Aspects of life-table studies and functional response of Lysiphlebia mirzai

The fecundity, reproductive rate, and survival of Lysiphlebia mirzai parasitising third instar nymphs of the cereal aphid Rhopalosiphum maidis were measured at six different host densities under constant laboratory conditions. The survival rate (l_x) of the female parasitoids was unaffected by host density, with an average adult life-span of 5–6 days at all densities. The age-specific fecundity rate (m_x) was host density-dependent. The value of m_x decreased rapidly from the first day of parasitisation. The number of hosts available determined the maximum possible number of mummies. At 200 hosts available per day, the average fecundity was 184.6 mummies/female; the maximum number of mummies yielded by any female was 200. The relationship between host density and the number of aphids parasitised per female was linear at 50 aphids/cage/day, but at higher host densities (100 aphids/cage/day) a significant curvilinear regression was observed. The intrinsic rate of natural increase (r_m) increased with increasing host density. Maximum value of r_m (0.262) was obtained at a host density of 200. The response of r_m to changes in host density and parasitoid sex ratio is shown. A typical type II functional response was observed for L. mirzai. The curve was described by a logistic curve, N_p=200/[1+exp(5.65–1.60 ln N_o)]. The search rate of the parasitoid was inverse host density-dependent. No significant variation in the sex ratio of F₁ offspring was observed at different initial host densities. Sex ratio values exceeded 0.5 at all host densities. The results evaluated the reproductive potential of L. mirzai as a promising biological control agent.     

Effects of parasitism by Praon pequodorum on age-specific fecundity and population growth of the pea aphid, Acyrthosiphon pisum

The effects of parasitism by Praon pequodorum Viereck (Hymenoptera: Aphidiidae) on the survival, development and reproduction of apterous pea aphids, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), were studied in the laboratory. Ten cohorts of aphids differing in age from 0.5 h to 9 days were tested. At 20°C, pea aphids survived an average of 7 days after parasitization. Parasitized first and second instars died before reaching the adult stage. Third instars died as adults but without producing any offspring. Parasitized fourth instars and adult aphids produced a variable number of offspring; their mean total fecundity increased as an exponential function of the age at parasitization. Host age did not significantly affect the period from the beginning of parasitism to the end of reproduction. Equations are provided to estimate the length of the reproductive period, the total fecundity, the intrinsic rate of increase, and the doubling time as functions of aphid age at parasitization. The data are discussed with regard to host population growth. It is shown that a parasite's potential impact on an aphid population is critically dependent on its preference for and successful oviposition in early host instars.

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Résumé Les effets du parasitisme par P. pequodorum Viereck (Hym.: Aphidiidae), sur la survie, le développement et la reproduction des aptères de A. pisum, ont été examinés au laboratoire. L'étude a porté sur 10 cohortes de pucerons dont les âges différaient de 0,5 heure à 9 jours. A 20°C, les pucerons parasités ont survécu en moyenne pendant 7 jours après avoir été parasités. Leur évolution ultérieure dépend au stade auquel ils ont été parasités: au premier et second stades, ils sont morts avant de devenir adultes; au troisième stade, ils sont morts adultes avant de se reproduire; au quatrième stade et adultes, ils ont donné un nombre variable de descendants. La fécondité totale moyenne a crû comme une fonction exponentielle de l'âge au moment où ils avaient été parasités. L'âge de l'hôte n'a pas modifié significativement la durée de la période entre le moment où ils ont été parasités et la fin de la phase de reproduction. Des équations ont été établies en fonction de l'âge des pucerons au moment où ils ont été parasités, pour estimer la longueur de la période de reproduction, la fécondité totale, le taux intrinsèque d'accroissement et le temps de doublement des cohortes de pucerons. Les résultats sont discutés sous l'angle de la dynamique de la population. On en déduit que l'impact potentiel d'un parasite sur une population de pucerons dépend d'abord de ses préférences pour les premiers stades de l'hôte et du succès de sa ponte sur ces stades.

