Host Egg Masses Research Articles

Local mate competition in the solitary parasitoid wasp Ooencyrtus kuvanae

Local mate competition (LMC) occurs when brothers compete with each other for mating opportunities, resulting in selection for a female-biased sex ratio within local groups. If multiple females oviposit in the same patch, their sons compete for mating opportunities with non-brothers. Females, in the presence of other females, should thus produce relatively more sons. Sex ratio theory also predicts a more female-biased sex ratio when ovipositing females are genetically related, and sex-ratio responses to foundress size if it differentially affects fitness gains from sons versus daughters. The mating system of the parasitoid wasp Ooencyrtus kuvanae meets assumptions of LMC. Females insert a single egg into each accessible egg of gypsy moth, Lymantria dispar, host egg masses. Wasps complete development inside host eggs and emerge en masse, as sexually mature adults, resulting in intense competition among brothers. We tested the hypothesis that O. kuvanae exhibits LMC by manipulating the number of wasp foundresses on egg masses with identical numbers of eggs. As predicted by LMC theory, with increasing numbers of wasp foundresses on an egg mass, the proportions of emerging sons increased. In contrast, the presence of a sibling compared to a non-sibling female during oviposition, or the size of a female, did not affect the number or sex ratio of offspring produced. The O. kuvanae system differs from others in that larvae do not compete for local resources and thus do not distort the sex ratio in favor of sons. With no resource competition among O. kuvanae larvae, the sex ratio of emergent son and daughter wasps is due entirely to the sex allocation by ovipositing wasp foundresses on host egg masses.

Comparative assessments of Gonatocerus ashmeadi and the ‘new association’ parasitoid Gonatocerus tuberculifemur (Hymenoptera: Mymaridae) as biological control agents of Homalodisca vitripennis (Hemiptera: Cicadellidae)

Egg age preference, competitive ability, and behavior of Gonatocerus tuberculifemur (‘new association’ parasitoid) and Gonatocerus ashmeadi (‘old association’ parasitoid) were investigated in the laboratory to determine if one species exhibited competitive superiority. When searching concurrently for Homalodisca vitripennis egg masses, G. ashmeadi consistently outperformed G. tuberculifemur by parasitizing 25–53% more eggs under three different experimental systems in the laboratory with varying host densities, egg ages, and exposure times. G. ashmeadi parasitism in control vials containing one parasitoid ranged from 81–97% across all egg ages. G. tuberculifemur in control vials parasitized 60–66% of eggs 1 and 3 days old, and just 18% of eggs 5 days old. G. ashmeadi produced 5–16% more female offspring than G. tuberculifemur for all experimental conditions. In comparison to G. ashmeadi, G. tuberculifemur was observed off leaves with host eggs 20% more frequently and it oviposited 15% less frequently . G. ashmeadi and G. tuberculifemur when confined together allocated ∼1% of behaviors to antennating or aggressively chasing competitors off egg masses, and up to 2% of behaviors to antennating host egg masses and/or ovipositing into eggs from the opposite side of the leaf. These latter behaviors did not occur when parasitoids were confined alone with host eggs.

Long‐term seasonal fluctuations of lepidopteran cereal stemborers and their natural enemies on maize and wild host plants in southern Benin

Abstract The seasonal fluctuation of lepidopteran cereal stemborers on maize and wild host plants (i.e., grasses and a few sedges) was investigated in southern Benin from 1988 to 1998 by time series analysis and repeated‐measures analysis of variance (ANOVA). In addition, a walk‐in light trap was used to study the flight behavior of adult moths. On both cereals and grasses, the noctuid Sesamia calamistis was the predominant species, followed by the pyralid Eldana saccharina. The noctuid Busseola fusca was rare on both maize and wild host plants. In general, pest populations increased during the course of the year to reach peak densities during the second short rainy season, and then crashed to close to zero during the dry season. On wild host plants, egg masses and other immature stages were collected throughout the year but they were higher on wild grasses than maize during the off‐season. Thus wild host plants can be considered as refuge for both borers and natural enemies during the off‐season, when maize is not available. However, only four out of the eleven wild host species played a discernable role. S. calamistis egg densities appeared to be influenced by density‐dependent factors, suggesting an effect of natural enemies. Temperature and rainfall had a negative effect on egg abundance. Larval parasitism by a Kenyan strain of the braconid Cotesia sesamiae, which was released in southern Benin in the early 1990s, and by the tachinid Sturmiopsis parasitica varied between seasons and years but there were no discernable patterns. For both parasitoids and borer host species, parasitism was positively correlated with trap catches of adult moths. The recovery of C. sesamiae during a 2‐year period suggests that the parasitoid has established its population in southern Benin.

