Foraging behavior and life history of the stemborer parasitoidCotesia flavipes (hymenoptera: Braconidae)

The gregarious parasitoidCotesia flavipes (Hymenoptera: Braconidae) attacks larvae of pyralid and noctuid stemborers by entering the stemborer tunnel. The short-range foraging behavior of femaleC. flavipes was studied on stemborerinfested plants, in patches with host-related products and in artificial transparent tunnels. In addition, the longevity under specific conditions and the potential and realized fecundity of femaleC. flavipes were determined. Larval frass, caterpillar regurgitate, and holes in the stem are used in host location byC. flavipes. The response to host products byC. flavipes seems not to be host species specific. FemaleC. flavipes respond to frass from four stemborer species and one leaf feeder. No differences are found in the behavior ofC. flavipes on maize plants infested with the suitable host,Chilo partellus (Lepidoptera: Pyralidae), or the unsuitable host,Busseola fusca (Lepidoptera: Noctuidae). Attacking a stemborer larva inside the stem is risky for the parasitoid. The mortality rate of the parasitoids inside the stem is high: 30–40% of the parasitoids are killed by the spitting and biting stemborer larva.C. flavipes is relatively shortlived: without food the parasitoids die within 2 days; with food and under high-humidity conditions they die within 5–6 days.C. flavipes is proovigenic and has about 150 eggs available for oviposition. A relatively large proportion of the available egg load (20–25%) is allocated to each host, so femaleC. flavipes are egg depleted after parasitizing only five or six hosts.     

Diachasmimorpha longicaudata and D. kraussii (Hymenoptera: Braconidae), potential parasitoids of the olive fruit fly

The olive fruit fly, Bactrocera oleae (Tephritidae), is a significant threat to California's olive industry. As part of a classical biological control program started in 2002, the parasitoids Diachasmimorpha kraussii and D. longicaudata (Hymenoptera: Braconidae) were imported to California from laboratory colonies in Hawaii. Studies on their biology and behavior as parasitoids of the olive fruit fly were conducted in quarantine. Both species tend to oviposit into 2nd and young 3rd instars, with the offspring completing development in the flies’ puparia. Most eggs are deposited in the first two weeks of adult life. Observed lifetime fecundity was low, possibly as a consequence of the relatively poor quality of the harvested olives used as a host substrate. Both pre-imaginal development and adult longevity were limited at constant temperatures above 30°C, which may indicate that these species will have difficulty establishing in the warmest regions of California.     

The influence of light and moisture gradients on the attack rate of parasitoids foraging for hosts in a laboratory arena (Hymenoptera: Pteromalidae)

Microhabitat preferences of four parasitoids (Hymenoptera: Pteromalidae) of house fly pupae were measured in a two-dimensional arena containing perpendicular light and moisture gradients. Parasitism by Muscidifurax raptorand Nasonia vitripenniswas greatest in dry substrates, with the latter preferring bright illumination and the former tending to prefer dark. Urolepis rufipesselected bright illumination and moist substrates, attacking the most hosts at bright-moist and dim-moist microhabitats. Spalangia cameroniexhibited no main-effect preference for light intensity or moisture, although parasitism was highest at dim-moist, dark-wet, and dark-moist microhabitats. These results demonstrate that simple abiotic attributes, such as light intensity and substrate moisture concentration, are important in defining some dimensions of the niches of these parasitoids.     

Sensilla on antennae,ovipositor and tarsi of the larval parasitoids,Cotesia sesamiae (Cameron 1906) and Cotesia flavipes Cameron 1891 (Hymenoptera: Braconidae): a comparative scanning electron microscopy study

Two braconid parasitoids of cereal stemborers in eastern Africa, Cotesia sesamiae and Cotesia flavipes, have been shown to display a similar hierarchy of behavioural events during host recognition and acceptance. In order to understand the mechanisms underlying host recognition and acceptance, the morphology of antennal sensilla on the last antennomeres, on the ovipositor, and on the fifth tarsomere and pretarsus of the prothoracic legs tarsi were studied using scanning electron microscopy followed by selective silver nitrate staining. It appeared that female C. sesamiae and C. flavipes shared the same types and distribution of sensory receptors, which enable them to detect volatiles and contact chemical stimuli from their hosts. In both parasitoids, four types of sensilla were identified on the three terminal antennomeres: (i) non-porous sensilla trichodea likely to be involved in mechanoreception, (ii) uniporous sensilla chaetica with porous tips that have gustatory functions, (iii) multiporous sensilla placodea, which are likely to have olfactory function, and (iv) sensilla coeloconica known to have thermo-hygroreceptive function. The tarsi of both parasitoids possessed a few uniporous sensilla chaetica with porous tips, which may have gustatory functions. The distal end of the ovipositor bore numerous dome-shaped sensilla. However, there were no sensilla coeloconica or styloconica, known to have gustatory function in other parasitoid species, on the ovipositors of the two braconid wasps.     

