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.     

Host color preferences and short-range searching behavior of the egg parasitoid Trichogramma ostriniae

The color of lepidopteran eggs often varies by species or egg condition, and parasitoids that attack lepidopteran eggs could therefore potentially use color to obtain information about host identity or quality. The objective of our study was to determine whether females of the egg parasitoid Trichogramma ostriniae Pang & Chen (Hymenoptera: Trichogrammatidae) showed differential responses to egg color when searching for hosts over short distances and when evaluating the suitability of encountered eggs. We examined the wasps’ host‐selection behavior in a Petri dish arena using white, yellow, green, and black clay beads as egg models presented against a green background (to mimic leaf color). In no‐choice tests, bead color had a significant effect on the proportion of tested wasps that accepted a bead for further examination, on the time it took wasps to find and begin examining a bead, and on the time that wasps spent examining the beads. However, bead color had only a marginally significant effect on the proportion of wasps attempting to drill into a bead with their ovipositors, and no significant effect on the amount of time they spent drilling. The wasps also showed significant color preferences when given a choice between two adjacent beads of different colors. The results of the no‐choice and choice trials taken together indicated a color preference ranking of yellow > white > green > black. The wasps’ higher preference for the yellow and white egg models generally corresponds to the white or yellowish‐white egg color of T. ostriniae's target host, the European corn borer moth, Ostrinia nubilalis Hübner (Lepidoptera: Crambidae). The wasps’ strong rejection of black egg models is likely to be an adaptive response that reflects the fact that eggs that are wholly or partially black are often unsuitable for parasitization due to advanced caterpillar development, damage to the egg, or previous parasitization.     

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.     

Influence of environmental conditions and parasitoid quality on field performance of Trichogramma minutum

The effects of weather conditions and two parasitoid quality attributes, realized fecundity and host acceptance, were assessed on the field efficacy of mass-released Trichogramma minutum. Temperature was the most important single variable, explaining up to 75% of the variation in field parasitism. There were significant positive relationships between both the sum of the maximum temperatures and the number of degree-hours above a 15 °C threshold, accumulated in the three days following the release, and parasitism in the field. There was a significant negative relationship between the mean relative humidity and the odds of parasitism in the field. Quality parameters based on parasitoid biology were not effective for predicting field efficacy if poor weather conditions persisted after a release. If weather conditions were good (i.e. accumulated maximum temperatures above 62 °C, in the 3 days following the release), then parameters such as release rate and fecundity in the lab were useful predictors of field performance. There was no relationship between host acceptance measured in the lab and field parasitism. Given the importance of field temperatures for field performance, selection for cold tolerance of T. minutum would be desirable.     

Ants as predators of the egg parasitoid Trichogramma cacoeciae (Hymenoptera: Trichogrammatidae) applied for biological control of the olive moth,Prays oleae (Lepidoptera: Plutellidae) in Portugal

The detrimental effect of predators on Trichogramma cacoeciae March. releases to control the olive moth, Prays oleae Bern., in the Trás-os-Montes region (Northeast of Portugal), was evaluated during three releases against the flower generation of the pest in 2002. At 1 and 3 h and at 1, 3, 7 and 14 days after each release, 30 Trichogramma releasing cards were examined in the field and predators were collected and identified. Furthermore, at 1, 3, 7 and 14 days after each release, the percentage of egg predation on the cards was also determined. Formicidae were the most abundant group of predators at 99.1% of the total individuals collected. Ten species were identified, Camponotus aethiops, C. lateralis, C. piceus, C. truncatus, Crematogaster auberti, C. scutellaris, Lasius niger, Leptotorax angustulus, Plagiolephis pygmaea and Tapinoma nigerrimum. T. nigerrimum was the most abundant species, both in total numbers as well as in the number of occupied cards. One day after release, the percentage of predation was 24.0% in the first release, 59.4% in the second and 38.0% in the third. Three days after release, the percentage of predation varied from 60.2 to 83.4% during the three release events. Seven days after release, the percentage of predation increased to 97.8% of the total eggs on cards.     

Non‐target habitat exploitation by Trichogramma brassicae (Hym. Trichogrammatidae): what are the risks for endemic butterflies?

