Physical and chemical plant characters inhibiting the searching behaviour of shape Trichogramma chilonis

Several plant characters are known to affect the searching behaviour and parasitization efficiency of Trichogramma spp. (Hymenoptera: Trichogrammatidae). In this study, plant characters contributing to the low Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) egg parasitism levels on pigeonpea (Cajanus cajan (L.) Millspaugh) were investigated. The efficiency of T. chilonis on pigeonpea was dependent on the plant structure on which the host eggs were found. In a cage experiment, more than 55% of eggs placed on leaves were parasitized, while 1% of eggs on calyxes and no eggs on pods were parasitized. In a filter paper bioassay, parasitoids were deterred by acetone and hexane surface extracts from pigeonpea pods but showed no response to water extract. The searching behaviour of the parasitoids was not affected by different solvent extracts from the surface of pigeonpea leaves. In a four-armed airflow olfactometer, T. chilonis was repelled by volatiles from pigeonpea pods but showed no response to volatiles derived from hexane extract of pod surfaces. Volatile infochemicals and hexane surface extracts from pods of two wild Cajanus species, C. scarabaeoides (L.) Thours and C. platycarpus (Bentham) van der Maesen, were similarly deterrent to T. chilonis. The movement of the parasitoids on pigeonpea pods and calyxes was inhibited by long trichomes and wasps were trapped by sticky trichome exudates. Parasitoids walked significantly faster on leaves than on pods. The walking speed on both pods and leaves increased significantly after washing with hexane. The results presented in this paper show that the plant growth stage and the plant structures preferred by H. armigera for oviposition are the least suitable for T. chilonis, contributing to the low parasitoid efficiency on pigeonpea.     

Source and characterization of an egg recognition kairomone of Telenomus heliothidis, a parasitoid of Heliothis virescens

ABSTRACT. The ability of Telenomus heliothidis Ashmead (Hymenoptera; Scelionidae) to recognize its host, the eggs of Heliothis virescens (F.) (Lepidoptera; Noctuidae), was determined in laboratory studies. The material present in the accessory gland of female H. virescens adults acted as an egg recognition kairomone for T. heliothidis. Host eggs which lacked the kairomone were not attacked, while glass beads the size of H. virescens eggs and coated with the accessory gland material were. The parasitoid failed to respond to the kairomone unless it was associated with a target the size and shape of normal hosts. The kairomone is heat stable, but was deactivated by proteolytic enzymes. The accessory gland contained 200 mg/ml protein which suggests that the kairomone is proteinaceous.     

Host recognition by the egg–larval parasitoid Chelonus inanitus: effects of physical and chemical cues

Parasitoid wasps are widely used as biocontrol agents. For successful deployment, it is important to know how they search for and recognize their hosts. They often use chemical cues in host searching and recognition. Little attention has been paid to the use of physical cues, particularly when combined with chemical cues, though a combination of cues may improve searching efficiency. Chelonus inanitus L. (Hymenoptera: Braconidae) is a solitary, egg–larval parasitoid wasp that parasitizes various lepidopteran species, including serious crop pests. In this study, effects of physical and/or chemical cues on host recognition were investigated in C. inanitus by observing its antennal searching, ovipositor probing, and the duration of arrestment. In a physical cue test, egg-mass models with glass beads differing in size were used, and a single-egg model with a specific size of bead. Egg-mass models with beads of 0.4–1.0 mm in diameter arrested C. inanitus, in accordance with egg size and arrangement of the host. In a chemical cue test, extract from egg masses of the host Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae), equivalent to half of a host egg mass and extract diluted 100-fold were used, and the undiluted extract stimulated C. inanitus. Untreated egg-mass models (0.2-mm-diameter glass beads) and diluted egg extract arrested C. inanitus less effectively; however, when glass beads were treated with the diluted extract, arrestment increased to the same degree as the undiluted extract. These results suggest that C. inanitus uses both physical and chemical cues to recognize eggs of its host, S. litura, and that these stimuli act synergistically.     

Colleterial glands of Sesamia nonagrioides as a source of the host-recognition kairomone for the egg parasitoid Telenomus busseolae

Abstract.  The maize stemborer Sesamia nonagrioides glues its egg masses under the leaf sheaths or ear bracts using colleterial gland secretion. In spite of such concealed oviposition sites, these eggs are parasitized by Telenomus busseolae. The colleterial glands of S. nonagrioides are investigated as a possible source of the host-recognition kairomone for T. busseolae . This secretion, applied on glass beads, elicits intense antennal drumming and oviposition probing behaviour in the parasitoid. Through an histochemical study, neutral and acid glycoconjugates are identified as components of the secretion. Finally, using ultrastructural techniques, the colleterial glands are described and classified as comprising class 3 secretory cells.     