     

Effect of host age at parasitization by Aphidius sonchi on the development, survival, and reproduction of the sowthistle aphid, Hyperomyzus lactucae

Nineteen cohorts of Hyperomyzus lactucae (L.) (Homoptera: Aphididae) reared at various temperaturelight regimes were exposed to attack by Aphidius sonchi Marshall (Hymenoptera: Aphidiidae) at different ages of their development. Irrespective of host age at the initial parasitization and rearing conditions, the rates of reproduction, development and survival were unaffected until the parasites within had completed approximately 30, 40 and 55% of their total development respectively. As a result, aphids parasitized in the first or early second instar failed to reach maturity. Thereafter, the numbers of young produced by parasitized aphids increased rapidly as the age of the hosts at initial parasitization increased, and aphids parasitized 3 days after the final moult or later showed similar potential to contribute to future population increase.In comparison with the effects on host moulting, those on wing development of the potentially alatiform nymphs appeared much sooner after the beginning of parasitization, but again with the time lags being more or less independent of host age at the initial parasite attack. Consequently, the extent of wing development depended entirely on the age of the hosts when attacked.These results showed that the age of the host at the initial parasite attack is crucial in determining the consequences of parasitization on the host.

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Résumé Dix-neuf cohortes d'Hyperomyzus lactucae L. (Homoptera: Aphididae), élevées dans différentes conditions de lumière et de température, ont été exposées à différents moments de leur développement aux attaques d'Aphidius sonchi Marsh. (Hym. Aphidiidae). Quels que soient les conditions d'élevage et l'âge des pucerons quand ils ont été parasités, la survie, le développement et la reproduction n'ont été affectés que lorsque les parasites avaient accompli 30, 40 et 55% de leur développement total. Ainsi, les pucerons parasités au premier stade ou au début du second ne parvenaient pas à atteindre la maturité. Par la suite, le nombre de jeunes produits par les pucerons parasités a cru rapidement au fur et à mesure que l'âge de ces derniers au moment où ils avaient été parasités la dernière mue ou plus tard présentaient la même potentialité pour contribuer à l'accroissement ultérieur de la population.Comparés aux effets sur la mue, les effets sur le développement alaire des larves potentiellement ailées apparaissent beaucoup plus tôt après le moment où le puceron a été parasité, mais là aussi avec des délais plus ou moins indépendants de l'âge de l'hôte lors de la première attaque du parasite. Par conséquent, le degré de développement des ailes dépendait totalement de l'âge du puceron lorsqu'ila été parasité.Ces résultats ont montré que l'âge du puceron lors de la première attaque détermine les conséquences du parasitisme de l'hôte.

     

Cotesia plutellae parasitizing Plutella xylostella: Host-age dependent parasitism and its effect on host development and food consumption

The braconid Cotesia plutellae(Kurdjumov) (Hymenoptera: Braconidae) is amajor solitary, larval endoparasitoid of thediamondback moth, Plutella xylostella(L.) (Lepidoptera: Plutellidae). Parasitism oflarvae of different host instars and fourdevelopmental ages of the 4th instar ofthe pest was examined. The effects of hostinstar at initial parasitization on thedevelopment, survival, size and fecundity ofthe parasitoid were determined in thelaboratory at 25 °C. The effects ofparasitism on host development and foodconsumption were investigated at 28 °C.Cotesia plutellae could parasitize larvaeof all four instars of P. xylostella, butpreferred 2nd and 3rd instars. In achoice test, the relative parasitism indicesfor 2nd, 3rd and 4th instarswere 0.37, 0.39 and 0.24, respectively.Parasitism decreased sharply with increasinghost age in the 4th instar and approachedzero in host larvae that had gone beyond 37%of 4th stadium. The development time andthe final adult size of the parasitoid variedwith the host instar at initial parasitization.Parasitoids with initial parasitism in the4th instar hosts had the shortestdevelopment time, followed by those in the3rd instar, and then by those in the2nd instar. Parasitoids startingparasitism in 2nd instar hosts weresmaller in body size than those starting in the3rd or 4th instar. However, resultantfemales starting parasitism in 3rd instarhosts had the highest fecundity. Parasitizedlarvae exhibited longer development time andincreased food consumption compared withunparasitized ones. This study presents thefirst record that a solitary parasitoidregulates host behavior leading to an increasein food consumption by the host.     

Host plant relationships and life cycles of the aphid genusCryptomyzus

The host plant relationships of the aphid genusCryptomyzus were studied by field sampling and laboratory experiments. Host plant suitability and host plant preference were assessed in the laboratory using parthenogenetic females of the summer generations (exules). Differences in reproductive performance and host plant preference were found between closely related taxa ofC. galeopsidis. Host plant preference was correlated with reproductive performance in these forms ofC. galeopsidis. This indicated that evolutionary divergence has occurred and this justifies their status as separate species. It did not prove possible to induce an improvement in the performance of theC. galeopsidis fromLamium galeobdolon onGaleopsis tetrahit, the host plant of a closely related taxon. The life cycles and host plant relationships ofCryptomyzus are defined, including the previously unknown life cycles ofC. heinzei, C. ballotae and two forms ofC. galeopsidis. The results are discussed in relation to host use and their significance for differentiation between closely related aphid taxa.

