Egg cannibalism in Helicoverpa armigera on sorghum and pigeonpea

Egg cannibalism by Helicoverpa armigeraHübner (Lepidoptera: Noctuidae) larvae was studied in the laboratory and in the field. In laboratory experiments, first instars were exposed to increasing densities of H. armigera eggs on sorghum, Sorghum bicolor (L.) Moench, and pigeonpea, Cajanus cajan (L.) Millsp. The number of eggs eaten per larva increasedsignificantly as egg availability increased on both sorghum and pigeonpea. In small cages 21–37% of eggs were eaten on sorghum, 4–12%on pigeonpea. Plant feeding declinedsignificantly on both sorghum and pigeonpea asegg density increased. Cannibalism was greateron sorghum than on pigeonpea while plantfeeding was greater on pigeonpea than onsorghum. Only around 8% of eggs were eaten inlarger cages with sorghum. The response toincreasing egg availability in all experimentswas linear. Immunoassay with an anti-vitellinmonoclonal antibody showed that egg cannibalismoccurs on pigeonpea under field conditions.Seven percent of all larvae had egg protein intheir gut. Cannibalism may make a significantcontribution to H. armigera populationsuppression.     

Parasitism in diversified agroecosystems: Phenology ofTrichogramma minutum [Hymenoptera: Trichogrammatidae]

Parasitism ofOstrinia nubilalis egg masses byTrichogramma minutum was observed in maize-bare ground monocultures and polycultures of maize/bean/squash and maize/clover. Parasitism rates were 1.9 times higher in monocultures than in polycultures; seasonal phenology of parasitism, however, was similar in both. Parasitism first occurred during the late whorl/early tassel stage of maize; peak parasitism occurred during the mid to late tassel stage, and then dropped off rapidly. We speculate that direct predation of egg masses, and ammensal preemptive competition for egg masses byColeomegilla maculata may have contributed to the decline in parasitism rates in both monocultures and polycultures during the latter part of the season.      

Parasitism of orangestriped oakworm (Lepidoptera: Saturniidae) eggs in the urban landscape

Orangestriped oakworm, Anisota senatoria (J. E. Smith), has caused widespread defoliation of oak trees in the urban landscape of southeastern Virginia since 1985. Egg masses were collected from 1988 to 1990 to determine the impact of native egg parasites on A. senatoria populations. The most abundant egg parasite was Aprostocetus new sp. and mean egg mass parasitism was 24.6%. The eupelmid Anastatus hirtus (Ashmead), a new host record, parasitized a mean of 11.7% of A. senatoria egg masses. The encyrtid Ooencytrus sp., a new host record, had a mean egg mass parasitism of 0.09%. Inundative releases of Trichogramma minutum (Riley) in 1989 and 1990 did not increase parasitism rates and mean egg mass parasitism was 2.3%. Parasitism of first generation A. senatoria egg masses was higher compared with second generation. The four egg parasites collected in this study parasitized 30% of A. senatoria egg masses and within egg mass parasitism was 7.9%. These relatively low parasitism rates may partially explain the presence of consistently high A. senatoria populations in southeastern Virginia.     

Effects of fine-grain habitat complexity on egg parasitism by three species of Trichogramma

Effects of microhabitat complexity on host foraging by three species of Trichogramma (T. deion, T. ostriniae, and T. pretiosum) were evaluated under simulated stored product conditions. All three species have been considered as potential biological control agents for the Indianmeal moth, Plodia interpunctella, in retail stores and warehouses. Trials were conducted with single naïve female parasitoids in 10-cm Petri dishes that were either empty, contained flour, or contained millet. Empty 15-cm Petri dishes, which served as a surface area control, comprised a fourth treatment. Females were allowed to forage for sentinel egg disks for 2 h, after which percentages of parasitism and egg mortality were computed. In addition, behavioral observations were made on a subset of the trials. Trichogramma deion parasitized more eggs than the other two species in the empty dishes and in the dish containing flour. For T. deion, rates of parasitism and egg mortality were significantly greater in both the small and large empty dishes than in the small dishes containing flour or millet. Parasitism was consistently low for all three species in the grain-filled dishes. Among species, T. ostriniae spent the most time walking, while T. pretiosum was the most sedentary. In addition, T. pretiosum spent significantly more time on the first egg visited compared with subsequent eggs. T. deion may be the best-suited for use as a biological control agent for P. interpunctella. However, the potential negative effects of fine-grain habitat complexity should be taken into account when developing a release protocol for Trichogramma spp.     