Host kairomone learning and foraging success in an egg parasitoid: a simulation model

Abstract 1. Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae) is an egg parasitoid that recognises chemical residues left by its host the green stink bug Nezara viridula (L.) (Heteroptera: Pentatomidae) as kairomone signals, enabling it to find egg masses in which to lay eggs. 2. Kairomones are usually present as patches deposited by N. viridula females, and recent results (Peri et al., Journal of Experimental Biology, 209 , 3629–3635, 2006) indicated that females of T. basalis are able to learn the features of their foraging environment and to adjust accordingly the amount of time spent on the patches of kairomones they are visiting, depending on whether or not host eggs are found. 3. In order to assess the impact of this learning ability, a Monte Carlo, spatially explicit and individual‐based simulation model was built to quantify the foraging efficiency of T. basalis females in environments with different levels of host abundance and distribution. In all cases, the present study compared the foraging efficiency of simulated T. basalis females having the ability to learn with those lacking this ability. 4. Learning females always visited a higher number of kairomone patches and attacked a higher number of hosts than non‐learning females, especially when there was a high density of kairomone patches in the environment. 5. Learning ability globally appears to allow the maintenance of efficient foraging success, especially when there is a low probability for the kairomone patches to contain discoverable hosts. 6. The increase in foraging efficiency for learning females appears to depend on the characteristics of the habitat in which they are foraging. Results thus suggest that significant variation in learning ability is likely to occur in natural wasp populations facing different environments with different host spatial distributions.     

Influence of rearing hosts on host size acceptance by Trichogramma australicum

We investigated the acceptance of different sized host models by Trichogramma australicum in the laboratory. We used isoline cultures of T. australicum reared in hosts of different sizes. Helicoverpa armigera represent relatively large hosts, and those of Sitotroga cerealella are small, termed the Ha and Sc biotypes, respectively. Five sizes of glass beads were tested for acceptance: diameter 0.5, 0.75, 1.0, 1.5 and 2.0 mm. The acceptance of a host model was determined by persistent attempted drilling of a glass bead by a female. The relationship between host egg size and number of eggs laid by a female was also investigated. We used three sizes of artificial egg (diameter 0.75, 1.00, and 1.50 mm of hemispherical cupules) each containing artificial diet. Ha biotype wasps accepted host models in the range 0.75--1.50 mm dia. (vol. 0.166--1.325 l), whereas those of the Sc biotype accepted host models in the range 0.50--1.00 mm dia. (vol. 0.05--0.393 l). This evidence suggests a lineal (possibly genetic) influence to host size acceptance for T. australicum, dependent on the size of the host in which the wasp has been reared. Also T. australicum lay fewer eggs in smaller artificial eggs than in larger ones. The role of host size in host acceptance and number of eggs delivered, and its implications, is discussed.     

Development, longevity and reproduction of Trissolcus basalis (Wollaston) and Telenomus podisi Ashmead (Hymenoptera: Scelionidae) in natural conditions during autumn and winter, in southern Paraná, Brazil

The development, longevity and reproduction of Trissolcus basalis (Wollaston) and Telenomus podisi Ashmead were investigated under natural conditions during autumn and winter from 1999 to 2001, in Southern Paraná State, Brazil, in order to understand how these parasitoids overwinter in subtropical regions. Adults of T. basalis e T. podisi emerged during autumn and winter from eggs parasitized between April and June. Adult longevity in natural conditions was higher than eight and seven months, for T. basalis and T. podisi respectively, showing that both species overwinter in the adult stage. Percentage survival of T. basalis and T. podisi females during autumn and winter was higher than 85% and mortality increased significantly in spring. Females maintained for six months in natural conditions parasitized E. heros eggs after transference to 25 degrees C, and the presence of females in the offspring showed that mating occurred during autumn and winter. Temperature during immature development influenced significantly the adult performance, regulating the longevity and reproductive capacity after dormancy. Female parasitoids that developed in higher temperatures lived longer and parasitized more host eggs after transference to 25 degrees C than females that developed under colder conditions.     