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Résumé Les relations des pucerons du genreCryptomyzus avec leurs plantes hôtes ont été étudiées dans la nature et au laboratoire. L'adéquation de la plante et le choix de l'insecte ont été examinés au laboratoire sur des femelles parthénogétiques des générations estivales (exules). Les différences de performances reproductives et de choix des hôtes étaient liées étroitement à la position taxonomique deC. galeopsidis; chez ces formes deC. galeopsidis les choix entre hôtes étaient liés aux performances reproductives. Ceci indique qu'il y a eu une divergence évolutive et justifie leur statut d'espèces distinctes. Ceci ne prouve pas qu'il soit possible d'induire une amélioration des performances deC. galeopsidis deLamium galeobdolon surGaleopsis tetrahit, plante hôte d'un taxon voisin. Les cycles et les relations avec les plantes hôtes de tous les taxa deCryptomyzus ont été précisés, y compris pour les cycles jusqu'alors inconnus deC. heinzei, C. ballotae et de 2 formes deC. galeopsidis. Ces résultats sont discutés en fonction de l'utilisation de l'hôte et de leur signification pour la différenciation de taxa très voisins de pucerons.

     

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.      

Effects of host age on parasitism and progeny allocation in Trichogrammatidae

The impact of host age on the number of hosts killed, survival of progeny, progeny allocation, and sex allocation was examined for several Trichogrammatidae (Hymenoptera) species in laboratory choice tests. Individual female parasitoids were provided with young, medium-aged and old eggs of one of three lepidopterous host species: Trichoplusia ni (Hübner) (Noctuidae), Pieris rapae (L.) (Pieridae), or Plutella xylostella (L.) (Plutellidae). Trichogrammatid species behaved as gregarious parasitoids with the first two host species, and as solitary parasitoids with eggs of the smaller latter one. They mostly preferred young eggs of T. ni, but did not discriminate among P. rapae eggs of different ages, and often preferred young or medium-aged P. xylostella eggs over old eggs. Survival of progeny did not vary constantly with host age, although it was often very low in P. rapae eggs of any age. Clutch size frequently decreased with host age in both T. ni and P. rapae. Offspring sex ratio did not change with age of T. ni and P. rapae eggs, and rarely did so in P. xylostella eggs. In regard to host age, the results with T. ni are the ones which are the most in agreement with optimal foraging theoretical predictions, as clutch size was the highest in preferred younger eggs.     

Reciprocal influences and costs of parasitism on the development of Corcyra cephalonica and its endoparasitoid Venturia canescens

Many endoparasitoids develop successfully within a range of host instars. Parasitoid survival is highest when parasitism is initiated in earlier host instars, due to age-related changes in internal (physiological) host defences. Most studies examining fitness-related costs associated with differences in host instar have concentrated on the parasitoid, ignoring the effects of parasitism on the development of surviving hosts that have encapsulated parasitoid eggs. A laboratory experiment was undertaken examining fitness-related costs associated with encapsulation of Venturia canescens (Hymenoptera: Ichneumonidae) eggs by fifth (L5) instar larvae of Corcyra cephalonica (Lepidoptera: Pyralidae). Growth and development of both host and parasitoid were monitored in C. cephalonica larvae containing 0, 1, 2, or 4 parasitoid eggs. Adult size and fecundity of C. cephalonica did not vary with the number of eggs per host. However, there was a distinct increase in host mortality with egg number, although most parasitoids emerged from hosts containing a single egg. The most dramatic effect on the host was a highly significant increase in development time from parasitism to adult eclosion, with hosts containing 4 parasitoid eggs taking over 2.5 days longer to complete development than unparasitized larvae. The egg-to-adult development time and size of adult V. canescens did not vary with egg number per host, as demonstrated in a previous experiment using a different host (Plodia interpunctella). The results described here show that there are fitness-related costs to the host associated with resistance to parasitism.     