Influence of crucifer cropping system on the parasitism ofPlutella xylostella (Lep., Yponomeutidae) byCotesia plutellae (Hym., Braconidae) andDiadegma semiclausum (Hym., Ichneumonidae)

Field experiments were conducted to study the influence of cabbage monoculture and mixed cropping on the parasitism of diamondback moth,Plutella xylostella (L.), a destructive pest of all crucifers, by 2 larval parasites,Diadegma semiclausum Hellén andCotesia plutellae Kurdjumov. There was no significant difference in parasitism by either species whether cabbage was planted in insecticide-free monoculture or in mixed cropping with 8 noncrucifers which were sprayed twice a week with chemical insecticides mevinphos, methamidophos and permethrin. Population ofP. xylostella increased as the cabbage plants grew older. Parasitism byC. plutellae was higher soon after cabbage transplanting but decreased as the plants grew older. Parasitism byD. semiclausum was very low soon after cabbage planting but increased as the plants grew older. A significant negative correlation was found betwen parasitism byC. plutellae andD. semiclausum. In a caged field study where only one parasite species was used in an individual cage, parasitism ofP. xylostella by both species decreased as theP. xylostella population increased. This is believed to be due to the absence of competition between the two parasites inside the cage. There was no relationship between host-plant age and parasitism ofP. xylostella larvae by either parasite species.     

Inoculative releases of Trichogramma ostriniae for suppression of Ostrinia nubilalis (European corn borer) in sweet corn: field biology and population dynamics

The effectiveness of inoculative releases of Trichogramma ostriniae Pang and Chen for suppression of Ostrinia nubilalis (Hübner) in sweet corn was assessed. Early-season, low-density (75,000 females ha⁻¹) releases were made, and establishment, levels of parasitism and sex ratios of emerging T. ostriniae quantified. T. ostriniae established effectively for each season that they were released, but appeared to be unable to overwinter. Parasitism levels tracked egg mass numbers closely, and T. ostriniae persisted in fields even where insecticides were applied. Parasitism by indigenous Trichogramma species was 3%. Field populations of T. ostriniae were distinctly female biased (78%), with males produced in the majority of broods. Numbers of males did not increase linearly with number of O. nubilalis eggs parasitized, but appeared to remain constant above an egg mass size of about 20 eggs. A Type-I functional response to increasing egg and egg mass density was found under field conditions, where the proportion of egg masses parasitized remained constant with increasing egg mass density. A relatively consistent percentage of eggs per egg mass was parasitized, with a linear increase in number of eggs parasitized with increasing number of eggs per egg mass. These results show that T. ostriniae established viable reproductive populations in sweet corn following inoculative release, with the potential to contribute to reduced dependence on insecticides for the control of O. nubilalis in an integrated pest management program.     

Effect of host plant on parasitism ofHelicoverpa armigera (Lep.: Noctuidae) byMicroplitis demolitor (Hym.: Braconidae)

Microplitis demolitor Wilkinson is an important larval parasitoid ofHelicoverpa armigera (Hübner) andH. punctigera (Wallengren) in Australia. The effect of host plant on parasitism of second instarH. armigera byM. demolitor was investigated in a glasshouse experiment. Parasitism was low (0%) on chickpea. Moderate to high levels of parasitism (22.4% to 75.4%) were recorded on sorghum, sunflower, maize, cotton and soybean. The results suggest that releases of larval parasitoids into chickpea are unlikely to enhance parasitismlevels during the first spring generation ofHelicoverpa spp.     

