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.      

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.      

Response of the braconid parasitoid Cotesia (= Apanteles) glomerata to volatile infochemicals: effects of bioassay set-up, parasitoid age and experience and barometric flux

Upon initiating a research project on the role of volatile infochemicals in the tritrophic system Cotesia (= Apanteles) glomerata (L.)-Pieris brassicae (L.)-cabbage, a bioassay was developed to investigate the response of C. glomerata. The bioassay should be effective in terms of high responsiveness and minimum variability and constructed through a comparative approach. Twenty seven treatments, organized in a factorial randomized block design, compared the effect of three bioassay set-ups (glasshouse flight chamber, wind-tunnel and Y-tube olfactometer), three parasitoid age groups (1–2, 4–5 and 8–9 days old females), three pre-treatment experiences (naive, damage experienced and oviposition experienced wasps) and the day-to-day effect on response of C. glomerata to clean cabbage (CC) and planthost complex (PHC) in a dual choice test.The best results with regard to the strength and consistency of response to the PHC were obtained in the glasshouse flight-chamber by 4–5 days old female wasps with either damage or oviposition experience (94 and 90%, respectively). It is therefore recommended as a suitable bioassay for studying the role of volatile infochemicals in host-habitat location by C. glomerata.A day-to-day variation in response was found in the glasshouse and wind-tunnel. It was correlated with the direction of change in barometric pressure within the time period of the experiment, showing that steadily increasing atmospheric pressure yields a significantly higher response than steadily decreasing or fluctuating barometric flux. To control for the day effect it is suggested to conduct further experiments in a block design, having day as a block. Several aspects of the infochemical ecology of C. glomerata are discussed.     

Effect of the number of parasitoid (Apanteles kariyai) eggs [Hym.: Braconidae] on the growth of host (Leucania separata) larvae [Lep.: Noctuidae]

The developmental interactions between a gregarious endoparasitoid,Apanteles kariyai Watanabe and its host,Leucania separata Walker, were investigated. The parasitoid laid more eggs in older hosts. Host size increased gradiently as the instar advanced, but the number of eggs laid per host did not increase accordingly. The net weight of the host was correlated positively with the number of eggs laid and with the total weight of parasitoids, especially in cases of parasitization at 3rd (5th-instar type), 4th and early 6th instar where the correlation was significant at 1% level. It follows therefore that the more parasitoids there are relative to their host size, the more they contribute to make the host size larger.     

Preference ofPholetesor ornigis [Hym.: Braconidae] for the sap-feeding larvae of its host,the spotted tentiform leafminer,Phyllonorycter blacerdella [Lep.: Gracillaridae]

Significantly more eggs were deposited by the braconid,Pholetesor ornigis (Weed), in the sap-feeding larvae (i.e. instars 1–3), than in the tissue-feeding larvae (i.e. instars 4–5), of its host, the spotted tentiform leafminer,Phyllonorycter blancardella (Fabr.).     

Host specificity ofCostesia yakutatensis [Hym.: Braconidae] on lepidoptera in peppermint and alfalfa

Seven species of Lepidoptera, common to alfalfa and peppermint in western Oregon, were tested as potential hosts forCotesia yakutatensis (Ashmead). Laboratory and field studies demonstrated that onlyAutographa californica (Speyer) andTrichoplusia ni (Hubner) were suitable. Percent parasitism, duration of oviposition, and number of parasitoids per host were highest whenC. yakutatensis was associated withA. californica.     

The effect of host age ofLymantria dispar larvae [Lep.: Lymantriidae] on the development ofGlyptapanteles liparidis [Hym.: Braconidae]

The endoparasitic development ofG. liparidis was examined in 3 different host stages of gypsy moth larvae. Hatching ofG. liparidis-larvae occurred 3 to 5 days after oviposition in hosts parasitized during their premoulting period, and after 5 to 7 days in those parasitized in the 3^rd midinstar state. The parasites generally moulted to the 2^nd larval instar between the 11^th and 13^th day in the first group, and between the 13^th and 15^th day in the latter, when they had reached a volume of 0.04–0.05 mm³. The positive correlation between host ecdysis and the ecdysis of 1^st stadium larvae to L₂ suggested that host moulting influenced the development of the parasitoid larvae. Emergence from the host larvae occurred at 20°C after 27 days on average, and coincided with the parasites moulting to the 3^rd instar. Five to 7 days after spinning their cocoons near the developmentally arrested host larva, the male, and 1 to 2 days later the female wasps eclosed. Due to the variation in the number of parasites per host, no difference was observed between the hosts parasitized at various stages; however, a tendency for later parasitized hosts to contain more parasite larvae was evident. The nutritional conditions of the moth parental generation influenced both host and parasite development. On the other hand no influence of host age was observed on emergence dates of larvae and wasps.      

