Oviposition behaviour ofEphedrus cerasicola [Hym.: Aphidiidae] parasitizing different instars of its aphid host

The parasitoidEphedrus cerasicola Starý oviposited in all 4 nymphal instars and in newly moulted adults ofMyzus persicae (Sulzer). The different host categories were offered with no choice. The duration of an oviposition increased with the age of nymphs, being about 13, 18, 21, 22, and 17 s from 1 st instars to adults, respectively. Observations of number of stabbing attacks prior to oviposition, percent of the encounters not resulting in oviposition, time from first encounter to oviposition, handling time and aphid defensive behaviour also indicated that 1 st instarM. persicae are most easily parasitized. The behaviour ofE. cerasicola in encounters with unparasitized and parasitized hosts, suggested that the parasitoid could discriminate. In encounters with parasitized 1 st to 4th instar aphids,E. cerasicola used only the antennae in 80% of the encounters that resulted in discrimination.     

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.      

Morphological observations on the preimaginal stages ofAphelinus varipes (Hym., Aphelinidae) and the effects of this parasitoid on the aphidRhopalosiphum padi (Hom., Aphididae)

Three instar larvae could be observed forAphelinus varipes. In the second and third instars, the colon which forms the largest part of the hindgut was composed of secretory cells. There was a reduction in the size and number of embryos produced by parasitized aphids. Fat cells of parasitized aphids also degenerated sooner than those of unparasitized aphids. The number of mycetocytes remained higher in parasitizedRhopalosiphum padi than in non-parasitized aphids. During the last instar ofA. varipes the host aphid developed into a mummy in which black pigments were incorporated into the exocuticle and the integument of the aphid became sclerotized.     

Parasitoids of the gall-forming aphidSmynthurodes betae [Aphidoidea: Fordinae] in Israel

In an ecological investigation of the gall-forming aphid,Smynthurodes betae Westw., we discovered that more than 20% of the fundatrix galls were parasitized byMonoctonia pistaciaecola Stary (Aphidiidae). This is a new host record for this parasitoid. A Pteromalid hyper-parasite was identified asPachyneuron? leucopiscida Mani. Ecological information on the parasitoid is provided, and the low frequency of parasitoids known from gall-forming aphids, compared with freeliving ones, is discussed.     

The effect of parasitism byHyposoter didymator [Hym.: Ichneumonidae] on food consumption and utilization bySpodoptera litura [Lep.: Noctuidae]

The effect of parasitism byHyposoter didymator (Thunb.) [Hym.: Ichneumonidae] on food consumption and utilization bySpodoptera litura (Fb.) [Lep.: Noctuidae] was studied for seven days, during which the parasitoid completed its larval development. Food consumption, weight gained and faeces produced were significantly less in parasitized larvae than in unparasitized larvae after the 4^th day following parasitization. Approximate digestibility was higher in parasitized larvae after the 2^nd day following parasitization. Efficiency of conversion of ingested and digested food into body weight was greater in unparasitized larvae after the 2^nd day of parasitization. There seems to be a definite immediate advantage to the crop on releasing the parasitoid due to the reduced consumption of food. Contribution No. 46004 of Biological Control Centre (NCIPM), Bangalore 560 024.     

Host age choice for parasitism by Lysiphlebia mirzai and its effect on the development and reproduction of brown citrus aphid

The effects of host age andparasitism by Lysiphlebia mirzaiShuja-Uddin (Hymenoptera: Braconidae) on the development, survivorship,reproduction, and life table parameters ofbrown citrus aphid, Toxoptera citricida(Kirkaldy) (Homoptera:Aphididae) were evaluated at 25 ± 1 °C, 80 ± 5% RH, and a photoperiodof 14:10 (L:D) h. The results showed that theduration from initial parasitization tomummification was independent of the aphid ageat the time of parasitization with a mean of6.0 d. Aphids parasitized at the 1st and 2ndinstar stages and 17% of those parasitized atthe 3rd instar stage failed to reach adulthood,while the rest of the aphids parasitized at the3rd and 4th instar stages and as adults reachedmaturity and produced a number of offspringthat increased with age at parasitization. Thelongevity and fecundity of parasitized aphidswere strongly correlated with the aphid age atparasitization. Aphids parasitized at the 1stand 2nd instar stages did not contribute to thepopulation growth of the aphids. The netreproductive rate (R_o) of the aphidsparasitized at the 3rd and 4th instar andadult stages were only 9, 20 and 43% of thatfor nonparasitized aphids, respectively. Hostage preference experiments involving all fiveaphid stages showed L. mirzai couldattack and parasitize all life stages of browncitrus aphid. Parasitism was highest in the2nd instar in a no-choice test, while in achoice test parasitism in the 2nd and 3rdinstars was similar. A relatively high rate ofparasitism was also observed in the 1st instarnymphs in both choice and no-choice tests. Theresults suggest that L. mirzai haspotential as a biocontrol agent of the browncitrus aphid and warrants a furtherevaluation.     