Fitness of two sibling species of Asobara (Braconidae:Alysiinae), larval parasitoids of Drosophilidae in different microhabitats

Abstract. 1. Two sibling species of larval endoparasitoids of Drosophilidae: Asobara tabida (Nees) and A.rufescens (Foerster) occur in the same macrohabitat, but inhabit different microhabitats. Each species is most attracted by odours of its own microhabitat.
2. In order to assess the adaptive value of the microhabitat preference we studied the survival of both parasitoids in the major host species that occur in these microhabitats.
3. Survival in the major host in the preferred microhabitat was shown to be 40% higher for A.tabida and 30% higher for A.rufescens when compared to survival in the major host in the non-preferred microhabitat.
4. Measurements of developmental rates, specific mortalities and dry weights of the parasitoids suggest that the differential survival is due to differences in synchronization with the hosts.
5. The possible evolutionary consequences of some biological characteristics in Asobara are discussed. Microhabitat selection, differential survival, development and mating behaviour are attributes likely to have played a role in the reduction of gene flow between populations of the ancestral species, either in primary or in secondary sympatry.     

Responses of the stem borer larval endoparasitoid Cotesia flavipes (Hymenoptera: Braconidae) to plant derived synomones: Laboratory and field cage experiments

Laboratory and field cage experiments investigated the response of females of the stem borer larval endoparasitoid Cotesia flavipes to two synthetic synomone components, the terpenoid (E)-β-farnesene and the green leaf volatile, (Z)-3-hexenyl acetate, both compounds identified previously in headspace volatiles of maize plants damaged by stem borer (Chilo partellus). In dose response tests performed in a Y-tube olfactometer, parasitoids were significantly more attracted to the arms bearing 10 or 15 µg of (Z)-3-hexenyl acetate and (E)-β-farnesene than to the control arm. (E)-β-Farnesene was as attractive as the essential oil from the plant Hemizygia petiolata (Lamiaceae) rich in the same compound (80% relative amount). The plant essential oil elicited responses from females of the parasitoid comparable to those elicited by two positive controls, stem borer larval frass and adult parasitoid diet (20% honey solution), tested in the laboratory assays. In field cage trapping experiments, captures in traps baited with the terpenoid, the plant essential oil, (Z)-3-hexenyl acetate and the control of 20% honey solution, were not significantly different relative to captures in unbaited traps. Addition of the green leaf volatile (Z)-3-hexenyl acetate to the plant essential oil to yield a 1:1 two-component blend captured significantly more female parasitoids than traps baited with either of the two components alone. The results show that blends of green leaf volatiles and sesquiterpenoids may have potential in monitoring C. flavipes populations in the field.     

Evolutionary patterns of host utilization by ichneumonoid parasitoids (Hymenoptera: Ichneumonidae and Braconidae)*