Influence of Diaphania hyalinata (L.) (Lepidoptera: Crambidae) egg density on the parasitization capacity of Trichogramma exiguum Pinto & Platner and Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae)

The effects of the egg density of Diaphania hyalinata (L.) on several biological parameters of Trichogramma exiguum Pinto & Platner and T. pretiosum Riley were investigated. For that, 24h-old egg masses were isolated in glass tubes (15 replicates; 1 egg mass = 1 replicate), and offered to parasitization by a newly-emerged female of T. pretiosum or T. exiguum 24h at the proportion of one female to 5, 10, 15, 20, 25, 30, 35 and 40 eggs of D. hyalinata. The following parameters were evaluated: number of parasitized eggs, number of individuals per egg, viability and sex ratio. Trichogramma exiguum parasitized more eggs than T. pretiosum when more than 25 eggs were available per female. The percentage of emergence was satisfactory to T. pretiosum in densities up to 15 eggs/female and up to 20 eggs/female for T. exiguum. The number of individuals per egg was not statistically different in both species except in the density of 25 eggs/female. It can be concluded that T. exiguum performed better than T. pretiosum at larger clutch sizes, as T. exiguum parasitization capacity increased as a result of the size of the host clutch size.     

Selectivity of neem to Trichogramma pretiosum Riley and Trichogrammatoidea annulata De Santis (Hymenoptera: Trichogrammatidae)

Trichogramma pretiosum Riley and Trichogrammatoidea annulata De Santis are commonly found in avocado and persimmon orchards in northern Parana state. However, their abundance depends on whether insecticides are used or not to control the key lepidopteran pests Stenoma catenifer (Wals.) (Lepidoptera: Elachistidae) and Hypocala andremona (Stoll) (Lepidoptera: Noctuidae), respectively. The aim of this work was to evaluate the effects of an aqueous neem seed extract (ANSE) at 15, 3 and 1.5%, and of an emulsifiable concentrate neem oil (ECNO) at 2.5, 0.5 and 0.25% on lifetime parameters of these trichogrammatids as a way of testing the feasibility of integrating the biological and chemical control methods. Chemicals were applied on Anagasta kuehniella (Zeller) (Lepidoptera: Pyralidae) eggs before or after parasitization (one, three or five days). ANSE was more deleterious to both parasitoid species than ECNO, regardless of the concentration and the time of application. The chemicals acted on a concentration and time dependent manner. Treating the host with neem before parasitism was less deleterious to wasp emergence, especially for T. annulata. Pre-treatments (24h) of the host eggs with ECNO at concentrations varying from 0.5% to 0.25% did not affect T. pretiosum longevity, but 2.5% reduced T. annulata survival. Feeding wasps with honey mixed with 0.25% ECNO negatively affected T. annulata survival.     

Ia-specific mixed leukocyte reactive T cell hybridomas: analysis of their specificity by using purified class II MHC molecules in synthetic membrane system

This study was undertaken to determine the nature of the antigens recognized in allogeneic and syngeneic mixed leukocyte reactions (MLR). Specifically, we wished to determine whether Ia antigens alone were recognized by MLR-reactive T cells, or whether the specificity was determined by the corecognition of non-MHC antigens together with syngeneic or allogeneic Ia. To do this we used 11 T cell hybrids that were characterized as being specific for Iad and were tested their capacity to respond to isolated I-Ad or I-Ed that had been incorporated into liposomes and had bound to the surface of glass beads. Of nine alloreactive T cell hybrids (five I-Ad-and four I-Ed-specific), seven were shown to be responsive to the relevant isolated Ia antigen on glass beads. Also, two of two syngeneic I-Ad-specific T cell hybrids responded to I-Ad on the glass beads. One of the two alloreactive T cell hybrids that failed to respond to the relevant Ia antigen on glass beads was shown to be specific for an antigen in fetal calf serum (FCS) that was recognized in the context of the allo-Ia antigen (I-Ed), because when intact accessory cells were used, a response by this hybrid was only observed when FCS was present in the assay culture medium or when the accessory cells were pre-pulsed with FCS. The possible involvement of FCS antigens and non-Ia accessory cell antigens in the stimulation of the nine T cell hybrids that responded to isolated Ia on glass beads was evaluated. T cell hybrids that were grown and were tested in serum free medium were still capable of reacting to Ia on beads. The isolated Ia preparations used were greater than 90% pure, and their capacity to stimulate the T cell hybrids did not correlate with the degree of contamination with non-Ia proteins. We conclude from these studies that the majority of T cells that respond to allogeneic or syngeneic Ia bearing stimulator cells are specific for the Ia antigens themselves, and do not require the co-recognition of other non-Ia antigens; nor is there any requirement for Ia antigen processing for this recognition.     

