptible’ to both Myzus persicae and Breicoryrie brassicae, as measured by aphid mean relative growth rate. The hypothesis that leaf disc would fail to reflect differences in ‘nutritionallybased’ plant resistance was confirmed with B.brussicue but not M.persicae. Both aphids grew more slowly on discs than leaves of ‘susceptible’ plants; the reverse tendency showed on ‘resistant’ material. Total:(, amino nitrogen proved poorly correlated with aphid performance. Previously published (van Emden & Bashford, 1971) equations relating individual amino acids to aphid performance gave a better fit to the results, but still failed to account for the reduced performance of the aphids on ‘susceptible’ discs.     

EAG and behavioral responses of the wingless tea aphid Toxoptera aurantii (Homoptera: Aphididae) to tea plant volatiles

Electrophysiological and behavioral responses of the wingless tea aphid, Toxoptera aurantii (Boyer), to 14 synthetic volatiles identified from tea shoots, their partial (GLV mixture) and full (ACB mixture) blends, and fresh young tea leaves, buds, tender stems, adult tea leaves and tea aphid-damaged young leaves (ADYL) were studied by using an electroantennography (EAG) and a four-arm olfactometer. ACB elicited the largest EAG responses. Major volatile components, Z-3-hexen-1-ol, E-2-hexenal, n-hexanol, methyl salicylate and benzylalcohol, from the tea shoots were strongly EAG active. All the 4 tested tea shoot tissues also elicited significant EAG responses, with the young tea leaves being the strongest, followed by buds, tender stems and adult tea leaves. Surprisingly, ADYL elicited a weakly negative EAG response. In the olfactory assays, the fresh and tender tea leaves, as well as the individual major volatile components, e.g. Z-3-hexenyl acetate, methyl salicylate, E-2-hexen-1-ol and Z-3-hexen-1-ol, from the tender shoots (EAG-active) were all attractive. This result might indicate that the wingless tea aphids may use tea shoot volatiles as kairomone to find their optimal feeding sites, e.g. fresh tender tea shoots.     

Intraspecific variation in alkaloid profile of four lupine species with implications for the pea aphid probing behaviour

The alkaloid profile of white lupine Lupinus albus L. cv. ‘Boros’ and ‘Butan’, narrow-leaf lupine L. angustifolius L. cv. ‘Bojar’, ‘Graf’, ‘Karo’, ‘Mirela’, and ‘Sonet’, yellow lupine L. luteus L. cv. ‘Dukat’, ‘Parys’, ‘Perkoz’, and ‘Talar’, and wild species big-leaf lupine L. polyphyllus Lindl. was studied. The pea aphid Acyrthosiphon pisum Harris probing behaviour was monitored using the electrical penetration graph (EPG) technique.Four types of feeding behaviour were recognized. First, on highly acceptable L. luteus cv. ‘Dukat’, the total and mean duration of probing, time to reach phloem phase, and the duration of the first phloem phase were comparable to those in aphids on control plant Pisum sativum. Second, on partially acceptable L. luteus cv. ‘Talar’, pathway activities were slightly impeded, and the probes were more numerous and slightly shorter than on control plants. The phloem phase occurred sporadically, and feeding was terminated early after a brief period of ingestion. Third, on unpalatable but acceptable L. angustifolius cv. ‘Bojar’ and ‘Sonet’, and L. luteus cv. ‘Parys’ and ‘Perkoz’, the probes were numerous and usually epidermal. The phloem phase occurred rarely, and when it did, it was short and consisted mainly of watery salivation. Finally, on unacceptable L. albus cv. ‘Boros’ and ‘Butan’, L. angustifolius cv. ‘Graf’, ‘Karo’, ‘Mirela’, and L. polyphyllus, total probing time and individual probes were short and phloem phase did not occur.Eighteen alkaloids were identified: one piperidine alkaloid (ammodendrine), one indole (gramine), ten quinolizidine alkaloids (one tricyclic and nine tetracyclic compounds), and six esters. All lupine varieties that contained lupanine, its derivatives and especially their esters appeared to be unacceptable to the pea aphid, independent of the total concentration of any specific lupanine alkaloid. In contrast, sparteine and its derivatives did not seem to affect aphid probing significantly.     