Abstract 1 Trichogramma brassicae Bezdenko is inundatively released against the European corn borer in Switzerland. Because parasitoids dispersing from the release fields might pose a threat to native butterflies, the searching efficiency of T. brassicae was investigated in nontarget habitats. 2 In field studies, T. brassicae was released at rates of 120 000 females/ha. Parasitism of sentinel Ephestia kuehniella egg clusters was 1.6–3.6% in meadows and 2.0–4.0% in flower strips. The respective figures were 57.6–66.7% and 19.2–46.9% in maize, significantly higher than the parasitism rates in the nontarget habitats. Experiments carried out in small field cages confirmed these results: Again, significantly higher parasitism rates were found in maize compared to meadows and flower strips, and also compared to hedgerows (in sleeve cages). 3 To elucidate potential factors underlying the low searching efficiency in nontarget habitats, the behaviour of individual T. brassicae females was investigated on four meadow plants comparatively to maize and a filter paper control. Mean (±SE) walking speed on maize was 2.2 ± 0.2 mm/s, similar to three of the plants tested and filter paper but significantly higher than on Trifolium pratense (0.85 mm/s). A higher turning rate was found on T. pratense, Viola wittrockiana and Plantago lanceolata, in contrast to the longer leaved maize and Alopecurus pratensis. The number of wasps leaving the plant within the observation period differed significantly between plant species, and was twice as high for T. pratense (and the filter paper control) compared to the other plant species. 4 In a choice experiment carried out in a climate cabinet with all five host plant species in cages, we obtained the highest parasitism rates on maize and the lowest parasitism on T. pratense, thus confirming the behavioural observations. 5 In conclusion, there is evidence for a decreased searching efficiency on plants in nontarget habitats compared to maize. However, the data explain only part of the differences found between parasitism in maize compared to nontarget habitats. Other factors, such as the structural complexity of a habitat, may also play a role. We conclude that the risk for butterfly populations in the tested nontarget habitat due to mass released T. brassicae is low.     

Biology ofTrichogramma ostriniae (Hym.: trichogrammatidae) reared onOstrinia nubilalis (Lep.: pyralidae) and survey for additional hosts

Trichogramma ostriniae has been identified as a candidate for biological control ofOstrinia nubilalis. As little was known about the biology of this parasitoid when reared onO. nubilalis, we undertook experiments to quantify biological parameters important to mass-rearing and ase ofT. ostriniae. When reared continuously onO. nubilalis, femaleT. ostriniae on average lived 2.7 days and produced 24 progeny. Continuous access to honey resulted in a four-fold increase in longevity and fecundity and a significant increase in the percentage of females parasitizing eggs. Rates of fecundity and parasitism decreased with age of female. Likewise, emergence rates and percentage of female progeny decreased with age of parental female.T. ostriniae successfully parasitizedO. nubilalis eggs until the blackhead stage. Most parasitism of eggs and eclosion of adults occurred during the first half of photophase. Eggs of 13 Lepidopterans were parasitized byT. ostriniae. Eggs of the Noctuidae, Pyralidae, and Plutellidae experienced higher levels of parasitism than others tested.T. ostriniae appears to be similar to other species ofTrichogramma in several respects and does not possess any characteristics that limit its potential for mass rearing and use for augmentative biological control ofO. nubilalis.     

Bioecology ofLydella thompsoni Herting, [Dip. Tachinidae] within the Rhone Delta in Southern France

Lydella thompsoni Hertin,Tachinidae, is an endoparasitoid frequently associated in southern France with larvae ofOstrinia nubilalis, Pyralidae, Sesamia nonagrioides, Noctuidae, Archanara geminipuncta andA. dissoluta, Noctuidae. The tachinid was reared successfully at 21°C in the laboratory by providing the adult flies with a high humidity, a light intensity of 8,000–10,000 lux for mating and a mixture of casein proteolysate and honey as food. Under such conditions, the flies lived for about 30 days and about half of them mated successfully. Hosts were infested by dissecting mature tachinid females and placing 1–2 of the extracted planidia onto each moth larva. Half of the planidia successfully entered their larval hosts. The biology of the tachinid larvae was studied on the 2 main hosts,O. nubilalis andS. nonagrioides. At 21°C, 25°C and 28°C, larval development took less time onO. nubilalis than onS. nonagrioides. At 25°C, female larvae onO. nubilalis required 9.0±0.5 days and onS. nonagrioides 10.5±0.3 days, male larvae onO. nubilalis required 8.3±0.5 days and onS. nonagrioides 10.6±0.3 days. Pupal duration was also influenced by the larval host. In winter, 2nd instar larvae ofL. thompsoni enter a resting or quiescent condition. This condition is terminated sooner (December–January) in larvae developing onS. nonagrioides than in those developing onO. nubilalis (February–March). The life cycle of the tachinid in the field was studied by trapping flies in water dishes and by collecting parasitized host larvae from various plants. Flies were caught from April to October, mainly in September. Larvae of the spring generation of the parasitoid developed on larvae of species ofArchanara that fed on the reed,Phragmites communis. From 1976 to 1982, parasitism averaged about 16%. Parasitism by summer generation onS. nonagrioides was highest (4–5%) in June. Parasitism ofO. nubilalis did not change by more than 2 fold in either of the 2 summers studied (10–17 % in 1981, 6–10 % in 1982). By September the numbers of host larvae had increased to 10–20 times the number available earlier in the season. Larval populations ofL. thompsoni similarly increased from 3–400 larvae per ha in June to 4–5,000 per ha in September. The stability of the relationship between this parasitoid and its hosts in southeastern France is discussed and compared to relationship described elsewhere.     

