Intraguild predation on the parasitoid Aphidius ervi by the generalist predator Harmonia axyridis: the threat and its avoidance

Interactions between natural enemies can be crucial for determining their overall control of pest species, yet the mechanisms that govern such interactions are often poorly understood. The risk of negative effects such as intraguild predation and the possibility of mitigating such risks are important components for ultimately determining the compatibility of biological control agents. We performed a group of experiments to determine whether the coccinellid Harmonia axyridis Pallas (Coleoptera: Coccinellidae) poses an intraguild threat to the parasitoid Aphidius ervi Haliday (Hymenoptera: Braconidae) and to see whether A. ervi is able to avoid predation by responding to the chemical tracks deposited by H. axyridis. We show that although H. axyridis does not readily consume A. ervi mummies, it preferentially consumes parasitized aphids over unparasitized aphids. We also show that A. ervi can defend against this threat by avoiding oviposition in the presence of H. axyridis chemical tracks. Aphidius ervi parasitized far fewer pea aphids Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae) on plants [Vicia faba L. (Fabaceae)] with H. axyridis chemical tracks in a no‐choice environment at a single‐plant scale. Similarly, when parasitoids could move freely between plants with and without tracks, A. ervi parasitism was higher on plants without tracks. Behavioral observations of A. ervi foraging suggested that this might be because of reduced A. ervi attack rates and patch residence times in the presence of H. axyridis tracks. Despite a risk of intraguild predation by H. axyridis, our study suggests that A. ervi may be able to mitigate this risk by altering its behavior in response to chemical cues.     

Cues of intraguild predators (Harmonia axyridis) and different temperatures alter foraging and oviposition strategies of the parasitoid Aphidius gifuensis

Organisms live in complex systems where they simultaneously balance responses to multiple factors. Insects are dealing with indirect pressures from predators under the influence of temperature. Currently, little is known about how they balance these factors. Under laboratory conditions, we investigated the effects of the predator Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) cues and temperature (23, 28, and 33 °C) on the foraging and oviposition behavior of the parasitoid Aphidius gifuensis Ashmead (Hymenoptera: Braconidae) using the aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) as a host. In all trials, the frequency and duration of stinging, walking, or stationary behavior of A. gifuensis were not influenced by H. axyridis cues. However, in trials with predator cues, A. gifuensis produced less offspring than trials without predator cues. On the other hand, the frequency of A. gifuensis stinging, walking, or stationary behavior, and the number of A. gifuensis larvae increased with rising temperature. Specially, when the predator cues were present, parasitoid responded to rising temperatures by increasing frequency of each behavior and an increase in offspring number. Our findings indicate that A. gifuensis might show flexible foraging and oviposition behavior in response to H. axyridis associated cues and different temperatures. Thus, the effects of both temperature and H. axyridis cues should be considered when assessing the foraging outcomes of A. gifuensis prior to combining these two enemies in aphid management practice.     

Interspecific host discrimination and intrinsic competition between Aphelinus asychis and Aphidius gifuensis in Myzus persicae

Aphelinus asychis Walker (Hymenoptera: Aphelinidae) and Aphidius gifuensis Ashmead (Hymenoptera: Braconidae: Aphidiinae) are solitary kionobiont endoparasitoids, which can parasitize the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae). We determined the influence of oviposition sequence and various time intervals (0, 24, 48, and 72 h) between two ovipositions on self‐ and conspecific discrimination and interspecific intrinsic competition between A. asychis and A. gifuensis. When offered unparasitized M. persicae and those parasitized by the other parasitoid species, the two parasitoid species oviposited more often in unparasitized hosts. Aphelinus asychis and A. gifuensis could, however, not avoid to multiparasitize hosts parasitized by the other species. Both parasitoid species had a limited interspecific discrimination ability through ovipositor insertion to detect internal cues. Aphidius gifuensis most often out‐competed A. asychis. The outcome of this interspecific competition was not influenced by oviposition sequence or time intervals between two ovipositions. Aphidius gifuensis eliminated competitors by physical combat at the first instar and probably by physiological suppression in later stages; A. asychis possibly used physiological suppression in all larval stages.     

