Colonization and hyperparasitism ofCotesia rubecula (Hym.: Braconidae), a newly introduced parasite ofPieris rapae,in Virginia

A Yugoslavian strain ofCotesia rubecula (Marshall) (Hymenoptera: Braconidae) was released in spring broccoli for control of the imported cabbageworm,Pieris rapae (L.), in Montgomery Co., Virginia, in 1987.C. rubecula reproduced and parasitized imported cabbageworm larvae in fall broccoli in 1987. It was found in moderate numbers in the summer and fall crops in 1988, and by fall had dispersed 0.8 km from the original release site. However, noC. rubecula were detected in our broccoli plots in Montgomery Country in 1989 or 1990. The hymenopteran hyperparasitesIsdromas lycaenae (Walker)(Ichneumonidae), Spilochalcis torvina (Cresson) (Chalcididae), andTetrastichus galactopus (Ratzeburg) (Eulophidae) were found attackingC. rubecula. Hyperparasites emerged from 31.8% and 41.1% of theC. rubecula cocoons in 1987 and 1988, respectively.T. galactopus was the most numerous hyperparasite in 1987, butS. torvina was dominant in 1988. Hyperparasite activity was low during early spring, but increased in July in both years. By August 1988, only hyperparasites emerged from theC. rubecula cocoons collected in the field. In spite ofC. rubecula's success in overwintering, hyperparasites, especiallyS. torvina, may be a limiting factor in the establishment ofC. rubecula in southwestern Virginia.      

Influences of plant species on life history traits of Cotesia rubecula (Hymenoptera: Braconidae) and its host Pieris rapae (Lepidotera: Pieridae)

The relative suitability of four plants was studied for larvae of Pieris rapae L. and its parasitoid Cotesia rubecula (Marshall). For unparasitized P. rapae, pupal dry weight and egg-pupa growth rate were higher on cabbage, radish and nasturtium than on Indian hedge mustard. Larval developmental rate and size were greatest for C. rubecula when its host was feeding on nasturtium. Wasp survival was not affected by the host insect/plant combination in which the parasitoid developed. These results indicate that the plant on which host larvae feed is an important factor in development of the parasitoid.     

Courtship and intersexual signaling in the parasitic waspCotesia rubecula (Hymenoptera: Braconidae)

The courtship behavior of the parasitic wasp Cotesia rubeculawas studied in a flight tunnel using standard quantitative ethological techniques. Emission of a female sex pheromone induces searching and signaling behavior in males. Males combine wing-fanning, which produces low-frequency airborne sound, with pulsing behavior, which transmits a vibrational signal through the substrate to the female and induces her receptivity. Female receptivity is indicated by a stereotyped antennal position, which may provide a visual or tactile signal to courting males. Comparison of successful and unsuccessful courtships indicated that courtship success was dependent primarily on the effective production or reception of the male pulse signal. Overall, the sequence of courtship behavior was similar to that reported for other parasitic wasps.     

闭弯尾姬蜂与菜蛾盘绒茧蜂寄生菜蛾幼虫时的种间竞争

在室内25℃下,以菜蛾3龄初幼虫作寄主,研究了菜蛾盘绒茧蜂Cotesia plutellae和半闭弯尾姬蜂Diadegma semiclausum的种间竞争。当寄主供2种蜂同时产卵寄生时,2种蜂各自的寄生率与其单独寄生时无显著差异,合计寄生率比一种蜂单独存在时有所提高,但差异不显著。2种蜂均能产卵寄生已被另一种蜂寄生了的寄主幼虫。当寄主被2种蜂寄生的间隔时间很短（少于10 h）时,所育出的蜂绝大部分（80%以上）为绒茧蜂;当寄主先被绒茧蜂寄生,并饲养2天以上再供弯尾姬蜂寄生时,所育出的全为绒茧蜂;当寄主先被弯尾姬蜂寄生,并饲养2天以上再供绒茧蜂寄生时,寄主幼虫绝大部分不能存活,只有少部分能育出寄生蜂,且多为弯尾姬蜂。当2种蜂的幼虫存在于同一寄主体内时,2种蜂的发育均受到另一种蜂的抑制;绒茧蜂1龄幼虫具有物理攻击能力,能将弯尾姬蜂卵或幼虫致死。这些结果表明,菜蛾盘绒茧蜂与半闭弯尾姬蜂在同一寄主中发育时,前者具有明显的竞争优势。     