Evaluation of induced responses, insect population growth, and host-plant fitness may change the outcome of tests of the preference-performance hypothesis: a case study

The preference‐performance hypothesis predicts that insect preference should correspond to host suitability for offspring development. We studied the pattern of within‐plant preference in the aphid Sipha flava and its consequences for offspring performance on the host‐plant Sorghum halepense, regarding the role of induced responses of plants to aphid feeding. The consequences of within‐plant preference on aphid population growth and host‐plant traits were also evaluated. Our results showed that winged and wingless aphids preferred to settle on mature rather than young leaves. In contrast, aphid individual growth rate was higher on young leaves when compared with mature leaves, suggesting that the outcome of this test rejected the preference‐performance hypothesis. However, the inclusion of the factor ‘previous aphid infestation’ changed the outcome from a maladaptive choice to a neutral one. Thus, individual growth rates of S. flava increased when aphids developed on leaves that had been previously infested. Interestingly, aphid growth rate on previously infested leaves did not differ between young and mature leaves. On the other hand, aphid population reproductive rate was higher and the percentage of winged aphids lower when infestation occurred on mature rather than young leaves. Aphid infestation reduced plant and shoot biomass, and increased leaf mortality. These negative effects on plant traits related to plant fitness were greater when aphid infestation occurred on young leaves. Likewise, whereas infestation on mature leaves did not cause a significant reduction in the number of flowering plants compared with control plants, aphid infestation on young leaves did reduce the number of plants at the flowering stage. Consequently, if both the reproductive rate of aphids in the mid‐term, and host‐plant fitness are taken into account, the results indicate that aphid preference for mature leaves may be an adaptive choice, thus supporting the preference‐performance hypothesis.     

Aphid Acceptance of Barley Exposed to Volatile Phytochemicals Differs Between Plants Exposed in Daylight and Darkness

It is well known that volatile cues from damaged plants may induce resistance in neighboring plants. Much less is known about the effects of volatile interaction between undamaged plants. In this study, barley plants, Hordeum vulgare cv. Kara, were exposed to volatiles from undamaged plants of barley cv. Alva or thistle Cirsium vulgare, and to the volatile phytochemicals, methyl salicylate or methyl jasmonate. Exposures were made either during natural daylight or darkness. Acceptance of exposed plants by the aphid Rhopalosiphum padi was assessed, as well as the expression of putative marker genes for the different treatments. Aphid acceptance of plants exposed to either barley or C. vulgare was significantly reduced, and an effect of the volatiles from undamaged plants was confirmed by the induction of pathogenesis-related protein, PR1a in exposed plants. However the effect on aphid acceptance was seen only when plants were exposed during darkness, whereas PR1a was induced only after treatment during daylight. Aphid acceptance of plants exposed to either methyl salicylate or methyl jasmonate was significantly reduced, but only when plants were exposed to the chemicals during daylight. AOS2 (allene oxide synthase) was induced by methyl jasmonate and BCI-4 (barley chemical inducible gene-4) by methyl salicylate in both daylight and darkness. It is concluded that (a) the effects on aphids of exposing barley to volatile phytochemicals was influenced by the presence or absence of light and (b) the response of barley to methyl salicylate/methyl jasmonate and to volatiles from undamaged plants differed at the gene and herbivore level.Key Words: methyl jasmonate, methyl salicylate, allelobiosis, barley, PR1, allene oxide synthase, Rhopalosiphum padi, light     

Behavioural responses of the seven‐spot ladybird Coccinella septempunctata to plant headspace chemicals collected from four crop Brassicas and Arabidopsis thaliana,infested with Myzus persicae

1 Insects using olfactory stimuli to forage for prey/hosts are proposed to encounter a ‘reliability–detectability problem’, where the usability of a stimulus depends on its reliability as an indicator of herbivore presence and its detectability. 2 We investigated this theory using the responses of female seven‐spot ladybirds Coccinella septempunctata (Coleoptera: Coccinellidae) to plant headspace chemicals collected from the peach‐potato aphid Myzus persicae and four commercially available Brassica cultivars; Brassica rapa L. cultivar ‘turnip purple top’, Brassica juncea L. cultivar ‘red giant mustard’, Brassica napus L. cultivar ‘Apex’, Brassica napus L. cultivar ‘Courage’ and Arabidopsis thaliana. For each cultivar/species, responses to plants that were undamaged, previously infested by M. persicae and infested with M. persicae, were investigated using dual‐choice Petri dish bioassays and circular arenas. 3 There was no evidence that ladybirds responded to headspace chemicals from aphids alone. Ladybirds significantly preferred headspace chemicals from B. napus cv. Apex that were undamaged compared with those from plants infested with aphids. For the other four species/cultivars, there was a consistent trend of the predators being recorded more often in the half of the Petri dish containing plant headspace chemicals from previously damaged and infested plants compared with those from undamaged ones. Furthermore, the mean distance ladybirds walked to reach aphid‐infested A. thaliana was significantly shorter than to reach undamaged plants. These results suggest that aphid‐induced plant chemicals could act as an arrestment or possibly an attractant stimulus to C. septempunctata. However, it is also possible that C. septempunctata could have been responding to aphid products, such as honeydew, transferred to the previously damaged and infested plants. 4 The results provide evidence to support the ‘reliability–detectability’ theory and suggest that the effectiveness of C. septempunctata as a natural enemy of aphids may be strongly affected by which species and cultivar of Brassica are being grown.     