Host discrimination and interspecific competition of Trissolcus nigripedius and Telenomus gifuensis (Hymenoptera: Scelionidae), sympatric parasitoids of Dolycoris baccarum (Heteroptera: Pentatomidae)

Trissolcus nigripedius Nakagawa and Telenomus gifuensis Ashmead (Hymenoptera: Scelionidae) are solitary egg parasitoids of Dolycoris baccarum L. (Heteroptera: Pentatomidae), a polyphagous seed-sucking bug of agricultural crops. Field examinations revealed that the two parasitoids are the most common species, but only a single species emerge from a host egg mass. To explain this observation we tested two hypotheses of interspecific host discrimination and asymmetry in competitive interaction between Tr. nigripedius and Te. gifuensis. Trissolcus nigripedius and Te. gifuensis could discriminate host egg pre-parasitized by either self or conspecific like other scelionid parasitoids that use external mark on host eggs. When provided with host eggs pre-parasitized by each other, both Tr. nigripedius and Te. gifuensis multiparasitized 94% and 100% of the host eggs without interspecific host discrimination, respectively. Interestingly, from the multiparasitized eggs irrespective of oviposition sequence, progeny of Te. gifuensis always survive better than Tr. nigripedius. Telenomus gifuensis is superior in immature competition probably due to shorter egg incubation period after oviposition, hence progeny of Te. gifuensis become first instar faster than that of Tr. nigripedius. However, adult Tr. nigripedius is always superior competitor in possessing and guarding the host eggs even after oviposition against Te. gifuensis. Therefore, the asymmetry in competitive interaction between Tr. nigripedius and Te. gifuensis may explain the emergence of a single species from a host egg mass in the field in spite of no interspecific host discrimination.

Reproductive Biology of <I>Fidiobia dominica</I> (Hymenoptera: Platygastridae), an Egg Parasitoid of <I>Diaprepes abbreviatus</I> (Coleoptera: Curculionidae)

The reproductive biology of Fidiobia dominica Evans (Hymenoptera: Platygastridae) was studied in the laboratory (25.6 +/- 1 degrees C) using host eggs of Diaprepes abbreviatus L. (Coleoptera: Curculionidae). F. dominica readily parasitized D. abbreviatus eggs on both host plant and wax paper substrates. The number of egg masses parasitized and the number of offspring produced were higher when females were offered more than one host egg mass but did not differ when either two or three egg masses were offered. Female parasitoids that were provided with host eggs and a honey food source lived significantly longer than those that were not provided a food source; however, they did not parasitize more D. abbreviatus eggs. Oviposition occurred in host eggs from 0 to 7 d old, and host mortality was relatively consistent for eggs 0-5 d old and lower for eggs 6-7 d old. Successful parasitoid emergence seldom occurred after host eggs were 4 d old, and by 7 d, no adults successfully emerged. Developmental time from egg to adult was 19.3 +/- 0.2 d for males, significantly more rapid than the females (20.4 +/- 0.1 d). The mean longevity of adult females was 8.0 +/- 0.4 d, with a mean oviposition period of 2.7 +/- 0.3 d; males survived 8.1 +/- 0.4 d. The demographic parameters including intrinsic rate of increase (r(m)), generation time (T), and net reproduction (R(o)) were 0.142/d, 22 d, and 22.4 female eggs/d, respectively.