异色瓢虫对设施栽培桃树桃蚜的捕食功能反应研究

为明确异色瓢虫对设施栽培桃树上桃蚜的自然控制力,在室内研究了异色瓢虫成虫自身密度和不同蚜虫密度对捕食功能的影响。结果表明,异色瓢虫对桃蚜的捕食功能反应符合Holling-Ⅱ圆盘方程,其拟合模型为Na=0.898Nt/(1+0.0045Nt),每头异色瓢虫在1 d内对桃蚜的最大捕食量为200头,捕食每头桃蚜的处置时间Th=0.005d。异色瓢虫自身密度对桃蚜捕食作用有一定制约,拟合Watt竞争模型方程为A=86.441P-0.6592。     

Performance of the parasitoid Aphidius colemani when reared on Myzus persicae on a fully defined artifical diet

Aphidius colemani Viereck(Hymenoptera: Aphidiidae) showed a developmenttime extended by 16% when reared on Myzus persicae Sulzer (Hemiptera: Aphididae) ofdifferent instars on artificial diet or onaphids on Brussels sprout plants. There wasalso a small but statistically significant 2%reduction in size (in hind tibia length) ofadult females. Rearing on diet had nosignificant effect on the number of eggsfemales contained at emergence. In a secondexperiment, aphids from Brussels sprouts ininstars 2–5 were compared with aphids from diettwo days older to give comparably sized aphidsfrom both substrates. Parasitisation by A.colemani gave the same direction of results,but showed that the effects in the firstexperiment were greater than predicted from thereduction in host size alone. However, in bothexperiments effects on parasitoids ofdiet-rearing the host were small, and culturingA. colemani on diet-reared aphids wassuccessful.     

Effect of floral and extrafloral resources on predation of Aphis spiraecola by Harmonia axyridis on Apple

Flowering companion plants and plants producing extrafloral nectar are being proposed to enhance biological control in apple (Malus domestica Borkh.) orchards. This experiment evaluated the impact of floral and extrafloral resources on predation of spirea aphid (Aphis spiraecola Patch) on apple by adult Harmonia axyridis (Pallas) under greenhouse conditions. Predation of spirea aphids was not affected by the presence of flowering buckwheat (Fagopyrum esculentum) as compared with either buckwheat with flowers removed or an uninfested apple shoot. However, there was a significant reduction in predation of spirea aphids on an apple shoot in the presence of a peach shoot with extrafloral nectar glands compared with either a peach shoot of the same cultivar without nectar glands or an uninfested apple shoot. These findings demonstrate that alternative food resources potentially could interfere with rates of biological control and, therefore, need to be carefully evaluated before incorporating in an orchard design. More studies are needed to adequately gauge the net effects of adding floral or extrafloral resources in orchards for conservation biological control.     

Behavioural responses of the aphid parasitoid Diaeretiella rapae to volatiles from Arabidopsis thaliana induced by Myzus persicae

In response to herbivory by insects, several plant species have been shown to produce volatiles that attract the natural enemies of those herbivores. Using a Y‐tube olfactometer, we investigated responses of the aphid parasitoid Diaeretiella rapae MacIntosh (Hymenoptera: Aphidiidae) to volatiles from Arabidopsis thaliana Columbia (Brassicaceae) plants that were either undamaged, infested by the peach‐potato aphid, Myzus persicae Sulzer (Homoptera: Aphididae), or mechanically damaged, as well as to volatiles from just the aphid or its honeydew. In dual‐choice experiments, female D. rapae given oviposition experience on A. thaliana infested with M. persicae were significantly attracted to volatiles from A. thaliana infested with M. persicae over volatiles from undamaged A. thaliana and similarly were significantly attracted to plants that had been previously infested by M. persicae, but from which the aphids were removed, over undamaged plants. Diaeretiella rapae did not respond to volatiles from M. persicae alone, their honeydew, or plants mechanically damaged with either a pin or scissors. We conclude that an interaction between the plant and the aphid induces A. thaliana to produce volatiles, which D. rapae can learn and respond to. Poor responses of D. rapae to volatiles from an A. thaliana plant that had two leaves infested with M. persicae, with the two infested leaves being removed before testing, suggested the possibility that, at this stage of infestation, the majority of volatile production induced by M. persicae may be localized to the infested tissues of the plant. We conclude that this tritrophic interaction is a suitable model system for future investigations of the biochemical pathways involved in the production of aphid‐induced volatiles attractive to natural enemies.     