Trichogramma egg parasitism of Helicoverpa armigera on pigeonpea and sorghum in southern India

Trichogramma spp. (Hymenoptera: Trichogrammatidae) only rarely parasitize eggs of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on pigeonpea (Cajanus cajan (L.) Millspaugh), while on other plants including sorghum (Sorghum bicolor (L.)) high parasitism levels of this host are found. In this study two strategies designed to increase the parasitoid activity on pigeonpea were tested in the field: intercropping pigeonpea with sorghum and mass-releasing T. chilonis Ishii. Neither strategy led to an increase in parasitism. On pigeonpea, H. armigera oviposited >74.8% of its eggs on calyxes and pods. Parasitism levels in host eggs collected from different plant structures varied significantly with 3.6, 0.3, and 40.7% of eggs on calyxes, pods, and leaves parasitized. Earlier studies have shown that calyxes and pods possess long glandular and non-glandular trichomes, and are covered by sticky trichome exudates which inhibit parasitoid searching behaviour. Parasitism levels between 27.9 and 100% were recorded from host eggs on the intercropped sorghum. Trichogramma chilonis was the dominant parasitoid species. The mean clutch size was 2.03, but up to six parasitoids emerged per egg. Progeny sex ratio (% females) decreased with clutch size, from 63.1% at a clutch size of one to 46.0% at a clutch size of five. Sticky trap catches showed that while the parasitoid population in sorghum increased when H. armigera started ovipositing, the population within pigeonpea did not benefit from either a high parasitoid population in sorghum or a high host egg density on pigeonpea. During one of five seasons studied, however, high parasitism levels (up to 73%) were recorded on pigeonpea. During this season, H. armigera oviposited on pigeonpea plants in the vegetative growth stage and a high proportion of eggs were collected from leaves. Parasitism levels were positively correlated with the percentage of eggs collected from leaves. This study shows that the parasitization efficiency of Trichogramma spp. on pigeonpea depends mainly on the location of the host eggs. This explains why parasitism levels of H. armigera eggs on pigeonpea did not increase when intercropped with sorghum or after mass-releasing T. chilonis.     

Aphelinus albipodus(Hymenoptera: Aphelinidae) andDiaeretiella rapae(Hymenoptera: Braconidae) Parasitism onDiuraphis noxia(Homoptera: Aphididae) Infesting Barley Plants Differing in Plant Resistance to Aphids

Russian wheat aphid,Diuraphis noxia(Mordvilko), as a pest of small grains, has prompted research into biological control and host plant resistance. In the presence of Russian wheat aphid, leaves of a susceptible barley (Morex) are curled and chlorotic and sustain large densities of this aphid, while leaves of a resistant barley (STARS-9301B) remain flat and green and sustain fewer aphids. Might parasitism of Russian wheat aphid byAphelinus albipodusHayat & Fatima andDiaeretiella rapaeMcIntosh be affected differently by these plant types? When presented the plants separately and based on parasitism rate relative to aphid density, the largerD. rapaewas more effective in parasitizing relatively high densities of aphids within curled leaves of Morex than relatively low densities of aphids on uncurled leaves of STARS-9301B. Parasitism byA. albipodusdid not significantly differ among the plants. When given a choice of plants, approximately equal rates of parasitism occurred on the two plant lines for both parasitoid species, and parasitism byD. rapaewas greater thanA. albipodus.These data indicate that using parasitoid size as an indicator of success in a physically restricted environment may be misleading, when considered in a plant environment responsive in several manners to aphids (chlorosis, curling, and ability to sustain Russian wheat aphid). We expect that use of resistant barley will result in decreased parasitoid abundance as aphid densities decrease. However, parasitism rates are expected to be approximately equal on resistant and susceptible barley. In this system, plant resistance and biocontrol are compatible management strategies.     

