Parasitoid Cocoons Research Articles

Conflicts between a Fungal Entomopathogen, Zoophthora radicans, and Two Larval Parasitoids of the Diamondback Moth

Zoophthora radicans (Zygomycetes: Entomophthorales), Diadegma semiclausum (Hymenoptera: Ichneumonidae), and Cotesia plutellae (Hymenoptera: Braconidae) are all natural enemies of the diamondback moth, Plutella xylostella (Lepidoptera: Yponomeutidae). Adult C. plutellae are not susceptible to Z. radicans infection but the pathogen can infect and kill adult D. semiclausum. Infection of adult D. semiclausum prior to exposure to P. xylostella host larvae significantly reduced the number of parasitoid cocoons subsequently developing from the host larvae. Although Z. radicans infection of P. xylostella larvae prior to parasitism by D. semiclausum or C. plutellae always resulted in the death of the immature parasitoids, neither species discriminated between healthy and Z. radicans-infected host larvae in an oviposition choice experiment. However, host larvae recently killed by Z. radicans were always rejected by D. semiclausum but sometimes accepted by C. plutellae. At 20°C, egg to pupa development took 6.7 and 7.8 days for D. semiclausum and C. plutellae, respectively. C. plutellae parasitism significantly increased host instar duration but D. semiclausum parasitism did not. Cadavers of P. xylostella larvae parasitized 1 day prior to fungal infection showed no reduction in Z. radicans conidia yield. However, cadavers of larvae parasitized 3 days prior to fungal infection demonstrated a marked decrease in Z. radicans conidia yield. Z. radicans infection of P. xylostella larvae ≤4 days after parasitism resulted in 100% parasitoid mortality; thereafter, the reduction in parasitoid cocoon yield decreased as the time between parasitism and initiation of fungal infection increased. The extended duration of the host larval stage induced by C. plutellae parasitism increased the availability of the parasitoid to the pathogen. Estimates of interspecific competition indicated a similar pattern for the interaction between Z. radicans and each species of parasitoid.

Effect of antifeedants on the diamondback moth (Plutella xylostella) and its parasitoidCotesia plutellae

Two neem preparations and the bitter-tasting synthetic chemical denatonium benzoate were tested in the laboratory as antifeedants against the diamondback moth, Plutella xylostella L. The effects of the three materials on Cotesia plutellae (Kurdjumov), a hymenopteran parasitoid of ­P xylostella, were also recorded. All three materials significantly reduced the food consumption of ­P xylostella larvae. Parasitoid cocoons were formed on approximately half of those larvae which had been exposed to female C plutellae, regardless of antifeedant treatment, but emergence of adult parasitoids from the cocoons was significantly reduced by antifeedant treatment. In terms of food consumption and mortality of unparasitised P xylostella larvae, and emergence of adult C plutellae, the effect of each antifeedant preparation was directly related to the concentration of material used, but the effects of the neem preparations were greater than those of denatonium benzoate. However, no adult P xylostella emerged on any antifeedant treatment, therefore some of the parasitoids survived antifeedant treatments which were fatal to the unparasitised hosts. © 2000 Society of Chemical Industry

Factors influencing reproductive strategies of the vespid parasitoid Sphecophaga vesparum vesparum (Hymenoptera: Ichneumonidae)