Inheritance of resistance to lettuce root aphid in the lettuce cultivars 'Avoncrisp' and 'Lakeland"

The inheritance of resistance in two lettuce cultivars to lettuce root aphid, Pemphigus bursarius, was studied in a series of laboratory and field experiments at Wellesbourne between 1989 and 1992. A source of total resistance in the cv. ‘Avoncrisp’ which is linked to the downy mildew resistance gene Dm6, was shown to be governed by a single dominant gene. There were no maternal effects evident in the inheritance of this resistance. The basis of the high level of resistance which exists in the cv. ‘Lakeland’ (formerly known as ‘Jubilee’) was also shown to be controlled by the same dominant gene. The linkage between Dm6 and root aphid resistance was broken in ‘Lakeland’ as this cultivar does not possess the Dm6 gene. The linkage was presumably broken when the original cross between the parents of cv. ‘Lakeland’, ‘Calmar’ and ‘Avoncrisp’ was made. Under laboratory conditions small numbers of aphids commence development on cv. ‘Lakeland’ but colonies fail to develop and under field conditions the resistance provides adequate Protectión against the pest. The resistance in both ‘Avoncrisp’ and ‘Lakeland’ was effective against a population of lettuce root aphid collected from an endive crop in southern France as well as being effective against the Wellesbourne population of this aphid.     

A facultative mutualism between aphids and an invasive ant increases plant reproduction

1. The consequences to plants of ant–aphid mutualisms, particularly those involving invasive ants, are poorly studied. Ant–aphid mutualisms may increase or decrease plant fitness depending on the relative cost of herbivory by ant‐tended aphids versus the relative benefit of increased ant suppression of other (non‐aphid) herbivores. 2. We conducted field and greenhouse experiments in which we manipulated the presence and absence of cotton aphids (Aphis gossypii) on cotton plants to test the hypothesis that a mutualism between cotton aphids and an invasive ant, the red imported fire ant (Solenopsis invicta), benefits cotton plants by increasing fire ant suppression of caterpillars. We also manipulated caterpillar abundance to test whether the benefit of the mutualism varied with caterpillar density. 3. We found that more fire ants foraged on plants with cotton aphids than on plants without cotton aphids, which resulted in a significant reduction in caterpillar survival and caterpillar herbivory of leaves, flower buds, and bolls on plants with aphids. Consequently, cotton aphids indirectly increased cotton reproduction: plants with cotton aphids produced 16% more bolls, 25% more seeds, and 10% greater seedcotton mass than plants without aphids. The indirect benefit of cotton aphids, however, varied with caterpillar density: the number of bolls per plant at harvest was 32% greater on plants with aphids than on plants without aphids at high caterpillar density, versus just 3% greater at low caterpillar density. 4. Our results highlight the potential benefit to plants that host ant–hemipteran mutualisms and provide the first experimental evidence that the consequences to plants of an ant–aphid mutualism vary at different densities of non‐aphid herbivores.     

Cultivar‐specific plant odour preferences of a generalist aphid parasitoid Aphidius colemani and a possible mechanism for maternal priming of resistance to toxic plant chemistry