Host volume measurement by the parasitoid wasp Trichogramma minutum: The roles of curvature and surface area

The number of eggs laid into its insect-egg host by Trichogramma minutum Riley (Hymenoptera: Chalcidoidea: Trichogrammatidae) depends on the volume of its lepidopterous host. The wasps allocated fewer progeny into Manduca sexta (L.) (Sphingidae) egg hosts partially embedded in the substrate than into fully exposed hosts, both in daylight and in total darkness. Since the hosts are of identical diameter and surface chemistry, the mechanism of volume determination is neither chemical nor visual, but essentially mechanosensory, based on accessible surface area. Before oviposition, the wasp examines the host surface by walking over it, turning at the edge, and drumming with its antennae. The number of edge turns (N_t) made by wasps when they examined glass beads presented as model hosts was inversely dependent on surface area, but independent of diameter. Conversely, the examination time (T_e) was directly dependent on diameter, but independent of surface area.A mechanism is proposed for host volume measurement. While the wasp examines a potential host, the relative curvature (and hence diameter) is measured, possibly by antennal angle. If this measure is within an acceptable range, the wasp initiates its drumming walk. The measure is also used to set T_c and to establish an estimate of a maximum possible volume (and hence progeny number) to the host object. With T_c fixed, the value for N_t depends on accessible surface area, the wasp turning more often on restricted surfaces. N_t allows the wasp to correct the estimate of host volume such that an appropriate number of eggs is laid in non-spherical hosts. The use of curvature to set T_e increases the accuracy of the wasp's measure of N_t, while also improving its coverage of the surface. The use of curvature and surface area allows Trichogramma to optimize its progeny allocation for a variety of host sizes and shapes.

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Die bestimmung des wirtsvolumen durch die parasitische wespe Trichogramma minutum: Die rolle von krümmung und oberfläche