Studies onBonnetia comta [Dipt.: Tachinidae] parasitizingAgrotis ipsilon [Lep.: Noctuidae] larvae

Laboratory studies showed that 1st-instarBonnetia comta (Fallén) maggots (planidia) had a significant impact (P<0.05) on mortality of all black cutworm (BCW),Agrotis ipsilon (Hufnagel), instars, either by killing 1st- and 2nd-instar BCWs 2.3 to 9.7 days after parasitization or by producing a puparium from older host instars. Diet consumption and utilization by BCW larvae parasitized byB. comta as 4th instars were similar to those of nonparasitized larvae until 1 to 2 days before the parasitoid emerged. In a 2-year host exposure study in Iowa, it was found thatB. comta primarily parasitized released BCWs in June through September and did not seem to play a role in controlling the damaging 1st generation of BCW larvae. Techniques were developed to produce and store large numbers ofB. comta planidia.Bonnetia comta deposited large numbers of planidia on filter paper treated with a fecal supernatant. These planidia could be stored on filter paper in a covered Petri dish at 4.4°C for 5 days with minimal mortality. Preliminary field data show that planidia placed around corn seedlings infested with 4th-instar BCW larvae do parasitize the pest and reduce the hosts cutting potential.     

Superparasitism and host discrimination byEphedrus cerasicola [Hym.: Aphidiidae], an aphidiid parasitoid ofMyzus persicae [Hom.: Aphididae]

Myzus persicae (Sulzer) at different densities (1 to 120 aphids) on a paprika plant in a 1.8 dm³ cage were exposed at 21°C to single females of the parasitoidEphedrus cerasicola Stary. Three different exposure periods were used: 1 hr, 6 hrs, 24 hrs. The aphids were dissected 6 days after parasitization. Superparasitism was measured as number of hosts superparasitized and number of parasitoid larvae per aphid. It attained a maximum around host density=5 and decreased with increasing host density and decreasing exposure time. Almost no superparasitism occurred during the 1st hour. A non-random larval distribution indicated thatE. cerasicola discriminates between unparasitized and parasitized aphids, but probably not between aphids with different numbers of parasitoid eggs. Larvae in superparasitized aphids developed slower than single larvae. The supernumerary larvae died during the 1st instar, probably killed by chemical means since no physical attacks between larvae have been observed.     

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

Interspecific host discrimination by adults, and larval competition among the endoparasitoidsMicroplitis croceipes (Cresson),Microplitis demolitor Wilkinson,Cotesia kazak (Telenga) andHyposoter didymator (Thunberg) were investigated usingHeliothis virescens (F.) as the host. In ovipositional choice tests, the mean number of encounters and ovipositions for unparasitized hosts was not significantly different from the mean number of encounters and ovipositions for parasitized hosts for each treatment combination (P>0.05). Thus, none of the parasitoid species discriminated between host larvae recently parasitized once by a female of another species und unparasitized hosts. However, in all but two cases, females did discriminate between unparasitized hosts and hosts in which an early first instar of the first-attacking species was developing.Cotesia kazak andH. didymator did not discriminate between unparasitized hosts and hosts parasitized by an early first instar ofM. demolitor. Larval competition among these parasitoid species was studied for three time intervals between the first and second species parasitization: 1) second species attack immediately (5–15 sec) after the first; 2) second species attack 24 h after the first; and 3) second species attack 48 h after the first. Time until egg eclosion was shortest forM. demolitor, thenC. kazak, thenM. croceipes, and longest forH. didymator. When the second parasitoid species attacked a host immediately after the first species, the species in which egg eclosion occurred first was the victor more frequently, except whenM. demolitor competed withC. kazak andH. didymator. With a 24 h delay between the first and second species to attack, the older first instar from the first parasitization usually outcompeted the younger first instar from the second attack. A first instar from the second species to attack generally outcompeted the second instar of the first species when the second parasitization had been delayed 48 h. Competiors were eliminated mainly by physical attack, butC. kazak andM. croceipes apparently also killedH. didymator eggs by physiological processes.     