The Response Specificity of Trichogramma Egg Parasitoids towards Infochemicals during Host Location

Parasitoids are confronted with many different infochemicals of their hosts and food plants during host selection. Here, we investigated the effect of kairomones from the adult host Pieris brassicae and of cues present on Brussels sprout plants infested by P. brassicae eggs on the behavioral response of the egg parasitoid Trichogramma evanescens. Additionally, we tested whether the parasitoid’s acceptance of P. brassicae eggs changes with different host ages. The wasps did not discriminate between olfactory cues from mated and virgin females or between mated females and males of P. brassicae. T. evanescens randomly climbed on the butterflies, showing a phoretic behavior without any preference for a certain sex. The parasitoid was arrested on leaf parts next to 1-day-old host egg masses. This arrestment might be due to cues deposited during oviposition. The wasps parasitized host eggs up to 3 days old equally well. Our results were compared with former studies on responses by T .brassicae showing that T. evanescens makes less use of infochemicals from P. brassicae than T. brassicae.

Genetics of host plant use and life history in the comma butterfly across Europe: varying modes of inheritance as a potential reproductive barrier

Comma butterflies (Nymphalidae: Polygonia c-album L.) from one Belgian site and three Spanish sites were crossed with butterflies from a Swedish population in order to investigate inheritance of female host plant choice, egg mass and larval growth rate. We found three different modes of inheritance for the three investigated traits. In line with earlier results from crosses between Swedish and English populations, the results regarding female oviposition preference (choice between Urtica dioica and Salix caprea) showed X-linked inheritance to be of importance for the variation between Sweden and the other sites. Egg mass and growth rate did not show any sex-linked inheritance. Egg mass differences between populations seem to be controlled mainly by additive autosomal genes, as hybrids showed intermediate values. The growth rates of both hybrid types following reciprocal crossings were similar to each other but consistently higher than for the two source populations, suggesting a nonadditive mode of inheritance which is not sex-linked. The different modes of inheritance for host plant preference vs. important life history traits are likely to result in hybrids with unfit combinations of traits. This type of potential reproductive barrier based on multiple ecologically important traits deserves more attention, as it should be a common situation for instance in the early stages of population divergence in host plant usage, facilitating ecological speciation.

The effect of intraspecific competition on progeny sex ratio in Gonatocerus spp. for Homalodisca coagulata egg masses: Economic implications for mass rearing and biological control

The eVect of the number of simultaneously ovipositing females on progeny sex ratio of three Homalodisca coagulata egg parasitoids, Gonatocerus ashmeadi, G. triguttatus, and G. fasciatus was investigated in the laboratory. When one female Gonatocerus parasitoid was present, progeny production was strongly female biased producing »1 male:8 females, 1:14 and 1:9 for G. ashmeadi, G. triguttatus and G. fasciatus, respectively. Increasing the number of simultaneous ovipositing females from 1 to 3, signiWcantly increased percentage of male oVspring by up to 61% for all three Gonatocerus species. Overall percentage male oVspring ranged from 31–34%, and did not signiWcantly diVer among species. Overall mean percentage parasitism by G. ashmeadi was up to 16% higher compared with G. triguttatus and G. fasciatus, whereas, average clutch size and mean progeny production was more than twofold higher for G. fasciatus when compared with G. ashmeadi and G. triguttatus. Additional laboratory trials with only G. ashmeadi demonstrated that when H. coagulata egg masses consisted of 2–13 eggs, 67–100% of females allocated one male oVspring per egg mass. When one egg mass was presented to Wve female G. ashmeadi searching concurrently, male oVspring was up to 22% higher compared with male oVspring from host eggs exposed to one female G. ashmeadi. Experiments indicated that allocation of male eggs was not inXuenced by constant female-to-female contact for 19 h prior to host exposure, and female G. ashmeadi did not alter allocation of male eggs when sibling and non-sibling conspeciWcs were contesting host egg masses. The economic signiWcance for mass rearing is substantial. For G. ashmeadi at 2003 production costs and under optimal conditions, estimated cost per female was $1.42, under suboptimal conditions, cost per female increased to $4.51; a 218% increase in production cost per female parasitoid. © 2006 Elsevier Inc. All rights reserved.