Influence of host species and age on host preference of Trissolcus semistriatus

Trissolcus semistriatus(Hymenoptera: Scelionidae) has a high potentialfor being an effective biological control agentfor the sunn pest, Eurygaster integriceps.This study was conducted to determine thepreferences of T. semistriatus in termsof host species and age of variousheteropteran host eggs (E. integriceps,Dolycoris baccarum, Graphosoma lineatum,Eurydema ornatum, Holcostethus vernalis). Theresults indicated that a small portion ofparasitism of E. ornatum eggs wasobtained (28.5%), although high parasitismrates were found in other host eggs(90.0–80.0%). A high percentage of adultemergence was also recorded. When tested for its ability toparasitize host eggs of different ages,T. semistriatus was found to preferyounger hosts: it showed parasitism ratesgreater than 50% with up to 3 daysold E. integriceps and D.baccarum, and with up to 4 days old G. lineatum and H. vernalis. However, theparasitism rates in all the ages of E. ornatum eggs were much lower than for other hostspecies. The developmental times in all hostspecies at different ages was extended withincreased host age. It was concluded that G. lineatum and D. baccarum could beused for mass production of egg parasitoids.     

Feeding behavior ofEuseius stipulatus andTyphlodromus phialatus on the citrus red mitePanonychus citri [Acari: Phytoseiidae,Tetranychidae]

Observations were made on the feeding behavior of the two main phytoseiid species in Spanish Citrus orchards,Euseius stipulatus (Athias-Henriot) andTyphlodromus phialatus Athias-henriot. The experiences were carried out by rearing the predatory mites on excised orange leaves, and always with an excess of the prey the Citrus Red Mite (=CRM)Panonychus citri (McGregor). In experiments with all stages of CRM, the number of prey killed per hour was 5.12 and 2.00, the percentage of successful attacks, 58% and 21%, and the mean time spent feeding on each prey was 5.1 and 12.2 minutes for starving females ofE. stipulatus andT. phialatus respectively.E. stipulatus feeds on all stages of the prey except eggs, andT. philatus, on all stages, except males. Both species attack much less successfully females ofP. citri rather than immatures. In experiments with adult females and eggs ofP. citri as prey, the mean number of prey killed daily was 4.51 females forE. stipulatus, and 2.01 females and 2.12 eggs forT. philatus. Considering this killing rate and the number of eggs laid by the predators in the same period, it can be concluded thatE. stipulatus consumes only 30% of the content of the preys killed, whereasT. philatus consumes a percentage of prey variable between individuals and ranging from 40% to 100%. These differences in feeding behavior between the two species could partly explain differences in their efficiency as biocontrol agents ofP. citri observed in the field.      

Host regulation by the aphid parasitoid Aphidius ervi: the role of teratocytes

The biochemical profile and metabolism of Acyrthosiphon pisum(Harris) (Homoptera, Aphididae) are markedly altered and redirected in response to parasitization by the endophagous braconid Aphidius erviHaliday (Hymenoptera, Braconidae). In the present study, the role played in the host regulation process by teratocytes, cells deriving from the dissociation of the embryonic membrane of the parasitoid, is taken into consideration. The protein synthesis activity of these cells of embryonic origin is analysed in vitroand an essential characterization of those proteins de novosynthesized and released in the incubation medium is provided. Teratocytes, obtained by dissecting parasitized host aphids, 3, 4 and 5 days after parasitoid oviposition, were incubated in vitroand, at the end of the incubation period, were separated from the medium for SDS-PAGE analysis of both cellular and secreted proteins. Various cellular proteins were more abundant as the time between parasitization and teratocyte collection increased. Furthermore, two proteins, showing an approximate molecular mass of 15 kD (p15) and 45 kD (p45) respectively, were abundantly secreted in the incubation medium by 5 day-old teratocytes. Incubations in presence of ³⁵S radiolabelled amino acids indicated that p15 and p45 are both synthesized by A. erviteratocytes. The amino acid composition of these two proteins was similar to that reported for other insect proteins with a demonstrated nutritional function. The p45 protein was found to be glycosylated. A tentative physiological model describing the host regulation role played by different parasitoid-derived factors is proposed.     

