Trichogramma bournieri Pintureau & Babault (Hymenoptera: Trichogrammatidae) and Chilo sacchariphagus Bojer (Lepidoptera: Crambidae) in sugarcane in Mozambique: A new association

Chilo sacchariphagus Bojer (Lepidoptera: Crambidae), a sugarcane stalk borer indigenous to South East Asia, and the nearby Indonesian Islands, was identified from African sugarcane in Mozambique in 1999. Prior to a classical biocontrol programme being implemented against it, intensive pre-release surveys for the presence of any indigenous natural enemies on life stages of the borer were completed. Negligible parasitism of larval and pupal stages was recorded. In contrast, egg batches found were heavily parasitised. Parasitoid adults emerging from the eggs were found to be only the indigenous Trichogramma bournieri Pintureau & Babault (Hymenoptera: Trichogrammatidae). Aspects of the impact of T. bournieri on C. sacchariphagus eggs in Mozambican sugarcane are presented, and the potential of using this egg parasitoid against C. sacchariphagus in an augmentation biocontrol programme is discussed.     

Importance of host oviposition pattern and plant size for the selection of Trichogramma strains to control the diamondback moth

The aim of this work was to select a candidate strain of Trichogrammatidae (Hymenoptera: Chalcidoidea) to control the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), an important pest of cabbage in Europe. The parasitic efficiency of Trichogramma chilonis Ishii from Japan and Réunion Island, Trichogramma evanescens Westwood from Egypt, Trichogramma ostriniae Pang & Chen from Japan, and Trichogramma semblidis (Aurivillius) from France was studied with sentinel eggs in greenhouse‐grown cauliflower. The percentage of parasitized eggs was measured 1 m from the release point and 3 days after release. Two factors were studied: host‐egg density (three eggs per stem vs. 50 eggs per stem) and plant size (50–100 cm high plants vs. 100–150 cm high plants). Trichogramma evanescens from Egypt achieved the best parasitism. Parasitism efficiency of T. ostriniae from Japan and T. chilonis from Réunion Island was not influenced by egg density. In contrast, parasitism efficiencies of the three other strains were higher at the lower egg density than at the higher egg density. Parasitism efficiency was lower when the plants were bigger, with the exception of T. chilonis from Réunion Island, for which the level of parasitism was not affected by plant size. Thus, T. chilonis from Réunion Island appeared to be the most suitable Trichogramma strain for use in controlling P. xylostella, regardless of the growth stage of the crop. However, T. ostriniae from Japan may also be more suitable for use on cauliflower crops at the early stage of crop development. If potential problems related to the introduction of exotic species are taken into consideration, it is possible to consider the native T. evanescens.     

The Effectiveness of Trichogramma chilonis,Trichogramma pretiosum and Trichogramma brasiliense (Hymenoptera: Trichogrammatidae) as Parasitoids of Helicoverpa armigera (Lepidoptera: Noctuidae) on Sunflower (Helianthus annuus) and Redgram (Cajanus cajan)

The performance of three species of trichogrammatids on the pest, Helicoverpa armigera was evaluated in the laboratory and screenhouse conditions in Karnataka, India during 1996-97. Laboratory studies indicated that Trichogramma chilonis and Trichogramma pretiosum were more effective parasitoids of H. armigera than Trichogramma brasiliense. In screenhouse conditions, T. chilonis was the most effective parasitoid of H. armigera eggs on sunflower plants in comparison to the other two trichogrammatid species. When releasing 50?000 per ha on sunflower and redgram, T. chilonis parasitised 50.1 and 11.4% H. armigera eggs, respectively. The position of H. armigera eggs on different plant parts of sunflower had no effect on parasitism by T. chilonis. However, parasitism by the same trichogrammatid among different plant parts of redgram varied significantly. It parasitized 43.4 and 18.7% H. armigera eggs on leaves and flowers, respectively, and significantly fewer, 3.9%, on pods (P<0.05). The growth stage of redgram plants also had an effect on parasitism by T. chilonis, parasitism being extremely low on plants with pods.     

