Analysis of variations of handling-time inTrichogramma maidis

Variation in handling-time is studied in the association betweenTrichogramma maidis Pintureau & Vœgelé [Hym.: Trichogrammatidae] and one of its factitious hosts: the eggs of the Mediterranean flour mothEphestia kuehniella Zeller [Lep.: Pyralidae]. It is shown that the duration of egg laying behaviour decreases exponentially from the first host egg encountered onwards. This decreasing kinetic, which corresponds to a learning ability, shows a high variability between females, but a mother-daughter regression analysis fails to demonstrate any genetic transmissibility of this learning ability over 2 successive generations. Once the learning is over, there remains a residual variability which is, in part, under genetic control. The possible consequences of these results on the stability of host-parasite associations are discussed.      

Genetic variation in progeny allocation in Trichogramma maidis

A considerable amount of work has been recently devoted to the study of progeny allocation strategies by insect parasitoids under different environmental constraints (see Waage, 1986, for a review). All these studies present each of the oviposition strategies (e.g. number of eggs laid per host, superparasitism) as a phenomenon which is progressively settled by natural selection during the course of generations. However, this optimal progeny allocation theory is conceivable only if the variation in wasp's biological traits involved are under a genetic control on which natural selection could act. We have decided therefore to look for a genetic variability in these traits in a Trichogramma maidis Pintureau & Voegelé (Hym.; Trichogrammatidae) population.Based on histological staining which allows to count the number of Trichogramma eggs deposited in each host (Ephestia kuehniella Zeller), we compared different wasp isofemale lines (i.e. families) each of which was submitted to different conditions (i.e. parasite/host ratios).The results show that the control of superparasitism seems to be genetically determined. This appears true both for the average number of eggs deposited in each host, and for the frequency distribution of wasp eggs among hosts.The evolutionary consequences of such results and their possible applications in order to improve the wasp's mass-rearing conditions are discussed.

---

Résumé Récemment, de nombreux travaux ont été publiés dans le but de mieux comprendre les différentes stratégies de reproduction (i.e. répartition de la progéniture parmi les hôtes) présentées par les insectes parasitoides sous différentes contraintes environnementales (cf. Waage, 1986, pour une synthèse). L'ensemble de ces travaux considère chacune de ces stratégies (e.g. nombre d'ufs déposés par hôte, décision de superparasiter) comme un phénomène progressivement mis en place par la sélection naturelle au cours des générations. Ceci n'est cependant concevable que si les caractères biologiques en cause chez les parasites sont sous la dépendance d'une variation génétique sur laquelle la sélection naturelle peut agir.Les expériences présentées ici ont donc eu pour but de voir si ces caractères sont effectivement déterminés génétiquement dans une population de Trichogramma maidis Pintureau & Voegelé (Hym.; Trichogrammatidae).Grâce à l'utilisation d'une coloration histologique qui permet de compter le nombre d'ufs de trichogrammes déposés dans chaque hôte, différentes lignées isofemelles (i.e. familles) ont été comparées, et ce selon différentes conditions expérimentales correspondant à différentes valeurs du rapport nombre de femelles parasites sur nombre d'hôtes offerts.Les résultats obtenus motrent que le phénomène du superparasitisme semble être déterminé génétiquement. Ceci est constaté aussi bien au niveau du nombre moyen d'ufs de trichograme déposés par hôte, que dans les caractéristiques des distributions des ufs de parasites parmi les hôtes.Les conséquences évolutives de tels résultats, ainsi que leurs applications possibles dans le but d'améliorer les conditions d'élevage de masse de ces insectes, sont discutées.

     

Sensory receptors of the ovipositor ofTrichogramma maidis [Hym.:Trichogrammatidae]

Sensory receptors of the ovipositor ofTrichogramma maidis are described. Sense organs are found on the 2^nd valvifers (1 type), on the tip of the 3^rd valvulae (2 types) and on the 1^st valvulae (4 types). The nature and possible functions of these sensilla are discussed.      