The four major biological strategies of ichneumonoid parasitoids, koinobiont and idiobiont, ecto-and endoparasitism, are discussed and the evolutionary radiations of the two families Ichneumonidae and Braconidae compared in an attempt to relate differences in patterns of host utilization to differences in evolutionary history. The most primitive members of both families are idiobiont ectoparasitoids of hosts concealed in plant tissue. Idiobiont ectoparasitic braconids are all still primarily associated with such hosts, but idiobiont ectoparasitic ichneumonids have radiated to attack hosts in other situations, such as in aculeate nests or in cocoons. A shift in emphasis between the behavioural steps, host habitat location and host location, is envisaged as being important in such evolutionary change. Idiobiont endoparasitism is postulated as having arisen amongst ectoparasitoids attacking cocooned hosts, as an adaptation that allows them to exploit pupae and puparia in relatively exposed positions; it is a fairly common strategy in the Ichneumonidae, but virtually unknown in the Braconidae. Koinobiosis is perceived as having evolved in association with hosts which feed in a relatively weakly concealed position, but pupate in a more secluded and safe location. The strategy is advantageous as it allows a parasitoid to oviposit on an easily discoverable host, but to use the host's pupation concealment to complete its own development. The evolution of koinobiosis has allowed parasitoids to exploit hosts that feed in exposed positions, and to attack hosts at a younger and numerically more common stage in the host's life cycle. Koinobiont ectoparasitism is envisaged, in some braconid and ichneumonid groups, to occupy an evolutionary transitional position between idiobiosis and endoparasitic koinobiosis; only in the Ichneumonidae have large radiations of koinobiont ectoparasitoids occurred. Endoparasitic koinobiosis is hypothesized as having arisen in the Braconidae in association with lepidopterous/coleopterous hosts, whilst in the major lineage of endoparasitic koinobiont ichneumonids, this habit is hypothesized as having arisen in association with symphytan hosts. The great majority of braconids are koinobiont endoparasitoids, but only about 50% of the Ichneumonidae have this habit. Very few koinobiont braconids develop as endoparasitoids of hymenopterous hosts, although many endoparasitic ichneumonids attack Hymenoptera. However, lineages of the Braconidae have radiated to exploit adult insects and exopterygote nymphs; ichneumonids do not utilize such hosts.     

Improvement of quality control methods for augmentative releases of the fruit fly parasitoids,Diachasmimorpha longicaudata and Psyttalia fletcheri (Hymenoptera: Braconidae)

Criteria were established to improve quality control methods for augmentative releases of the opiine parasitoids, Diachasmimorpha longicaudata (Ashmead) and Psyttalia fletcheri (Silvestri). These included correlating puparial weight with adult emergence and sex ratio at the Honolulu rearing facility, and determining the effect of air shipments and field releases on parasitoid emergence and subsequent mortality. There was a positive relationship between the weight of 7–10‐day‐old host puparia and percentage of emergence for both D. longicaudata and P. fletcheri. Standardization of shipping methods included placement of ice blocks in the top levels of the ice chests, prompt shipment and pick‐up of samples, and cooling of puparia before shipment to minimize metabolic heat generated in the samples, and to delay emergence of samples. Before standardization, emergence losses of up to 58% were observed for D. longicaudata and 18% for P. fletcheri. When shipping methods were standardized, emergence was no longer reduced. In addition, low emergence rates were associated with reduced flight propensity of D. longicaudata (R_s = ‐ 0.45 at Kilauea and ‐ 0.54 at Kealia). At the two release sites, 88–95% of adult D. longicaudata that did not escape the release containers were males.     

Intraspecific and Interspecific Competition Between Cotesia flavipes and Cotesia sesamiae (Hymenoptera: Braconidae), Gregarious Larval Endoparasitoids of Lepidopteran Stemborers

Super and multiple parasitism of Chilo partellus (Lepidoptera: Pyralidae) and Sesamia calamistis (Lepidoptera: Noctuidae) by Cotesia flavipes Cameron and Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) were investigated in the laboratory. Progeny production of Co. flavipes increased as a result of increasing the number of ovipositions, from one to three per one Ch. partellus host larva, then decreased as a result of four and five ovipositions per larva. Cocoon weight, sex ratio and emergence of the parasitoid progeny were not affected by superparasitism. Low progeny production of Co. sesamiae and poor survival of Ch. partellus host larvae were found as a result of superparasitism. When S. calamistis was the host, the duration of immature stages of Co. flavipes , parasitoid emergence, progeny production and sex ratio were not affected by superparasitism, but cocoon weight, adult longevity and the potential fecundity of adult females decreased. Superparasitism of S. calamistis by Co. sesamiae did not affect emergence, longevity or sex ratio of adult progeny of the parasitoid, but prolonged immature development, lowered cocoon weight and decreased potential fecundity of adult female progeny. Co. flavipes out-competed Co. sesamiae when Ch. partellus was parasitized by both species. The potential for local displacement of Co. sesamiae by Co. flavipes in areas dominated by Ch. partellus in East Africa is discussed.     