Parasites of the spotted stalk borer,Chilo partellus [Lepidoptera: Pyralidae] in South Africa

One egg parasite, 7 larval parasites, 2 pupal parasites and 3 larval hyperparasites were recorded parasitizing the spotted stalk borer,Chilo partellus (Swinhoe) on maize and grain sorghum in South Africa.Trichogrammatoidea lutea Girault [Trichogrammatidae] parasitized eggs ofC. partellus mainly in mid-summer. The larval parasites were active throughout the season with occasional peaks of up to 75% parasitism.Apanteles sesamiae Cameron [Braconidae], proved to be the most abundant larval parasite. It was recorded fromca. 93% of parasitized larvae but its efficiency was reduced by the hyperparasite,Aphanogmus fijiensis (Ferriére) [Ceraphronidae], which reached sometimes up to 100% parasitism on cocoons ofA. sesamiae. The efficiency ofIphiaulax sp. [Braconidae], the 2^nd most abundant larval parasite, was also hindered by the hyperparasite,Eurytoma sp. [Eurytomidae] Pupal parasites were sometimes very abundant reaching up to 100% parasitism without any interference by hyperparasites. The most abundant pupal parasites wereDentichasmias busseolae Heinrich [Ichneumonidae] andPediobius furvus (Gahan) [Eulophidae].      

Influence of the food plants on the degree of parasitism of larvae ofHeliothis armigera byCotesia kazak

Influence of the food plants ofHeliothis armigera (Hb.) on the degree of parasitism by exotic parasiteCotesia kazak Telenga (Hymenoptera: Braconidae) was studied in cages in the laboratory on 7 food plants such as cotton (Gossypium hirsutum L.), tomato (Lycopersicon esculentum Mill), okra [Abelmoschus esculentus (L.) Moench], Dolichos (dolichos lablab L.), pigeonpea [Cajanus cajan (L.) Millsp.], Cowpea (Vigna unquiculata (L.) and chickpea (Cicer arietium L.). To determine the preference of the parasite 2 test methods were employed. In single plant choice test cotton was most preferred. Next in order of preference were tomato and okra. Dolichos, pigeonpea, cowpea and chickpea were least preferred. In multiple choice test, however, cotton and okra were preferred followed by tomato. Parasites were seen visiting these plants very frequently and high parasitism was recorded on these plants. Chick pea, pigeon pea, cowpea and Dolichos were the least preferred food plants. There appears to be some difference in fecundity as affected by some food plants. Exposure on okra, cotton and tomato resulted in higher cocoon production as compared to pigeonpea, Dolichos, cowpea and chickpea. There was, however, no difference in sex-ratio and longevity of the progeny as affected by food plants. This exotic parasite should be released first in crops such as cotton, okra and tomato on whichH. armigera is a very serious pest in India and elsewhere. Contribution No. 140/86 of the Indian institute of Horticultural Research, Bangalore-560 089     

Influence of the chickpea cropping system onHelicoverpa armigera (Lep.: noctuidae) populations and their rate of parasitism byCampoletis chlorideae (Hym.: ichneumonidae)

The effect of intercropping chickpea with coriander or linseed onHelicoverpa armigera Hübner egg and larval populations and on the rate of larval parasitism was examined. There were significantly moreH. armigera larvae per plot in the sole chickpea treatment than in the intercropped treatments. The reduction was not the result of a negative effect of the companion crops on the numbers of larvae attacking chickpea. Larval density on chickpea was higher in the intercropped plots than the plots of sole chickpea. The presence of the flowering companion crops did not result in either the attraction of otherwise uncommon parasitoids to the crop or an increase in the proportion ofH. armigera larvae parasitized byCampoletis chlorideae Uchida. The results suggest that chickpea is a more suitable host forH. armigera than coriander or linseed, and that the reduction in the density ofH. armigera larvae in the intercroped treatments was due to the lower number of chickpea plants in these treatments.     