Host examination walk and oviposition site selection ofTrichogramma minutum: Studies on spherical hosts

The host examination behavior of the parasitoid wasp Trichogramma minutumon spherical Manduca sextahosts is described. The mean walking speed during host examination was 0.64 ± 0.03 mm s^–1and is independent of wasp size. The paths taken by the wasps are not evenly distributed over the host surface; the majority of time is spent below 45 ° latitude. The distribution of oviposition sites is also nonrandom with respect to latitude and is not influenced by phototaxic and geotaxic responses. The initial transit made by the wasps over the host surface is a straight path which frequently passes across the highest point on the host. The length and duration of the initial transit are independent of wasp body length. However, stride length and stepping rates are proportional to wasp body length, and small wasps take more steps to complete their initial transit. The roles of the examination walk in host recognition and host volume measurement by Trichogrammaare also discussed.     

Flight initiation in the egg parasitoid Trichogramma minutum: Effects of ambient temperature, mates, food, and host eggs

Emergence, preening, and flight initiation were studied in laboratory-reared Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae). Male parasitoids emerged first and flew before females. When both sexes were present in flight cylinders, female parasitoids flew before males. Flight propensity in males was negatively related to the number of emerging females, while flight propensity in females was independent of the number of males present. Ambient temperature significantly affected the propensity and timing of flight; between 70–80% of the parasitoids flew at 25 and 30 °C while less than 4%, mostly males, flew at 20 °C. No flights were observed at 15 °C. The presence of fresh host eggs caused a reduction in the proportion of female parasitoids that flew and a delay in the time to flight for the females that did fly. The presence of food increased the flight propensity of female parasitoids, but did not affect the timing of flight. The relationship between flight behaviour and the efficiency of mass-reared Trichogramma is discussed in terms of its importance for inundative release programmes.     

Genetic variability and interpopulational differentiation of Artemia strains from South America

Seven Artemia samples from three South American countries (Chile, Brazil, Peru) were studied by starch electrophoresis with the aim of comparing levels of genetic variation and genetic similarity to representative populations of A. franciscana (San Francisco Bay, California, USA) and A. persimilis (Buenos Aires, Argentina), which are species endemic to the New World. Based on the analysis of 22 loci, parameters measuring genetic variability were, for some populations, found to be among the highest reported for Artemia so far. The percentage of polymorphic loci varied from 31.8% (Piura, Peru; Buenos Aires) to 50% (Los Vilos and Salar de Atacama, Chile), while the observed heterozygosity varied from 0.025 (Piura) to 0.165 (Los Vilos, Chile). A dendrogram based on Nei's genetic distance (D) produced four major groups. The Argentinian form, A. persimilis; the San Francisco Bay strain together with samples from Brazil (Macau and Rio Grande do Norte) and Chile (Pichilemu and Salar de Atacama); two coastal populations from Chile (Los Vilos and Iquique) and the sample from Peru (Piura). These four groups have inter-group D values that are, in some cases, far above those normally associated with conspecific populations.     

Pathogenicity of fungal isolates (Ascomycota: Hypocreales) against Peregrinus maidis, Delphacodes kuscheli (Hemiptera: Delphacidae), and Dalbulus maidis (Hemiptera: Cicadellidae), vectors of corn diseases

Preliminary screening assays were carried out on 17 isolates from five fungal species Beauveria bassiana, Lecanicillium muscarium, Metarhizium anisopliae, Isaria farinosa, and I. fumosorosea. The three most effective isolates against Peregrinus maidis (Hemiptera: Delphacidae) were B. bassiana CEP 147, CEP 150, and CEP 189. There were no consistent differences found in males and females regarding fungal susceptibility. However, more females than males were proportionally infected. There was not a correlation between the percentage of conidial germination and the percentage of mortality caused by fungal infection in any of the treatments. Only B. bassiana CEP 147, which caused a cumulative mortality of 69.8 ± 6.4% after 7 days post-inoculation, was selected to be assayed against adults of P. maidis, Delphacodes kuscheli (Hemiptera: Delphacidae), and Dalbulus maidis (Hemiptera: Cicadellidae). In pathogenicity tests significant differences were observed among treatments. After 2 weeks post-inoculation, both D. kuscheli (cumulative mortality of 73.3 ± 9.0%) and P. maidis (cumulative mortality of 68.6 ± 6.7%) were significantly more susceptible than D. maidis (cumulative mortality of 49.9 ± 9.7%) to the selected isolate.     