Host plant changes produced by the aphid Sipha flava: consequences for aphid feeding behaviour and growth

Induced plant responses may affect the behaviour and growth of the attacking herbivore insect. The aphid Sipha flava (Forbes) produces reddish spots on the infested leaf of its host plant Sorghum halepense (L.). In order to assess the consequences on the aphid of this presumptive induced plant response, we studied the feeding behaviour and growth of S. flava on previously infested and non-infested leaves of S. halepense. Considering that the reddish pigment could play a defensive role, its effect on aphid survival was determined in artificial diets. In addition, changes in the histology of the leaf and the chemical nature of the induced pigment were also studied. Aphids devoted a significantly shorter total time to non-penetration activities in infested than in non-infested leaves. Time before the first phloem ingestion tended to be shorter in infested leaves. The mean relative growth rate of S. flava nymphs was significantly higher on infested than on non-infested leaves. Survival of aphids on diet containing the reddish extract was not significantly different from that on the control diet. Infestation of S. halepense by S. flava produced a reddish coloration in the leaf, which was identified as an anthocyanin by UV-visible spectrometry. Light microscopy showed that only mesophyll cells of previously infested plants presented swelled, dispersed, and heterogeneously stained chloroplasts with a higher accumulation of starch granules, no grana arranged in stacks, and reduction in the amount of inner membranes (thylakoids), relatively to chloroplasts of non-infested leaves. Scanning electron micrographs of leaf surface revealed reduced presence of crystalline epicuticular waxes of epidermal cells in infested leaves as compared to non-infested ones. The main conclusion is that the attack of S. flava to S. halepense leaves induced plant susceptibility where aphid feeding behaviour and growth were both enhanced on previously infested leaves.     

Effects of the concurrent exclusion of ants and earwigs on aphid abundance in an organic citrus grove

Based on the well-known mutualism between ants (Hymenoptera: Formicidae) and aphids (Homoptera: Aphididae), we conducted a five-year experiment of ant-exclusion from the canopies of citrus trees as a possible method of biological control of aphids. However, our results showed that the exclusion of ants from the canopies increased, instead of reducing, aphid abundance. To explain this unexpected result, we reasoned that the exclusion of ants from the canopies might also have excluded crawling insects that prey on aphids, such as the European earwig (Forficula auricularia L., Dermaptera: Forficulidae). Such a possibility is supported by the negative relationship between aphid density and the abundance of earwigs, consistent with a top-down control of aphids by earwigs. In contrast, the abundance of other aphid predators (Coleoptera: Coccinellidae, and Heteroptera) had no such negative effect on aphid density but a positive one, suggesting a bottom-up control, and showed no differences between control and ant-excluded trees. Thus, the most likely explanation for the increase in aphid abundance in the ant-excluded trees is the absence of earwigs from the canopies of the experimental trees, providing further evidence of the major role that earwigs play as control agents of aphids in cultivated trees.     

Parasitism ofTrialeurodes ricini byEncarsia formosa: Level of parasitism,development time and mortality on different host plants

The effects of the host plant on the level of parasitism, development time and mortality ofEncarsia formosa Gahan parasitizing castor whitefly,Trialeurodes ricini Misra were studied. The level of parasitism varied significantly between host plants; ranging from an average high of 13/50T. ricini larvae parasitized per parasitoid per day on aubergine to an average low of 1.6/50 host larvae on potato. Development time ofE. formosa varied according to whitefly host plant; minimum average development time was 17.7 days on cotton. The mortality ofE. formosa was high on all host plants tested, and the type of host plant had no significant influence on mortality. Aubergine proved to be the most satisfactory laboratory plant for rearingE. formosa onT. ricini.     

Host discrimination and larval competition in the aphid parasite Ephedrus californicus

Naive and experienced females of Ephedrus californicus Baker (Hymenoptera: Aphidiidae) were tested for their ability to discriminate between parasitized and unparasitized pea aphids, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae). Attacks lasting 6 s generally resulted in oviposition; the average length was 11.8 s. The proportion of parasitized aphids that was rejected varied with the interval length between attacks. It is suggested that host discrimination is time-dependent and can be induced by a pheromone-like external marker left by a first-attacking female (0–9 h), or by changes in host quality associated with parasite development ( 14 h). Experienced, but not naive, females responded to the external marker, which became less effective with time. In superparasitized aphids, the older of two E. californicus larvae usually eliminated a younger competitor; but younger larvae survived under certain conditions. Mechanisms for the elimination of supernumerary larvae varied with the relative developmental stage of the competitors and included physical combat and physiological suppression. Host instar had no effect on larval competition or the female's ability to discriminate.