Microsporidiosis in a Daphnia pulex population

The impact of parasitism by Thelohania sp., an intracellular microsporidian, on Daphnia pulex inhabiting a vernal pond was studied for three years. Three issues were considered: the distribution of parasites among hosts, the effect of parasites on individuals, and the impact of parasitism on population growth. Each year, Thelohania infected members of at least half of the generations of Daphnia produced in the pond. When the frequency of infection was low, parasites were found only in large adults. As infection frequency increased, parasitism spread downward through host size classes. However, parasites were rarely found in juveniles. Parasitism reduced clutch size drastically, increased mortality to a variable extent, had little impact on egg size or on per instar growth and none on molt frequency. Interaction with other stresses, such as food limitation, exacerbated some of these effects. Parasitism reduced instantaneous birth rate much more than it elevated instantaneous death rate. Population growth was reduced significantly but it is unlikely that Thelohania alone regulates the growth of this Daphnia population.     

Spatio‐temporal variation in Helicoverpa egg parasitism by Trichogramma in a tropical Bt‐transgenic cotton landscape

• 1 Understanding the spatio‐temporal dynamics of insects in agroecosystems is crucial when developing effective management strategies that emphasize the biological control of pests.
• 2 Wild populations of Trichogramma Westwood egg parasitoids are utilized for the biological suppression of the potentially resistant pest species Helicoverpa armigera (Hübner) in Bt‐transgenic cotton Gossypium hirsutum L. crops in the Ord River Irrigation Area (ORIA), Western Australia, Australia.
• 3 Extensive, spatially‐stratified sampling during a season of relatively high Trichogramma abundance found that spatial patterns of pest egg parasitism in the ORIA tend toward heterogeneity, and do not necessarily coincide with host spatio‐temporal dynamics. Both patterns of host egg density and mean rates of parasitism are not good indicators of parasitoid spatio‐temporal dynamics in ORIA cotton crops.
• 4 Parasitism rates can be significantly higher within the middle strata of the cotton plant canopy before complete canopy closure, despite a similar number of host eggs being available elsewhere in the plant.
• 5 Spatial variation in egg parasitism by Trichogramma in Bt‐transgenic cotton is evident at the between‐field, within‐field and within‐plant scale, and is not solely driven by host spatial dynamics. These factors should be considered when estimating Trichogramma impact on pest species during biological control and spatio‐temporal studies of host‐parasitoid interactions in general.

     

Potential for the biological control ofLeptinotarsa decemlineata [Col.: Chrysomelidae] by the egg parasite,Edovum puttleri [Hym.: Eulophidae] in Maryland, 1981–84

The biological control potential ofEdovum puttleri Grissell, an exotic egg parasite ofLeptinotarsa decemlineata (Say), was examined in experimental potato plots. The parasite does not overwinter in Maryland, but through annual inoculative releases it consistently parasitized Colorado potato beetle (CPB) egg masses throughout the season. Approximately 50% of all egg masses collected were parasitized and maximum parasitism byE. puttleri occurred in egg masses produced by first generation adults.Edovum puttleri reproduced and maintained itself in potato plots for 15 weeks. The random sampling of CPB egg masses to evaluate the parasite in the field is described.      