Response ofChelonus blackburni [Hym.: Braconidae] to different ages and densities of potato tuber moth eggs

The response of an efficient egg-larval parasitoidChelonus blackburni Cameron to different ages and densities of potato tuber mothPhthorimaea operculella (Zeller) eggs was studied in a laboratory system. The parasitoid accepted 0–1, 1–2 and 2–3 day old eggs for parasitization. However, the eggs belonging to the first two age groups were significantly more acceptable when compared to the last age group. At low host density levels of 2 and 5 eggs per parasitoid, parasitoid emergence was zero. On increasing the host density, percent progeny production increased till a plateau was reached at a parasitoid-host ratio of 1∶50. This ratio thus proves to be ideal for obtaining maximum percent progeny production in the case of 0–1 and 1–2 day old eggs. Further increase in host density did not result in any significant increase in percent progeny production.      

Influence of parasitoid-host density and host availability on the laboratory propagation ofMicroctonus aethiops [Hym.: Braconidae] parasitoid ofHypera postica [Coleop.: Curculionidae]

Laboratory studies of the arrhenotokous braconid wasp,Microctonus aethiops (Nees) were conducted relative to maximizing parasitoid production without adversely affecting sex ratios of the progeny. The influence of hostHypera postica (Gyllenhal) and parasitoid densities on parasitoid productivity was evaluated. Maximum production or a mean 25.8M. aethiops progeny were obtained per female when the host parasitoid ratio was 50∶1. More than one parasitoid per rearing cage resulted in fewer parasitoid progeny per female and increased host mortality. Oviposition significantly increased when female parasitoids were exposed to 25 different weevils every 24 hours. The most intense ovipositional activity usually occurred during the first 48 hours of exposure. However, superparasitism occurred if exposure to 25 hosts continued for more than 24 hours. Continuous and discontinuous oviposition patterns did not affect the numbers of parasitoid progeny produced. However, fewer females were produced when new weevils were provided every 24 hours as in the continuous oviposition group.     

The influence of female age and host size on the sex ratio of the parasitoid Opius concolor

The sex ratio of the progeny of single females parasitizing large hosts favoured the females (sex ratio=0.26); but on small hosts favoured the males (0.73). No differences in mortality of the sexes were detected. The sex ratio was independent of female age when large hosts were used. The percentage of males observed in the progeny of the first day of female oviposition was significantly greater than the mean, irrespective of the age at which female oviposition began. When females were exposed to small hosts, a greater percentage of females was observed in the progeny from the last days of oviposition.

---

Résumé L'influence de la taille de l'hôteret de l'âge de la femelle sur le taux sexuel de la descendance a été étudiée sur le parasitoïde Opius concolor Szépl.Le taux sexuel de la descendance des femelles isolées est favorable aux femelles (t.s.=0,26) quand elles ont à leur disposition des hôtes de grande taille, tandis qu'avec des hôtes petits le taux sexuel est favorable aux mâles (t.s.=0.73). On n'a pas détecté de mortalité différentielle des sexes.Les pourcentage de mâles obtenu le premier jour de ponte des femelles sur les hôtes de grande taille est significativement différent de la moyenne, indépendamment de l'âge de la femelle à ce moment. Cependant, sur des hôtes petits, bien que restant favorable aux mâles dans l'ensemble, une plus grande proportion de femelles à partir des premiers jours de ponte a pu être observée.

     

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.      

Bionomics ofTrioxys indicus [Hym.: Aphidiidae], a parasitoid ofAphis craccivora [Hem.: Aphididae]: 31. Effect of host haemolymph on the numerical response of the parasitoid

The influence of kairomones on the numerical response of the parasitoidTrioxys indicus against its hostAphis craccivora at its varying density was studied. The kairomones (applied as aqueous extract of the host) significantly enhanced the rate of parasitisation and multiplication and the area of discovery of the parasitoid and also the K-values of mortality of the host at all parasitoid densities introduced (1, 2, 4, 8, 12 and 16 parasitoids) into troughs having about 200 hosts. The sex-ratio of F₁ offspring decreased at lower parasitoid densities and remained more or less unchanged at higher parasitoid densities after the application of kairomones. The present findings indicate that if kairomones are applied properly, the number of hosts destroyed by a stimulated parasitoid will be about 200, twice the number reported earlier, thus fewer parasitoids will be needed to regulate an estimated population of the hosts.      