Development of the parasitoid,Cotesia rubecula (Hymenoptera: Braconidae) in Pieris rapae and Pieris brassicae (Lepidoptera: Pieridae): evidence for host regulation

Several recent models examining the developmental strategies of parasitoids attacking hosts which continue feeding and growing after parasitism (=koinobiont parasitoids) assume that host quality is a non-linear function of host size at oviposition. We tested this assumption by comparing the growth and development of males of the solitary koinobiont endoparasitoid, Cotesia rubecula, in first (L1) to third (L3) larval instars of its preferred host, Pieris rapae and in a less preferred host, Pieris brassicae. Beginning 3 days after parasitism, hosts were dissected daily, and both host and parasitoid dry mass was determined. Using data on parasitoid dry mass, we measured the mean relative growth rate of C. rubecula, and compared the trajectories of larval growth of the parasitoid during the larval and pupal stages using non-linear equations. Parasitoids generally survived better, completed development faster, and grew larger in earlier than in later instars of both host species, and adult wasps emerging from P. rapae were significantly larger than wasps emerging from all corresponding instars of P. brassicae. During their early larval stages, parasitoids grew most slowly in L1 P. rapae, whereas in all other host classes of both host species growth to pupation proceeded fairly uniformly. The growth of both host species was markedly reduced after parasitism compared with controls, with the development of P. brassicae arrested at an earlier stage, and at a smaller body mass, than P. rapae. Our results suggest that C. rubecula regulates certain biochemical processes more effectively in P. rapae than in P. brassicae, in accordance with its own nutritional and physiological requirements. Furthermore, we propose that, for parasitoids such as C. rubecula, which do not consume all host tissues prior to pupation, that parasitoid size and host quality may vary independently of host size at oviposition and at larval parasitoid egression.     

Influence of dietary nicotine and colony source ofManduca sexta [Lepidoptera: Sphingidae] on its suitability as a host ofCotesia congregata [Hymenoptera: Braconidae]

Larval tobacco hornworms,Manduca sexta (L.), of 2 different colonies were exposed to parasitism by the gregarious endoparasitoid,Cotesia congregata (Say). A comparison was made of parasitoid larval, pre-pupal, and pupal mortality, female and male dry weight and larval development time. In general, “Maryland” hornworms were more suitable hosts than “North Carolina” hornworms. Although the presence of dietary nicotine increased parasitoid mortality in individuals reared from hornworms of both colonies, the effect was more severe among individuals parasitizing the North Carolina hornworms. Scientific contribution No. 8125, article No. A-5066 of the Maryland Agricultural Experiment Station, Department of Entomology.     

The biology and behaviour ofIphiaulax varipalpis [Hymenoptera: Braconidae] as a parasite ofDirphya nigricornis [Coleoptera: Cerambycidae]

The ability of the braconid parasite,Iphiaulax varipalpis Cary to control the beetleDyrphya nigricornis Olivier was evaluated. Field collected samples and specimens reared in polyethylene paper tubes under laboratory conditions (23.0°C±1.0 at 70% r.h) were used. Field parasitism was low (10.72%) while laboratory parasitism was high (57.66%). The parasite detected the hosts very easily in the laboratory. This ability is minimised in thick canopies ofCoffea arabica L. Host colonization was brisk (90 seconds) and confined to a near absolute area of discovery, measuring 4.18±0.41 cm. The parasite reproduces gregariously with female lifespan being approximately double the male period. The parasites are very active at the age of 10 days. As they age their potential fecundity (232 oocytes) reduces drastically with oviposition.      

Oviposition pattern byCotesia ayerzai [Hym.: Braconidae] onAscia monuste [Lep.: Pieridae] under laboratory conditions

Various aspects of the parasitims of caterpillars ofAscia monuste orseis byCotesia ayerzai, were studied in laboratory choice tests. Individual ♂♂ were found to be extremely variable in ovipositional duration, as well as in the number of eggs oviposited. To simulate parasitoid dispersal, or low host density, we isolated ♂♂ for 60 min following initial exposure and compared our tests with ♂♂ which had not been isolated. No differences in (1) the number of eggs oviposited per host instar; (2) the conditional probability of host encounter; (3) host acceptance; and (4) the conditional probability of instar specific parasitism were found between these groups. Held ♂♂ did, however, reject hosts after ovipositor insertions in a higher proportion.      