Changes in host acceptance and host suitability as an effect of rearing Trichogramma maidis on a factitious host

Host acceptance and suitability of Ostrinia nubilalis Hbn. for Trichogramma maidis Pint. et Voeg. (Hymenoptera: Trichogrammatidae) were studied, after rearing the parasitoids on O. nubilalis or Ephestia kuehniella Oliv. (Lepidoptera: Pyralidae) for various numbers of generations. In cages, containing two maize plants with in total 30 egg masses of the natural host (O. nubilalis), wasps continuously reared on either E. kuehniella or O. nubilalis found egg masses in equal proportions. The former however, did not parasitize the eggs successfully, due to either low degree of host acceptance or insufficient host suitability or both. Subsequently, host acceptance behaviour of individual females from different strains was studied by means of direct observations after releasing them into a small arena containing eggs of O. nubilalis or E. kuehniella. Wasps continuously reared on O. nubilalis or 1–3 generations on E. kuehniella accepted egg masses of the natural host better than wasps continuously reared on E. kuehniella. Acceptance of O. nubilalis by the wasps gradually decreased with increasing numbers of generations reared on E. kuehniella. By rearing T. maidis, previously cultured on E. kuehniella, for five generations on O. nubilalis, acceptance of egg masses of this host species did not change. Host suitability of O. nubilalis appears to correspond with host acceptance of the strains. Contrary to the observations on O. nubilalis, acceptance and suitability of E. kuehniella were not influenced by the host on which T. maidis was reared. Results of this study show that host acceptance and suitability of the natural host are important quality factors for T. maidis when mass produced on a factitious host.

---

Zusammenfassung Wirtsakzeptanz und Wirtseignung von Ostrinia nubilalis Hbn. für den Eiparasitoiden, Trichogramma maidis Pint. et. Voeg., wurden untersucht nach der Zucht auf dem natürlichen Wirt, O. nubilalis, oder auf dem Ersatzwirt, der Mehlmotte, Ephestia kühniella Zell.. Versuche mit Käfigen, in denen je zwei Maispflanzen mit insgesamt 30 Eigelegen von O. nubilalis und 40 Weibchen von T. maidis eingesperrt waren, zeigten, dass Weibchen, die seit über 150 Generationen auf O. nubilalis bzw. E. kühniella gezüchtet worden waren, die Eigelege gleich gut fanden. Während die auf O. nubilalis gezüchteten Parasitoide die Eigelege zu 80% parasitierten, war die Parasitierungsrate der auf E. kühniella gezüchteten Parasitoide gleich Null. Die Ursachen dieses Phänomens wurden in weiteren Versuchen durch direkte Beobachtungen über Wirtsakzeptanz und Wirtseignung untersucht. Einzelne Weibchen von Stämmen, die nur auf O. nubilalis oder während einer zunehmenden Generationenzahl auf E. kühniella gezüchtet worden waren, untersuchte man während 15 Minuten unter der Stereoskoplupe in einer kleinen Arena, die ein Eigelege des Maiszünslers oder Eier der Mehlmotte enthielt. Dabei zeigte sich, dass Wespen, die ausschliesslich auf Maiszünslereiern oder nur 1–3 Generationen auf Mehlmotteneiern gezüchtet worden waren, die Eigelege von O. nubilalis besser akzeptierten als solche, die seit vielen Generationen auf E. kühniella vermehrt worden waren. Die Wirtsakzeptanz verschlechterte sich mit zunehmender Generationenzahl auf E. kühniella. Wenn T. maidis nach 23 Generationen auf E. kühniella wieder während 5 Generationen auf O. nubilalis gezüchtet wurde, verbesserte sich die Akzeptanz der Eigelege von O. nubilalis nicht. Die Wirtseignung der Eigelege von O. nubilalis, stimmt überein mit der Wirtsakzeptanz der verschiedenen Stämme. Dies ergaben Versuche mit 15 Minuten Direktbeobachtung und bei 24 Stunden Expositionszeit. Im Gegensatz zu den Beobachtungen auf Eigelegen von O. nubilalis wurde die Akzeptanz und Eignung der Eier von E. kühniella durch die Zucht auf verschiedenen Wirten nicht beeinflusst. Das Ergebnis dieser Untersuchung zeigt, dass Akzeptanz und Eignung des natürlichen Wirtes wichtige Qualitätsfaktoren für T. maidis in der Massenzucht auf Ersatzwirten sind.

