Multiple host use by the egg parasitoid Trissolcus basalis (Wollaston) in a soybean agricultural system: biological control and environmental implications

1 Species of bugs (Hemiptera: Pentatomidae and other families) that are parasitized by the egg parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae) in the soybean agricultural system on the Darling Downs in south-eastern Queensland, Australia, are reported. The degree to which eggs of each bug species are used by T. basalis is quantified, which allows assessment of the role of these alternative host species in the biological control of the green vegetable bug Nezara viridula (L.). 2 Egg masses of nine species of pentatomid bugs and one unidentified bug species were collected. Parasitism rates of egg masses of all species averaged 50–70% but were significantly lower for the more important pest species, including the green vegetable bug, than for some of the agriculturally less important species. 3 Trissolcus basalis emerged from nearly all species collected and was the major parasitoid to emerge from most species. A number of native species were parasitized heavily by T. basalis and parasitism of such species may enhance biological control of the green vegetable bug, but may also pose environmental concerns. Parasitism of predatory bugs by T. basalis may have a negative impact on the biological control of other pests, especially lepidopterous pests. 4 Although the impact of T. basalis on native and predatory host species was not directly quantified, these host species remain abundant and therefore do not appear to be affected adversely by such high rates of parasitism.     

Pollen beetle (Meligethes aeneus) oviposition and feeding preference on different host plant species

The oviposition and feeding preferences of the pollen beetle, Meligethes aeneus, were determined in choice and no-choice tests in field, semi-field and greenhouse trials. Plant species used were Brassica napus, B. campestris, B. juncea, B. nigra, B. carinata, Sinapis alba and Crambe abyssinica. With respect to number of eggs laid, S. alba and C. abyssinica were inferior to the other species. Pollen beetles laid fewer eggs on B. nigra than on the other Brassica spp. in no-choice tests, however this difference was partly due to fewer eggs laid per bud rather than fewer buds used for oviposition. Most eggs, for all plant species, were deposited in buds sized 2–3 mm. Feeding damage on all plant species was relatively similar. Pollen beetles seem to have a wider host range for feeding than for oviposition. There was good agreement in plant species ranking as oviposition hosts between the field, semi-field and greenhouse trials.     

Effects of storage at low-temperature of various heteropteran host eggs on the egg parasitoid, <Emphasis Type="Italic">Trissolcus semistriatus</Emphasis>

Various heteropteran host eggs stored under two low-temperatures were tested in the laboratory for their usability in the production of sunn pest egg parasitoid, Trissolcus semistriatus. Parasitism, adult emergence rate and development time were assesed on stored and fresh eggs of Eurygaster integriceps, Dolycoris baccarum, Graphosoma lineatum and Eurydema ornatum. Masses of fresh host eggs in microcentrifuge tubes were maintained at +6 °C and −20 °C. Every 30 days, 50 eggs of host species were exposed to parasitism by T. semistriatus. The host eggs stored at 6 °C remained viable to parasitism by T. semistriatus up to 2 months, while those of stored at −20 °C were parasitized at high rates up to 4 months, alhough succesful parasitism rates decrease with time. However, it was indicated that both fresh or stored E. ornatum eggs were not preferred to parasitism by the parasitoid. A longer development time from egg to adult was observed in stored eggs under two tested storage techniques when compared with fresh eggs.     

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.

     

茶翅蝽沟卵蜂和黄足沟卵蜂对茶翅蝽的寄生潜能研究

茶翅蝽Halyomorpha halys(Stl)是水果和蔬菜生产中的重要害虫。为了寻找优势卵寄生蜂用于其生物防治,本文进行了相关的野外调查和室内试验。通过定期野外采集茶翅蝽卵块,培育、收集和鉴定寄生蜂,发现在自然环境中茶翅蝽卵粒的寄生率为56.29%,其中茶翅蝽沟卵蜂比例最高,占77.66%;其次是黄足沟卵蜂占20.44%。Y型嗅觉仪测定结果显示,茶翅蝽沟卵蜂和黄足沟卵蜂对茶翅蝽卵均具有明显的选择趋性。室内寄生能力试验结果表明,茶翅蝽沟卵蜂与黄足沟卵蜂单独作用的寄生率分别为94.06%和84.21%,与两种寄生蜂混合寄生茶翅蝽卵的寄生率91.65%均无显著性差异。两种寄生蜂混合寄生时,茶翅蝽沟卵蜂与黄足沟卵蜂的寄生比例分别为58.95%和41.05%,二者之间无显著差异。     