Aphidius colemani Viereck, emerging from Myzus persicae (Sulzer) mummies on the Brussels sprout cultivar ‘Bedford Winter Harvest’ (BWH), responds positively in the olfactometer to the odour of that cultivar in comparison with air. Responses to the odours of other sprout cultivars, cabbage and broad bean could be explained by the humidity from plant leaves. In a choice between BWH and other sprout cultivars, the BWH odour is preferred, or that of cv. ‘Red Delicious’ (RD) if the parasitoids are reared on RD. This confirms previous work showing that the secondary chemistry of a cultivar is learnt from the mummy cuticle during emergence. Adults emerging from pupae excised from the mummy show a similar but less pronounced preference. Parasitoids developing in aphids on an artificial diet do not discriminate between the odours of BWH and RD, unless allowed contact with a mummy from the same cultivar that the mother develops on. This suggests a cultivar‐specific maternal cue. This cue is speculated to consist of a small amount of the secondary chemistry (probably glucosinolates in the present study) that are left in or on the egg at oviposition, which subsequently induces enzymes that detoxify plant‐derived toxins in the aphid host. Indeed, when parasitoids emerging from diet‐reared aphids are released on aphid‐infested sprout plants, fewer mummies are produced than by parasitoids emerging from mummies of plant‐reared aphids or from excised pupae. Only parasitoids that emerge from mummies of plant‐reared aphids prefer the cultivar of origin as shown by the number of mummified hosts.     

A controlled environment study of the effect of leaf physiological age on the movement of apterous Myzus persicae on sugar-beet plants

Apterous Myzus persicae were found to move frequently from leaf to leaf on sugar-beet plants in controlled environment conditions. It is suggested that aphid movement can be related to changes in the rate and content of translocate flow during leaf development. These changes make newly-emerged leaves nutritionally favourable to colonising aphids and make expanding leaves slowly wane in favourability during the process of ‘sink to source’ conversion leading to aphid dispersal from the leaf. Variation in temperature was not found to alter the rate of aphid movement or the period (measured in thermal time) that aphids spent on particular leaves. However, the lower temperature was found to increase the rate of aphid development, aphid size and fecundity; these effects could also be due to nutritional factors. This dispersal behaviour may be a tactic to maximise food intake by a polyphagous aphid and increase the probability that nymphs are deposited on nutritionally-favourable leaves. The implications of the interleaf dispersal of apterous M. persicae for within- and between-plant spread of beet yellows virus (BYV) and beet mild yellowing virus (BMYV) are discussed.     

Aphelinus albipodus(Hymenoptera: Aphelinidae) andDiaeretiella rapae(Hymenoptera: Braconidae) Parasitism onDiuraphis noxia(Homoptera: Aphididae) Infesting Barley Plants Differing in Plant Resistance to Aphids

Russian wheat aphid,Diuraphis noxia(Mordvilko), as a pest of small grains, has prompted research into biological control and host plant resistance. In the presence of Russian wheat aphid, leaves of a susceptible barley (Morex) are curled and chlorotic and sustain large densities of this aphid, while leaves of a resistant barley (STARS-9301B) remain flat and green and sustain fewer aphids. Might parasitism of Russian wheat aphid byAphelinus albipodusHayat & Fatima andDiaeretiella rapaeMcIntosh be affected differently by these plant types? When presented the plants separately and based on parasitism rate relative to aphid density, the largerD. rapaewas more effective in parasitizing relatively high densities of aphids within curled leaves of Morex than relatively low densities of aphids on uncurled leaves of STARS-9301B. Parasitism byA. albipodusdid not significantly differ among the plants. When given a choice of plants, approximately equal rates of parasitism occurred on the two plant lines for both parasitoid species, and parasitism byD. rapaewas greater thanA. albipodus.These data indicate that using parasitoid size as an indicator of success in a physically restricted environment may be misleading, when considered in a plant environment responsive in several manners to aphids (chlorosis, curling, and ability to sustain Russian wheat aphid). We expect that use of resistant barley will result in decreased parasitoid abundance as aphid densities decrease. However, parasitism rates are expected to be approximately equal on resistant and susceptible barley. In this system, plant resistance and biocontrol are compatible management strategies.     

Effects of aphid herbivory on volatile organic compounds of Artemisia annua and Chrysanthemum morifolium

We showed the effect of aphid infesting on the volatile organic compounds (VOCs) emitted by the infested Artemisia annua and Chrysanthemum morifolium cultivar ‘Nan nong hong feng’ plants by using headspace solid-phase microextraction (HS-SPME) method combined with gas chromatography mass spectrometry (GC–MS). In olfactometer bioassay experiment, aphids showed a preference for the odour of both healthy and infested chrysanthemum, while we found an opposite result in A. annua. Aphids tend to healthy plants compared with the infested, and the phenomenon became obvious with time. Different extracts were tested with the healthy plants and aphid infested plants. Eucalyptol, β-caryophyllene, (E)-β-farnesene, and germacrene D were released as the major constituents in both species. After aphid infesting, we observed a great increase in artemisia ketone and (E)-β-farnesene and a decrease in germacrene D in A. annua; comparatively, eucalyptol, isoborneol and β-caryophyllene increased in chrysanthemum. Combined with the GC–MS data and olfactometer bioassay results we concluded that (E)-β-farnesene and artemisia ketone emitted from A. annua might act as a potential volatile compound to resist aphids, and the two compounds would be useful for future ecological control of aphid in chrysanthemum cultivation.     