Seasonal phenology and stage-specific parasitism of the apple ermine moth, Yponomeuta malinellus Zeller, in Korea

The apple ermine moth, Yponomeuta malinellus Zeller (Lepidoptera: Yponomeutidae), is a tent caterpillar that feeds on Malus spp. in Korea. Populations of the moth in native areas appeared to be regulated by the assemblage of parasitoids. Phenological associations between host stages and parasitoids, susceptible stage(s) of the host for each parasitoid, and stage‐specific parasitism were studied. The egg larval parasitoid Ageniaspis fuscicollis (Dalman) had highest parasitism of first instar larvae (24%), with 14% parasitism of other larval stages. Dolichogenidea delecta (Haliday) was recovered from all larval instars with the highest parasitism rate of second instar larvae (20.1%), followed by 19.9% parasitism of mid‐larval hosts. Herpestomus brunicornis Gravenhorst was reared from second instar larvae through to pupal collection, and had the highest parasitism rate (29.9%) at the pupal stage. The larval pupal parasitoid Zenillia dolosa (Meigen) was recovered from mid‐larval to pupal stages with the highest parasitism rate (5.5%) occurring in third to fourth instar larvae. The host stages for developing A. fuscicollis completely overlap with those of D. delecta, and with those of H. brunicornis to some degree. A statistically significant negative correlation exists between A. fuscicollis and these dominant parasitoids, indicating competitive interaction within the host.     

Evaluation of an endosulfan tolerant strain of <Emphasis Type="Italic">Trichogramma chilonis</Emphasis> on cotton

The performance of an endosulfan tolerant strain of Trichogramma chilonis Ishii was evaluated against Helicoverpa armigera (Hübner) eggs on cotton plants in a net house. Under pesticide pressure, the tolerant strain could provide significantly higher parasitism in comparison to the susceptible strain. The parasitoid adult emergence was also significantly higher in the treatment with the tolerant strain in comparison to the susceptible strain, when parasitoids were released within 3 days of endosulfan spraying. Release of the tolerant strain of T. chilonis in conjunction with endosulfan spray application resulted in significantly higher pest mortality in comparison to the endosulfan treatment or release of T. chilonis alone. It could be inferred from the results that T. chilonis should be released only 3 days after endosulfan spray application as during the first 3 days after the spraying, endosulfan provided the required protection and adversely affected the performance of the parasitoid.     

Effect of fertilized,unfertilized, and UV‐irradiated hosts on parasitism and suitability for Trichogramma parasitoids

Trichogramma spp. (Hymenoptera: Trichogrammatidae) parasitoids have been commonly used as biological control agents in insect pest management. Host quality is believed to influence parasitism, host preference, and suitability for parasitoids. To date, limited studies have compared the parasitism of Trichogramma parasitoids on fertilized, unfertilized, and sterilized host eggs. Hence, we studied the performance of three Trichogramma egg parasitoids, Trichogramma japonicum Ashmead, Trichogramma chilonis Ishii, and Trichogramma leucaniae Pang & Chen, on fertilized, unfertilized, and ultraviolet (UV)‐irradiated fertilized (UVF) eggs of rice moth, Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae). In a no‐choice test, T. japonicum and T. leucaniae parasitized significantly more fertilized or UVF than unfertilized hosts, and T. chilonis parasitized significantly more UVF than either fertilized or unfertilized hosts. In a choice test, all three Trichogramma parasitoids parasitized UVF hosts the most, and unfertilized hosts the least. There were similar percentages of adult emergence and female progeny among fertilized, unfertilized, and UVF hosts for all three Trichogramma parasitoids, except that T. japonicum had significantly lower adult emergence on fertilized hosts. We also found that all three Trichogramma parasitoids developed slower on unfertilized hosts. Regardless of host treatments, T. leucaniae had the longest developmental time and T. chilonis had the shortest. We conclude that Trichogramma parasitoids prefer parasitizing UVF eggs of C. cephalonica without negative effects on their emergence and sex allocation.     

Functional response and egg distribution among hosts by Pseudapanteles dignus,a larval endoparasitoid of Tuta absoluta

The functional response of a biocontrol agent has been classically pointed out as a quantitative evaluation criterion to understand its killing capacity to an arthropod pest. In this paper, we revisited the functional response of the internal larval parasitoid Pseudapanteles dignus (Muesebeck) (Hymenoptera: Braconidae), a candidate for biocontrol of the South American tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), measured as the daily egg oviposition of single parasitoid females at increasing densities of T. absoluta larvae through dissection of hosts. The functional response curve of the number of parasitized hosts was fitted out taking into account the number of eggs laid and their distribution among hosts at each T. absoluta larval density. The data also allowed us to discuss the self-superparasitism strategy of this parasitoid as an adaptive trait. Pseudapanteles dignus showed a sigmoid shape functional response and a contagious distribution of eggs among hosts, favouring self-superparasitism and laying a similar number of eggs in each superparasitized host at each T. absoluta density. This research is firstly intended to ascertain about the oviposition behaviour of P. dignus and additionally to provide information on its reproduction to be applied in mass rearing procedures and augmentative releases against T. absoluta.     