Plant and host effects on the leafroller parasitoid Dolichogenidia tasmanica

Parasitism by the braconid wasp Dolichogenidia tasmanica of first instar larvae of the lightbrown apple moth Epiphyas postvittana, established on four different species of potted host plants, was assessed after 2 weeks of field exposure in an apple orchard. Parasitism varied significantly between larval host plants (apple 58%, broom 59%, clover 30%, poplar 19% ). Parasitism on potted apple seedlings of the co-evolutionary host, E. postvittana, was compared in a field trial with that of two native New Zealand leafroller species (to which D. tasmanica has had exposure for 5 decades only). Parasitism varied significantly with larval host (E. postvittana, 83%; Ctenopseustis herana, 58%;Planotortrix octo, 26% ). Larval collections were made from mature apple trees and identification of larvae was achieved by DNA analysis for the leafroller species using PCR-RFLP of ITS1 + ITS2, and for the parasitoid by specific PCR of partial 18S. Parasitism under natural field conditions on mature apple trees was not different between larval hosts (mean 32.5% ). In laboratory studies, more P. octo larvae departed in response to parasitoid probing behaviour than E. postvittana, which is likely to contribute to the difference in parasitism rates. This study conclusively shows that D. tasmanica parasitises native New Zealand leafrollers, despite their different evolutionary origins.     

Influence of method of presentation on results of plant-host preference tests with two species of grasshopper

Leaf material of two Piper spp. (Piperaceae) was presented to two different generalist herbivores (Orthoptera: Acrididae) to determine whether method of leaf presentation in preference trials affects choice. For the grasshopper Leptomerinthoprora brevipennis, the method of presentation had no effect on preference ranking: more of Piper sancti-felicis was eaten than of P. arieianum, regardless of whether leaf material was presented as leaf disks, whole leaves supplemented with water, or whole leaves without water. In contrast, preference of the grasshopper Abracis flavolineata depended on presentation method. In that case, whole leaves of P. scancti-felicis supplemented with water were preferred over the same of P. arieianum, while dry weight consumption of leaf disks of P. arieianum was greater than that for disks of P. sancti-felicis. When presented with leaves not supplemented with water, A. flavolineata showed no significant preference for one plant species over another.

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Résumé Des feuilles provenant de deux espèces de Piper (Piperacae) ont été proposées à deux Orthoptères, Acrididae, herbivores généralistes, pour déterminer si la méthode de présentation des feuilles modifiait le choix. Pour Leptomerinthoprora brevipennis, la méthode de présentation est sans influence sur l'ordre de préférence; la consommation de Piper sancti-felicis est toujours supérieure à celle de P. arieianum, quelque soit le mode de présentation: disques de feuilles, feuilles entières humidifiées, ou feuilles entières sans addition d'eau. A l'opposé, l'ordre de préférence de Abracis flavolineata dépend du type de présentation; les feuilles entières humidifiées de P. sancti-felicis sont préférées à celles de P. arieianum proposées de la même façon, tandis que la consommation de disques secs de P. arieianum est plus importante que celle des disques secs de P. sancti-felicis. En présence de feuilles entières humidifiées, A. flavolineata ne manifeste aucune préférence.