Short-term effects of aphid feeding on photosynthetic CO2 exchange and dark respiration in legume leaves

Net CO₂ exchange rates and dark respiration rates were determined for single attached legume leaves (leaflets) after 6 to 9 days of aphid infestation. Plant-aphid combinations used were broad bean ( Vicia faba L. cv. Aquadulce) and cowpea [ Vigna unguiculata (L.) Walp. cv. Caloona)] infested with cowpea aphids ( Aphis craccivora Koch) and broad bean and garden pea ( Pisum sativum L. cv. Victory Freezer) infested with pea aphids [ Acyrthosiphon pisum (Harris)]. Leaves from all aphid-infested plants had significantly greater net CO₂ exchange rates in the light than their respective controls and rates of dark respiration of leaves from infested cowpea and garden pea were also significantly greater than those of controls. Dark respiration, as a percentage of net CO₂ exchange rates in the light, was greater in aphid-infested than in control plants. When the mean net daily carbon gain was calculated for the leaves of each plant-aphid combination, leaves from aphid-infested plants had the greatest gain. It is proposed that net CO₂, exchange rates increased due to increased sink demand and dark respiration rates increased to meet the increased energy requirements of phloem loading and cellular maintenance associated with aphid feeding. The apparent compensatory carbon gain of infested leaves was consumed by the aphids.     

无翅茶蚜对茶树挥发物的触角电生理和行为反应

分别使用昆虫触角电位仪(EAG)和四臂嗅觉仪,测定了无翅茶蚜Toxopteraaurantii Boyer对14种茶树挥发性化合物、14种挥发物中"绿叶气味"组成的混合物(GLV)、14种挥发物的混合物(ACB)、以及新鲜嫩叶、芽、嫩茎、成叶和茶蚜为害嫩叶(ADYL)的EAG反应和行为反应。ACB引出最大的EAG反应值,茶树挥发物主要组分Z-3-己烯-1-醇、E-2-己烯醛、n-己醇、水杨酸甲酯和苯甲醇也引起较大的EAG反应值。4种正常茶梢的器官也引出较大的EAG反应,以嫩叶最强、依次为芽、嫩茎和成叶。有趣的是ADYL引出弱的负的EAG值。用嗅觉仪进行的生物测定表明,嫩叶以及主要的茶梢挥发性成分乙酸-Z-3-己烯酯、水杨酸甲酯、E-2-己烯-1-醇和Z-3-己烯-1-醇等也具有较强引诱活性。研究显示无翅茶蚜可能利用茶梢挥发物作为利它素而寻觅适宜的取食场所,如茶树嫩梢。     

Effects of infection with the cabbage black ringspot strain of turnip mosaic virus on turnip as a host to Myzus persicae and Brevicoryne brassicae

When turnip plants with 3–7 leaves were inoculated with cabbage black ringspot virus (CBRSV) on the 3rd rough-leaf, symptoms only appeared on leaves that had been less than 15 mm long at the time of inoculation, although infection decreased the area and both fresh and dry weight of all leaves. Leaves were ‘aged’ by their appearance and placed in Leaf Age Categories (LACs). Leaves with symptoms senesced (‘aged’) prematurely. CBRSV-infection of cv. Green Top White did not change the distribution of populations of Myzus persicae between LACs, but increased the proportion of the plant suitable for colonisation. All suitable LACs were quickly colonised by adult apterae and nymphs. On CBRSV-infected plants the nymphal period was shorter, F₁ adults deposited larvae more frequently and the live body weight and tibial length of the F₂ generation was greater, than on healthy plants. The distribution of Brevicoryne brassicae populations on cv. Green Top White differed from that of M. persicae but was also unchanged by CBRSV-infection. On healthy plants the largest colonies were on mature leaves, so that on virus-infected plants premature senescence shortened the life of the colony. On CBRSV-infected plants the nymphal period was prolonged and the live weight of F₁ and F₂ adult apterae was less than on healthy plants. The differences between the biology of M. persicae and B. brassicae on CBRSV-infected cv. Green Top White were associated with the accelerated senescence of CBRSV-infected leaves. The possibility that CBRSV-infection might reduce the resistance of turnips to aphid infestation was tested. M. persicae and B. brassicae were cultured on two favourable and two less favourable cultivars. No improvement in population growth rate was found when the less favourable host cultivars were infected with CBRSV, but both aphid species weighed less and/or had smaller nymphal populations on cultivars showing the severest symptoms. These results are discussed in relation to the evolution of non-persistent virus transmission by aphids.     