Interference between parasitoids [Hym.: Aphidiidae] and fungi [Entomophthorales] attacking cereal aphids

In field populations of cereal aphids parasitism levels declined through the season as fungal infection increased. In laboratory trials the fungusErynia neoaphidis Remaudiere & Hennebert took 3 to 4 days to kill the rose-grain aphid,Metopolophium dirhodum (Walker), whereas the parasitoidAphidius rhopalosiphi De Stefani-Perez took 8 to 9 days at 20°C. When aphids were infected by the fungus less than 4 days after being parasitized the parasitoids were prevented from completing their development. Conversely, when infection occurred more than 4 days after parasitization development of the fungus was significantly impaired. There was no histological evidence that the fungus invaded the tissues of the parasitoid when both attacked the same aphid. Interference between parasitoids and fungal pathogens must be taken into account when estimating the impact of these mortality agents on pest populations.     

In vitro rearing ofTrissolcus basalis [Hym., Scelionidae] an egg parasitoid ofNezara viridula [Hem., Pentatomidae]

In vitro rearing of the egg parasitoidTrissolcus basalis (WOLL.) from eggs collected on the natural hostNezara viridula (L.) was initiated. Several oligidic diets containing insect material (Manduca sexta hemolymph or host egg content) were tested. Our initial medium with 50% hemolymph induced a high egg mortality, but by decreasing the hemolymph concentration, increasing the hen egg yolk concentration and adding 15% of free amino acids mixture, a hatching rate of 85% of the parasitoid eggs was obtained with 39% reaching the second instar and 33% the third instar. In a medium without hemolymph, but with 18% liquid from parasitized host eggs we obtained 90% to 100% hatching, 25 to 27% reaching the second instar and 8% the third instar. We did not obtain pupation from eggsin vitro, but did get pupae and adults from larvae rearedin vivo to second instar and transfered to anin vitro system.      

Life history,immature morphology and adult behavior ofTelenomus solitus [Hymenoptera: Scelionidae]

The results of laboratory studies on the life history, morphology of immature stages, effects of food and water on adult longevity, host age preference for oviposition, parthenogenesis, and adult behavior ofTelenomus solitus Johnson are presented.Telenomus solitus completed its development in 10.8 days (egg, 0.3 day; 1^st instar, 2.7 days; 2^nd instar, 3.7 days; and pupa, 4.1 days). The adults lived longest when provided with both honey and water. Without food, they survived less than 24 h. Parasitization of host eggs varied significantly with their age, being highest in 42 h old eggs. Fewer than 10% of eggs older than 60 h were parasitized successfully. The periodicity of oviposition was unimodal; it occurred throughout the 24 h period and peaked in the late photophase. Females ofT. solitus are arrhenotokous. The behavioral sequences during courtship, mating, and oviposition are described.      

In vitro rearing ofLysiphlebus fabarum [Hym.: Braconidae]

In vitro rearing of the aphid endoparasitoidLysiphlebus fabarum (Marshall) (Hymenoptera, Braconidae) was attempted. Successful permanent cultures ofAphis fabae Sc. andMyzus persicae Sulz. cells were not obtained. Therefore, parasitoid larvae were reared in 2 unnatural media rone of which included cells ofCeratitis capitata Wied. (Diptera, Trypetidae). A group of larvae was reared in a substrate to which parasitoid teratocytes had been added. SinceLysiphlebus fabarum females did not oviposit into paraffin droplets including the substrates, the larvae were directly transferred from parasitized aphids into the rearing media. Several larvae reached the final instar, but only 2 out of the 48 tested in the 3 substrates became adults. The meaning of teratocytes inin vitro rearing of Aphidiine, Braconids is discussed. This work was supported by a grant from the italian Ministry of Education (M.P.I. 40%).     