     

Cross-mating tests and the species status of Trissolcus basalis reared from the eggs of differentheteropteran species

Laboratory choice and no-choice cross-mating tests were conducted to establish whether Trissolcus basalis individuals from green vegetable bug, Nezara viridula, and nine other host species sharemating characteristics and belong to the same species. In no-choice cross-mating tests, all individuals in self- and out-crosses mated within 10 minutes. Although all females mated, they were not all inseminated successfully. However, a similar proportion of females was inseminated across all self- and out-crosses in each set of cross-mating tests. Mate-choice tests indicated that males and females selected mates at random. Overall, the results indicate that T. basalis individuals from the ten host species represent a single genetical species. This revised version was published online in July 2006 with corrections to the Cover Date.     

Leaf age preference for oviposition by three species of whitefly on lemon

The leaf age preferences for oviposition by three species of whitefly (Dialeurodes citri [Ashmead],Aleurothrixus floccosus [Maskell], andParabemisia myricae [Kuwana]) were tested on lemon,Citrus limon (L.). Four categories of leaf age were tested (I: incompletely expanded, growing leaves; II: young leaves that are completely expanded but not yet dark green; III: completely mature leaves [dark green]; IV: completely mature leaves judged to be older than III as determined by the age of the twigs to which they were attached). Paired choice experiments were conducted in the laboratory using excised leaves and in the field using intact leaves. In both laboratory and field tests,P. myricae preferred I over all other leaf ages. It rarely oviposited on II and never oviposited on III or IV, even when they were the only two choices. The order of preference forD. citri in laboratory and field tests was II>I>III>IV. In laboratory tests,A. floccosus exhibited the same order of preferences asD. citri, but in the field, II was preferred over all others, III was slightly preferred over IV, and I varied greatly among replicates in comparisons against III or IV. In related experiments, the choice between I & III byA. floccosus andD. citri was not affected by confining the whiteflies to either I or III for three days prior to testing.

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Sélection pour la ponte des feuilles deCitrus limon en fonction de l'âge par trois espèces d'aleurodes

Résumé Des feuilles de 4 tranches d'âges appartenant àCitrus limon L.: 1) en cours de croissance et incomplètement développées; 2) développées mais pas encore vert sombre; 3) complètement développées (vert sombre) 4) plus âgées que le lot 3 d'après l'âge du rameau, ont été proposées pour pondre à 3 espèces d'aleurodes (Dialeurodes citri Ashmead,Aleurothrixus floccosus Maskell,Parabemisia myricae Kuwana). Les femelles étaient isolées dans des cages dont les ouvertures sur deux côtés opposés étaient obstruées par la face inférieure de feuilles de citronniers d'âges différents. Les feuilles utilisées au laboratoire étaient coupées, les expériences dans la nature étaient faites avec des feuilles intactes. Récoltées au bout de 2 jours, leurs ufs étaient dénombrés.Dans les 2 cas,P. myricae a préféré significativement le lot 1, les pontes sur lot 2 étaient rares, et nulles sur les lots 3 et 4 même en l'absence de choix. Les préférences significativement différentes deD. citri au laboratoire et dans la nature étaient les suivantes: 2>1>3>4.A. floccosus a présenté au laboratoire les mêmes préférences queD. citri (P0,0004), mais certains résultats étaient contradictoires. Au laboratoire et dans la nature, le lot 2 était préféré; de même le lot 3 était préféré au lot 4. Cependant de nombreuses expériences de choix dans la nature entre les lots 1 et 3 et 1 et 4 ont montré la même tendance qu'au laboratoire, mais pour d'autres, les résultats étaient inversés. Après regroupement des résultats dans la nature, le lot 3 a été préféré au lot 1 (résultats à la limite du seuil de validité); aucune différence significative n'est apparue entre les lots 1 et 4. Les choix deA. floccocus etD. citri entre les lots 1 et 3 n'ont pas été modifiés par la présence de l'un des lots pendant les 3 jours précédant l'expérience.