Diurnal pattern of aphid feeding and its effect on cotton leaf physiology

Cotton aphid (Aphis gossypii G.) populations seemed to fluctuate over the past years in cotton (Gossypium hirsutum L.) perhaps as a result of excessive use of insecticides for controlling more problematic pests. Contradictory plant responses have been observed depending upon the aphid/plant system, and it is unclear if cotton aphids, abiotic stress or both are responsible for cotton yield reduction in aphid-infested fields. Our objectives were to investigate the diurnal changes in the physiology of cotton leaves following aphid herbivory, and the diurnal pattern of aphid feeding. The experiment was conducted in a growth chamber using the cotton cultivar ‘Stoneville 474’. Leaves of the same age and size were infested with wingless adults plus nymphs. Cotton aphids were allowed to increase in numbers without restriction for 9 days, after which the amounts of carbohydrates in aphid-honeydew, and the number of honeydew droplets excreted per aphid were measured. Photosynthetic rates, dark respiration rates and foliar non-structural carbohydrates were measured. The amount of individual carbohydrates found in the honeydew was significantly different with time. The total amount of carbohydrates excreted per aphid within a 24-h period averaged 2.5 μg. The number of honeydew droplets excreted per aphid varied significantly from time to time period. Cotton aphids did not significantly alter photosynthesis or respiration rates or non-structural carbohydrates on leaves. Aphid populations of approximately 300 per leaf on the 9th day of infestation did not appear to significantly alter the physiology of cotton leaves.     

Introduction and establishment ofTrioxys pallidus [Hym.: Aphidiidae] in Oregon,U.S.A. for control of filbert aphidMyzocallis coryli [Hom.: Aphididae]

Hazelnut orchards in Spain, France, and Italy were searched for parasitoids of the filbert aphid,Myzocallis coryli (Goetze). A biotype ofTrioxys pallidus Haliday was found to parasitize the aphid throughout western Europe. Wasps were imported, quarantined, mass-reared, and released in Oregon orchards. The wasp successfully attacked and completed its development on Oregon populations of the filbert aphid. A greenhouse culture of the parasitoid was maintained continuously for over 50 generations, and approximately 30,000 adult wasps were released in western Oregon. Overwintering survival has been documented in at least 12 different locations. In 3 commercial hazelnut orchards, the parasitoids proved capable of reducing aphid population peaks by 33–48%.      

Cotton TCTP1 gene encoding a translationally controlled tumor protein participates in plant response and tolerance to aphids

Cotton aphid (Aphis gossypii Glover) is one of the most important economic pests in the world. Long-term unreasonable usage of insecticides has made cotton aphid developing insecticide-resistance, which frequently leads to serious occurrences of cotton aphid in many regions. It is regarded effective and environmentally friendly to control aphids through utilizing plant resistance. In this study, a translationally controlled tumor protein gene, GhTCTP1, was isolated in cotton. It belongs to TCTP subfamily and encodes a protein of 168 amino acids. GhTCTP1 expression was suppressed in cotton plants under cotton aphid attack, but its expression level was up-regulated in the wounded cotton leaves. The choice test and no-choice test demonstrated that overexpression of GhTCTP1 in Arabidopsis enhanced plant resistance to green peach aphid (Myzus persicae). Quantitative RT-PCR analysis revealed that the defense response genes related to salicylic acid signaling pathway were activated in the GhTCTP1 overexpressing transgenic plants. Content of total amino acids was decreased, and phenylalanine ammonialyase activity was altered in leaves of the transgenic Arabidopsis plants, compared with those in wild type. Furthermore, the callose amount in transgenic Arabidopsis leaves was more than that of wild type. These data suggested that GhTCTP1 might be involved in regulation of plant tolerance to aphids, and can be potentially applied in improving aphid-resistance of crops by genetic manipulation.