Kairomone stimulates increased probes and host stings in a cleptoparasitoid

Abstract.  Eupelmus vuilleti acts as a cleptoparasitoid when encountering a host parasitized by Dinarmus basalis . The encounter of a parasitized host stimulates an increasing number of ovipositor probes directly above the parasitized host, an increasing number of host stings and the destruction of approximately 40% of the D. basalis eggs. The stimulation of ovipositor probes appears to be due to the detection of a stimulus that is different from the stimulus allowing interspecific host discrimination. It appears that a proteinacious substance produced by the D. basalis venom gland and deposited on the edge of the drilled hole induces probing behaviour of E. vuilleti .     

Desert locusts <Emphasis Type="Italic">Schistocerca gregaria</Emphasis> (Acrididae: Orthoptera) do not lay eggs in old sand: Why?

Schistocerca gregaria sometimes refuse to lay eggs into the “old sand” that is kept in their cages for several days. We investigated why they rejected the old sand for oviposition. Locusts exclusively laid eggs into new sand when presented together with old sand, indicating that the old sand contained an oviposition-inhibiting (OI) factor. We examined whether this factor was derived from locust feces or fed grass (Bromus catharticus). Locusts laid all eggs into the sand with grass when presented together with sand containing feces. In contrast, few eggs were laid into the sand with grass when clean sand was offered at the same time, suggesting that the OI factor originated from the grass and was concentrated in the feces. The OI factor was efficiently extracted from feces with water compared with ethanol and acetone. OI activity was detected by extraction of feces with water for 1 min, although a longer extraction time yielded higher activity. The water extract of feces retained OI activity after boiling. None of the eggs which were buried in sand containing fecal extract hatched, whereas most of the eggs buried in clean sand or sand containing grass extract hatched, showing a correlation between OI activity and a lethal effect on eggs.     

Parasitism and predation of stink bug (Heteroptera: Pentatomidae) eggs in Georgia corn fields

Nezara viridula L. and Euschistus servus (Say) are the predominant species of phytophagous stink bugs on corn, Zea mays L., in Georgia. Oebalus pugnax pugnax (F.) occurs in relatively low numbers, and the predatory stink bug Podisus maculiventris (Say) is commonly found. Limited information is available on natural biological control of these four stink bug species in Georgia corn fields; therefore, a 6-yr study of parasitism and predation of their eggs was initiated in 2003. Naturally occurring stink bug eggs were parasitized by six scelionid species, Trissolcus basalis (Wollaston), T. thyantae Ashmead, T. brochymenae (Ashmead), T. euschisti (Ashmead), Telenomus podisi Ashmead, Telenomus calvus Johnson, and one encyrtid species, Ooencyrtus sp. T. basalis was the most prevalent parasitoid of N. viridula, parasitizing E. servus and P. maculiventris eggs at low levels. T. podisi, the predominant parasitoid species emerging from eggs of E. servus and P. maculiventris, also parasitized O. p. pugnax eggs exclusively and parasitized N. viridula eggs at low levels. T. euschisti and T. thyantae parasitized E. servus egg masses. T. brochymenae parasitized eggs of both E. servus and P. maculiventris. T. calvus parasitized only P. maculiventris eggs. The same species of egg parasitoids that parasitized naturally occurring eggs of N. viridula and E. servus parasitized sentinel eggs of these bugs, except that no T. calvus and Ooencyrtus sp. were obtained from sentinel eggs, and T. thyantae and T. brochymenae emerged from sentinel eggs of N. viridula. Generally, parasitization of an egg mass was either greater than or equal to predation of sentinel eggs of N. viridula and E. servus. However, on some dates in late June and July, predation of sentinel egg masses was numerically approximately twice as high as parasitism. Results indicate stink bug egg parasitoids and predators are significant factors in the natural biological control of stink bugs in corn fields.     