Use of ablated stalks to assess field rates of parasitism of Diatraea saccharalis (Lepidoptera: Crambidae) by Cotesia flavipes (Hymenoptera: Braconidae)

We evaluated a technique that used ablated sections of corn stalks infested with larvae of Diatraea saccharalis F. to assess parasitism by Cotesia flavipes (Cameron) in a corn field. Stalkborer larvae were retrieved successfully from the artificially infested, ablated stalks for at least 96 h after deployment in the field. Levels of parasitism in ablated stalks attached to corn plants were comparable to levels of parasitism measured using whole plants that were artificially infested. Olfactometer comparisons showed preference by female C. flavipes for both whole plants and ablated stalks containing larval D. saccharalis, over uninfested stalks and plants. This technique provides a means to estimate parasitism of stalkborer larvae by C. flavipes without destructive sampling of agronomic plants.     

Influence of plant structural complexity on the foraging success of Trichogramma minutum: a comparison of search on artificial and foliage models

The influence of structural complexity on the foraging success for host eggs (Ephestia kuehniella Zeller) by Trichogramma minutum Riley was investigated in the laboratory. Naive females were released into arenas with structurally different paper models or foliage (simple: trembling aspen Populus tremuloides Michx., complex: balsam fir Abies balsamea L.). Observations of individual females were made every 15 min and searching success was measured by the number of host egg clusters found and the amount of time taken to find them, within a period of 196 min. Females found significantly more egg clusters and were quicker at finding them on the sample paper and foliage surfaces than on the most complex paper or foliage surfaces. Older females (2–3 days) were more successful and searched quicker than younger (<24 h) females on all paper surfaces. The timed observations suggested that wasps which spent more time walking had a significantly decreased probability of finding an egg mass and were significantly slower at finding them. Females that spent more time on paper surfaces had an increased probability of finding an egg mass. The significance of searching differences is discussed in relation to the potential effects of plant surfaces on Trichogramma movements and to the physiological readiness of the wasp.     

Single-step PCR differentiation of Cotesia sesamiae (Cameron) and Cotesia flavipes Cameron (Hymenoptera: Braconidae) using polydnavirus markers

Cotesia sesamiae (Cameron) and Cotesia flavipes Cameron (Hymenoptera: Braconidae) are the main larval parasitoids of cereal stemborers in sub-Saharan Africa. Cotesia sesamiae is endemic to eastern and southern Africa, while C. flavipes was introduced into the region for biological control against the exotic lepidopteran Chilo partellus (Swinhoe) (Lepidoptera: Crambidae). The two are sibling parasitoids, difficult to distinguish morphologically. The introduced insect could potentially lead its African biotype to extinction because of their similar ecological niche. In order to distinguish the two species, multiplex primer-specific and PCR-RFLP tests were developed. Rapid identification of the two species was possible using primer-specific tests on DNA extracts as well as on pieces of tissue in a single PCR step followed by gel electrophoresis. The CRV1 gene of the polydnavirus, a symbiont to the wasps, was used as the marker. The results show that the morphological identifications, validated by molecular tests, are accurate in 93% of cases.     

Interactions between Phaedrotoma scabriventris Nixon (Hymenoptera: Braconidae) and Diglyphus isaea Walker (Hymenoptera: Eulophidae), parasitoids of Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae)

Liriomyza leafminer flies represent a serious threat to horticultural production in East Africa. Total field parasitism rates recorded in Kenya are below 5%, with the indigenous ectoparasitoid Diglyphus isaea Walker being one of the key parasitoid species. The International Centre of Insect Physiology and Ecology (icipe), in collaboration with the International Potato Centre (CIP), imported into Kenya the endoparasitoid Phaedrotoma scabriventris Nixon to improve natural control of leafminers. The objective of this study was to investigate the interactions between D. isaea and P. scabriventris when used together for the biological control of Liriomyza species. These interactions were studied under laboratory conditions, using treatments that involved single, simultaneous and sequential releases of the different parasitoid species onto plants infested by L. huidobrensis larvae. While used separately, parasitism rates of D. isaea and P. scabriventris were 30.4 ± 10.9% and 63.6 ± 7.7% respectively. However, when used simultaneously, the total parasitism rate increased to 77.0 ± 5.3%. Although P. scabriventris had no effect on D. isaea, the presence of D. isaea reduced the specific parasitism rate of P. scabriventris. In addition, both parasitoids induced leafminer mortality through larval-feeding and stinging. However, feeding and stinging mortality induced by D. isaea (41.9 ± 9.1%) was significantly higher compared to P. scabriventris (11.9 ± 8.7). Similarly, pupal mortality due to feeding and stinging activity was 49.1 ± 6.5% and 21.6 ± 1.9% when exposed to D. isaea and P. scabriventris respectively. The implication for simultaneous use of both parasitoids in East Africa is discussed.     