Zusammenfassung Bei dem Insekten-Eiparasiten Trichogramma minutum (Hymenoptera: Trichogrammatidae) hängt die Anzahl der abgelegten Eier vom Volumen der Wirtseier ab. Es wurden Untersuchungen zur Bestimmung der sensorischen Grundlagen dieses Verhaltens unternommen. Die Wespe weist sowohl im Tageslicht, als auch in totaler Dunkelheit jenen Manduca sexta (L.) (Lepidoptera: Sphingidae) Eiwirten (Diameter c. 1.3 mm) weniger eigene Eier zu, die teils (30%) in Substrat eingebettet sind, als solchen, die ganz herausragen. Da die Wirte einen identischen Radius und gleichen Oberflächengeruch haben, kann der Mechanismus der Volumenbestimmung weder chemisch noch optisch sein, sondern ist dem Wesen nach mechanosensorisch, und von der zugänglichen Oberfläche abhängig. Vor de Eiablage untersucht die Wespe die Wirtsoberfläche, indem sie darüber läuft, an den Ecken umkehrt und mit ihren Antennen trommelt. In Experimenten mit Glaskugelmodellen war die Anzahl der von der Wespe gemachten Wendungen an den Ecken (N_t) umgekehrt proportional zur Oberfläche, aber unabhängig vom Radius. Im Gegensatz dazu, war die Untersuchungszeit (T_e) direkt proportional zum Radius, aber unabhängig von der Oberfläche.Ein Mechanismus für die Volumenmessung wird vorgeschlagen. Gleich beim Besteigen des potentialen Wirtes wird die relative Kurve (und infolgedessen der Radius), wahrscheinlich durch den Antennenwinkel gemessen. Wenn diese Messung innerhalb einer bestimmten Spanne liegt, beginnt die Wespe ihren Trommelgang. Die Messung wird auch dazu benutzt, ein maximales Volumen (und folglich die Anzahl der Nachkommen) des Wirtes und eine maximale Untersuchungzeit (T_e) zu erzielen. Wird T_e konstantgehalten, hängt die Anzahl der Wendungen (N_t) von der zugänglichen Oberfläche ab, wobei die Wespe öfter bei kleineren Oberflächen wendet. Die Anzahl der Wendungen gestattet der Wespe, die ursprüngliche Einschätzung des Wirtsvolumens so zu verändern, daß eine angemessene Anzahl von Eiern in nicht kugelige Wirte gelegt wird. Die Anwendung von kurven-und oberflächenabhängigen Messungen ermöglicht eine optimale Zuweisung von Nachkommen für eine Anzahl von unterschiedlichen Wirtsgrössen und-formen. Die Oberflächenmessung gestattet eine bessere Volumenbestimmung von nicht-kugeligen Objekten. Die gezeigte Abhängigkeit von der Oberfläche ist wahrscheinlich auch eine Anpassung an Wirte, die ihre Eier in Gruppen ablegen. Unter solchen Bedingungen von grosser Wirtsdichte ist es günstiger für die Wespe, weniger Eier in jeden Wirt der Gruppe zu legen, weil diese Verteilung zu grösseren, fruchtbareren Nachkommen führt.

     

Release density,efficiency and disappearance ofTrichogramma nubilale for control of European corn borer

We evaluated how manyTrichogramma nubilale should be released at a single location to controlOstrinia nubilalis in sweet corn. Six 8.6×16 m plots received 18.4 to 2 090 ΦΦT. nubilale/SAI when plants were in the mid to late whorl stage, where SAI, surface area index, is the plant surface area/m². To evaluate the potential control by our releases, we exposed laboratory-rearedO. nubilalis egg masses to the released parasitoids at 4 times after the release. When an egg mass was parasitized byT. nubilale, 75.7% of the eggs in the egg mass were parasitized. We developed an equation to estimate the percent of egg masses that a single female was expected to parasitize in a day (efficiency of parasitism) and female disappearance (death and dispersal) rates, if both were constant during our experiment. The exponential disappearance rate was −0.52±0.03 day⁻¹, which implied that 40% of the remaining ΦΦ disappeared per day. The efficiency of parasitism was 0.050% parasitism/Φ/SAI/day, which implied that at least 351,000 ΦΦ/ha would be needed to achieve 90% parasitism. Clearly, forT. nubilale to be a successful biological control agent, efficiency of parasitism must be increased and disappearance rates must be reduced.      

Influence of leaf surfaces on movements by the hymenopterous parasitoid Trichogramma exiguum

Walking speeds of female Trichogramma exiguum Pinto & Platner were fastest on maize and soybean (12 cm/min), intermediate on tomato (8 cm/min), and slowest on woolly mullein, Verbascum thapsus (3 cm/min). Similarly, rates of turning along the paths of walking T. exiguum were smallest on maize (median angle=0°±15°), intermediate on soybean and tomato, and greatest on V. thapsus (median angle=30°±15°). Leaf trichome density and morphology influenced walking behavior. Walking was slowed and flight initiation delayed for T. exiguum walking on Amaranthus hybridus leaves compared to either maize or filter paper. When inundative releases are conducted, the effects of plant surfaces on searching rates and arrestment should be considered in determining release rates of Trichogramma spp.