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Résumé L'aptitude à choisir entre Acyrthosiphon pisum Harris (Hom. Aphididae) parasités ou non a été examinée chez des femelles nouvelles ou expérimentées d'E. californicus Baker (Hym. Aphidiidae). Les attaques durant 6 s étaient généralement suivies de pontes; la durée moyenne d'une attaque était 11,8 s. La proportion de pucerons parasités refusés, variait avec le laps de temps écoulé entre des attaques. Les femelles nouvelles aussi bien qu'expérimentées rejetaient généralement les pucerons contenant les stades les plus âgés de parasites (13–15 h). Cependant, seules les femelles expérimentées évitaient de pondre dans des pucerons attaqués par une autre dans les 9 h précédentes. Quand des femelles expérimentées pouvaient choisir entre 20 pucerons parasités et 20 pucerons sains, en moyenne 73% des 20 premières attaques étaient sur pucerons sains pour des intervalles 9 h. Des attaques non suivies de pontes, c'est-à-dire durant 5 s, n'intervenaient que pour 3% parmi toutes les premières attaques sur pucerons sains; ces attaques atteignaient ultérieurement 17% pour les pucerons sains et 40% pour les parasités.On en a déduit que la sélection des hôtes est temporelle et peut-être induite par un marqueur externe type phéromone, laissé par la lère femelle attaquante (0–9 h), ou par un changement dans la qualité de l'hôte lié au développement du parasite. Les femelles expérimentées, et non les nouvelles, répondaient au marqueur externe, dont l'efficacité diminue avec le temps.Chez les pucerons superparasités, les mécanismes pour l'élimination des larves en surnombre ont varié avec le stade larvaire des compétiteurs, ils comportaient un combat physique et une suppression physiologique. La larve de E. californicus la plus âgée éliminait généralement une compétitrice plus jeune. Cependant les larves les plus jeunes ont survécu dans certaines conditions; c'est-à-dire quand les premiers stades mandibulés luttaient contre les 2e et. 3e stades sans mandibules. Le stade de l'hôte était sans effet sur la compétition ou sur l'aptitude au choix des femelles.

     

Incidence of parasitism by Aphidius rhopalosiphi in colour forms of the aphid Sitobion avenae

Aphidius rhopalosiphi parasitises green colour forms of Sitobion avenae more frequently than brown forms. The handling time is longer for brown than for green nymphs, even when the two forms are members of the same clone. Parasite development lasts longer in brown forms than in green forms, and mortality is higher.

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Résumé A. rhopalosiphi a parasité les stades jeunes de S. avenae avec plus de succès que les stades âgés, et les types verts plus fréquemment que les bruns. Dans tous les cas, la mortalité était élevée; significativement plus de pucerons du premier et du second stade ont été tués par l'attaque du parasite que ceux des 3è et 4è stades. La fréquence de pucerons bruns formant des momies a augmenté avec le nombre de pipûres, de 0,1 pour une piqûre à 0,4 pour 8 piqûres. Lorsqu'il n'y a qu'une piqûre, le nombre d'oeufs émis est le même pour les deux types. A 20–22 °C, le développement du parasite dure jusqu'à 9 jours dans les pucerons verts et 12 jours dans les bruns. Lorsqu'il y a choix, les parasites préfèrent les verts aux bruns (Même quand ils sont du même clone) et les bruns clair aux bruns sombres. Les verts ont besoin de moins de rencontres que les bruns pour être piqués, mais pour une souche de parasites recueillie depuis peu, la différence était faible, pourtant cette nouvelle souche ne parasitait pas les pucerons bruns avec plus de succès que l'ancienne souche.

     

Host-habitat conditioning in the eulophid egg parasitoid, Edovum puttleri: effects of herbivore's host and its food plant

The egg parasitoid, Edovum puttleri Grissell, was cultured from eggs of two Leptinotarsa hosts, L. decemlineata (Say) and L. texana Schaeffer, and experienced on eggs from three L. decemlineata food plants, namely potato, Solanum tuberosum tuberosum L., eggplant, S. melongena L., and tomato, Lycopersicon esculentum Mill. Host preference of the various cultures was determined using choice tests. parasitoid choices were influenced by the Leptinotarsa rearing host. Wasps, reared from L. decemlineata eggs from a mixture of all three food plants and experienced on egg masses from all three food plants, preferred to parasitize egg masses from potato. Wasps, reared from L. texana eggs from silver leaf nightshade, S. elaeagnifolium L., and experienced on egg masses from all three food plants, preferred to parasitize egg masses from tomato. Choices were also influenced by the herbivore's food plant that wasps were conditioned to. Wasps, reared from L. texana and experienced on egg masses from potato, preferred to parasitize egg masses from potato. Wasps, reared from L. decemlineata on potato and experienced on egg masses from potato, preferred to parasitize egg masses from potato. Wasps, reared from L. decemlineata on tomato and experienced on egg masses from tomato, did not display a distinct host preference. Within-egg mass parasitism (i.e., number of eggs per mass that were parasitized, probed, etc.) did not consistently differ among the three food plants. The implications of these data in parasitoid ecology and biological control programs for L. decemlineata are discussed.