A simple action treshold for timing applications of a granulosis virus to controlPieris rapae [Lep.: Pieridae]

Pieris rapae (L.) an important pest of cole crops in the northeastern United States, is susceptible to a granulosis virus,Pieris rapae GV (PrGV), that has been shown to be an effective control measure by researchers in several countries. As an alternative to weekly applications of virus to protect cabbage, we tested the use of an action threshold of one small (first-third instar) larva per plant. Results were compared with those obtained using the same threshold with permethrin, and with weekly applications of virus. Plots treated weekly with virus received 5 applications but the action threshold was exceeded only once. In all virus-treated plots, numbers of large (fourth-fifth instar) larvae remained below 0.35 per plant, and were lower at the end of the season (0.07 in plots treated weekly and 0.1 in plots treated once) than in either the untreated or permethrin-treated plots (0.5). In late August, numbers of large larvae in the check plots reached almost 3 per plant. At harvest the number of feeding holes over 0.3 cm in diameter in the 4 innermost frame and the 4 wrapper leaves were counted. Check plots differed from treated plots by an average of 124.2±6.5 holes per plant in the frame and wrapper leave; virus-treated plots had 51.1±6.9 holes more than the permethrin plots. The difference in overall damage between plots treated 5 times with virus during the season and those treated once was not significant. Plots treated once with virus had significantly more damage (7.6±2.7) to wrapper leaves than those treated five times and marketability ratings were somewhat lower, based on fresh market standards. There were no significant differences in head weight among the treatments. At harvest, a high proportion of larvae collected from the check plots were diseased (77% versus an average of 46% in the treated plots). Because of the high numbers of large larvae in the check plots in late August and the extensive damage to plants, we assumed that virus did not affect a significant number of larvae in these plots until late in the growing season. These results indicate the usefulness of PrGV in a cabbage IPM program and that the use of action thresholds can be highly effective, particularly when insect numbers only occasionally reach damaging levels. While cabbage treated with permethrin had the least amount of injury, that treated weekly with virus was not significantly different by fresh market standards, and all cabbages treated with virus met processing standards. For the fresh market, in which cosmetic standards are more important, PrGV may have to be used weekly or with an action threshold lower than one small larva per plant.      

Innate responses of the parasitoidsCotesia glomerata andC. rubecula (Hymenoptera: Braconidae) to volatiles from different plant-herbivore complexes

To determine and compare innate preferences of the parasitoid speciesCotesia glomerata andC. rubecula for different plant-herbivore complexes, long-range (1-m) foraging behavior was studied in dual-choice experiments in a wind tunnel. In this study we tested the hypothesis that naive females of the specialistC. rubecula should show more pronounced preferences for different plant-herbivore complexes than females of the generalistC. glomerata. The herbivore species used were the pieridsPieris brassicae, P. rapae, P. Napi, andAporia crataegi and the nonhostsPlutella xylostella andMamestra brassicae. All herbivore species feed mainly on cabbage and wild crucifers, exceptAporia crataegi, which feeds on species of Rosaceae. Both parasitoid species preferred herbivore-damaged plants over nondamaged plants. NeitherC. rubecula norC. glomerata discriminated between plants infested by different caterpillar species, not even between plants infested by host-and nonhost species. Both parasitoid species showed preferences for certain cabbage cultivars and plant species. No differences were found in innate host-searching behavior betweenC. glomerata andC. rubecula. The tritrophic system cabbage-caterpillars-Cotesia sp. seems to lack specificity on the herbivore level, whereas on the plant level differences in attractiveness to parasitoids were found.     