Characteristic of parasitism of diamondback moth by two larval parasites

Laboratory and greenhouse studies were conducted to investigate the suitability of 2 hymenopterous parasites,Diadegma eucerophaga Horstmann andApanteles plutellae Kurdjumov for introduction to control diamondback moth (DBM),Plutella xylostella (L.), a destructive pest of crucifers in tropical to subtropical Southeast Asia. Parasitism byD. eucerophaga was high at temperature range of 15°C to 25°C and that ofA. plutellae, at 20°C to 35°C. Both parasites were active in searching for host and oviposited only during photophase. No parasitism was observed during darkness. WhereasA. plutellae could parasitize all instars of DBM larvae,D. eucerophaga parasitized only the first 3 instars and failed to parasitize the 4^th. Parasitism byD. eucerophaga was greater when DBM larvae were feeding on common cabbage (Brassica oleracea var.capitata L.), than on cauliflower (B. oleracea var.italica L.), broccoli (B. oleracea var.botrytis L.) or Chinese cabbage [Brassica campestris L. ssp.pekinensis (Lour) Olsson].A. plutellae parasitism was greater when DBM larvac were feeding on Chinese cabbage than on common cabbage, cauliflower or broccoli. Storage of pupae at 0°C and 4°C to 6°C for up to 2 weeks reduced emergence ofD. eucerophaga adults more than that ofA. plutellae. A non-selective insecticide, deltamethrin, was toxic to adults of both parasites but selective ones such asBacillus thuringiensis, teflubenzuron, and pirimicarb were not. Pupae were more tolerant than adults to insecticides. The insecticide-resistant Luchu strain and susceptible laboratory strain of DBM suffered an equal level of parasitism by both parasites.      

Natural occurrence of Wolbachia-infected and uninfected Trichogramma species in tomato fields in Portugal

Minute egg parasitoids of the genus Trichogramma (Hymenoptera; Trichogrammatidae) are promising candidates for biological control of lepidopteran pests in tomato in Portugal. This certainly applies to native Trichogramma strains that have thelytokous reproduction, i.e., produce only daughters. In Trichogramma wasps, thelytoky is mostly induced by the intracellular bacterium Wolbachia. In this study, we carried out a field survey of native Trichogramma species in four locations in Ribatejo, the main processing tomato region of Portugal, and determined the prevalence of Wolbachia in those species. Five Trichogramma species were found to emerge from lepidopteran eggs collected in the field, namely Trichogramma bourarache, Trichogramma cordubensis, Trichogramma evanescens, Trichogramma pintoi, and Trichogramma turkestanica. T. evanescens and T. pintoi were by far the dominating species representing, respectively, 64.9 and 26.4% of the trichogrammatids collected. Total natural parasitism rates of the collected lepidopteran eggs by Trichogramma wasps ranged from 28.2 to 64.6%. Three Trichogramma species were found to be infected with Wolbachia, namely T. cordubensis, T. evanescens, and T. turkestanica. All the wasp broods belonging to T. cordubensis were infected, whereas low infection rates were found in T. evanescens (0.9% of the broods) and T. turkestanica (4.5% of the broods). The latter represents the first record of a Wolbachia infection in T. turkestanica. Sequencing of the Wolbachia surface protein, wsp, revealed this Wolbachia infection to be related to other Wolbachia infections in Trichogramma wasps. As Wolbachia-infected thelytokous strains exist for T. evanescens, the most abundant Trichogramma species naturally occurring in the tomato fields of the Ribatejo region, this species offers interesting and powerful options for biological control of lepidopteran pests in processing tomato in this region.     

Efficacy of inoculative releases of Trichogramma ostriniae (Hymenoptera: Trichogrammatidae) against European corn borer Ostrinia nubilalis (Lepidoptera: Crambidae) in field corn

We evaluated the egg parasitoid Trichogramma ostriniae (Hymenoptera: Trichogrammatidae) to control European corn borer [Lepidoptera: Crambidae: Ostrinia nubilalis (Hübner)] in field corn in 2001 and 2002. Inoculative releases of 75,000 T. ostriniae/ha occurred in New York and Virginia in 5–10 cornfields per state when corn was at mid-whorl. Incidence of egg mass parasitism, number of stalk tunnels, incidence of ear damage, and whole-plant yield were evaluated. Parasitism of European corn borer egg masses ranged from 0 to 75% in release plots and was greater in release plots than in control plots. Individual comparisons between paired release and control plots showed no reductions in either stalk or ear damage. However, when data were combined across both years and fields, stalk and ear damage were significantly reduced in New York. In Virginia, no significant differences were detected using data obtained from one year. There were no differences in yield between release and control plots. Low densities of European corn borer, drought conditions in 1 year, and a larger plant canopy in field corn are possible reasons why T. ostriniae releases provided less control than has been observed in previous trials in sweet corn. Additional research focused on improved timing and frequency and number of releases is warranted.     