Chemical protection of Calvia quatuordecimguttata eggs against intraguild predation by the invasive ladybird Harmonia axyridis

Intraspecific and interspecific predation of eggs is a well documented phenomenon amongst aphidophagous coccinellids. The invasive species Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is known to be a top intraguild predator and reported to attack the eggs of many coccinellid species both in a laboratory setting and in the wild. A previous laboratory study highlighted that while many species’ eggs were highly palatable to H. axyridis, the eggs of Calvia quatuordecimguttata (Linnaeus) (Coleoptera: Coccinellidae) appeared to be extremely well protected from attack. Here we present the results of behavioural experiments testing the hypothesis that substances on the egg surface are responsible for this protection, and report preliminary results of GC-MS analysis of these compounds. When the coatings of C. quatuordecimguttata eggs were removed using hexane, they became significantly more susceptible to predation by neonate H. axyridis larvae. However, their overall palatability was not affected, in that complete consumption was never or rarely observed. This suggests that the surface compounds are a true indicator of unpalatability in this species. The effect of hexane-washing on already palatable conspecific eggs was also analysed but had no significant effect on the susceptibility of eggs to cannibalism. We conclude that the eggs of at least one European species are effectively protected by surface deterrents from intraguild predation by H. axyridis. This effect might be due to both the diversity and abundance of hydrocarbons present within the egg coating, the presence of alkenes and/or the presence of patches of a red substance on the eggs’ surface, which is thought to belong to the acid group. In conjunction with data on the susceptibility of other immature stages of C. quatuordecimguttata, this finding may indicate a decreased risk of the species falling victim to invasive H. axyridis, despite their coincident habitat ranges.     

Population dynamics of Myzus persicae on tobacco in Yunnan Province,China, before and after augmentative releases of Aphidius gifuensis

The population dynamics of Myzus persicae were investigated in the field in a year without releases of Aphidius gifuensis (1998–1999), in a year with A. gifuensis releases (2000–2001) and several years later (2005–2007). The results showed that both high mean population densities and damage rates did not differ between 1998 and 1999, but were significantly lower in 2000–2001 and 2005–2007. Moreover, farmers also reported the decrease of M. persicae populations and attributed the declines to augmentative releases of A. gifuensis in their own fields, indicating farmers’ recognition in the effectiveness of A. gifuensis for M. persicae control. In addition, compared with the historical data on pesticide use for M. persicae control, the number of insecticide applications and cost of M. persicae control was sustained at a low level in 2007 (several years after release of A. gifuensis). This suggests that the augmentative releases of A. gifuensis could be effective and sustainable in M. persicae control.     

A maternal influence on the conditioning to plant cues of Aphidius colemani Viereck, parasitizing the aphid Myzus persicae Sulzer