The effect of insecticides on the distribution of foracing parasitoids,Diaeretiella rapae [Hym.: Braconidae] on plants

Foraging aphid parasitoids,Diaeretiella rapae M'Intosh, were exposed to sublethal doses of the insecticides pirimicarb, permethrin and malathion on brusslls sprouts plants. Observations on wasp distribution over time revealed that wasps spent less time on sprayed plants, relative to controls and, while on these plants, tended to concentrate activity on unsprayed surfaces. For permethrin and malathion, pesticide residues reversed the stereotypic upward foraging pattern of the wasp. Negative consequences of sublethal pesticide doses for parasitoid foraging efficiency are discussed.      

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.     

Ultrastructure and migration of screening pigments in the retina of Pieris rapae L. (Lepidoptera,Pieridae)

Summary The retinal morphology of the butterfly, Pieris rapae L., was investigated using light and electron microscopy with special emphasis on the morphology and distribution of its screening pigments. Pigment migration in pigment and retinula cells was analysed after light-dark adaptation and after different selective chromatic adaptations. The primary pigment cells with white to yellow-green pigments symmetrically surround the cone process and the distal half of the crystalline cone, whilst the six secondary pigment cells, around each ommatidium, contain dark brown pigment granules. The nine retinula cells in one ommatidium can be categorised into four types. Receptor cells 1–4, which have microvilli in the distal half of the ommatidium only, contain numerous dark brown pigment granules. On the basis of the pigment content and morphology of their pigment granules, two distal groups of cells, cells 1, 2 and cells 3, 4 can be distinguished. The four diagonally arranged cells (5–8), with rhabdomeric structures and pigments in the proximal half of the cells, contain small red pigment granules of irregular shape. The ninth cell, which has only a small number of microvilli, lacks pigment. Chromatic adaptation experiments in which the location of retinula cell pigment granules was used as a criterium reveal two UV-receptors (cells 1 and 2), two green receptors (cells 3 and 4) and four cells (5–8) containing the red screening pigment, with a yellow-green sensitivity.     

Postemergence learning in the insect parasitoid,Cotesia congregata (Say) (Hymenoptera: Braconidae)

Exposing newly emerged females of Cotesia congregata(Say) to wild cherry, an inherently unattractive plant, and their host larvae at 0–4 h after adult emergence induced a positive searching response to wild cherry and an inhibited response to cabbage, an attractive plant. Inherent responses were not affected when females were exposed to their hosts at 0–12 h and to cherry at 8–12 h after emergence. The induced response to cherry was constant until its disappearance at 6–7 days;inhibition of the response to cabbage was released at 4–5 days after emergence. Postemergence exposure to cherry and parasitoid cocoons induced similar but weaker searching responses. Induced searching responses exhibit features of associative learning and receptor modification. In addition to its presumed role in foraging, postemergence experience with plants may encourage assortative mating of C. congregatawithin suitable host habitats and, thus, facilitate local adaptations to specific plants.     

Parasitism of Pieris rapae (Lepidoptera: Pieridae) by a pupal endoparasitoid, Pteromalus puparum (Hymenoptera: Pteromalidae): effects of parasitization and venom on host hemocytes

In contrast to the situation with egg-larval and larval endoparasitic wasps, little is known about the effects of pupal endoparasitoids and their secretions on the hemocytes of their insect hosts. This study focuses on the pupal endoparasitoid, Pteromalus puparum, and its host, the small white butterfly, Pieris rapae. Parasitism by P. puparum, resulted in a significant increase in the total number of host hemocytes up to day five after parasitization. From day one to day four after parasitization, the percentage of plasmatocytes significantly decreased, and the proportion of granular cells increased. Moreover, from 12 h to day three after parasitization, hemocyte mortality in parasitized pupae was noticeably higher. When P. rapae pupae were parasitized by adult females of P. puparum irradiated by gamma-ray (pseudoparasitization), it was clear that the treated wasps could induce similar hemocyte changes. However, such phenomena did not occur in punctured host pupae (mimic-parasitization). After treatment with P. puparum venom, both the percentages of spreading plasmatocytes and encapsulated Sephadex G-25 beads were lessened significantly in vitro. Electron microscopy analysis and visualization of hemocyte F-actin with phalloidin-FITC showed that hemocytes treated with venom had a rounded configuration and neither spread nor extended pseudopods, while there was no marked alteration of hemocyte cytoskeletons after venom treatment. The results suggested that venom of P. puparum could actively suppress the hemocyte immune response of its host, but not by destroying the host hemocyte cytoskeleton.     