     

Locomotor activity ofTrichogramma brassicae (Hymenoptera) under the influence of high-temperature shocks

In order to assess the effects of high temperatures prevailing during the releases ofTrichogramma brassicae Bezdenko parasitoid used against the European corn borerOstrinia nubilalis Hübner, we exposed wasps in the white pupa stage (WP) to single or double shocks (at 35 or 44°C for 6 h) in the laboratory. The locomotor activity of adults in the presence ofO. nubilalis egg masses is greater than in pure air. Single or double shocks at 35°C have little effect on the females. On the contrary, wasps exposed to single or double shocks at 44°C had a lower motility than control wasps.     

Ovarian cycle in immature and adult stages ofTrichogramma cacoeciae andT. Brassicae (Hym.: Trichogrammatidae)

The ovarian cycle was studied in two species ofTrichogramma, the thelytokousT. cacoeciae and the arrhenotokousT. brassicae. For both species, egg development was recorded (1) in the immature stages (2) in adult females before and after one bout of oviposition. The two species differed in the numbers of immature eggs formed and stored in the ovaries, and in the pattern of egg replenishment after oviposition.     

Observations on egg-laying behaviour of the banana weevil,Cosmopolites sordidus (Germar)

Banana weevil females laid on an average 2.7 eggs/week in rhizome material and 0.7 eggs/week in pseudostem material in the laboratory. At extremely high weevil population densities the egg-laying activity declined. Under controlled field conditions 0.7 eggs/week were laid in banana suckers and 1.3 eggs/week in stumps of harvested suckers. 25% of the weevil stages found in suckers in the field were eggs of which 78% were laid in the rhizome and 22% in the pseudostem base. The majority of eggs was deposited in the crown area of the rhizome followed by the remaining surface area of the rhizome, the walls of abandoned larval tunnels in rhizome and pseudostem and the leaf sheaths. 58% of the eggs found were considered accessible to egg predators.     

Olfactory responses ofTrichogramma maidis Pint,et Voeg.: Effects of chemical cues and behavioral plasticity

Oriented responses of Trichogramma maidisPint, et Voeg. to airborne odors were observed in a four-armed olfactometer. Experiments were carried out with odors of host eggs, the sex pheromone of Ostrinia nubilalisHbn, and maize extract, offered singly or in combination, both to naive wasps and to wasps previously exposed to the tested odor during an oviposition experience. The exploratory behavior in the olfactometer was quantified by means of a computer program which performed a space-time analysis of the insect 's movements. Whereas the naive wasps did not respond to the odor of the eggs, the synthetic sex pheromone of O. nubilalis,or the maize extract presented singly, they did react to a mixture of these three volatile cues. Prior oviposition in the odor of maize extract or in the combination of odors induced an increased preference toward the conditioning scent. This phenomenon did not occur when the wasps were conditioned to egg odor or sex pheromone alone. These results suggest that females can learn to associate some olfactory cues with the presence of the host. Immediately following the presentation of the combination of odors, a strong attraction of experienced wasps occurred; it decreased as the experiment progressed and finally reached the level presented by naive insects. Adult conditioning to the combination of odors also resulted in reduced variability in the behavioral responses.     