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Résumé La vitesse de marche a été déterminée en lâchant des individus sur chaque substrat végétal et en traçant leur parcours sur une plaque de verre placée à 9 mm au dessus du sujet. Les déviations angulaires de portions successives des tracés, longues de 1 mm, ont été utilisées pour mesurer les taux de changement de direction. Dans une deuxième expérience, des individus ont été lâchés au milieu d'une cercle de 40 mm de diamètre sur chaque substrat et les temps écoulés avant l'envol ou pour atteindre le bord du cercle à la marche ont servi à évaluer respectivement la propension au vol et la vitesse de déambulation.Les vitesses de marche ont été plus rapides sur maïs et soja (12 cm/min), moyennes sur tomate (8 cm/min) et les plus lentes sur Verbascum thapsus (Scrophulariaceae) (3 cm/min). De le même façon, les angles de changement de direction au cours des marches effectuées par T. exiguum ont été plus petits sur maïs, moyens sur soja et tomate, et plus grands sur V. thapsus. Chez T. exiguum marchant sur des feuilles d'Amaranthus hybridus L. (Amaranthaceae), la marche a été plus lente et l'envol plus tardif que sur maîs ou papier filtre.Lors de lâchers inondatifs, les effets des surfaces végétales sur les vitesses d'exploration et d'arrêt devraient être pris en compte pour déterminer les vitesses de lâcher des Trichogramma spp.

     

Mass rearing and augmentative releases of the native parasitoid Chouioia cunea for biological control of the introduced fall webworm Hyphantria cunea in China

The fall webworm, Hyphantria cunea Drury, is an economically important introduced pest in China. A native pupal endoparasitoid, Chouioia cunea Yang (Hymenoptera: Eulophidae, Tetrastichinae) causes considerable mortality of H. cunea pupae in some areas of China. Alternative hosts of C. cunea were tested to find potential substitute hosts for mass rearing the parasitoid. Antheraea pernyi Guerin-Meneville (Lepidoptera: Saturniidae) was chosen as a surrogate host as a single pupa produced an average of 6552 wasps and a maximum of 11,256 per pupa. A mass-rearing technique and successful release program of this parasitoid is described. Parasitism by C. cunea in the areas where it was released averaged 67.74% and was usually over 80%. Other native parasitoids, such as Coccygomimus disparis (Viereck), C. parnasae (Viereck) (Hymenoptera: Ichneumonidae) and Exorita japonica Townes (Diptera: Tachnidae), caused the total average parasitism to exceed 90% on average, reaching a maximum of 96.28% in the release areas. These successful releases indicate that an introduced pest species can also be controlled by the mass-rearing and release of native parasitoids in the country of introduction.     

Interactions among three trophic levels: the influence of host plant on performance of Pieris brassicae and its parasitoid, Cotesia glomerata

The relative suitability of four host plants was determined both for unparasitized Pieris brassicae L. caterpillars and for Cotesia glomerata (L.) developing in P. brassicae. For unparasitized P. brassicae, growth rate and pupal weight were highest on Brussels sprouts and Swedish turnip, intermediate on rape, and lowest on nasturtium. In contrast, C. glomerata larval developmental rate and adult longevity were greatest for wasps from P. brassicae reared on nasturtium.On all four plants, the host-parasitoid complex attained a lower final weight than unparasitized P. brassicae, and it is argued that this difference is due primarily to reduced consumption by parasitized P. brassicae. Among parasitized caterpillars, however, complex weight was positively correlated with clutch size, suggesting that C. glomerata larvae are able to partially counteract the effect of parasitization per se on host consumption.The host plants of P. brassicae appear to face an evolutionary dilemma: in order to increase the total mass of parasitoids produced, they must suffer greater loss of foliage. This trade-off, if common in nature, may represent a formidable constraint on coevolution between host plants and parasitoids.     

Host Preferences of Trichogramma pretiosum and the Influence of Prior Ovipositional Experience on the Parasitism of Plutella xylostella and Pseudoplusia includens Eggs

Trichogramma wasps are generalist egg parasitoids used in biological control efforts. In a multi host situation they may preferentially parasitize a non-target host species to the detriment of the control program. Plutella xylostella Linnaeus (Lepidoptera: Plutellidae) is a very serious pest of cabbage, but is only one in a number of species in the ‘cabbageworm’ complex. We investigated the host preferences of Trichogramma pretiosum Riley (Hymenoptera: Chalcidoidea) when offered the eggs of Plutella xylostella and the eggs of Pseudoplusia includens Hübner (Lepidoptera: Noctuidae), another species in the ‘cabbageworm’ complex. Trichogramma pretiosum reared on the eggs of the factitious host Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) parasitized both Plutella xylostella and Pseudoplusia includens eggs under laboratory conditions. For both choice and no-choice experiments, T. pretiosum parasitized significantly more P. xylostella eggs than P. includens eggs. Prior ovipositional experience with one or other of the two host species had no effect on the subsequent parasitism levels of the two host species. The preference for P. xylostella eggs was also not affected by this prior ovipositional experience.     