Determination of Homalodisca coagulata (Hemiptera: Cicadellidae) egg ages suitable for oviposition by Gonatocerus ashmeadi, Gonatocerus triguttatus, and Gonatocerus fasciatus (Hymenoptera: Mymaridae)

Homalodisca coagulata (Say) (Hemiptera: Cicadellidae) eggs 1–10 days of age were exposed to Gonatocerus ashmeadi Girault, Gonatocerus triguttatus Girault, and Gonatocerus fasciatus Girault (all Hymenoptera: Mymaridae) in no choice laboratory trials to investigate egg age utilization and to determine which egg ages are vulnerable to attack by these three parasitoids. The H. coagulata egg ages that were most suitable for oviposition by G. ashmeadi, G. triguttatus, and G. fasciatus were eggs 3, 4, and 2 days of age, respectively. Egg ages least suitable for parasitoid development were 6–10 days for G. ashmeadi (resulting in <50% parasitism), 1–2 and 7–10 days for G. triguttatus (resulting in <25% parasitism), and 3–10 days for G. fasciatus (resulting in <11% parasitism). Pooling parasitism data across all egg ages showed that parasitism by G. ashmeadi was 12.9 and 28.5% higher compared with G. triguttatus and G. fasciatus, respectively, and G. triguttatus resulted in 15.6% higher percentage parasitism compared with G. fasciatus. Egg age had a significant effect on the percentage of female G. ashmeadi offspring produced, but this was not significant for G. triguttatus, and low G. fasciatus parasitism prevented statistical analyses for comparisons. Results from tests where females were offered a choice for oviposition between eggs 1, 3, and 5 days of age demonstrated that G. ashmeadi and G. triguttatus showed no significant oviposition preference, while percentage parasitism by G. fasciatus was 29.4 and 7.4% higher when females were presented eggs 1 and 3 days of age, respectively, compared with eggs 5 days of age. Choice tests indicated that an overlap in egg age suitability for oviposition exists between G. ashmeadi, G. triguttatus, and G. fasciatus, and that interspecific competition for eggs 1, 2, and 3 days of age may occur in the field environment.     

Assessment ofTrichogramma species for biological control of forest lepidopteran defoliators

In a laboratory study, we determined the potential of threeTrichogramma (Hymenoptera: Trichogrammatidae) species,T. brassicae Bezdenko,T. minutum Riley andT. nr.sibiricum Sorokina, for biological control against six species of forest lepidopteran pests, black army cutworm, hemlock looper, eastern spruce budworm, western spruce budworm, white-marked tussock moth, and gypsy moth. Females of each parasitoid species were offered eggs from each of the six host species. Parasitization and the effect of the host species on the emerging progeny were examined and recorded.Trichogramma minutum had the broadest host range and successfully parasitized four host species out of the six offered.Trichogramma nr.sibiricum had the narrowest host range and parasitized only two species of hosts. Of the six host species, black army cutworm was the most preferred by all threeTrichogramma species; white-marked tussock moth and gypsy moth were not parasitized by any parasitoids. There was a positive correlation between the size of female offspring and their corresponding egg complement in all three parasitoid species. The developmental time of parasitoids from egg to adult was influenced by both the parasitoid and host species. Our results suggest thatT. minutum has the greatest potential for biological control against various forest lepidopteran pests and that the black army cutworm may be the best target candidate for further study.