Abstract. The offspring of parasitoids, Aphidius colemani Viereck, reared on Brussels sprouts and emerging from Myzus persicae Sulzer on a fully defined artificial diet, show no preferences in a four-way olfactometer, either for the odour of the diet, the odour of Brussels sprouts, or the odour of two other crucifers (cabbage and Chinese cabbage). A similar lack of odour preferences is shown when the host aphids are exposed for parasitization (for 48 h) on cabbage, Chinese cabbage or wheat. However, if parasitization occurs on Brussels sprouts, a weak but statistically highly significant response to Brussels sprout odour is observed. Although as many as 30–35% of the parasitoids show no response to any odour, another 35% respond positively to the odour of Brussels sprout compared with responses to the odours of cabbage, Chinese cabbage or wheat of only approximately 10%. An analagous result is obtained when the parent parasitoids are reared on cabbage. In this case, significant positive responses of their offspring to cabbage odour occur only if the 48-h parasitization has occurred also on cabbage. However, with parasitoids from Brussels sprouts parasitizing the aphids for 48 h also on Brussels sprouts, the offspring subsequently emerging from pupae excised from the mummies show no preference for Brussels sprout odour. Thus, although the Brussels sprout cue had been experienced early in the development of the parasitoids, they only become conditioned to it when emerging from the mummy. Both male and female parasitoids respond very similarly in all experiments. It is proposed that the chemical cue (probably glucosinolates in these experiments) is most likely in the silk surrounding the parasitoid pupa, and that the mother may leave the chemical in or around the egg at oviposition, inducing chemical defences in her offspring to the secondary plant compounds that the offspring are likely to encounter.     

不同龄期异色瓢虫对烟蚜的捕食潜能研究

异色瓢虫是烟田烟蚜的优势天敌种类之一,本文在室内进行了异色瓢虫成虫及各龄幼虫对烟草蚜虫的捕食功能反应试验,采用Holling-Ⅱ型功能反应模型进行拟合以明确其捕食潜能,利用Hassell模型和Watt模型拟合并测定了异色瓢虫种内干扰以及自身密度对烟蚜捕食作用的影响,结果表明:异色瓢虫各虫态对烟蚜的捕食量有明显的差异,在相同的烟蚜密度条件下,异色瓢虫4龄幼虫的日最大捕食量最大,为107.41头;其次是成虫,其日最大捕食量为94.34头;3龄幼虫、2龄幼虫和1龄幼虫的日最大捕食量分别为40.32头、14.25头和12.15头。在一定空间和相同比例猎物存在的条件下,种内干扰作用对1龄异色瓢虫幼虫的捕食量影响最为明显,干扰常数为1.1731,而对4龄幼虫干扰最小。各虫态自身密度对其捕食作用的干扰效应明显,1-4龄异色瓢虫幼虫以及成虫的竞争参数b值分别为0.5199、0.1848、0.1351、0.6757、0.6528。本研究表明异色瓢虫对烟蚜捕食潜力很大,尤其是4龄幼虫及成虫对烟蚜具有较大的捕食潜能。     

Lethal and behavioral sublethal side effects of thiamethoxam on the predator Harmonia axyridis

Thiamethoxam (TMX) is one of the most effective neonicotinoid insecticides for the control of green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), and various side effects can be expected in its natural enemies. The multicolored Asian lady beetle or harlequin ladybird, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), is an important predator against M. persicae in greenhouses and fields. In this study, we evaluated the toxicity of TMX to H. axyridis and the effect on the functional response of this predator to M. persicae through three routes of exposure. Acute toxicity bioassays indicated that LC₅₀ values of TMX on H. axyridis through direct residual contact (‘contact’), systemic application (‘systemic’), and leaf‐dip treatment (‘leaf‐dip’) were 18.99, 21.26, and 15.39 mg a.i. l^?1, respectively. The hazard quotient indicated a potential hazard of this agrochemical regardless of the exposure routes. The mortality caused by the lowest rate, 2 mg a.i. l^?1, was not significantly different compared with the control group. For the three routes of sublethal TMX exposure, the type‐II functional response was a good fit to the prey consumption of H. axyridis. Predation was most affected by leaf‐dip treatment, followed by contact and systemic treatments, which had similar effect. For all exposure routes, the predation capacity of the predator recovered quickly after transfer to untreated cabbage leaves. Thiamethoxam applied systemically was the least toxic to H. axyridis and did not affect the functional response of the predator. However, the sublethal effects of TMX through both contact and leaf‐dip application may reduce the population growth of H. axyridis and consequently impair the biological control of M. persicae by this predator. These results illustrate that the assessment of potential effects of TMX on H. axyridis is crucial to develop effective integrated pest management programs for M. persicae in China.     