Effects of fertilization of four hemlock species on Adelges tsugae (Hemiptera: Adelgidae) growth and feeding preference of predators

Understanding how fertilization affects host resistance to hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), is important because fertilizers are often used to grow resistant selections to a suitable size for testing. We evaluated four hemlock species (Tsuga) under three different fertilizer regimes to assess whether fertility affected resistance to the adelgid and to determine whether it affected feeding preferences of the adelgid predators Laricobius nigrinus Fender and Sasajiscymnus tsugae (Sasaji & McClure). Treatments were long-term fertilization (from June 2008 to June 2009), short-term fertilization (from March to June 2009), and no fertilizer. Fertilizer was applied biweekly with 240 ppm N by using water-soluble fertilizer (N-P-K, 20:20:20). Plants (>1 yr old) were artificially infested with adelgids on 31 March 2009. Among unfertilized hemlocks (n=10 per species), foliar N was highest in Tsuga mertensiana (Bong.) CarriBre and lowest in T. chinensis (Franch.) E. Pritz. Significantly more progredien ovisacs or sisten eggs were present on T. mertensiana than on the other hemlock species with none on unfertilized T. chinensis. A. tsugae adults on T. heterophylla (Raf.) Sarg. were unaffected by fertility, but densities of developing A. tsugae nymphs were higher on unfertilized T. heterophylla plants than on fertilized T. heterophylla plants regardless of fertilizer treatment. Both L. nigrinus and S. tsugae consumed more adelgid eggs that developed on fertilized T. canadensis than from unfertilized plants. The predators did not exhibit this preference for adelgid eggs from females that developed on T. heterophylla or T. mertensiana.     

Effects of host age on parasitism and progeny allocation in Trichogrammatidae

The impact of host age on the number of hosts killed, survival of progeny, progeny allocation, and sex allocation was examined for several Trichogrammatidae (Hymenoptera) species in laboratory choice tests. Individual female parasitoids were provided with young, medium-aged and old eggs of one of three lepidopterous host species: Trichoplusia ni (Hübner) (Noctuidae), Pieris rapae (L.) (Pieridae), or Plutella xylostella (L.) (Plutellidae). Trichogrammatid species behaved as gregarious parasitoids with the first two host species, and as solitary parasitoids with eggs of the smaller latter one. They mostly preferred young eggs of T. ni, but did not discriminate among P. rapae eggs of different ages, and often preferred young or medium-aged P. xylostella eggs over old eggs. Survival of progeny did not vary constantly with host age, although it was often very low in P. rapae eggs of any age. Clutch size frequently decreased with host age in both T. ni and P. rapae. Offspring sex ratio did not change with age of T. ni and P. rapae eggs, and rarely did so in P. xylostella eggs. In regard to host age, the results with T. ni are the ones which are the most in agreement with optimal foraging theoretical predictions, as clutch size was the highest in preferred younger eggs.     

Cell adhesive peptide screening of the mouse laminin α1 chain G domain

Cell adhesive peptides have been widely applied for therapeutic drugs, drug delivery systems, and biomaterials. Previously, we identified various cell adhesive sequences in the G domains of four laminin α chains (α2-α5) by the systematic soluble peptide screening. We also identified five cell-binding sequences in the laminin α1 chain G domain using synthetic peptide-polystyrene beads. Here, we re-screened cell adhesive peptides in the laminin α1 chain G domain by the systematic soluble peptides screening. The 110 soluble peptides were evaluated for their cell adhesive activities using human fibrosarcoma HT1080 cells and human dermal fibroblasts. Fourteen peptides were newly identified as a cell adhesive. Additionally, four peptides (AG22: SSFHFDGSGYAM, AG42: TFDLLRNSYGVRK, AG76: HQNQMDYATLQLQ, AG86: LGGLPSHYRARNI) promoted integrin-mediated cell adhesion. Further, neurite outgrowth activity with rat pheochromocytoma PC12 cells was evaluated and two peptides (AG20: SIGLWNYIEREGK, AG26: SPNGLLFYLASNG) were newly identified for neurite outgrowth activity. These results suggested that the systematic soluble peptides screening approach is an accurate and powerful strategy for finding biologically active sequences. The active sequences newly identified here could be involved in the biological functions of this domain. The active peptides are useful for evaluating molecular mechanisms of laminin-receptor interactions and for developing cell adhesive biomaterials.     