Molecular phylogenetics and the evolution of wing reduction in the Baeini (Hymenoptera:Scelionidae): parasitoids of spider eggs

Members of the tribe Baeini are unique among the Scelonidae as endoparasitoids of the eggs of spiders, whereas all other scelionids parasitise insect eggs. The monophyly of the Baeini has previously been assumed based on this host association and several morphological characteristics, none of which are unequivocal. Here we present a phylogeny for the group using sequence data from two genes and 32 ingroup taxa, mostly from Australia. Combined analysis of the nuclear 28S rRNA gene and the mitochondrial CO1 gene showed that the tribe is not monophyletic, because two genera (Neobaeus Austin and Mirobaeoides Dodd) are resolved in a clade separate from the rest of the Baeini. The two most speciose genera, Idris Foerster and Ceratobaeus Ashmead, are not resolved as monophyletic, indicating that a metasomal horn, which acts as a recess for the internally retracted ovipositor, has evolved multiple times within the tribe. Mapping of wing reduction states that occur in the Baeini revealed multiple wing reduction events, possibly associated with adaptations for searching for host egg masses in crytobiotic habitats, and/or penetrating the silk egg sacs of spiders. The molecular phylogeny generated in this study differs significantly from previous morphological phylogenies, and has resolved relationships that have otherwise been intractable in morphological studies because of homoplasy associated with reduction in body size.

Successful oviposition and reproductive biology of Aprostocetus vaquitarum (Hymenoptera: Eulophidae): A predator of Diaprepes abbreviatus (Coleoptera: Curculionidae)

Abstract Aprostocetus vaquitarum (Wolcott) causes 78–91 percent mortality to eggs of Diaprepes abbreviatus (L.), under field conditions in southern Florida. In the laboratory, A. vaquitarum was reared on D. abbreviatus eggs at 25 °C, a photoperiod of 12:12 (L:D) and with abundant hosts, A. vaquitarum adult females lived around 15 days. Oviposition was significantly affected by the age of the host egg mass. Egg masses aged 0- to 3-day-old were accepted significantly better than those aged 4–6 days. The mean number of eggs deposited per female was around 53, with extreme values of 124 and 19 eggs per female. Using these data in combination with the sex ratio observed in the field (0.16) and the duration of the preimaginal stages, r m (0.168–0142 day −1 ), T (22.39–22.89 days), and R 0 (43.03–25.81 females per female) were calculated.

Massas de Ovos de Diatraea saccharalis (Fabr.) (Lepidoptera: Pyralidae) em Cana-de-Açúcar: Número de Ovos e Porcentagem de Parasitismo por Trichogramma spp. (Hymenoptera: Trichogrammatidae) em Condições Naturais

Estudos de campo para avaliar o parasitismo de ovos de Diatraea saccharalis por Trichogramma spp. em cana-de-acucar exigem, as vezes, infestacoes artificiais de ovos do hospedeiro. Assim, massas de ovos de populacoes naturais do inseto foram coletadas para a determinacao do numero de ovos/massa e do numero de ovos parasitados por Trichogramma em cada massa, visando adequar convenientemente a quantidade de ovos de D. saccharalis a ser utilizada por ponto de postura, em infestacoes artificiais na folha da cana-de-acucar. As coletas foram realizadas em canaviais comerciais com altas densidades populacionais do hospedeiro e do parasitoide, na regiao norte dos Estados do Rio de Janeiro e Espirito Santo. Foram analisadas 634 massas (7.621 ovos), das quais 53 (785 ovos) estavam completamente isentas de ovos parasitados e 581 (6.836 ovos) tinham pelo menos 1 ovo parasitado por Trichogramma. Constatou-se que D. saccharalis oviposita em media 11,8±6,3 ovos/massa, com variacao de 2 a 37 e maior frequencia de 9 ovos. As massas com ovos parasitados continham em media 11±5,9 ovos parasitados por Trichogramma, com variacao de 1 a 35 e maior frequencia de 9 ovos. O numero de ovos parasitados/massa apresentou correlacao positiva (r = 0,89) com o numero de ovos/massa. As massas com ovos parasitados apresentaram a media de 93,3 % de parasitismo. Com base nessas informacoes, sugere-se que nas infestacoes artificiais sejam utilizadas massas de ovos do hospedeiro com numero de ovos proximos aos valores obtidos em condicoes naturais.