Host-stage selection by Trybliographa rapae, a parasitoid of the cabbage root fly Delia radicum

Host-stage selection by Trybliographa rapae Westwood (Hymenoptera: Figitidae) was studied in choice and no-choice experiments in the laboratory. The parasitoid was able to reproduce in first, second, and third instars of the cabbage root fly, Delia radicum L. (Diptera: Anthomyiidae), but oviposition occurred more frequently in third instars when all three developmental stages were offered simultaneously. Oviposition in third instars increased the rate of development of offspring and their body size, but did not alter sex ratio. Results are discussed in the light of predictions made by the theory of optimal host acceptance.     

Sunflower stem weevil and its larval parasitoids in the Central and Northern Plains of the USA

The sunflower stem weevil, Cylindrocopturus adspersus (LeConte) (Coleoptera:Curculionidae), is apest of cultivated sunflower (Helianthusannuus L) from the southern to the northernGreat Plains. The incidence of weevilinfestation in fields from the six differentstates sampled during 1996 and 1997 ranged from33% (Minnesota) to 100% (Kansas, Colorado,Nebraska). Weevil populations in the fieldssampled were statistically greater in thecentral Plains (Colorado, Kansas, Nebraska)with a mean of 12.3 and 19.5 larvae per stalkcompared with the northern Plains (North andSouth Dakota, Minnesota) of 0.7 and 1.3 larvaeper stalk in 1996 and 1997, respectively.Parasitization of weevils varied from field tofield ranging from 1 to 100%, but was usuallyless than 20%. The nine species oflarval parasitoids recovered were allHymenoptera and included: Nealioluscurculionis (Fitch), N. collaris(Brues), Bracon sp. (Braconidae); Neocatolaccus tylodermae (Ashmead), Chlorocytus sp., Pteromalus sp.(Pteromalidae); Quadrastichus ainslieiGahan (Eulophidae), Eurytoma tylodermatisAshmead (Eurytomidae); and Eupelmus sp.(Eupelmidae). Nealiolus curculionis wasthe most prevalent parasitoid reared from C. adspersus, and it was recovered from allstates sampled. Parasitoid species richness wasgreatest in the central Plains. Thereduced number of parasitoid species foundattacking C. adspersus in the northernPlains may be caused by low host populationlevels, slow migration by parasitoids into theregion, or lack of adaptation to climaticconditions. Additional work to understandthe population dynamics of the parasitoidcomplex associated with C. adspersus mayresult in improved biological control of thesunflower stem weevil in cultivatedsunflower.     

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.

     

Role of kairomones from host accessory gland secretion in host recognition by Telenomus remus and Trichogramma pretiosum, with partial characterization

Accessory gland materials from Spodoptera frugiperda (J. E. Smith) and Heliothis zea (Boddie) (Lepidoptera: Noctuidae) contained kairomones that influenced the host recognition or acceptance behavior of Telenomus remus Nixon (Hymenoptera: Scelonidae) and Trichogramma pretiosum Riley (Hymeoptera: Trichogrammatidae), respectively. Material from S. frugiperda accessory glands stimulated ovipositor probing and drilling by female T. remus but not T. pretiosum. Accessory gland material from H. zea stimulated ovipositor probing and drilling by female T. pretiosum but not T. remus. An active material for T. remus is found in the 700 K protein fraction of accessory gland material from S. frugiperda. The oviposition behavior of the parasitoids is also discussed.

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Résumé Cette étude a utilisé une technique voisine de celle employée par Strand & Vinson (1982), pour examiner les réactions de parasitoïdes à des billes de verre enduites de substances, afin de déterminer l'influence des sécrétions des glandes annexes (AGM) de Spodoptera frugiperda et Heliothis zea dans le repérage des hôtes par Telenomus remus et Trichogramma pretiosum.Les femelles de T. remus réagissaient plus aux billes enduites d'AGM de S. frugiperda qu'aux billes témois non enduites; celles de T. pretiosum réagissaient plus aux billes enduites d'AGM de H. zea qu'aux témoins. T. remus n'a pas réagi aux billes enduites d'AGM de H. zea, ni T. pretiosum à celles enduites d'AGM de S. frugiperda.Les poids moléculaires des protéines des glandes annexes de H. zea sont 1.100 K et 50 K, et ceux de S. frugiperda de 700 K et 30 K (Strand & Vinson, 1983a). T. remus a mieux réagi aux billes enduites de la fraction 700 K de S. frugiperda qu'a celles enduites de la fraction 30 K, aux deux fractions de H. zea et aux billes témoins. Les billes enduites de la fraction 1.100 K de H. zea ont provoqué aussi une réaction significative de T. remus. Les sécrétions des glandes annexes de S. frugiperda et de H. zea contiennent des kairomones qui interviennent dans le repérage des hôtes respectifs de T. remus et de T. pretiosum. Mais, il semble peu probable que ces substances soient seules responsables de la reconnaissance de l'hôte.