Identification of compounds from the eggs of Ostrinia nubilalis and Mamestra brassicae having kairomone activity on Trichogramma brassicae

In the presence of an extract of Ostrinia nubilalis or Mamestra brassicae eggs, female Trichogramma brassicae exhibited increased rates of upwind locomotion in the tubes of a linear olfactometer. GC and GC-MS analyses of O. nubilalis and M. brassicae egg extracts revealed the presence of fatty acids, their ethyl esters, and various hydrocarbons. Exposing the wasps to a mixture of the five main saturated hydrocarbons (heneicosane, tricosane, pentacosane, heptacosane and nonacosane) increased the upwind progression in the olfactometer. Single hydrocarbons elicited reduced or no activity. Ethyl palmitate and palmitic acid were also effective in increasing upwind locomotion. Z11-14:Ac, the main component of the female sex pheromone of O. nubilalis was inactive, regardless of its concentration. It is concluded that various compounds present on the surface of the O. nubilalis egg masses may play a role in the orientation of T. brassicae to its host.     

Genetic variability of fragmented stands of pedunculate oak (Quercus robur) in Finland

The genetic structure of 33 natural Quercus robur stands in Finland was studied using 13 allozyme loci to analyze the effects of fragmentation in a wind-pollinated tree species. The present fragmented and discontinuous distribution of oak is a result of both short-term human impact and long-term climatic and geological change, including post-glacial land uplift. In accordance with general expectations, genetic diversity in small populations was lower than that in large populations, and differentiation among small populations was higher than that among large populations. Heterozygote deficiency was more pronounced in large populations, which is proposed to be a Wahlund effect created by either spatial sub-structuring or the existence of synchronized flowering lineages. Also genetic differentiation was higher and diversity lower in Finland than the estimates reported for Central Europe. There were differences in the genetic structure on sites of different geological age. We suggest that on most geologically old sites drift has a prominent effect whereas on younger sites also founder effects may be important.     

Isoenzyme patterns and biology ofTrichogramma minutum as influenced by rearing temperature and host

Females ofTrichogramma minutum Riley reared at temperatures below 17°C had lower percent emergence, lower fecundity on the first day of emergence, and a reduced rate of population increase (r_i) than those reared at temperatures above 17°C. Parasitoids were more fecund and lived longer when raised onChoristoneura fumiferana (Clemens) compared toEphestia kuehniella (Zeller). The parasitoids performed better when parasitizing the same species of host on which they had been reared. Isoenzyme patterns were not affected whenT. minutum was reared at 13 or 27°C but additional bands appeared when parasitoids were reared onSitotroga cerealella (Olivier) compared toC. fumiferana. No correlation could be made between biological and biochemical changes inT. minutum. Isoenzymes have the potential to assess the quality of parasitoids during mass production.

---

Einfluss von Zuchttemperatur und Wirt auf Isoenzymmuster und Biologie vonTrichogramma minutum Riley

Zusammenfassung Weibchen vonTrichogramma minutum, welche bei 17°C gezüchtet wurden, hatten eine geringere Schlüpfrate, eine geringere Fruchtbarkeit am ersten Tag nach dem Schlüpfen sowie ein reduziertes Populationswachstum (r_i) im Vergleich zu Tieren welche sich bei Temperaturen über 17°C entwickelt hatten. Wurden die Parasitoiden aufChoristoneura fumiferana gezogen, so war ihre Fruchtbarkeitsrate wie auch Lebensdauer grösser als wennEphestia kuehniella als Wirt diente. Die parasitische Fähigkeit vonT. minutum war immer auf derjenigen Wirtsart am grössten auf der die Schlupfwespen vorher gezogen wurden. Aufzuchttemperaturen von 13°C oder 27°C hatten keinen Einfluss auf den Isoenzymbändern wenn die Tiere statt aufC. fumiferana aufSitotroga cerealella gezogen wurden. Es konnte aber kein Zusammenhang zwischen den biologischen und biochemischen Veränderungen gefunden werden. Hingegen besteht die Möglichkeit während der Massenproduktion die Qualität der Parasitoiden anhand von Isoenzymprofilen zu überwachen.