The potential impacts of the arrival of the harlequin ladybird, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), in Britain

Abstract.  1. The harlequin ladybird, Harmonia axyridis , has recently arrived in Britain.
2. This species has been introduced from Asia into many parts of the world for biological control purposes.
3. In many parts of North America it has become the predominant aphidophagous coccinellid in less than 20 years, and in north-western Europe it is spreading and increasing in number rapidly.
4. Since establishment in North America and continental Europe, reports of its effectiveness as a biological control agent of aphids and coccids have been accompanied by accounts of negative effects on other aphidophagous species and humans.
5. Here the potential impacts of the arrival of the harlequin ladybird in Britain are assessed.     

Nitrogen fertiliser affects the functional response and prey consumption of Harmonia axyridis (Coleoptera: Coccinellidae) feeding on cereal aphids

Predator–prey interactions are influenced by nitrogen availability. Wheat (Triticum aestivum cv. Solstice) plants were provided with four levels of nitrogen and examined the responses of coccinellid predator, Harmonia axyridis to cereal aphids, Rhopalosiphum padi and Sitobion avenae. Increased nitrogen application improved nitrogen contents of the plants and also the body weight of cereal aphids feeding on them. In no‐choice feeding trials, H. axyridis consumed more aphids on low fertilised plants, suggesting a compensatory consumption to overcome reduced biomass (lower aphid size). Total biomass devoured by H. axyridis on all nitrogen fertiliser treatments was not statistically different. Logistic regression analysis of the proportion of prey consumed demonstrated that all developmental stages (larval and adult) of H. axyridis exhibited the type II functional response on all nitrogen fertiliser treatments. The rate of successful search (a′) of third and fourth instars and adults were the same across all fertiliser treatments suggesting that nitrogen fertilisation did not affect a′. Maximum handling time for the first instars of H. axyridis on R. padi (3.81 h^?1) and S. avenae (4.59 h^?1) was on the highest nitrogen treatment while minimum handling time was for the adults of H. axyridis on R. padi (0.20 h^?1) and S. avenae (0.20 h^?1) on the lowest nitrogen treatment. Handling time varied at varying fertiliser treatments within all instars and affected the predator's efficiency. The functional response curve, rate of successful search and handling time provide the information needed to understand the predator–prey interaction between H. axyridis and these cereals aphids. This could lead to the development of a better strategy for the biological control of R. padi and S. avenae at any particular level of nitrogen fertiliser regime in the field crops.     

Feeding behavior of Myzus persicae on asparagus species susceptible and resistant to Asparagus virus 1

Asparagus virus 1 (AV‐1) infects Asparagus officinalis L. (Asparagaceae) in the field worldwide. However, various wild relatives of A. officinalis are resistant to AV‐1. Here we study the behavior of the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), on 19 AV‐1‐resistant wild relatives of A. officinalis. We focus on behavior that is associated with regular cell penetration, relevant for inoculation of AV‐1, and sieve element penetration to check for vector resistance and its potential influence on AV‐1 transmission. Parameters, relevant for the transmission of non‐persistent viruses and host plant acceptance, were obtained by the electrical penetration graph technique. Furthermore, phylloclade architecture of A. officinalis and its wild relatives was examined to study its influence on aphid behavior. Behavior of M. persicae displays many cell penetrations and long ingestion periods on A. officinalis, compared to the generally shorter cell penetrations (reduced potential for virus transmission) and reduced or no ingestion (phloem‐located aphid resistance) on wild relatives. Because effects on aphid behavior are not consistent throughout the group of the tested wild relatives of A. officinalis, with some wild relatives being susceptible to M. persicae, a common genetic background for AV‐1 and aphid resistance appears to be unlikely. However, the reduced potential of virus transmission as well as aphid resistance shown by some wild relatives may be useful for future breeding programs.     