Source of the host marking pheromone in the egg parasitoid Trissolcus basalis (Hymenoptera: Scelionidae)

After oviposition, Trissolcus basalis females always mark the host's surface, depositing host marking substances for herself and to warn other ovipositing females. The perception of these host marking substances, probably through the antennae, can induce the female to leave and seek healthy hosts. Parasitoid females exposed to conspecific parasitized egg masses left the host egg masses significantly more often than when exposed to non-parasitized egg masses. More egg mass leaving behavior also was observed when the egg masses were treated with Dufour's gland secretion but not when treated with secretion from the common oviducts. The common oviduct has a secretory epithelium that produces electron-dense vesicles, probably containing proteinaceous substances. The secretory cells of the accessory gland, Dufour's gland, contain electron-lucid vesicles, whose secretion appears to be a lipid similarly to that found in pheromone secreting glands. Ultrastructural and behavioral evidence suggests that Dufour's gland is the host marking pheromone source.

Biological characteristics. Growth and development of the egg parasitoid Trichogramma dendrolimi (Hymenoptera: Trichogrammatidae) on the cabbage armyworm Mamestra brassicae (Lepidoptera: Noctuidae).

The growth and development of Trichogramma dendrolimi in the host, Mamestra brassicae, egg was morphologically observed. T. dendrolimi grew rapidly to full size by 2 d after parasitism, sucking up nearly all of the host yolk as the food resource. Thereafter, they did not increase in size. The parasitoid became a first larval instar on day 1, prepupa on day 4, and pupa on day 5 after parasitization. Emergence of adult wasps from the host egg occurred 9 d after parasitization. A well developed ovary was observed 8 d after parasitization, suggesting that the wasp can oviposit immediately after emergence. To clarify host stage suitability for successful parasitism, 1 to 4.2 d old eggs of M. brassicae were offered to female wasps. T. dendrolimi was able to parasitize M. brassicae eggs of all ages. The parasitoid wasp appears to arrest the development of the host by a venom. However, successful parasitism significantly decreased on 4 d and 4.2 d old host eggs. The female ratio of the progeny decreased with the aging of the female wasps, but neither the sequential change of the host age nor variation of the host egg mass size affected the female ratio of the progeny, which was about 80%.

Effectiveness of Trichogramma ostriniae and T. nubilale for controlling the European corn borer Ostrinia nubilalis in sweet corn

AbstractSeven field releases of Trichogramma ostriniae and T. nubilale (Hymenoptera: Trichogrammatidae) were made separately and in combination in a sweet corn field to compare the level of parasitism in sentinel eggs of the European corn borer, Ostrinia nubilalis (Lepidoptera: Pyralidae). The results indicate that the levels of egg parasitism among different release dates differed mainly because of changes in weather and plant architecture within the season. The level of egg parasitism by releasing T. ostriniae alone was found to be 15% higher than that by releasing T. nubilale alone, and 20% higher than by releasing the combination of the two species. Further analyses using the logistic regression model for independent and correlated data indicated T. ostriniae to be more efficient at discovering host egg masses and to have higher levels of egg parasitism than T. nubilale. Mutual interference between T. ostriniae and T. nubilale was the main factor for the lower level of egg parasitism when T. ostriniae and T. nubilale were released together. The results suggest that T. ostriniae is the better candidate for augmentative releases for control of the European corn borer, and the two species should not be released into a corn field at the same time.