     

The role of host species, age and defensive behaviour on ovipositional decisions in a solitary specialist and gregarious generalist parasitoid (Cotesia species)

The main objective of this study was to determine the extent to which host acceptance behaviour as related to host species, age, and defensive behaviour might explain the differences in host use that exist between two congeneric and sympatric species of parasitic wasps. Cotesia glomerata (L.) (Hymenoptera: Braconidae) is gregarious and generalist on several species of Pieridae, whereas C. rubecula (Marshall) is solitary and specific to Pieris rapae (L.). Cotesia species differed in their responses to host species (P. brassicae (L.), P. napi (L.) and P. rapae) and developmental stage (early and late 1st, 2nd and 3rd instars). In no-choice tests, host acceptance by C. rubecula was higher for p. rapae and females did not distinguish among the 6 host ages. In contrast, when foraging for P. brassicae and P. napi, C. rubecula females more readily attacked early first instar. Cotesia glomerata showed a higher degree of behavioural plasticity towards acceptance of Pieris host species and host age than did C. rubecula. Cotesia glomerata females parasitized the three Pieris species and showed higher acceptance of first and second instars over third instar. Oviposition success was also influenced by host defensive behaviour. The frequency and the effectiveness of defensive behaviour rose with increasing age of the host, P. brassicae being the most aggressive Pieris species. Furthermore, the mean duration of C. glomerata oviposition was significantly reduced by the defensive reactions of P. brassicae, which would likely affect parasitoid fitness as oviposition time is positively correlated to clutch size in C. glomerata. Acceptance frequencies corresponded well to field reports of Pieris-Cotesia associations and to patterns of parasitoid larval performance, suggesting that the acceptance phase might be used as a reliable indicator of Cotesia host-specificity.     

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.

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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.

     

Host age choice for parasitism by Lysiphlebia mirzai and its effect on the development and reproduction of brown citrus aphid

The effects of host age andparasitism by Lysiphlebia mirzaiShuja-Uddin (Hymenoptera: Braconidae) on the development, survivorship,reproduction, and life table parameters ofbrown citrus aphid, Toxoptera citricida(Kirkaldy) (Homoptera:Aphididae) were evaluated at 25 ± 1 °C, 80 ± 5% RH, and a photoperiodof 14:10 (L:D) h. The results showed that theduration from initial parasitization tomummification was independent of the aphid ageat the time of parasitization with a mean of6.0 d. Aphids parasitized at the 1st and 2ndinstar stages and 17% of those parasitized atthe 3rd instar stage failed to reach adulthood,while the rest of the aphids parasitized at the3rd and 4th instar stages and as adults reachedmaturity and produced a number of offspringthat increased with age at parasitization. Thelongevity and fecundity of parasitized aphidswere strongly correlated with the aphid age atparasitization. Aphids parasitized at the 1stand 2nd instar stages did not contribute to thepopulation growth of the aphids. The netreproductive rate (R_o) of the aphidsparasitized at the 3rd and 4th instar andadult stages were only 9, 20 and 43% of thatfor nonparasitized aphids, respectively. Hostage preference experiments involving all fiveaphid stages showed L. mirzai couldattack and parasitize all life stages of browncitrus aphid. Parasitism was highest in the2nd instar in a no-choice test, while in achoice test parasitism in the 2nd and 3rdinstars was similar. A relatively high rate ofparasitism was also observed in the 1st instarnymphs in both choice and no-choice tests. Theresults suggest that L. mirzai haspotential as a biocontrol agent of the browncitrus aphid and warrants a furtherevaluation.     

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.     

Biological control and the species status of two host-associated populations of Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae).

Abstract Populations of the morphologically defined taxon Trissolcus basalis (Wollaston) from two major hosts (Nezara viridula [L.] and Agonoscelis rutila [F.]) were tested, using biological criteria, to determine whether they represented populations of one genetical species, or whether they represented populations of two host-associated sibling species. Individuals from both hosts exhibited no obvious courtship differences and they selected mates at random in mate-choice experiments. In addition, female wasps produced offspring of both sexes after mating with a male from either population. We conclude that the individuals of the two populations tested constitute a single genetical species.     