Phylogenetics and genetic diversity of the Cotesia flavipes complex of parasitoid wasps (Hymenoptera: Braconidae), biological control agents of lepidopteran stemborers

The Cotesia flavipes complex of parasitoid wasps (Hymenoptera: Braconidae) are economically important for the biological control of lepidopteran stemboring pests associated with gramineous crops. Some members of the complex successfully parasitize numerous stemborer pest species, however certain geographic populations have demonstrated variation in the range of hosts that they parasitize. In addition, the morphology of the complex is highly conserved and considerable confusion surrounds the identity of species and host-associated biotypes. We generated nucleotide sequence data for two mtDNA genes (COI, 16S) and three anonymous nuclear loci (CfBN, CfCN, CfEN) for the C. flavipes complex. To analyze genetic variation and relationships among populations we used (1) concatenated mtDNA and nDNA data, (2) a nDNA multilocus network approach, and (3) two species tree inference methods, i.e. Bayesian estimation of species trees (BEST) and Bayesian inference of species trees from multilocus data with (*)BEAST. All phylogenetic analyses provide strong support for monophyly of the complex and the presence of at least four species, C. chilonis (from China and Japan), C. sesamiae (from Africa), C. flavipes (originating from the Indo-Asia region but introduced into Africa and the New World), and C. nonagriae (from Australia and Papua New Guinea). Haplotype diversity of geographic populations relates to historical biogeographic barriers and biological control introductions, and reflects previous reports of ecological variation in these species. Strong discordance was found between the mitochondrial and nuclear markers in the Papua New Guinea haplotypes, which may be an outcome of hybridization and introgression of C. flavipes and C. nonagriae. The position of Cotesia flavipes from Japan was not well supported in any analysis and was the sister taxon to C. nonagriae (mtDNA, (*)BEAST), C. flavipes (nDNA) or C. flavipes+C. nonagriae (BEST) and, may represent a cryptic species. The concatenated five gene phylogenetic analyses did not support the overall separation and monophyly of clades associated with different host species, although some clades did show specific host associations, possibly due to localized host availability, rather than host specificity. Our results provide a framework for assessing whether distinct lineages represent cryptic species, and for examining parasitoid-host evolution and compatibility more generally. Given the limitations of morphological based identification for members of this complex, molecular identification is recommended prior to any biological control introductions.     

斑痣悬茧蜂对不同寄主密度斑块的选择和最优搜寻行为

在圆柱形透明有机玻璃罩内,观察了斑痣悬茧蜂对不同寄主密度斑块的选择和滞留时间,并用Cox比例风险模型分析了寄主密度、产卵次数和搜寻特征对斑痣悬茧蜂在斑块上的驻留时间及其影响因素.结果表明:斑痣悬茧蜂对高密度寄主斑块的初次选择次数、访问次数均高于低密度寄主斑块,导致在高密度斑块上具有更高的寄生率;斑痣悬茧蜂在各斑块的驻留时间随寄主密度的增加而增加.Cox模型分析结果显示,斑块内寄主密度和产卵数均对其离开斑块的倾向起消极作用,即随寄主密度和产卵数的增加而倾向于留在斑块上;而寄主密度与产卵数的互作反而对寄生蜂离开斑块倾向具有促进作用,这两种作用可使寄生蜂利用寄主斑块获得最大适合度.     

Inhibitory effects of permethrin on flight responses,host‐searching,and foraging behaviour of Cotesia vestalis (Hymenoptera: Braconidae), a larval parasitoid of Plutella xylostella (Lepidoptera: Plutellidae)

