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.      

Parasitism-induced effects of Glyptapanteles liparidis (Hym., Braconidae) on the juvenile hormone titer of its host, Lymantria dispar: the role of the parasitoid larvae

Parasitization by the gregarious larval endoparasitoid Glyptapantles liparidis induces a dramatic increase in the hemolymph juvenile hormone (JH) titer (especially JH III) of its host larva, Lymantria dispar. Here, we investigated the role of the parasitoid larvae in JH synthesis and release by in vitro and in vivo experiments. GC-MS analyses confirmed that the rising hemolymph JH titer coincided with the time at which the parasitoids molt to the second larval instar. Peak values in host hemolymph titers were observed prior to parasitoid emergence, and titers dropped to negligible levels within 24 h after parasitoid emergence. Whole body extracts from excised second instar parasitoids yielded JH III and trace amounts of JH II. The in vitro secretory activity of the corpora allata (CA) of L. dispar larvae was not enhanced by parasitization. When the host's CA were separated by neck ligation, we found elevated JH III titers, but no JH II in the hemolymph of the posterior section, which contained the parasitoids. Parasitoids that were kept in in vitro culture produced and released only JH III. The parasitoids’ ability to secrete JH and to molt independently from their host's molting cycles indicates that at least second instar parasitoids are hormonally self-reliant.     

Inhibition of juvenile hormone esterase activity in Lymantria dispar (Lepidoptera, Lymantriidae) larvae parasitized by Glyptapanteles liparidis (Hymenoptera, Braconidae)

Glyptapanteles liparidis is a gregarious, polydnavirus (PDV)-carrying braconid wasp that parasitizes larval stages of Lymantria dispar. In previous studies we showed that parasitized hosts dramatically increase juvenile hormone (JH) titers, whereas JH degradation is significantly inhibited in the hemolymph. Here we (i) quantified the effects of parasitism on JH esterase (JHE) activity in hemolymph and fat body of penultimate and final instars of L. dispar hosts and (ii) assessed the relative contribution of individual and combined wasp factors (PDV/venom, teratocytes, and wasp larvae) to the inhibition of host JHE activity. The effects of PDV/venom was investigated through the use of gamma-irradiated wasps, which lay non-viable eggs (leading to pseudoparasitization), while the effects of teratocytes and wasp larvae were examined by injection or insertion of these two components in either control or pseudoparasitized L. dispar larvae. Parasitism strongly suppressed host JHE activity in both hemolymph and fat body irrespective of whether the host was parasitized early (premolt-third instar) or late (mid-fourth instar). Down-regulation of JHE activity is primarily due to the injection of PDV/venom at the time of oviposition, with only very small additive effects of teratocytes and wasp larvae under certain experimental conditions. We compare the results with those reported earlier for L. dispar larvae parasitized by G. liparidis and discuss the possible role of JH alterations in host development disruption.     

Parasitoids in low-level populations ofLymantria dispar [Lep.: Lymantriidae] in different forest physiographic zones

A 2-year study was conducted on the distribution of parasitoids of gypsy moth,Lymantria dispar (L.) (Lep.: Lymantriidae), in mesic and adjacent higher elevation transition and xeric forest habitats in Vermont (U.S.A.). In both years, overall parasitism ranged from 12–18% in each habitat. When analyzed according to the life stage at which the host was collected, parasitism rates of greater than 40% were obtained among the late instars.Parasetigena silvestris (Robineau-Desvoidy) andPhobocampe disparis (Viereck) were recovered most commonly from the mesic habitat, andCotesia melanoscelus (Ratzeburg) andBlepharipa pratensis (= Sturmia scutellata) (Meigen) were most common in collections from the xeric area. Parasitism byCompsilura concinnata (Meigen) occurred at similar levels in all three habitats, and this species was responsible for the highest parasitism rates on the site, reaching 40% among the late instars in 1985. Percent parasitism byC. concinnata increased three-four-fold from 1984 to 1985, while parasitism by other species declined.     

Improved rearing and release procedures forCotesia melanoscela (Hym.: Braconidae), an early season parasitoid ofLymantria dispar (Lep.: Lymantriidae)

Rearing and release procedures forCotesia melanoscela (Ratzeburg) (Hymenoptera: Braconidae), an early-season parasitoid ofLymantria dispar (L.), were evaluated in 1995 and 1996 at the Beltsville Agricultural Research Center, Beltsville, Maryland, USA. Mass rearing procedures were developed during the winter/spring of 1995/1996 to produce diapausingC. melanoscela cocoons for experimentation. Program efficiency as measured by percent adult emergence was estimated to be 84% with a measured sex ratio of 48:52 M:F, at an estimated cost per 1 000 cocoons of U.S. $5.26 for materials and a labor requirement of approximately 6 hours. A host larvae:female parasitoid ratio of 100:1 was found to be most efficient in terms of number of parasitoid cocoons produced per female parasitoid, but a ratio of 100:2 was most efficient in terms of number of cocoons per rearing cup. OverwinteringC. melanoscela cocoons under natural conditions for 25 weeks (November placements) before expectedL. dispar egg hatch (mid-April) resulted in excellent synchrony with host egg hatch. Alternatively, holdingC. melanoscela cocoons in cold storage for 23 or more weeks at 5°C resulted in adult parasitoid emergence beginning 10 days after removal from cold storage, and proper timing of removal would result in similar synchrony of adult emergence with host egg hatch. These alternative release strategies give managers increased program flexibility.     