Biology and host preference of the planthopper Taosa longula (Hemiptera: Dictyopharidae), a candidate for biocontrol of water hyacinth

Taosa longula Remes Lenicov (Hemiptera: Dictyopharidae) is a planthopper from the South American tropics that feeds on water hyacinth, Eichhornia crassipes (Mart.) Solms-Laubach (Pontederiaceae). The biology of T. longula was studied in the laboratory and field to evaluate it as a potential biological control agent for this widespread aquatic weed. The developmental time of nymphs was recorded at different temperatures (15, 19, 23, 25, 27 and 30 °C), and developmental threshold temperatures were obtained for the different instars. The host range was evaluated in terms of development and feeding preference. Development from instar I to adult was recorded in two no-choice trials, one with cut leaves of Pontederiaceae, and a second with growing whole plants. In the cut-leaf tests, adults were obtained from Pontederia cordata var. cordata, P. rotundifolia and water hyacinth. In the whole plant test, T. longula adults were obtained only from water hyacinth. Feeding preference was evaluated by means of a paired-choice test with 10 T. longula first instars on whole plants of P. c. cordata, P. rotundifolia and water hyacinth. The number of insects that fed on water hyacinth was significantly higher than on P. c. cordata and P. rotundifolia. Taosa longula showed a clear preference for water hyacinth and exhibited warm climate requirements, making it an attractive candidate for water hyacinth biological control in tropical and subtropical areas.     

Interaction of a solitary larval endoparasitoid, Microplitis mediator, with its host, Mamestra brassicae: host acceptance and host suitability

Abstract:  Microplitis mediator (Haliday) (Hym., Braconidae) is an important parasitoid of early instar larvae of the European cabbage moth, Mamestra brassicae L. (Lep., Noctuidae). In the laboratory, we examined attack responses of female M. mediator to the first three larval instars of M. brassicae . Females were presented with M. brassicae larvae either one individual at a time in a no-choice experiment, or three individuals, one from each instar, simultaneously in a choice experiment. Whether or not there was choice, naïve female parasitoids attacked a high proportion of larvae and did not discriminate among instars. In the no-choice experiment, attacked larvae were reared, and parasitoid cocoons were produced from about 76% of larvae attacked as first and second instars, but from only 19% of larvae attacked as third instars. Dissections of attacked larvae from the choice experiment showed that about 79% of attacks on first and second instars resulted in oviposition compared with only 49% for third instars. When given choice, frequency and number of attacks on first instar larvae increased with increasing parasitoid experience. Our results suggest that first and second instar larvae of M. brassicae are suitable hosts for M. mediator , but that third instar larvae are suboptimal both because oviposition attempts were frequently unsuccessful and because immature parasitoids failed to complete development. Nevertheless, naïve attacking parasitoids exhibited minimal discrimination among instars, although experienced parasitoids most frequently attacked first instar larvae. The host selection behaviour of M. mediator is discussed in the context of optimal foraging theory and implications for biological control.     

Host age and host selection byTrichogramma nubilale

Selection byTrichogramma nubilale (Ertle & Davis) for different aged egg masses ofOstrinia nubilalis (Hübner) was examined by separating components of parasitism. FemaleT. nubilale were exposed to egg masses of 2 different ages (freshly laid egg masses versus 1, 2, 3 or 4 day old egg masses), and the age of the initial egg mass inspected, number and percent of eggs and egg masses parasitized, and the emergence rate of pharate parasitoids was recorded. When there was a large difference in age between young and old egg masses, ♀♀ inspected initially more young egg masses (>2 days difference), parasitized a greater percent of young egg masses (>2 days difference), and parasitized more eggs/parasitized egg mass in young egg masses (>3 days difference) than old egg masses. Females did not discriminate between host age when hosts were similar in age. Successful emergence of parasitoids was greater from younger eggs than older eggs, although emergence was better from one-day-old eggs than from fresh eggs. These results imply that when the hosts were sufficiently different in age, ♀♀ were attracted to younger egg masses more than older egg masses, and they tended to remain ovipositing for longer periods of time on younger egg masses than older egg masses. Moreover, ♀♀ appeared to prefer to oviposit in hosts in which their young are more likely to complete development.      