黄玛草蛉幼虫对草地贪夜蛾卵和低龄幼虫的捕食能力

【目的】明确本地优势天敌黄玛草蛉Mallada basalis对入侵我国的重大农业害虫草地贪夜蛾Spodoptera frugiperda卵及低龄幼虫的捕食能力和生防潜力。【方法】在实验室条件下采用功能反应模型评价了黄玛草蛉2和3龄幼虫对草地贪夜蛾卵及1和2龄幼虫的捕食能力。【结果】黄玛草蛉幼虫对草地贪夜蛾卵和低龄幼虫的捕食量均随猎物密度的升高而增加,最后趋于捕食饱和状态,而其捕食率随猎物密度的升高而逐步下降,对不同发育阶段的草地贪夜蛾均表现为Ⅱ型功能反应。黄玛草蛉2龄幼虫对草地贪夜蛾卵及1和2龄幼虫的瞬时攻击率a分别为0.150, 0.084和0.094,处理时间Th分别为0.282, 0.333和0.519 h,理论日最大捕食量T/Th分别为85106粒、72072头和46.242头;黄玛草蛉3龄幼虫对草地贪夜蛾卵及1和2龄幼虫的瞬时攻击率分别为2.018, 0.288和0.259,处理时间分别为0.102, 0.311和0.375 h,理论日最大捕食量分别为235294粒、77170头和64000头。【结论】黄玛草蛉2和3龄幼虫对草地贪夜蛾卵和低龄幼虫均具较强的捕食能力,其中黄玛草蛉3龄幼虫比2龄幼虫具有更强的捕食效率。     

Semiochemical and physical stimuli involved in host recognition by Telenomus podisi (Hymenoptera: Scelionidae) toward Euschistus heros (Heteroptera: Pentatomidae)

The egg parasitoid, Telenomus podisi, was shown to recognize its host, Euschistus heros, through both chemical and physical cues. These were determined in short-range bioassays. The cues comprised fertile and infertile host eggs, egg extracts, crude extracts of adult males and females and successive dilutions of the synthetic racemic mixture of methyl 2,6,10-trimethyltridecanoate, a male-produced pheromone of E. heros. Some of the treatments used induced a selection process in T. podisi, through host recognition behaviour, indicating a consistent response of this species to E. heros. The possibility that some of these compounds could be exploited as long-range kairomones, by T. podisi, is discussed. Using GC analysis, an unidentified compound (Rt 24.8 min), possibly from the egg adhesive material, was detected from E. heros egg extracts. Its retention time compared to the methyl 2,6,10-trimethyltridecanoate showed a lower volatility, suggesting that the egg adhesive may act as a short-range kairomone. Physical cues appeared to be an important component in the host selection process by T. podisi. The parasitoid discriminated infertile eggs which are differently shaped and smaller than fertile eggs.     

Levels of encapsulation and melanization in two larval instars of Ostrinia furnacalis Guenée (Lep., Pyralidae) during simulation of parasitization by Macrocentrus cingulum Brischke (Hym., Braconidae)

Abstract:  The hymenopteran Macrocentrus cingulum is a polyembryonic endoparasitoid that uses larvae of the lepidopteran Ostrinia furnacalis as one of its host insects. Previous studies indicated that although this parasitoid does not transmit polydnaviruses when it lays its eggs, a layer of fibrous tissue on the surface of the eggs helps them to avoid being encapsulated by the immune system of the host insect. However, as eggs of M. cingulum that are laid into late instar larvae of O . furnacalis often do not survive, there is a tendency for the adults to lay their eggs in earlier instar larvae. We studied the amounts of encapsulation and melanization around beads of DEAE-Sephadex A-25 injected into the haemoceol of fourth and fifth larval instars of O. furnacalis . The beads were injected to simulate the presence of eggs of the parasitoid M. cingulum . We found that the levels of encapsulation and melanization around the beads increased with the age of the O. furnacalis larvae. Likewise, the total counts of the haemocytes circulating within the haemolymph increased with the age of the O. furnacalis larvae and were correlated negatively with the percentage of larvae parasitized by M. cingulum . It appears that young O. furnacalis possess a weak cellular defence, and as a result are more susceptible to being parasitized. Hence, the correlation between the levels of encapsulation and the age of the host insect appears simply to reflect passive evasion.     

Could the egg itself be the source of the oviposition deterrent marker in the ectoparasitoid Dinarmus basalis?

Females of Dinarmus basalis, a solitary ectoparasitoid, strongly avoid superparasitising hosts bearing eggs which are 20 or more hours old. Our objective was to determine the mechanism by which the factors inducing host discrimination and such an oviposition deterring effect act, and the origin of the deterrent. This study showed that the information is carried by the parasitised host. It is acquired by a transfer of molecules from the wasp egg onto the host and it requires contact between egg and host for at least 4 h. The factors transferred do not, as commonly reported in other species, come from the female's genital apparatus but from the live egg itself. Consequently, the D. basalis egg directly participates in the success of parasitism by releasing factors which elicit the oviposition host deterring effect. The originality and the ecological importance of these results are discussed.