Host selection and larval interactions among three primary parasitoids ofPlathypena scabra (Lep.: noctuidae)

Three hymenopteran parasitoids that attackPlathypena scabra (F.) larvae often oviposit into consecutive instars of the host. We investigated host discrimination by adults and competitive interactions among larvae of these three parasitoid species. Avoidance of superparasitism byCotesia marginiventris (Cresson) andDiolcogaster facetosa Ashmead was tested. Females of each species were presented either withP. scabra parasitized by a different female of the same species 6 h earlier or unparasitizedP. scabra. Under these conditions,C. marginiventris attacked similar numbers of parasitized and unparasitized hosts.D. facetosa attacked 31% fewer parasitized than unparasitizedP. scabra. The avoidance of multiple parasitism byD. facetosa was studied in a similar bioassay. AlthoughD. facetosa females parasitized fewerP. scabra that had been attacked byC. marginiventris 6 h previously, the reduction in parasitism was only about 23%. In competition studies, immatureD. facetosa were better competitors than immatureC. marginiventris. Aleiodes (=Rogas) nolophanae (Ashmead) was an inferior competitor against bothC. marginiventris andD. facetosa when the duration between parasitism events was 1 h, but their competitive ability increased when they multiply parasitized hosts at least 32 h after the initial oviposition.     

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.      

Life history ofAphis gossypii on cucumber: influence of temperature, host plant and parasitism

Life table data forAphis gossypii Glover (Homoptera: Aphididae), an important pest in glasshouse cucumber crops, were studied at 20, 25 and 30°C on two cucumber cultivars (Cucumis sativus L.) in controlled climate cabinets. The development time on the cucumber cv. ‘Sporu’ ranged from 4.8 days at 20°C to 3.2 days at 30°C. Immature mortality was approximately 20% and did not differ between temperatures. Most mortality occurred during the first instar. Reproduction periods did not differ among temperatures, but at 25 and 30°C more nymphs were produced (65.9 and 69.8 nymphs/♀, respectively) than at 20°C (59,9 nymphs/♀) because of a higher daily reproduction. Intrinsic rate of increase was greatest at 25°C (r _m =0.556 day⁻¹). At 20 and 30°C the intrinsic rate of increase was 0.426 and 0.510, respectively. On cv. ‘Aramon’, the development time ofA. gossypii was approximately 20% longer at all temperatures. Immature mortality did not differ between the two cultivars. The intrinsic rate of increase on cv. ‘Aramon’ was 15% smaller than on cv. ‘Sporu’. The use of cucumber cultivars partially resistant to aphids is discussed in relation to biological control of cotton aphid in glasshouses. Development time and immature mortality on leaves of the middle and upper leaf layer of glasshouse grown cucumber plants (cv. ‘Aramon’) were comparable to development in the controlled climate cabinets. On the lower leaves immature mortality was much higher (approximately 82%) than on leaves of the middle (24.0%) and upper leaf layer (24.5%). Reproduction was less on the lower leaf layer (45.9, 70.5 and 70.1 nymphs/♀ on leaves of the lower, middle and upper leaf layer, respectively). Aphids, successfully parasitized byAphidius colemani Viereck (Hymenoptera: Braconidae) only reproduced when they were parasitized after the third instar. Fecundity was 0.1 to 0.9 and 10.5 to 13.3 nymphs/♀ for aphids parasitized in the fourth instar or as adults, respectively. Reproduction of aphids that were stung but survived the attack was lower than for aphids not stung. Average longevity of these aphids was equal to the longevity of aphids not stung byA. colemani.     

The effects of parasitism by an encyrtid parasitoid, Anagyrus pseudococci on the survival, reproduction and physiological changes of the mealybug, Planococcus citri