Cytotoxic effects of parasitism and application of venom from the endoparasitoid Pimpla turionellae on hemocytes of the host Galleria mellonella

In parasitoid species devoid of polydnaviruses and virus‐like particles, venom appears to play a major role in suppression of host immunity. Venom from the pupal endoparasitoid Pimpla turionellae L. (Hymenoptera: Ichneumonidae) has previously been shown to contain a mixture of biologically active components, which display potent paralytic, cytotoxic, and cytolytic effects toward lepidopteran and dipteran hosts. The current study was undertaken to investigate if parasitism and/or envenomation by P. turionellae affects the frequency of apoptotic and necrotic hemocytes, hemocyte viability and mitotic indices in Galleria mellonella L. (Lepidoptera: Pyralidae) pupae and larvae. Our study indicates that parasitism and experimental envenomation of G. mellonella by P. turionellae resulted in markedly different effects on the ratio of apoptotic hemocytes circulating in hemolymph depending on the host developmental stages. The ratio of early and late apoptotic hemocytes increased in G. mellonella pupae and larvae upon parasitization and at high doses of venom when compared to untreated, null and Phosphate Buffered Saline (PBS) injected controls. In contrast, an increase in necrotic hemocytes was only observed in parasitized pupae at 24 h and no difference was observed in larvae. The lowest hemocyte viability values were observed with pupae as 69.87%, 69.80%, and 72.47% at 4, 8, and 24 h post‐parasitism. The ratio of mitotic hemocytes also decreased in pupae and larvae upon parasitization and at high doses of venom. Staining of hemocytes with annexin V‐FITC revealed green fluorescent ‘halos’ along the plasma membranes of venom treated cells within 15 min following exposure to venom. By 1 h post‐venom – treatment, the majority of hemocytes displayed binding of this probe, indicative of early stage apoptosis. These same hemocytes also displayed a loss of plasma membrane integrity at the same time points as evidenced by accumulation of propidium iodide in nuclei.     

Chemotactic responses and parasitism of Trichogramma pretiosum after successive generations in Spodoptera frugiperda

Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) is an important parasitoid of lepidopteran pests. Its parasitism success is related to its foraging behavior, mediated by kairomones from its hosts. We aimed to evaluate the chemotactic responses and parasitism of T. pretiosum from Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae) eggs as well as the parasitoid maintained for three generations in Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) eggs. Chemotactic responses of T. pretiosum from both hosts were evaluated in a dual choice olfactometer. Females were submitted to a choice between washed vs. unwashed eggs of E. kuehniella or S. frugiperda, as well as to unwashed eggs of both hosts. Egg extracts of both hosts were also contrasted with hexane and with each other. Parasitism of T. pretiosum exposed to eggs of the two species was also evaluated. Females from E. kuehniella were more attracted to odors from eggs of this host whenever it was present. Third generation parasitoids from S. frugiperda eggs were more attracted to eggs and egg extract of S. frugiperda than to those from E. kuehniella. The highest number of parasitized eggs and emerged parasitoids in S. frugiperda was observed in parasitoids coming from the third generation in this host. Therefore, imaginal conditioning could be an alternative to be considered for T. pretiosum learning before releasing, possibly optimizing its search and parasitism process in S. frugiperda eggs.     

Forest composition, host-population density, and parasitism of spruce budworm Choristoneura fumiferana eggs by Trichogramma minutum

The frequency of egg parasitism in the spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae) by Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae) was recorded in several host populations during the rising phase of an outbreak in the Gatineau Valley (Quebec, Canada) in 1999 and 2000. Some of the observed spruce budworm populations were subjected to experimental aerial applications of Bacillus thuringiensis var. kurstaki during the course of the study. Untreated spruce budworm population densities at the onset of the study were directly related to stand composition (the proportion of non‐host basal area) but unrelated to plant species diversity. Much of the variation in budworm egg mass parasitism rates was accounted for (77.1% of total variance) by three variables: year, spruce budworm egg population density, and proportion of non‐host basal area in the stand. The exploitation of eggs within parasitised egg masses was related to year, B. thuringiensis treatment, egg mass size, and the proportion of egg masses parasitised in the host population (76.9% of variance). The yearly variation in parasitism rate was considerable, and was consistent with climatic conditions, namely heat accumulation and precipitation during the spruce budworm oviposition period. Parasitism by T. minutum on eggs of C. fumiferana was recorded in 16 additional sites in 2000, to confirm the general form of the inverse density dependence of parasitism. Observations recorded by Neilson in the Green River area of New Brunswick (Canada) between 1948 and 1957 are discussed in the context of the present analysis. These results indicate that parasitism by T. minutum may be more predictable than previously believed and may be an important and consistent source of mortality in the several years preceding an outbreak of C. fumiferana, especially in mixed‐wood stands and in warmer, drier portions of the spruce budworm's range.     