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Résumé L'oophage, E. puttleri a été élevé à partir des oeufs de Leptinotarsa decemlineata et L. texana. Il a été mis en expérience sur l'une des 3 plantes consommées par L. decemlineata: Solanum tuberosum tuberosum, S. melongena et Lycopersicon esculentum. Des expériences de choix ont permis de déterminer ses préférences pour les différentes catégories d'oeufs. Le choix de l'oophage est influencé par l'espèce de Leptinotarsa sur laquelle il a été élevé. E. puttleri élevé sur oeufs de L. decemlineata récoltés sur un mélange des 3 solanées, et mis en présence d'un choix de groupes d'oeufs provenant de ces 3 plantes, a parasité préférentiellement les oeufs récoltés sur S. t. tuberosum; élevé à partir d'oeufs de L. texana récoltés sur S. elaeagnifolium, et mis en présence d'un mélange de pontes des 3 solanées, il a préféré parasiter les oeufs provenant de L. esculentum. Son choix a été influencé aussi par la plante qui l'avait conditionné. E. puttleri, élevé à partir de L. texana et mis en expérience sur des pontes provenant de S. t. tuberosum a préféré pondre sur les oeufs provenant de cette solanée. De même, élevé à partir d'oeufs de L. decemlineata pondus sur S. t. tuberosum, il a préféré pondre sur les oeufs provenant de cette plante. Cependant, les oophages élevés à partir d'oeufs de L. decemlineata provenant de L. esculentum, et mis en présence de pontes provenant de L. esculentum, n'ont pas préféré significativement ces oeufs au détriment de ceux provenant des autres solanées, bien que les pontes récoltées sur L. esculentum aient été parasitées plus fréquemment quand 2 des 3 pontes (une de chaque plante) avaient été sondées ou parasitées. Le parasitisme à l'intérieur d'une ponte (nombre d'oeufs de la ponte parasités, sondés, etc) ne varie pas significativement avec la solanée d'origine. La discussion a porté sur les conséquences de ces observations sur l'écologie de l'oophage et sur la lutte biologique contre L. decemlineata.

     

Host specificity and biology ofHeteropsylla spinulosa [Hom.: Psyllidae] introduced into Australia and Western Samoa for the biological control ofMimosa invisa

The biology and host specificity of the psyllidHeteropsylla spinulosa Muddiman, Hodkinson & Hollis collected fromMimosa invisa Von Martius, was studied in Brazil and in Australia. Oviposition was recorded on 19 of 100 plant species tested but nymphs died without feeding, except onM. invisa. H. spinulosa was shown to be specific toM. invisa and was subsequently released and established in Australia and Western Samoa.      

烟粉虱成虫对黄瓜叶龄的喜好性及与后代发育适合度间的关系

在室内采用笼罩和发育测定方法,研究了烟粉虱成虫对黄瓜叶龄的喜好性及其与后代生长发育、存活之间的关系,同时调查了叶毛密度与成虫喜好性之间的相关关系。结果表明(1)烟粉虱成虫比较喜欢在黄瓜植株的中部叶片取食和产卵。(2)叶龄对烟粉虱的存活率没有显著影响,对烟粉虱的发育历期只在卵期和若虫四龄期表现出显著影响,对其他龄期或整个世代均没有显著影响。(3)叶毛密度随着叶龄的增大而顺次显著减小;在接虫初始阶段,烟粉虱成虫的叶片选择性与叶毛密度成显著负相关关系,但72h后具有中等叶毛密度的叶片上的成虫数量和着卵量均显著高于叶毛密度较大或较小的叶片。研究结果对培育抗烟粉虱的黄瓜品种和改进烟粉虱的防治措施具有一定指导意义。