     

Trichogramma platneri (Hym.: Trichogrammatidae): Host choices between viable and nonviable codling moth,Cydia pomonella,and three-lined leafroller,Pandemis limitata (Lep.: Tortricidae) eggs

In laboratory host-preference studies,Trichogramma platneri Nagarkatti (Hym.: Trichogrammatidae) females, reared on viable codling moth,Cydia pomonella (L.) (Lep.: Tortricidae) eggs, parasitized significantly more viable than nonviable codling moth eggs produced by cobalt 60 irradiated adults. This ovipositional preference was maintained when competition increased per host egg. Similarly, one, three and fiveT. platneri females consistently oviposited more eggs into viable versus nonviable host eggs. A single femaleT. platneri parasitized a similar number of viableC. pomonella and three-lined leafroller,Pandemis limitata (Robinson) (Lep.: Tortricidae) eggs. However, as the number of females per host eggs increased, a significantly larger number of codling moth versus leafroller eggs were parasitized. One, three and fiveTrichogramma females parasitized significantly moreP. limitata versus nonviableC. pomonella eggs. NonviableC. pomonella eggs deflated to less than 25% of their original volume in four and ten days when held under dry and humid conditions respectively. The blackened prepupal stage of the parasitoid generally occurred in the nonviableC. pomonella eggs four days post-parasitization whereas the parasitized viable eggs blackened zero to one day earlier. Incubation under dry or humid conditions did not appear to influence the number of parasitized eggs that were able to blacken and show evidence of parasitism. Summerland Research Centre Contribution No. 938.     

Genetic variability in the reactive distance inTrichogramma brassicae after automatic tracking of the walking path

Efficiency of hymenopterous parasitoids to control pests in a biological control release program probably increases with increasing searching ability of the females, which, in return, likely depends on the distance from which females perceive their hosts (i.e., reactive distance). In this study, we first analyse this hypothesis with the help of a stochastic model simulating the walking path of isolatedTrichogramma females during their searching behaviour. Then, this reactive distance is estimated using automatic recording and analysis of the walking path of female wasps. Finally, the genetic variability for this trait is analysed in aTrichogramma brassicae Bezdenko (Hym.; Trichogrammatidae) population. Three types of hosts were used: Eggs ofEphestia kuehniella Zeller (Lep.; Pyralidae), eggs ofMamestra brassicae L. (Lep.; Noctuidae) and 0.45 mm glass beads.M. brassicae eggs are perceived from 4.01±0.15 mm, which is a significantly longer perceptive distance than forE. kuehniella eggs (3.69±0.10 mm) and glass beads (3.67±0.10 mm). Moreover, whatever the host tested, a significant genetic variation is observed in this trait in the population studied. The ecological and evolutionary implications and the agronomical importance of these results are discussed.     

Overwintering of the egg parasitoid Trichogramma brassicae in Northern Switzerland