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.      

Literature review ofOoencyrtus kuvanae [Hym.: Encyrtidae], an egg parasite ofLymantria dispar [Lep: Lymantriidae]

Literature onOoencyrtus kuvanae (Howard) from throughout the world is reviewed. References from Asia, Japan, Europe, Africa, and North America, covering the years 1900–1983, are included. The information is divided into the following subject areas: taxonomy, host range, distribution and introductions, biology and life history, host suitability, behavior and spatial distribution, effectiveness, and population dynamics. Suggestions for future research are presented.     

Effect of parasitism byAscogaster reticulatus [Hym.: Braconidae] on growth of the host,Adoxophyes sp. [Lep.: Tortricidae]

The developmental interaction between the egg/larval parasitoid,Ascogaster reticulatus Watanabe (Hymenoptera: Braconidae) and its host,Adoxophyes sp. (Lepidoptera: Tortricidae) was examined. Prior to the egress of a final-instar parasitoid larva from the 4^th-instar host larva, host weight decreased by 22% from the maximum weight. The final body weight of a host larva was 27% of the maximum weight of a healthy 5^th-instar host. Food consumption was significantly reduced in both 3^rd-and 4^th-instar parasitized larvae compared with healthy ones. In the 4^th instar, a parasitized larva consumed 28% less artificial diet and produced less frass than a healthy larva. The growth rate of the endoparasitoid larvae greatly increased after their host's molt to the 4^th instar. Parasitoid larval volume increased 40 fold in the 4^th-instar host.      

Influence of maternal age and host deprivation on egg production and parasitization byMicroplitis croceipes [Hym.: Braconidae]

The effect of maternal age and hostHeliothis virescens (F.) deprivation on egg production and allocation byMicroplitis croceipes (Cresson) was determined in the laboratory on 0.5, 1.0, 3.0, 6.0, 9.0, and 12.0 days old parasitoids. In host-deprived parasitoids, newly-emerged (0.5-day old) females produced significantly fewer eggs than older ones; egg production peaked 3 to 6 days after emergence and declined thereafter. However, the number of eggs found in undeprived parasitoids at various ages suggested a cyclical pattern of egg production. The rate of parasitization by host-deprivedM. croceipes was higher in 1.0 to 6.0 days old than in newly-emerged or older females and was correlated strongly with egg production (r=0.93). The first observation on premature larval hatching inM. croceipes was documented.      

Incidence of parasites ofLymantria obfuscata [Lymantriidae: Lepidoptera] in Kashmir

Incidence of parasites ofLymantria obfuscata Walker [Lymantriidae: Lepidoptera] was studied in Kashmir during 1983 and 1984. The only egg parasite reared wasAnastatus kashmirensis Mathur parasitising between 4.49 to 11.92 percent of eggs. From 15 study sites as many as 10475 larvae of different stages and pupae were collected and reared in laboratory.Exorista rossica [Tachinidae: Diptera] was recorded to parasitize upto 8.42 per cent of larvae compared to 0.89 percent byCompsilura sp.Tetrastichus sp. [Eulophidae: Hymenoptera] was observed to be most dominant of the 6 pupal parasites, accounting for 33.41 percent of the measured parasitism, followed byPimpla sp. [Ichneumonidae: Hymenoptera] andTheronia atalantae atalantae [Ichneumonidae: Hymenoptera] which parasitized 6.84 and 4.03 per cent of pupae respectively.Brachymeria intermedia Nees [Chalcididae: Hymenoptera] was recorded to parasitize upto 2.98 per cent whereasBrachymeria lasus Walker recorded for the first time in Kashmir was found to parasitize up to 2.01 per cent, but was not widely distributed in the State.     