Host recognition by the gypsy moth [Lymantria dispar] [Lep.: Lymantriidae] hyperparasite,Eurytoma appendigaster [Hym.: Eurytomidae] of cocoons ofCotesia melanoscela [Hym.: Braconidae]

Artificial and modified natural hosts were exposed to females of the gypsy moth [Lymantria dispar (L.)] hyperparasite,Eurytoma appendigaster (Swederus), to investigate its host recognition behavior on the primary host, which are cocooned larvae of the gypsy moth parasite,Cotesia melanoscela (Ratzeburg). Material(s) which caused drilling behavior by the hyperparasite on host cocoons were extracted with both polar and non-polar solvents. However, cocoons washed with large volumes of solvent still caused substantial drilling activities by females, suggesting that additional cues may be important. Results suggest that host recognition in this hyperparasite involves a variety of host characteristics.      

Allorhogas pyralophagus [Hym.: Braconidae], a gregarious external parasite imported into texas,USA, for biological control of the stalkborerEoreuma loftini [Lep.: Pyralidae] on sugar cane

Allorhogas pyralophagus Marsh is a recently discovered doryctine braconid with potential for field trials against stalk borers infesting both large- and small- stemmed Graminacea. This external gregarious parasite was originally reared fromEoreuma loftini (Dyar) larvae infesting Johnson grass [Sorghum halepense (L.) Pers.] and sugar cane (Saccharum officinarum L.) from the states of Sinaloa and Nuevo Leon, Mexico. The parasite is easily reared in the laboratory using a wide range of host larvae [Diatraea spp.,E. loftini, Chilo sp. andTryporyza nivelli (F)]. Hosts are placed in grass stems or paper straws for exposure to ovipositing females.A. pyralophagus has been field released and recovered from the following hosts infesting sugar cane:E. loftini andD. saccharalis (F.) in Texas.Diatraea spp. in Trinidad,D. rufescens in Bolivia andT. nivella in Sumatra, Indonesia. Approved as Contribution No. TA-20743 of the Texas Agricultural Experiment Station.     

Interactions between an eucoilid [Hymenoptera] and a staphylinid [Coleoptera] parasitoid of the cabbage root fly

The interaction betweenTrybliographa rapae andAleochara bilineata, 2 parasitoids of the cabbage root fly, is discussed. Larvae ofA. bilineata could not differentiate between cabbage root fly pupae containingT. rapae in its endoparasitic state and unparasitized pupae but could recognize pupae containingT. rapae once the latter had reached its ectoparasitic state. Attack byA. bilineata whileT. rapae was still in its endoparasitic state usually resulted in the staphylinid killing the eucoilid. IfT. rapae had reached the ectoparasitic state before the host pupa was attacked byA. bilineata larvae the eucoilid survived attack by the beetle larva. Multiparasitism, however, resulted in increased levels of mortality of both parasitoid populations.      

Observations on the oviposition behaviour ofGoniozus sensorius [Hymenoptera: Bethylidae] a parasite ofDiaphania indica [Lepidoptera: Pyralidae]

Goniozus sensorius Gordh (Hymenoptera: Bethylidae) was recorded as a major parasite of the pumpkin caterpillar,Diaphania indica (Saunders) (Lepidoptera: Pyralidae). This paper provides detailed information on the oviposition behaviour ofG. sensorius. Prior to oviposition, the parasite temporarily paralyses the host larva. The paralysed condition lasts for about 2 h. The egg laying process on each larva requires 30 to 60 min. The maximum number of eggs are laid on the 6^th and 7^th segment, and none in the terminal segments. Generally, oviposition is restricted to 1 segment of the host larva and occasionally on 3 segments. The maximum number of eggs are laid on the 2^nd and 3^rd day after emergence and the mean number of eggs laid on each host larva was 7.1.     

Competition betweenBracon mellitor [Hym.: Braconidae] andCatolaccus grandis [Hym.: Pteromalidae] for their hostAnthonomus grandis [Col.: Curculionidae]

BioControl - Laboratory studies of competition between populations of 2 parasitoids of the cotton boll weevil,Anthonomus grandis Boheman, showed that populations ofCatolaccus grandis (Burks)...