     

Methods for improving both the quantitative and qualitative aspects of rearing Delia brassicae for sterile release programmes

The method of rearing Delia brassicae (Bouché) on rutabaga, one of its favoured hostplants, was improved and partly mechanized. During 3 months in 1978, about 2 million pupae were produced at an approximate cost of $ 720 U.S. The pupal yield averaged 50% of the number of eggs inoculated. Special attention was given to the number of eggs inoculated/g of plant food, to the conditions used during the rearing process and to the choice of a substrate suitable for larval pupation. The pupae were maintained at laboratory temperature until the first adults emerged and then they were stored for a maximum of 24 days at 3°. When such pupae were returned to laboratory temperatures, flies emerged from about 62% of them within 7days. A system for marking and collecting the emerging adults is described. The effects that rearing, storage, irradiation, marking and handling had on the quality of the adult flies are discussed.

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Résumé L'élevage de la Mouche du chou, Delia brassicae (Bouché), sans conditionnement spécial et sur l'une des ses plantes-hôtes, le rutabaga, a été amélioré et partiellement mécanisé. En 1978, deux millions de pupes ont été produites en trois mois pour un prix de revient de 720 U.S. $. Un bon rendement est obtenu (50% des ufs donnent des pupes de poids supérieur ou égal à 12 mg) en inoculant 0,7 à 0,9 uf par gramme de rutabaga, dont la durée de conservation à 3° n'a pas excédé les six mois.L'influence du moment de refroidissement et de la durée de conservation des pupes à 3°, sur le taux et l'échelonnement des éclosions des adultes, a été examinée; 62% des pupes refroidies pendant un mois à partir du moment de l'éclosion des premiers adultes, ont donné des adultes en 7 jours après avoir été replacées dans les conditions ambiantes. Une méthode de marquage et de collecte des adultes est décrite.L'influence des techniques d'élevage, du stockage des pupes, de l'irradiation, du marquage et de la collecte sur la qualité des mouches est discutée en détails. La limitation à 30 jours de la période de stockage des pupes afin d'éviter une forte diminution de la qualité, constitue un obstacle capital à la réalisation de lâchers inondatifs.Bien qu'un stockage des pupes à 3° pendant 3 à 4 semaines, diminue de 5 jours la longévité des mâles, un schéma approprié de lâchers peut compenser cette diminution de qualité.

     

A space-efficient contact toxicity bioassay for minute Hymenoptera, used to test the effects of novel and conventional insecticides on the egg parasitoids Anaphes iole and Trichogramma pretiosum

We developed and tested anovel bioassay method for assessment of contactresidues of pesticides to minute Hymenoptera. This method maintained a plant-toxin-insectinterface representative of natural conditionsin the field or greenhouse, and wasspace-efficient. The procedure was useful instudies with both foliar residues and systemicuptake. Furthermore, the method was relativelystraightforward, easy to setup, andinexpensive. Tests with the egg parasitoidsAnaphes iole Girault (Hymenoptera:Mymaridae) and Trichogramma pretiosumRiley (Hymenoptera: Trichogrammatidae)confirmed that this method provided consistent,repeatable assessment of concentration-responserelationships for several insecticide classes. Other researchers studying pesticide effects onminute Hymenoptera might find this bioassaymethod helpful, especially in situations wherespace is limited. We discovered differentialsusceptibility of these parasitoids tospinosad, thiamethoxam, and oxamyl. The orderof toxicity for A. iole wasspinosad>thiamethoxam>oxamyl, and for T. pretiosum wasthiamethoxam>spinosad>oxamyl. Our resultsunderscored the danger of generalizingpesticide effects across even closely relatedinsects, and demonstrated that novel`selective' insecticides are highly toxic toA. iole and T. pretiosum.