Effect of host switching on performance of mass‐reared Trichogramma minutum

The effect of host switching on parasitism by Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae) (TM) was examined for parasitoids attacking a factitious host, the Mediterranean flour moth, Ephestia kuehniella Zell. (Lepidoptera: Pyralidae) (MFM), and a natural host, the eastern spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae) (SBW). Parasitoids that were switched from rearing on the natural host to rearing on the factitious host had lower realized fecundities on both MFM and SBW eggs than a control line that was maintained continuously on the natural rearing host, SBW eggs. Conversely, T. minutum reared on the factitious host and switched to rearing on the natural host showed greater realized fecundities. This increase in realized fecundity was lost in the first generation after switching parasitoids back to the factitious rearing host. T. minutum that were maintained on the natural rearing host (SBW eggs) showed more variation in realized fecundity and host acceptance of both MFM and SBW eggs, than parasitoids that were reared on MFM eggs.     

Effects of host-egg ages on host selection and suitability of four Chinese Trichogramma species,egg parasitoids of the rice striped stem borer,Chilo suppressalis

The striped stem borer, Chilo suppressalis (Walker), is one of the most economically important rice pests worldwide. However, biological control of this pest using natural-enemy insects has been rarely documented to date. With the objective of screening suitable candidate species for controlling the striped stem borer, we investigated the effect of the age of host eggs on the host selection and suitability by four indigenous Trichogramma species on their native host, C. suppressalis. The results indicated that the differently aged eggs of C. suppressalis were all accepted by T. japonicum, T. dendrolimi and T. chilonis, and there was a clear tendency to parasitize older eggs less under no-choice and choice conditions. The number of parasitized host eggs by T. ostriniae also decreased with the increasing host age in the no-choice test, but more 2-day-old host eggs were parasitized in the choice test. When 0-, 2-day-old eggs were offered, T. dendrolimi, T. japonicum and T. chilonis exhibited similar parasitism ability, whereas T. ostriniae appeared to have a stronger ability to attack the older host eggs (4-day-old). Trichogramma japonicum developed and emerged on parasitized C. suppressalis eggs of all ages tested, while showing a better adaptation to younger host eggs with significantly faster developmental time, higher survival and more female progeny on 0-day-old eggs. No adults for each of the other three Trichogramma species emerged from parasitized 4-day-old host eggs, and they had similar developmental time, survival and female progeny on parasitized 0-, 2-day-old host eggs with an exception of female progeny for T. chilonis. On 0-day-old host eggs, T. japonicum developed faster and T. ostriniae had lower progeny survival than the other three Trichogramma species evaluated, respectively. The current study provides useful information to select suitable Trichogramma species for controlling the striped stem borer, C. suppressalis.     

Isolation of microbes associated with field-collected populations of the egg parasitoid,Trichogramma chilonis capable of enhancing biotic fitness

Four bacterial and one yeast species, cultured and identified as Stenotrophomonas maltophilia, Acinetobacter sp., Pseudomonas sp. and Ochrobactrum sp. and the yeast as Metschnikowia reukaufii, were isolated from the internal organs of four collections of field-sourced egg parasitoid, Trichogramma chilonis, obtained as parasitised Helicoverpa armigera eggs. Bacteria were identified through 16 rRNA amplification and sequencing. The single species of yeast was identified through internal transcribed spacer sequences. A single bacterial species could be isolated from each of the four T. chilonis collections; however, all four T. chilonis collections yielded the yeast, M. reukaufii. In order to study the influence of the association of each of the bacterial species and the yeast, microbe-free laboratory-bred populations of T. chilonis were fed with the individual cultures and fitness parameters as parasitisation vigour and female bias were studied in T. chilonis over 10 generations. T. chilonis fed with either S. maltophilia or Acinetobacter sp. and Pseudomonas sp. showed a mean percent increase in female ratio of 26.2%, 30% and 30.3% and mean percent parasitisation of H. armigera eggs significantly increased by 38%, 32.2% and 31.3%, respectively. However, T. chilonis fed with Acinetobacter sp. did not positively influence the two T. chilonis fitness factors. The ubiquitous yeast, M. reukaufii, which could be isolated from all four collections of T. chilonis, could significantly increase both female count and percent parasitism ratio by 22% and 65%, respectively. This study has opened the possibility of modulating the parasitisation fitness of laboratory-bred T. chilonis, prior to field release, using microbes associated with them in the wild.     