Infectivity of beetle spiroplasmas for new host species

Five beetle spiroplasmas, the Colorado potato beetlespiroplasma (CPBS, strain LD-1), the Cantharis carolinusspiroplasma (CCBS, strain CC-1), the Ellychnia corrusca fireflyspiroplasma (FS, strain EC-1), the Diabrotica undecimpunctatacorn rootworm spiroplasma (CRS, strain DU-1), and the Spiroplasmafloricola fall flower spiroplasma (FFS), all associated withbeetles, were fed to beetles (Maladera matrida and Carpophilushumeralis) and mosquitoes (Aedes aegypti and Culex pipiens). CPBSand CCBS were also injected into M. matrida. Attempts to recoverspiroplasmas from regurgitates and hemolymph were conducted 1–10days after their introduction. After day 1, orally administeredspiroplasmas could not be recovered from M. matrida beetles;however, at 2–5 days, four out of five spiroplasmas wererecovered from adult C. humeralis. Injected spiroplasmas survivedin the hemolymph of M. matrida beetles for a relatively longperiod (at least 22 days). All five spiroplasmas were recoveredfrom mosquitoes 1 day post feeding, but only two (CCBS and CRS)survived for five or more days. The results show short andvariable persistence in orally challenged non-host insects, withgeneral failure to pass the gut barrier. Such evidence should beconsidered when attempting to use these microbes in biocontrolprograms.     

Multiple host use by a sap-sucking membracid: population consequences of nymphal development on primary and secondary host plant species

Aconophora compressa is a gregarious, sap-sucking insect that uses multiple host plant species. Nymphal host plant species (and variety) significantly affected nymphal survival, nymphal development rate and the subsequent size and fecundity of adults, with fiddlewood (Citharexylum spinosum) being significantly best in all respects. Nymphs that developed on a relatively poor host (Duranta erecta var “geisha girl”) and which were moved to fiddlewood as adults laid significantly fewer eggs (mean ± SE = 836 ± 130) than those that developed solely on fiddlewood (1,329 ± 105). Adults on geisha girl, regardless of having been reared as nymphs on fiddlewood or geisha girl, laid significantly fewer eggs (342 ± 83 and 317 ± 74, respectively) than adults on fiddlewood. A simple model that incorporates host plant related survival, development rate and fecundity suggests that the population dynamics of A. compressa are governed mainly by fiddlewood, the primary host. The results have general implications for understanding the population dynamics of herbivores that use multiple host plant species, and also for the way in which weed biological control host testing methods should be conducted. Handling Editor: Robert Glinwood     

The influence of plant species on attraction and host acceptance inCotesia glomerata (Hymenoptera: Braconidae)

Females of the larval parasitoidCotesia glomerata (L.) use plant-associated cues to locate their lepidopteran host,Pieris rapae L. In this study we investigated the influence of four host plant species,Brassica oleracea var.acephala (‘Vates’ kale),Tropaeolum majus (nasturtium),Lunaria annua (honesty), andCleome spinosa (spider flower), on two components of the host selection process inC. glomerata, namely, attraction and host acceptance. Choice tests in a flight tunnel showed that parasitoids were attracted to some host plant species more than to others in the absence of host larvae.B. oleracea was the most attractive plant species, followed byL. annua, T. majus, andC. spinosa. In previous studies it was shown thatB. oleracea carries highly suitable hosts forC. glomerata and that, in the field, parasitization rates on this plant were the highest. When host larvae were reared on the four host plant species and then transferred to a common substrate (B. oleracea var.capitata, cabbage), plant species that had served as diet for the hosts did not have a significant effect on acceptance for parasitization. Thus, parasitoids were attracted to host plant species differentially, but they did not discriminate among host larvae based on the dietary history of their hosts. ForC. glomerata, it appears that phytochemistry mediates host selection more by influencing parasitoid attraction than it does by affecting host acceptance.