Long-term effects of elevated CO2 and temperature on populations of the peach potato aphid Myzus persicae and its parasitoid Aphidius matricariae

Model terrestrial ecosystems were set-up in the Ecotron controlled environment facility. The effects of elevated CO₂ (ambient + 200 mol/mol) and temperature (ambient + 2.0°C) on plant chemistry, the abundance of the peach potato aphid Myzus persicae, and on the performance of one of its parasitoids Aphidius matricariae, were studied. Total above-ground plant biomass at the end of the experiment was not affected by elevated atmospheric CO₂, nor were foliar nitrogen and carbon concentrations. Elevated temperature decreased final plant biomass while leaf nitrogen concentrations increased. Aphid abundance was enhanced by both the␣CO₂ and temperature treatment. Parasitism rates remained unchanged in elevated CO₂, but showed an increasing trend in conditions of elevated temperature. Our results suggest that M. persicae, an important pest of many crops, might increase its abundance under conditions of climate change. Received: 26 January 1998 / Accepted: 20 April 1998     

Attraction of the predator,Harmonia axyridis (Coleoptera: Coccinellidae), to its prey,Myzus persicae (Hemiptera: Aphididae), feeding on Chinese cabbage

The predatory multicolored Asian lady beetle, Harmonia axyridis, was attracted to volatiles released from Chinese cabbage infested by the green peach aphid, Myzus persicae, in T-tube olfactometer choice tests. However, lady beetle adults and larvae did not respond to clean air, Chinese cabbage alone or green peach aphid alone. Of different prey densities, H. axyridis adults were most attracted to Chinese cabbage infested by 60 M. persicae adults after 24 h. However, H. axyridis larvae were not attracted to Chinese cabbage infested by M. persicae. Mechanically damaged Chinese cabbage attracted neither lady beetle adults nor larvae. Predatory adults were attracted to 60 M. persicae adults after 24 and 48 h, and to 90 M. persicae adults after 12 h, suggesting that the predatory response depends on the prey density. Lady adult beetles did not prefer the volatiles induced by Diamondback moth, Plutella xylostella, indicating that specific host insect specificity attracts respective natural enemies. It can be explained that the volatile compounds emitted from the host plant as a result of herbivore attack preferred by the specific insect species.     

The influence of secondary plant substances on the growth and development of Myzus persicae of Beijing

Green peach aphids Myzus persicae from the Beijing region, maintained on greenhouse tobacco plants, were reared on modified artificial diet; sinigrin, tomatine, nicotine, gossypol, phlorizin, inulin and malic acid were added separately in concentrations of 0.1% or 0.2%. In preference tests none of the diets enriched by secondary substances was more acceptable than the basal diet. Diet uptake during larval development was determined quantitatively by using C¹⁴ glycine in the diets. For the basal diet the total uptake during larval development was about 1.16 l/aphid. The addition of secondary plant substances to the diet caused reductions of uptake to different degrees in the order: nicotine>phlorizin>gossypol>tomatine>malic acid>inulin>sinigrin. The larvae feeding on diets containing sinigrin or tomatine from the second day after birth seemed to have a much higher tolerance for sinigrin than tomatine, with a mortality of 9.6% within 7 days of rearing for the former and 89.4% for the latter. Hence this aphid differs from that occurring in the Netherlands in that the latter has a higher tolerance towards tomatine. The addition of inulin, malic acid or sinigrin did not cause a significant difference in the rate of larval development or in adult longevity. Diets containing these substances could support the aphid's development and reproduction for at least three generations.