Intraspecific host discrimination and larval competition inMicroplitis croceipes,Microplitis demolitor,Cotesia kazak (Hym.: Braconidae) andHyposoter didymator (Hym.: Ichneumonidae), parasitoids ofHeliothis virescens (Lep.: Noctuidae)

Intraspecific host discrimination and larval competition were studied forMicroplitis croceipes (Cresson),Microplitis demolitor Wilkinson,Cotesia kazak (Telenga), andHyposoter didymator (Thunberg), solitary endoparasitoids of the tobacco budworm,Heliothis virescens (F.). In ovipositional choice tests between unparasitized and parasitized hosts, the mean number of ovipositions for unparasitized hosts was significantly higher than the mean number of ovipositions for hosts parasitized once by a conspecific female forC. kazak andH. didymator, demonstrating that females of these 2 species discriminate against hosts recently (within a few seconds) parasitized by a conspecific female. No significant difference in oviposition occurred between these 2 kinds of hosts forM. croceipes andM. demolitor. Mean percent parasitization by a 2^nd conspecific female was determined at 24, 48, and 72-h delays in time between the 1^rst and 2^nd female attack, and with no delay. Except for the 0 h time delay forC. kazak andH. didymator, percent parasitization by a 2^nd conspecific female generally decreased as the delay in time between the 1^rst and 2^nd female attack increased. When the 2^nd parasitization immediately followed the 1^rst, one parasitoid larva always eliminated the other by physical combat. With a 24 or 48 h delay between the 1^rst and 2^nd parasitization, the younger larva was the victor over the older larva forM. croceipes, M. demolitor andC. kazak in at least 50% of the cases. Elimination of older larvae by younger larvae was by physical attack. However, forH. didymator, the older instar was the victor, and elimination of younger larvae by older larvae was probably through physiological processes. Further, older larvae ofH. didymator apparently killed the eggs of the 2^nd female by physiological processes.      

Effect of host age on life cycle and morphological characteristics of Glyptapanteles liparidis (Hymenoptera: Braconidae), a parasitoid of Acronicta rumicis (Lepidoptera: Noctuidae)

The life cycle of Glyptapanteles liparidis was 23.75 ± 1.26, 21.95 ± 2.44 and 20.83 ± 0.78 days when fed on the first, second and third instar larvae of Acronicta rumicis, respectively. Although insufficient numbers hindered statistical analysis, the life cycle of G. liparidis appeared to be shortest, 19 days, when fed on fourth instar larvae. The life cycle of G. liparidis tends to shorten as the larvae of A. rumicis fed upon are more advanced. The body length, forewing length and head capsule width of female G. liparidis fed on first instar larvae of A. rumicis were greater than those of males, while the antennae of males were longer than those of females. When fed on second instar larvae, there was no difference in body length and head capsule width between males and females, but the male antennae were longer than the female, and the female forewings were longer than the male. When fed on third instar larvae, there was no significant difference in head capsule width between the sexes, but female body length and forewing length were greater than the male, and the male antennae were longer than the female. On the whole, females were bigger than males in terms of body length and forewing length, while antennae of the males were longer than those of the females. There was no difference in head capsule width between males and females. Body length, antenna length, forewing length and head capsule width of male and female G. liparidis were relatively larger when fed on first instar larvae of A. rumicis than when fed on second and third instar larvae.     

Effects of parasite density and host availability on progeny production byBiosteres (Opius) longicaudatus, [Hym.: Braconidae], a parasite ofAnastrepha suspensa [Dip.: Tephritidae]

Progeny production ofBiosteres (Opius) longicaudatus Ashmead, a larvalpupal parasite of the Caribbean fruit fly,Anastrepha suspensa (Loew) was affected by host availability, previous ovipositional experience, and parasite density and age. Parasitization rates were evaluated in 24.5 cm³ ovipositional cages at parasite densities of 25, 125, and 250 male-female pairs by exposingB. longicaudatus adults to (a) 500A. suspensa larvae for a 24 h period or (b)ad libitum host larvae for each of the 14 days following eclosion. The mean numbers of parasite progeny produced at the 25, 125, and 250 densities were 1076, 1896, and 2038, respectively. The number of progeny produced per surviving female parasite was inversely proportional to the adult parasite density and relatively more female progeny were produced as the adult parasites aged. Host mortality was significantly higher among parasitized larvae. Maximum rearing efficiency was achieved at the 125 density.     

Intrinsic competition between the gregarious parasite,Cotesia glomeratus and the solitary parasite.Cotesia rubecula [Hymenoptera: Braconidae] for their host.Artogeia rapae [Lepidoptera: Pieridae]

The solitary endoparasite,Cotesia rubecula, was superior to the gregarious endoparasite,Cotesia glomeratus, in tests of intrinsic competition for their hostArtogeia rapae. When an egg ofC. rubecula was oviposited in the host prior to those ofC. glomeratus, C. rubecula always won the ensuing competition. When an egg ofC. rubecula was laid in the same host within 48 h after oviposition byC. glomeratus, C. rubecula was successful in more than 90% of the interactions. Even when the egg ofC. rubecula was oviposited in the same host 72 to 96 h after oviposition byC. glomeratus, C. rubecula won the competition approximately 33% of the time. The implications of intrinsic competition are discussed in relation to the establishment ofC. rubecula in an ecosystem containingA. rapae andC. glomeratus.      