The vespid wasp parasitoid Sphecophaga vesparum vesparum (Curtis) (Hymenoptera: Ichneumonidae) produces three types of cocoons, “white”, “weak‐walled yellow” and “yellow”. The adults that emerge from them represent a transition from wingless female morphs that emerge in a few weeks to alate females that remain dormant for 1–4 years. To determine the role of host age, nest temperature, and any intrinsic differences in the eggs on parasitoid cocoon type, newly emerged adult parasitoids were placed individually onto pieces of worker or queen comb containing Vespula vulgaris (L.) hosts of known age, and kept at different temperatures. Cocoon forms showed a continuous gradient in type rather than discrete morphs as was previously suggested. Cocoon type was principally determined by the age of the host on which the parasitoid oviposited; yellow cocoons resulted from eggs laid in early stages after the pupal cap was spun, and white cocoons from eggs laid on more developed pupae. Host age also influenced parasitoid cocoon weight. Temperature affected the rate of development of vespid immatures relative to the parasitoid, and so indirectly influenced cocoon type by altering the length of time parasitoid larvae were able to extract nutrients from developing wasp pupae. Low temperatures did not restrict cocoon production, as parasitoid cocoons developed at lower temperatures (19°C) than those at which the host could successfully complete development (lower limit between 25 and 26.3°C). There was no evidence of different parasitoid egg types, but adult parasitoids influenced cocoon type by preferential oviposition on host immatures that had recently spun caps. Only 20% of eggs laid produced weak‐walled yellow or white cocoons, which are the only cocoon types that reinfest the same nest. If this proportion reflects productivity in the field, then the spread of parasitoid populations within wasp colonies will be restricted. This effect will limit the impact of Sphecophaga as a biological control for Vespula spp.

Perfectionnement des méthodes de production et de lâcher deCotesia melanoscela, parasite de début de saison deLymantria dispar

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.

A Model for the Effect of Sphecophaga vesparum vesparum as a Biological Control Agent of the Common Wasp in New Zealand

1. A model of intermediate complexity is described to predict and understand the reasons for the ultimate impact of Sphecophaga vesparum vesparum (Hymenoptera : Ichneumonidae), introduced as a classical biological control agent of Vespula vulgaris (Hymenoptera : Vespidae) in New Zealand. The model was parameterized as far as possible from independent field data then fitted to the observed performance of the parasitoid over the first 5 years after release. 2. Wasp nest densities monitored over 5 years and seven sites in beech (Nothofagus spp.) forests averaged 12.2 ha -1 , with a maximum of 33 ha -1 . These are among the highest Vespula densities in the world. A Ricker model accounted for changes in nest density from year to year, giving a maximum ratio of increase in nest density of 3.3 per year and overcompensating density dependence at high densities, probably caused by queen competition and nest usurpation in spring. 3. The parasitoid has established at low levels in two sites, one of which has been studied in detail. Here parasitism levels (% autumn nests parasitized) have remained around 5% for 5 years, with a slight suggestion of an upward trend. 4. The model suggests that ultimate parasitism levels depend almost entirely on the parasitoid's effective ratio of increase, R, defined as the maximum number of spring adults produced per spring adult (spanning several intermediate summer generations). Ultimate suppression of wasp nest densities depends on R, the rate of increase in parasitism within a year, and the mortality of parasitized early spring nests. The initial rate of build-up of parasitism additionally depends on the pattern of emergence of parasitoid cocoons, which may extend over 4 years. 5. R for S. vesparum vesparum at the site where it has established appears to be about 1.3-1.6, which is close to the lower limit of 1 for persistence. Such values suggest an ultimate suppression of wasp nest density and level of parasitism of about 10% and 25%, respectively. 6. The low value of R at this site and the parasitoid's limited likely impact, appear to be due to a combination of delayed emergence of overwintering cocoons, low overwintering cocoon survival, and low production of cocoons per parasitized autumn nest. Additionally, a reduced or variable attack rate may contribute to the parasitoid's lack of establishment at other sites, possibly due to poor synchrony between spring emergence of wasp queens and adult parasitoids. 7. A more successful parasitoid species or ecotype would need to have a higher R value, which requires cocoon emergence after 1 year rather than 2 or more, and/or higher values for the above parameters, particularly overwintering survival of cocoons. In addition, it would have to : act after the spring host density dependence ; cause a high (> 80%) mortality of parasitized spring nests ; and ideally also reduce queen output from autumn nests. An alternative to an agent causing mortality to spring nests would be a microbial one which significantly reduced queen fertility without impairing her competitive ability. 8. A 50% reduction in queen output from autumn nests, due to parasitism by S. vesparum vesparum, contributes little to host suppression because of its timing relative to host density dependence. If an alternative agent reduced wasp densities to a greater extent, the additional contribution of reduced queen output would become relatively more significant as density declined and the density dependence became less intense.