Although it is well known that the application of broad‐spectrum synthetic insecticides reduces the effectiveness of natural enemies, the details of the actual mechanisms, including the lethal and sublethal effects of this reduction, are not fully understood. The inhibitory effects of a pyrethroid insecticide (permethrin), Adion 20% EC on the flight responses, host‐searching behaviour and foraging behaviour of Cotesia vestalis (Hymenoptera: Braconidae), a larval parasitoid of the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae), were investigated under laboratory conditions. In choice trials, the wasps showed significant preference for P. xylostella‐infested Komatsuna plants over insecticide‐treated plants, suggesting an inhibitory effect of the insecticide on the flight response of C. vestalis. When offered a pair of plants, the wasps showed a significant preference for P. xylostella‐infested plants compared to uninfested plants. However, significantly more wasps were attracted to infested permethrin‐treated plants than to uninfested plants, suggesting that the wasps are attracted to the volatile infochemicals from the infested plants, even if treated with permethrin. The searching time was significantly shorter and the mortality of C. vestalis adults on the insecticide‐treated plants significantly higher than in the control plants treated with distilled water. These results suggest that the application of the insecticide had an inhibitory effect on the wasps’‐searching behaviour and consequently reduced the effectiveness of C. vestalis as a biological control agent against P. xylostella. In addition, the strength of the inhibitory effect of permethrin on the attraction of the wasps to the plants is critical to the survival of C. vestalis. Our results suggest that the attraction of the wasps to the permethrin‐treated infested plants increases the risk of their exposure to this insecticide.     

Life history of Spalangia gemina Boucek (Hymenoptera: Pteromalidae), a fast-breeding microhymenopteran pupal parasitoid of muscoid flies

Laboratory studies at 25.5 degrees C and 70-75% r.h. demonstrated that the average daily survival rate for females of the parasitoid Spalangia gemina Boucek (Hymenoptera: Pteromalidae) was 0.907 over a 20-day period, with 50% mortality in 17.3 days. Mean immature developmental time of S.gemina was 22 days and the population growth rate was c. 40-fold per generation. The females successfully parasitized 1-, 2- and 3-day-old pupae of Musca domestica L. and parasitism of 98-100% was obtained at parasitoid to host ratios of 1:0.5-2.5. Parasitism of 81-87% was obtained at parasitoid to host ratios of 1:10. The male to female sex ratio was 1:1.59. S.gemina appears to have advantages over other Spalangia spp., which have immature development times of 28-32 days under comparable conditions, for the biological control of Muscidae.     

Effect of temperature on the reproductive biology of Peristenus spretus (Hymenoptera: Braconidae), a biological control agent of the plant bug Apolygus lucorum (Hemiptera: Miridae)

Peristenus spretus Chen et van Achterberg (Hymenoptera: Braconidae), a parasitoid of the plant bug Apolygus lucorum (Hemiptera: Miridae), has been studied for use in augmentative biological control in China. Under laboratory conditions, we explored the development, survival, age-specific and potential lifetime fecundity, oviposition period and progeny sex ratio of P. spretus reared at six constant temperatures (15°C, 19°C, 23°C, 27°C, 31°C, 35°C) on the second instar nymphs of A. lucorum. At 15°C, male and female P. spretus took 48.7 ± 0.3 and 52.5 ± 0.3 days to complete their immature development, while developmental time was reduced by more than half at 23°C and 27°C. The parasitoid can only develop to the larval stage at 31°C and neither larva nor pupa survived at 35°C. The estimated lower developmental threshold of the immature stage was 7.3°C. When parasitoid adults were exposed at 15°C, females laid 90% of their eggs at first 19 days of oviposition and had an extended reproductive life. In contrast, females held at 27°C laid most of their eggs (90%) in their first of 10 days of oviposition and had shorter longevity. The highest potential lifetime fecundity of P. spretus was 671.2 ± 34.7 SE eggs produced over 23.4 ± 1.4 SE days at 23°C. At 15°C, 19°C and 23°C, sex ratios of reared parasitoids were male-biased, but at 27°C there was no male bias.     

Biological parameters and thermal requirements of the parasitoid Praon volucre (Hymenoptera: Braconidae) with Macrosiphum euphorbiae (Hemiptera: Aphididae) as host

The effect of temperature on the biology of Praon volucre (Haliday, 1833) (Hymenoptera: Braconidae) in Macrosiphum euphorbiae (Thomas, 1878) (Hemiptera: Aphididae) hosts was studied and the thermal requirements of the parasitoid were determined. Experiments were carried out at 16, 19, 22, 25, and 28 ± 1°C with 70 ± 10% relative humidity and 12 h photophase. The developmental time of P. volucre males and females decreased between 16 and 23°C. The highest percentages of aphid parasitism and adult parasitoid emergence were observed at 16, 19, and 22°C. The sex ratio (expressed as % females) decreased between 16 and 23°C. Male and female longevity was high between 19 and 22°C and decreased strongly at 25°C. The lower temperature threshold for P. volucre was 5.17°C and the thermal constant was 243 degrees-days.     

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.