As part of a general risk assessment study weinvestigated the overwintering abilities ofTrichogramma brassicae Bezd. (Hym.: Trichogrammatidae) in Northern Switzerland. Eggs of six host species parasitized by T. brassicae were exposed under outdoor conditions every two weeksbetween 26 September and 7 November 1998. Wefound that T. brassicae is able tooverwinter successfully on six lepidopteranspecies in the families Tortricidae, Noctuidae,Plutellidae, Pyralidae and Crambidae. Between75 and 100% emergence was observed in thefollowing spring for all of the six tested hostspecies exposed on 26 September. On laterexposure dates, spring emergence decreasedsignificantly and no development of T. brassicae offspring occurred from host eggsparasitized on 7 November.Emergence of T. brassicae from eggs ofEphestia kuehniella Zeller parasitized atweekly intervals in autumn 1999 occurred in thesame year until the end of October if the eggswere parasitized by 10 September. All offspringfrom eggs that were parasitized from 17September onwards went into diapause. Springemergence of T. brassicae adults wasobserved between end of April and beginning ofMay both in 1999 and 2000. Fecundity of T.brassicae females that overwintered on E.kuehniella was not significantly different fromthe fecundity of control females that werereared without diapause under optimalconditions at 25 °C. Our resultsdemonstrate that the egg parasitoid T.brassicae is able to overwinter successfullyin Northern Switzerland and has the potentialto establish in Switzerland. As a result,potential non-target effects are not locallyrestricted but may occur on a largegeographical scale.     

The influence of host's age on the selectivity of parasitism and fecundity ofTrichogramma

Laboratory studies showed that ♀♀ ofTrichogramma embryophagum (Hartig) andT. semblidis (Aurivillius) when offered an alternative of young and old eggs of the grain moth,Sitotroga cerealella Oliv., prefer ovipositing into young eggs. The fecundity of ♀♀ that are simultaneously offered both young and old eggs was lower in comparison to ♀♀ offered only young eggs (inspite of the fact that in both variants young eggs were in excess). The results suggest that old eggs can inhibit the oviposition of some species ofTrichogramma.      

Increased survival of Dalbulus maidis, a specialist on maize, on non-host plants infected with mollicute plant pathogens

The leafhopper Dalbulus maidis DeLong & Wolcott survived significantly longer on aster, Callistephus chinensis Nees, infected with any one of 3 strains of aster yellows (AY) mycoplasma-like organism (MLO) than on healthy asters. After 7 or more days on AY-diseased aster, females were conditioned to survive longer on healthy asters than were leafhoppers of the same age previously exposed only to maize. Females were also conditioned to survive longer on healthy aster by prior exposure to AY-MLO-infected celery (Apium graveolens L.). Males were not so conditioned. Leafhoppers injected with infectious extracts of AY-MLO dit not live longer on aster nor transmit the AY-MLO to aster. Conditioning on AY-diseased aster did not cause D. maidis to transmit AY-MLO and did not interfere with the transmission to maize of the mollicute (Spiroplasma kunkelii Whitcomb et al.) that causes corn stunt disease. Spiroplasma citri Saglio et al. infection of aster but not of turnip (Brassica rapa L.), Plantago major L. or periwinkle (Catharanthus roseus (L.)), improved the longevity of D. maidis on these plants and conditioned leafhoppers for enhanced subsequent survival on healthy asters.

---

Résumé La cicadelle du maïs, D. maidis à survécu significativement plus longtemps sur aster (Callistephus chinensis Nees) contaminé par l'une des trois souches de l'agent mycoplasmique (MLO) de la jaunisse de l'aster (AY), que sur des asters sains. Après 7 jours ou plus sur des asters AY-MLO, les femelles (et non les mâles) étaient conditionnées de telle sorte qu'elles survivaient plus longtemps sur asters sains que des femelles du même âge précédemment sur maïs. Sur des céleris (Apium graveolens) atteints de AY, D. maidis a survécu plus longtemps que sur céleri sain, mais moins que sur aster AY. Des extraits, contaminés par AY injectés à D. maidis n'ont pas augmenté sa longévité sur aster, ni provoqué la transmission de AY-MLO. Le conditionnement sur aster AY n'a pas entrainé la transmission de AY-MLO par D. maidis, et n'a pas interferé avec son aptitude à transmettre l'agent du nanisme du maïs, Spiroplasma kunkelii. S. citri a aussi conditionné D. maidis sur aster, mais a été sans effet sur navet (Brassica rapa), sur plantain (Plantago major) et sur pervenche (Vinca).