Experimental studies upon the parasitoid complex of the gypsy moth (Lymantria dispar L.) (Lep., Lymantriidae) in lower host populations in eastern Austria*

Abstract: The parasitoid complex of low gypsy moth populations, using the host exposure technique, was studied in eastern Austria in the late 70s. The following 10 larval parasitoid species were recovered: Braconidae: Apanteles melanoscelus (Ratzeburg), Apanteles liparidis (Bouché), Meteorus pulchricornis (Wesmael); Ichneumonidae: Casinaria sp., Hyposoter tricoloripes (Viereck), Phobocampe disparis (Viereck); Tachinidae: Parasetigena silvestris (Robineau‐Desvoidy), Blepharipa pratensis (Meigen), Compsilura concinnata (Meigen), Exorista fasciata (Fallen).Parasitism obtained from the rearing of 1961 host larvae amounted to 58.1% and based on both the larval rearings and the collection of parasitoid cocoons to about 87%. Parasitism encountered by dissecting gypsy moth larvae showed generally high values (37–89%) 3–4 weeks after release. The dominating parasitoid species were the braconid A. melanoscelus and the tachinids B. pratensis, P. silvestris and later in the season C. concinnata. The braconid suffered an average mortality of almost 50% by 16 hyperparasitoid species. Notes on the dominating parasitoid species are given.

Potential of an Unnatural Host, Galleria mellonella (Lepidoptera: Galleriidae), in Rearing the Corn Earworm Endoparasitoid Microplitis croceipes (Hymenoptera: Braconidae)

Females of the endoparasitoid Microplitis croceipes (Cresson) oviposited in early 5th instars of an unnatural host, greater wax moth, Galleria mellonella (L.), after they had been treated with hemolymph and frass from the natural host corn earworm, Helicoverpa zea (Boddie). Third-instar H. zea , similar in size to 5th-instar G. mellonella were used for comparison. Forty-one percent of the G. mellonella larvae were accepted for opposition, and 90% of 3rd instars of the natural host. Parasitoid cocoons weighed 8.30 ± 0.34 mg (mean ± SE) compared with 14.08 ± 0.16 mg from H. zea . Adult emergence was 46.9 and 92.6% on G. mellonella and H. zea , respectively. The sex ratio of parasitoids reared on G. mellonella (40% male to 60% female) was not significantly different from parasitoids reared on H. zea (35% male to 65% female). F1 adults reared on G. mellonella were smaller than those reared on H. zea . When the F1 progeny of G. mellonella -reared parents were reared back on the natural host, H. zea , the resultant adult parasitoids were of normal size.

Usurpation of host behaviour by a parasitic wasp

Abstract. Host behaviour manipulation was examined in caterpillars, Pieris brassicae , parasitized by the gregarious braconid wasp, Cotesia glomerata. Following egression of the parasitoids from the host, the moribund caterpillar remains on the pupating parasitoids, spins a web over the parasitoid cocoons, and responds aggressively when disturbed. Cross-species experiments indicated that C. glomerata, but not the congener C. rubecula, has the capacity to interfere with the post-egression behaviour of the host. Dying hosts are viewed as a transient 'functional extension' of the parasitoid that may contribute to parasitoid survival during pupal development by protecting the pupae from natural enemies. This is thought to be the first report on host behaviour manipulation that occurs beyond the intimate physical association between the parasite and the host.

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.