Age-Related Fecundity and Learning Ability of the Egg-Larval ParasitoidAscogaster reticulatusWatanabe (Hymenoptera: Braconidae)

Abstract We investigated the relationship between age and learning ability of femaleAscogaster reticulatusWatanabe, an egg-larval parasitoid of the smaller tea tortrixAdoxophyessp. (Lepidoptera: Tortricidae). Females 1, 3, 5, 7, 9, 11, and 13 days old had higher fecundity than 0-day-old females and could associate tea leaf extract with the host egg mass through oviposition. Experienced females 1 ≈ 13 days old walked more than 10 cm along an extract-treated line while exhibiting the antennating response. However, the learned responses of 0-day-old females was significantly lower [mean = 1.4 ± 0.8 (S. E.) cm] than that of older females (1 ≈ 13 days). In considering the relation between fecundity and the learned response, a low response in 0-day-old females could be due to a low propensity by them to learn cues associated with host eggs. Average longevity was 12.0 ± 1.5 days, but even 13-day-old females could oviposit a large number of eggs and learn to associate the tea leaf extract with host presence. This suggests that females can learn as long as they are able to oviposit. This learning ability would be advantageous forA. reticulatusfemales throughout their lives.

Temporal patterns of host availability, brown-headed cowbird brood parasitism, and parasite egg mass.

I studied relationships between temporal patterns of host availability, brood parasitism, and egg mass for the parasitic brown-headed cowbird (Molothrus ater). At a study site consisting largely of edge habitat in north-eastern Illinois, I found 834 bird nests from 27 species. A total of 407 cowbird eggs and nestlings were found in these nests over three laying seasons. Nearly all (n= 379; 93%) were found in the nests of seven host species. For these species and all taken together, weekly nest availability generally decreased whereas parasitism frequency generally increased throughout the cowbird laying season, but the proportions of nests parasitized and the mean number of cowbird eggs in them did not. Additionally, no correlation was found between the proportions of nests parasitized and nest availability. Cowbird egg mass generally increased throughout the laying season, indicating that foraging conditions improved and that, early in the laying season, egg mass and quality may be less important than quantity. Consistently high weekly levels of parasitism indicate that cowbird reproduction was less limited by resources needed for egg production and more by the availability of suitable host nests. Fluctuating weekly host availabilities suggest that previously established, constant rates of cowbird egg laying would produce an excess of eggs during periods of low host availability. Further, the low frequency of parasitism (1%) of nests in stages too advanced for successful parasitism, and of abandoned nests, is consistent with the hypothesis that cowbirds' consistently high rate of egg production helps assure an egg is available when an appropriate nest is found. Frequently, nests were parasitized multiple times, raising the possibility that cowbirds were interfering with their own reproduction. A diverse host community increases the possibility that a decline of any one host species is unlikely to affect cowbird reproduction significantly.

Effects of Host Egg Mass Size on Sex Ratio and Oviposition Sequence of Trissolcus basalis (Hymenoptera: Scelionidae)

This study examines the influence of the size of the host patch (egg mass size) on the sex ratio produced by the scelionid egg parasitoid Trissolcus basalis (Wollaston) under laboratory conditions. The influence of this factor on the sequence in which male and female eggs are laid also is analyzed. Our detailed study shows that the size of the host patch offered to females strongly influenced both the overall sex ratio they produced, and the organization of the sequence in which male and female eggs are laid. Females adjusted their sex ratio with host number per host egg mass in qualitative agreement with the predictions of the local mate competition model and independently of oviposition sequence. Variations in the sex allocation sequences produced by T. basalis do not seem to depend on the ability of female wasps to assess the number of hosts per patch before oviposition. Females start egg-laying sequences by laying male eggs early in an oviposition bout in accordance with the males 1st strategy. As long as the sequences are completed, the pattern of sex allocation changes as an indirect modification in response to variation in the size of the egg mass. Such a modification in sex-sequence patterns can be considered to be an adaptive mechanism leading the females to adjust their sex ratio to different environmental conditions.