Host-handling behavior of the parasitoid,Diglyphus minoeus [Hym.: Eulophidae], parasitizing the honeysuckle leaf-miner,Phytomyza lonicerae [Dipt.: Agromyzidae]

The host-handling behavior of individual female waspsDiglyphys minoeus which attack the larvae of the honeysuckle leaf-miner,Phytomyza lonicerae, include 4 types of behavior: probing, ovipositor insertion, host-feeding, and resting. Ovipositor insertion may either be injection of venom, probing of the host by the sensilla on the ovipositor's tip or egg laying. Three types of attacks were distinguished: oviposition attack for unparasitized larvae, host-feeding attack for unparasitized host larvae and host rejection for previously parasitized host larvae. Oviposition attack was characterized by frequent alternation between probing and ovipositor insertion, long duration of ovipositor insertion and resting, and the long duration of host-handling. Resting behavior is thought to protect the progeny against superparasitism, host-feeding by other wasps or hosts' recovery from paralysis. Host-feeding attack was characterized by frequent alternation between host-feeding and ovipositor insertion and long duration of host-feeding. Host rejection was composed mainly of probing and ovipositor insertion and short handling time.      

Effects of temperature and photoperiod on the development and oviposition ofApanteles sp. groupUltor [Hym.: Braconidae], a larval parasite of the carob mothEctomyelois ceratoniae [Lep.: Pyralidae]

Development of the solitary parasitoidApanteles sp. groupultor in larvae ofEctomyelois ceratoniae was investigated at different constant temperatures. Temperature had a significant effect upon parasitoid development during both host-internal and host-external phases. The duration of the host-internal phase varied from 41 days at 15–17°C to 8.6 days at 29°C, the duration of the host-external phase varied from 16.5 days at 16–17°C to 5.4 days at 29°C. Effect of photoperiod upon parasite development and parasitization of hosts were determined under daily photophases, of 24, 16, 12, 8 and 0 hours. No significant differences in oviposition rate were found among the 5 treatments. In any photoperiod studied, the parasite progeny developed normally without entering diapause.      

Laboratory studies of host finding,acceptance and suitability of the dung-breeding fly,Haematobia thirouxi potans [Dipt.: Muscidae], byAleochara sp. [Col.: Staphylinidae]

Aleochara sp. from southern Africa is a potential candidate for introduction to Australia for control of the Australian buffalo fly,Haematobia irritans exigua De Meijere. Aspects of its host searching and acceptance behaviour were studied in South Africa usingHaematobia thirouxi potans (Bezzi), to assess, in part, its potential value as a biological control agent and to provide a basis for the development of a mass rearing technique. First instars ofAleochara sp. were found to parasitize most effectively those hosts that had buried themselves in the substrate, probably by orienting to a chemical cue and using the tunnels made by the post-feeding larvae. Lower rates of parasitization occurred in pupae placed on the surface of the substrate or buried by the experimenters. They would accept, parasitize and develop on all ages ofH. thirouxi potans pupae, but showed reduced survival in the very oldest ones. Although there was no difference in relative acceptability among hosts of different ages, a higher proportion of younger hosts were parasitized when these had buried themselves, probably due to a tendency of the parasitoids to follow fresher tunnels into the substrate. Survival was high (>80%) at relative humidities from 10–91% but was less than 20% at an R.H. of 100%. In rearing trials, the most economical ratio of parasitoid eggs: hosts was 1∶1.5, with 70% of the parasitoids developing successfully to adults.      

Effect of parasitoid density on the functional response and sex ratio of a cynipoid hyperparasitoidAlloxysta pleuralis [Hym.: Alloxystidae]

Experiment where variable densities (1, 2, 5, 10, 25, 50, 100 and 150) of the parasitoid (5–7 d postparasitised aphids (Aphis craccivora Koch). — parasitised by aphidiid parasitoidTrioxys indicus Subba Rao & Sharma) were exposed to individual hyperparasitoidAlloxysta pleuralis (Cameron) indicated following: (1) with increase of initial host (primary parasitoid) densities the number of hosts hyperparasitised increases sigmoidally reaching to a plateau at 50 host similar to thetype 3 functional response of Holling; the curve was described by a logistic eqution [N_hyp=44.0/(1+exp (4.0–0.16 N_p))], (2) greater host mortality was recorded at lower initial host densityes (≤50); (3) the area of discovery of the hyperparasitoid is inversely density-dependent at higher host densities (≥25); and (4) the variation in host number has no significant influence on the sex ratio of F₁ offspring of the hyperparasitoid which ranges between 0.56–0.67. The implications of these responses of the hyperparasitoidA. pleuralis are discussed.