Biology ofMicroplitis mediator [Hym.: Braconidae] a gregarious endoparasite ofAgrotis segetum [Lep.: Noctuidae]

Microplitis mediator (Haliday) a gregarious endoparasite was recorded for the first time fromAgrotis segetum (Schiff) in Ankara, Turkey. The female parasites found their hosts by responding to the faeces of the caterpillars. An average, females laid 15.5±1.6 eggs in the bodies of their hosts. The newly laid eggs were elongated, oval in shape and 0.23±0.004 mm long and 0.07 mm wide. They hatched in 5, 4 and 3 days at 20±2°C, 25±2°C and 30±2°C respectively when maintained at 60–70% R.H. and 14∶10 light∶dark regime. At the same temperatures, the larval stage lasted for 24.9±0.6, 18.2±0.4 and 17.1±0.5 days respectively. The prepupal stage was completed in 2 days at 25±2°C, whereas the prepupal and pupal (cocoon) stage lasted 10.9±0.2, 7.0±0.1 and 6.2±0.1 days respectively at the temperatures mentioned above. The adults started mating and feeding shortly after emergence. Female parasites started laying after one day, 7–11 hours and 5–7 hours at the temperatures stated above. At these temperatures females lived for 10.8±0.2, 5.4±0.1, 4.6±0.1 days and laid on average 556, 484 and 363 eggs respectively, whereas the males survived 10.5±0.3, 4.7±0.1 and 4.4±0.1 days respectively.      

Biology ofPhanerotoma hendecasisella [Hym: Braconidae] a parasitoid ofDiaphania indica [Lep.: Pyralidae]

Studies were conducted on the solitary egg-larval endoparasitoidPhanerotoma hendecasisella Cam. [Hymenoptera: Braconidae] to determine its biology onDiaphania indica (Saunders) [Lepidoptera: Pyralidae]. Larvae pass through 3 stages as determined by the shape and size of the mandibles. Mean developmental period from egg to adult was 26.51 days at 26.06 °C and 73.88% RH. There is no preoviposition period. The sex ratio was 1∶1.12 (male/female). Mean adult longevity was not different for ♂♂ and ♀♀.      

Cold tolerance of coccons ofAllorhogas pyralophagus [Hym.: Braconidae]

Cold tolerance studies were conducted under laboratory conditions for coccons ofAllorhogas pyralophagus Marsh, a Mexican parasitoid of graminaceous borers. By storage, developmental time (from cocoon to adult emergence) could be extended by 2 to 6 times. However, cocoons stored for more than 14 days at 2°C failed to survive, while at 5 and 10°C, about 50% emergence was recorded for upto 21 days of storage. With respect to survival and adult longevity, 10°C seemed to be the most suitable storage temperature. Pre-emergence period was also significantly increased by storing cocoons for 21 to 35 days at this temperature. Sex-ratio of emerging adults was not significantly affected by storage. Fecundity was adversely affected in all the treatments except in the case of females emerging from cocoons stored at 5°C for 7 days. The progeny of parasitoids which emerged from cocoons stored at 5 and 10°C for 35 days consisted of only males. It is clear from the present study thatA. pyralophagus cocoons are more amenable to short-term storage. Contribution No. 285/87 of the Indian Institute of Horticultural Research, Bangalore-560 089.     

The effect of varying alkaloid concentrations on the feeding behavior of gypsy moth larvae, Lymantria dispar (L.) (Lepidoptera: Lymantriidae)

Nine alkaloids (acridine, aristolochic acid, atropine, berberine, caffeine, nicotine, scopolamine, sparteine, and strychnine) were evaluated as feeding deterrents for gypsy moth larvae (Lymantria dispar (L.); Lepidoptera: Lymantriidae). Our aim was to determine and compare the taste threshold concentrations, as well as the ED₅₀ values, of the nine alkaloids to determine their potency as feeding deterrents. The alkaloids were applied to disks cut from red oak leaves (Quercus rubra) (L.), a plant species highly favored by larvae of this polyphagous insect species. We used two-choice feeding bioassays to test a broad range of biologically relevant alkaloid concentrations spanning five logarithmic steps. We observed increasing feeding deterrent responses for all the alkaloids tested and found that the alkaloids tested exhibited different deterrency threshold concentrations ranging from 0.1 to 10 mM. In conclusion, it appears that this generalist insect species bears a relatively high sensitivity to these alkaloids, which confirms behavioral observations that it avoids foliage containing alkaloids. Berberine and aristolochic acid were found to have the lowest ED₅₀ values and were the most potent antifeedants. Handling Editor: Joseph Dickens.     

Effects of bacterial contamination on development ofMicroplitis croceipes [Hym.: Braconidae]

Bacterial contaminants ofHeliothis virescens (F.) influenced the development ofMicroplitis croceipes (Cresson). Among the four bacterial species studied, the most virulent wasPseudomonas maltophilia Hugh and Ryschenkow followed byBacillus subtilis (Ehrenberg) Cohn. Both bacteria caused severe mortality in all stages ofMicroplitis tested.Microplitis larvae were less susceptible toEscherichia coli (Migula) Castellani and Chalmers andLeuconostoc mesenteroides (Tsenkovskii) van Thieghem than toB. subtilis andP. maltophilia. AlthoughE. coli did not affect the number of cocoons produced, adult emergence was lower than in controls. Longevity of adultMicroplitis exposed to bacterially contaminated honey-water was greatly reduced in all bacterial treatments.      