Enhancement of learned response to plant chemicals by the egg-larval parasitoid, Ascogaster reticulatus Watanabe (Hymenoptera : Braconidae)

A study was conducted to determine the most effective conditions for enhancing the learned response by Ascogaster reticulatus Watanabe, an egg-larval parasitoid of the smaller tea tortrix, Adoxophyes sp. (Lepidoptera : Tortricidae). Female parasitoids were found to learn tea leaf extract with the host egg mass and walk along an extract-treated line. We compared the learned response of females with zero to five oviposition experiences as well as females with various lengths of oviposition time (from contact with host to different lengths of oviposition). Furthermore, we investigated the effect of the length of intervals between experiences on the learned response of females. The learned response of females tended to increase with the number of conditionings (1-3 times) and the oviposition time during conditioning (0-120 s×3). However, responses were low after a single conditioning regardless of oviposition time. The length of the intervals between conditionings (5-120 min) did not affect the learned response of females. It is suggested that learned response through experience is essentially a gradual process in which the number of experiences and the oviposition time during conditioning are major elements.

Oviposition behavior of Eumicrosoma blissae (Maki) (Hymenoptera : Scelionidae), an egg parasitoid of the oriental chinch bug, Cavelerius saccharivorus Okajima (Heteroptera ; Lygaeidae)

Oviposition behavior of the parasitoid, Eumicrosoma blissae (Maki) toward unparasitized eggs of the oriental chinch bug, Cavelerius saccharivorus Okajima was observed in the laboratory. After the female encountered a host egg mass, her oviposition behavior could be divided into nine discrete steps: drumming, extension of ovipositor sheath, probing, drilling, insertion of ovipositor, withdrawal of ovipositor, withdrawal of ovipositor sheath, marking, and retraction of ovipositor sheath. In some cases, insertion of ovipositor did not occur. The parasitoid egg was found only in hosts where a female exhibited ovipositor insertion and marking. When a female attack a parasitized host, she often marked it without ovipositor insertion after drilling. The duration of marking was long when the ovipositor was inserted. The frequency distribution of the number of attacks per host egg was not random. There was a tendency for E. blissae to attempt to insert its ovipositor in the same host egg only once. The characteristics of the oviposition behavior of E. blissae are discussed in comparison with those of other egg parasitoids.

Assays with Commercially Produced Trichogramma (Hymenoptera: Trichogrammatidae) To Determine Suitability for Obliquebanded Leafroller (Lepidoptera: Tortricidae) Control

Laboratory assays were used to compare the ability of commercially produced Trichogramma spp. to parasitize eggs of the obliquebanded leafroller, Choristoneura rosaceana (Harris), in the laboratory and field. Trichogramma platneri Nagarkatti parasitized more obliquebanded leafroller eggs per egg mass than did Trichogramma pretiosum Riley or Trichogramma minutum Riley produced by either of 2 insectaries. T. minutum produced at 1 insectary caused significantly more host mortality by host feeding and repiercing than by parasitism. Variation in parasitoid performance from different insectaries and among shipments from the same insectary was common. Young egg masses were more heavily parasitized than old egg masses. Parasitism increased as the number of conspecific female Trichogramma spp. placed on the same host increased, but the number of eggs parasitized per female decreased. Exposure of host egg masses to female Trichogramma spp. prevented additional oviposition in the same egg mass by conspecific, ovipositionally experienced females but had no effect on parasitism by conspecific, ovipositionally naive females. The method used to attach sentinel egg masses to foliage influenced parasitism rates. Moistening the leaf with water and adhering the egg mass to the moistened leaf had the least impact. Inundative releases of Trichogramma spp. into an apple orchard paralleled laboratory assays by showing greater parasitism of obliquebanded leafroller egg masses by T. platneri than with T. minutum . However, extreme differences observed in field performance between the 2 species was not predicted from the assays.