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Résumé Des Myzus persicae de la région de Beijing, conservés sur tabac en serre, ont été élevés sur un régime artificiel voisin de celui de Dadd & Mittler (1966); sinigrine, tomatine, nicotine, gossypol, phlorizine, inuline et acide malique ont été ajoutés séparément aux concentrations de 0,1 et 0,2%. En comparant les préférences, aucun des régimes enrichis en substances secondaires n'était supérieur au régime de base. La prise alimentaire pendant le développement larvaire a été quantifiée en utilisant de la glycine C¹⁴ dans le régime. Les èlevages étaient conduits à 25±1 °C et H. R. 85% et une photopériode J/N: 16/8. Le prélèvement total de régime de base pendant le développement larvaire était environ 1,16 l/puceron. L'addition de substances secondaires végétales au régime induit de façon inégale le prélèvement, dans l'ordre suivant: nicotine>phlorizine>gossypol>tomatine>acide malique>inuline>sinigrine. Les larves consommant sur des régimes contenant de la sinigrine ou de la tomatine à partir du second jour après la naissance semblent prèsenter une plus grande tolèrance pour la sinigrine que la tomatine, avec une mortalité de 9,6% en 7 jours d'élevage pour la première et 89,4% pour la seconde. Ainsi ces pucerons diffèrent de ceux de Hollande, puisque ces derniers tolèrent plus la tomatine (Schoonhoven & Derksen-Koppers, 1976). L'addition d'inuline, d'acide malique ou de sinigrine ne provoque pas de différence significative dans le taux de développement larvaire ou la longévité des adultes. Des régimes contenant ces substances pourraient permettre le développement et la reproduction de pucerons pendant au moins 3 générations.

     

Effect of fertilization levels, age and canopy height of Lycopersicon hirsutum on the resistance to Myzus persicae

The effects of different levels of fertilization with nitrogen and potassium (NK), height within the canopy and plant age of Lycopersicon hirsutum f. glabratum (PI 134417) C. H. Mull and L. esculentum on the density of foliar cristalliferous idioblasts and trichomes, and on the levels of 2- tridecanone (2-TD) and 2-undecanone (2-UD) and their influence on the resistance to Myzus persicae (Sulzer) were investigated. NK levels were inversely related to densities of trichomes and cristalliferous idioblasts in L. esculentum, but only to densities of cristalliferous idioblasts in L. hirsutum. Trichome density increased with increasing height within the canopy and with plant age in L. esculentum and L. hirsutum. Density of cristalliferous idioblasts in L. hirsutum increased with canopy height reaching a maximum at mid-height within the canopy in opposition to L. esculentum in which a small decrease in density with height within the canopy was found. There was also a small decrease of idioblast density with increasing plant age for L. esculentum, while a greater and opposite variation took place in L. hirsutum. L. esculentum has mainly non- glandular leaf trichomes (90%), while L. hirsutum has mainly glandular trichomes (97%). The main glandular trichomes of L. hirsutum are producers of 2-TD and 2-UD, whose leaf content increases with increase of trichome density. A negative effect of 2-TD concentration and cristalliferous idioblast density on the survival and longevity of M. persicae was observed. Since L. hirsutum presented much higher levels of 2-TD and cristalliferous idioblast density than L. esculentum, L. hirsutum seems a promising source of resistance to M. persicae for tomato breeding programs.     

Effect of experience on in-flight orientation to host-associated cues in the generalist parasitoidLysiphlebus testaceipes

The effect of experience on the responsiveness of the aphidiid parasitoidLysiphlebus testaceipes (Cresson) (Hymenoptera: Aphidiidae) to host-associated cues was investigated using a wind-tunnel bioassay. Naive females were able to discriminate between uninfested wheat (Triticum aestivum L.) and wheat infested withSchizaphis gramimum (Rondani) (Homoptera: Aphididae), but oviposition experience significantly increased the parasitoid's propensity to respond to aphid-infested plants with upwind, targeted flight. The behavioural change associated with such experience was acquired rapidly (within five minutes) and persisted for at least 24 h. The parasitoid could be successfully conditioned to associate a novel odour with the presence of hosts, suggesting that the increase in response to aphid-infested plants which occurs as a result of experience is probably due to associative learning of olfactory cues from the plant-aphid complex.