Survival, reproduction and some biochemical changes in the citrus mealybug, Planococcus citri (Risso) parasitized by the endoparasitoid, Anagyrus pseudococci (Girault) are reported. The parasitized younger mealybugs were more likely to die than be successfully parasitized. The mean duration (±SE) required for mortality other than mummification were 1.85 ± 0.06, 2.48 ± 0.14 and 2.89 ± 0.17 days for first, second and third instar P. citri respectively. Hosts parasitized in the first instar did not produce any mummies while the second and third instar nymphs and adult stages of the mealybugs were mummified on average 8 to 11 days after attack. Parasitization caused cessation of normal fecundity as well as induction of early egg maturation of the mealybugs. The mealybugs parasitized in the adult stage produced a few eggs but the fecundity of unparasitized mealybugs was about 40 fold higher than that of parasitized mature adults. Parasitized pre-ovipositing and mature adults laid eggs within 24 h of attack. SDS-PAGE analysis of the body content of the parasitized mealybugs after 24 h and 48 h of parasitization and before egg hatch revealed an increase in the concentration of some proteins. Response to wound reactions was not visible either as formation of extra protein bands or increased density of the existing bands. The possible effect of parasitism on the changes of the reproductive physiology of the host is discussed.     

Development of the polyembryonic parasitoid Copidosoma floridanum in Trichoplusia ni

Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae) parasitized by the polyembryonic egg-larval parasitoid Copidosoma floridanum (Ashmead) (Hymenoptera: Encyrtidae) attained significantly larger final weights and head capsule widths than unparasitized controls. The difference in weight between parasitized and unparasitized hosts was not entirely accounted for by the weight of the C. floridanum brood. The head capsule widths of all parasitized and unparasitized fifth instars used in the study exceeded the critical threshold of 1.66 mm previously established for T. ni metamorphosis. The critical ratios associated with each T. ni instar of: 1) maximum weight within the instar:head capsule width and 2) maximum weight within the instar:weight at the beginning of the instar differed between parasitized and unparasitized larvae. Development of C. floridanum was synchronized with that of its host. Germ band formation and gastrulation of morulae destined to produce reproductive larvae invariably coincided with the host molt to the ultimate, fifth instar. Reproductive larvae had two instars. Eclosion from the egg to the first instar occurred during day 2 of the host's fifth instar, and ecdysis from the first to the second instar was synchronized with host cocoon spinning. Conversely, embryogenesis of morulae destined to produce precocious larvae began during the host first instar, continued through the second and third instar and ceased during the penultimate, fourth instar. Precocious larvae never molted and died when the host was consumed by the reproductive larvae.

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Résumé T. ni Hübner parasité par le parasitoïde ovo-larvaire C. floridanum Ashmead à développement polyembryonnaire atteint un poids final signficativement plus élevé avec une capsule céphalique plus grosse que les témoins non parasités, sans subir de mues surnuméraires. La différence de poids entre noctuelles parasitées ou non ne correspondait pas entièrement au poids des C. floridanum. Les largeurs des capsules céphaliques de tous les T. ni du cinquième stade dépassaient toutes le seuil critique de 1,66 mm lié à la métamorphose, mais les seuils critiques de taille du corps:largeur de la capsule céphalique et/ou taille et corps, taille initiale du corps au début du stade associé à la mue, différaient chez T. ni parasités ou non. Les développements de T. ni et de C. floridanum étaient synchrones. La formation de la bande germinative et la gastrulation de la morula produisant la multiplication des larves ont coïncidé invariablement avec la mue de l'hôte donnant le dernier stade. Les larves polyembryonnaires ont présenté deux stades. L'éclosion des oeufs s'est produite le deuxième jour du cinquième stade de T. ni, et le passage du premier au second était synchrone de la formation du cocon de l'hôte. Réciproquement, l'embryogenèse de la morula qui donnait des larves précoces commençait pendant le premier stade de l'hôte et se poursuivait à travers les second et troisième, pour cesser pendant le quatrième et pénultième stade.

     

Low field performance of an aphid parasitoid,Aphelinus abdominalis,efficient in the laboratory [Hym., Aphelinidae]

Life history traits of two inbred lines of the aphid parasitoidAphelinus abdominalis (Dalman) were evaluated in the laboratory. Both lines exhibited high fecundities, produced a high proportion of female offspring and showed to be long-lived. However, release experiments in winter wheat fields failed to achieve establishment of the parasitoids. In addition, the wasps parasitized considerably fewer aphids in two types of field cages than they did in the laboratory. AsA. abdominalis eggs and/or larvae arrested in development were not found in dissected aphids from field cages, we conclude that the wasps were unable or unwilling to parasitize high numbers of hosts in the cages. The reason for this odd behaviour is unknown.