Effects of Glyptapanteles liparidis (Hym.: Braconidae) parasitism, polydnavirus, and venom on development of microsporidia-infected and uninfected Lymantria dispar (Lep.: Lymantriidae) larvae

Effects of parasitism, polydnavirus, and venom of the endoparasitoid Glyptapanteles liparidis on Lymantria dispar larvae infected with the microsporidium Vairimorpha sp. and uninfected hosts were studied. We tested the impact on growth and development of hosts, as well as on microsporidian infection. Both parasitism and polydnavirus/venom treatment alone caused a slight increase in growth rate and relative growth rate in uninfected fourth instar hosts. This effect was more pronounced with the addition of Vairimorpha infection. With no parasitism, however, infection reduced host growth markedly. Microsporidiosis delayed larval molts of L. dispar, and additional polydnavirus/venom treatment or parasitization induced significantly earlier molting. Polydnavirus/venom treatment of uninfected L. dispar resulted in prolonged larval development due to supernumerary molts and in higher pupal mortality. Infected larvae treated with polydnavirus/venom died earlier than infected larvae that were not treated and produced more Vairimorpha spores per unit fresh mass of the host.     

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.      

Parasites recovered from pupae ofLymantria dispar [Lep.: Lymantriidae] in Romania, 1978

In a survey at 5 sites in southern Romania for parasites of pupalLymantric dispar (L.), 8 species were recovered: 3Tachinidae (Dip.); Blepharipa pratensis (Meigen),Parasetigena silvestris (Robineau-Desvoidy), andExorista larvarum (L.); 1Chalcididae (Hym.); Brachymeria intermedia (Nees); 4Ichneumonidae (Hym.); Theronia atalantae atalantae (Poda),Coccygomimus instigator (F.),C. turionellae turionellae (L.), andEphialtes compunctor compunctor (L.). This was the 1 st reported recovery ofE. c. compunctor from L.dispar. Overall parasitism was low, and it is unlikely that additional surveys in this area will yield new parasites for introduction into the U.S.

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Résumé Cinq localités dans le sud de la Roumanie ont été prospectées pour recenser les parasites des nymphes deLymantria dispar (L.). Huit espèces de parasites ont été obtenues:Blepharipa pratensis (Meigen),Parasetigena silvestris (Robineau-Desvoidy),Exorista larvarum (L.),Brachymeria intermedia (Nees),Theronia atalantae atalantae (Poda),Coccygomimus instigator (F.),C. turionellae turionellae (L.), etEphialtes compunctor compunctor. Cette dernière espèce étant nouvelle surL. dispar. Le parasitisme total étant très bas, les auteurs en déduisent que des prospections supplémentaires dans cette région ont peu de chance d'être valables en vue de l'introduction aux états-Unis de nouvelles espèces contreL. dispar.

     

Forest and laboratory evaluations of hybridizedApanteles melanoscelus [Hym.: Braconidae], a parasitoid ofPorthetria dispar [Lep.: Lymantriidae]

Hybrids ofApanteles melanoscelus (Ratzeburg) were produced from colonies originating from France, Yugoslavia, and Connecticut. All strains, as well as freshly collected “wild” Connecticut parasitoids of the same species were evaluated in the laboratory for developmental rate, host attack rate, and sex ratios. Development was significantly slower in all the laboratory strains compared to the progeny of forest collected Connecticut females. Progeny production was greater (almost 2X) for the “wild” females and the French-Yugoslavian-Connecticut hybrid than for the laboratory Connecticut strain. The proportion of females collected from the “wild” (Connecticut) strain was higher than that observed in any laboratory strain. A field test was conducted using the triple hybrid in 3 release plots with ca. 6000A. melanoscelus cocoons released per plot in central Connecticut, U.S.A. Weekly collections of gypsy moth larvae showed that the % parasitism was significantly higher in release plots than in the 3 check plots. These results suggest the value of inundative releases ofA. melanoscelus for reduction of sparse gypsy moth populations, but they did not show that hybridization of these strains produced a more effective parasitoid under forest conditions.     

Avoidance of super-parasitism of stem-boring larvae byChasmodon apterus [Hym.: Braconidae]

The major parasitoid attackingOscinella spp. larvaeChasmodon apterus, demonstrates an ability to avoid superparasitism. However, avoidance is imperfect and in the present work 13% of parasitized larvae were superparasitized. When superparasitism occurred the parasitoid larvae competed, apparently by physiological methods, although physical fighting was observed on one occasion. Multiple parasitism was rare.