Microplitis croceipes (Hymenoptera: Braconidae) Diapause Response to Insectary Conditions

Annual cycles of activity and development occur across the class Insecta and have evolved as a strategy to avoid or exploit environmental extremes (Saunders 1982). Parasitoids, especially host-specific species, necessarily respond to seasonal activities, or occurrence, of their host. Understanding the seasonal relationship between agricultural pests and their parasitoids is important to understand the parasitoids' potential for biological control (Powell et al. 1989). To better understand the seasonal synchrony between Heliothis spp and Microplitis croceipes (Cresson), photoperiod and temperature studies were undertaken in the laboratory and insectary during 1984 and 1985 at the University of Arkansas. Diapause is induced in H. virescens by a photoperiod of 10:14 (L:D) and inhibited by a photoperiod of 14:10 (L:D) in a Louisiana biotype (Phillips & Newsom 1966). High temperature (270C) counters the effect of short daylengths. The sensitive stage is the larva, in which M. croceipes is endoparasitic. In the laboratory, M. croceipes demonstrates 50% diapause induction in response to a critical Light:Dark ratio of 10.30:13.30 (21?C) and 11.00:13.00 (18?C) (Brown & Phillips 1990). Temperature alone (15?C) also induces 100% diapause at a photoperiod of 14:10 (L:D). The M. croceipes larva is the sensitive stage and the diapausing stage is the prepupa. There is significant interaction between photoperiod and temperature in diapause induction. Development times from cocoon formation to adult emergence is highly variable. This variability may be favorable in that it allows M. croceipes to cope with erratic and unfavorable conditions during the spring when host populations may be low or seasonal climatic changes have not stabilized. For the insectary study, 20 H. virescens were reared to third instar at 24?C and 14:10 (L:D) photoperiod (non-diapausing conditions) in 180 ml waxed paper cups (rearing chamber) containing approximately 5 ml of pinto bean medium (Burton 1969). Parasitoids were reared from field-collected Heliothis spp. and held at 26C, 50% RH, and 14:10 (L:D) photoperiod. Hosts were exposed to the parasitoid by placing two 5-7 day-old M. croceipes females in the above rearing chamber for 8 h. Parasitized hosts were then transferred to individual 30 ml rearing cups containing pinto bean diet and placed in the insectary on different dates during a two year period (Table 1). The insectary was 3.7 by 6.1 by 2.4 m with vertical walls made of standard mesh screening material. Media cups containing the host and diet were placed in the insectory and observed on a biweekly basis until 22 December, when the parasitoid cocoons were removed. Cocoons were then placed in a 14:10 (L:D) (long day) photoperiod and 24?C regimen and monitored daily for emergence. Ambient temperatures and humidities in the insectary were recorded with a Model 594 Bendix Hygrothermograph (Bendix Environmental Science Division, Baltimore, Maryland 21204). Diapause response averaged 3.4% when the parasitized hosts were placed in the insectary in late August (Table 1). Diapause increased to 98.6% when hosts and parasitoids were placed in the insectary on 25 September. This 30 day period represents

Release and recovery of the introduced wasp parasitoid,Sphecophaga vesparum vesparum(Curtis) (Hymenoptera: Ichneumonidae) in New Zealand

Abstract The introduced European wasp parasitoid, Sphecophaga vesparum vesparum (Curtis) was reared in the laboratory at DSIR Lincoln then distributed in the South Island and at one location in the North Island, from 1985 to 1987. In early November 1986, one yellow parasitoid cocoon was recovered from an overwintered nest of the German wasp, Vespula germanica (F.), in suburban Christchurch. Before that recovery about 197 female parasitoids had emerged from release boxes in the area, and 41 wasp nests had been collected. There have been no other recoveries in this area, despite the emergence of about 1585 parasitoids from released cocoons and the collection of a further 385 wasp nests. Systematic searches for and examination of wasp nests from 17 sites in the north and west of the South Island recovered rapidly multiplying parasitoid populations from 2 out of 42 nests of the common wasp, Vespula vulgaris (L.) at Pelorus Bridge, 42 km east of Nelson. The nests were 33 m and 625 m away in separate directions...