Trichogramma chilonis Ishii: A potential biological control agent of Crocidolomia pavonana in Samoa

Crocidolomia pavonana F. (Lepidoptera: Crambidae) is a major pest of Brassica crops in tropical and sub-tropical regions of Africa, Asia and the Pacific. There are no previous reports of effective natural enemies of the pest across this range but in Samoa an arrhenotokous population of the generalist egg parasitoid Trichogramma chilonis Ishii (Hymenoptera: Trichogrammatidae) frequently attacks it. This is the first record of T. chilonis in Samoa. A three-year field recruitment study showed that although C. pavonana eggs occurred at all times of the year, their abundance was greatest during drier periods. Parasitism of C. pavonana egg masses by T. chilonis was variable (0–87% of egg masses attacked) but the parasitoid was recovered from eggs collected at all times of the year and it is well established in the major Brassica growing regions of the island of Upolu. When partial lifetables were constructed for C. pavonana, the rate of egg disappearance (likely due to predation and the physical effects of rainfall) ranged from 0 to 0.839 and the marginal rate of mortality due to T. chilonis ranged from 0 to 0.474. When it was present, T. chilonis was the major mortality factor affecting C. pavonana eggs in all but one of the recruitment studies. The historical problems surrounding the identity and species status of T. chilonis are discussed and its host range and distribution in the Asia-Pacific region is reviewed briefly. Finally, the potential of this population of T. chilonis for development as a biological control agent of C. pavonana is considered.     

Host Preferences of Trichogramma pretiosum and the Influence of Prior Ovipositional Experience on the Parasitism of Plutella xylostella and Pseudoplusia includens Eggs

Trichogramma wasps are generalist egg parasitoids used in biological control efforts. In a multi host situation they may preferentially parasitize a non-target host species to the detriment of the control program. Plutella xylostella Linnaeus (Lepidoptera: Plutellidae) is a very serious pest of cabbage, but is only one in a number of species in the ‘cabbageworm’ complex. We investigated the host preferences of Trichogramma pretiosum Riley (Hymenoptera: Chalcidoidea) when offered the eggs of Plutella xylostella and the eggs of Pseudoplusia includens Hübner (Lepidoptera: Noctuidae), another species in the ‘cabbageworm’ complex. Trichogramma pretiosum reared on the eggs of the factitious host Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) parasitized both Plutella xylostella and Pseudoplusia includens eggs under laboratory conditions. For both choice and no-choice experiments, T. pretiosum parasitized significantly more P. xylostella eggs than P. includens eggs. Prior ovipositional experience with one or other of the two host species had no effect on the subsequent parasitism levels of the two host species. The preference for P. xylostella eggs was also not affected by this prior ovipositional experience.     

Influence of Landscape Diversity and Composition on the Parasitism of Cotton Bollworm Eggs in Maize

We deployed >50,000 Helicoverpa armigera eggs in maize fields to assess the rate of parasitism by Trichogramma chilonis across 33 sites during a three-year span (2012–2014) in northern China. Subsequently, we used a partial least squares (PLS) regression approach to assess the relationship of landscape diversity with composition and parasitism potential. The parasitism rate of H. armigera eggs by T. chilonis ranged from 0–25.8%, with a mean value of 5.6%. Landscape diversity greatly enhanced parasitism at all four different spatial scales (0.5, 1.0, 1.5 and 2.0 km radius). Both the proportion of arable area and the total planting area of two major crops (cotton and maize) had a negative correlation to the parasitism rate at each scale, whereas parasitism was positively correlated to the proportion of host crops of H. armigera other than cotton and maize at the 0.5 to 2.0 km radius scales as well as to that of non-crop habitat at the 0.5 and 1.0 km radius scales. The study indicated that maintaining landscape diversity provided an important biocontrol service by limiting H. armigera through the egg parasitoid T. chilonis, whereas rapid agricultural intensification would greatly reduce the presence and parasitism of T. chilonis in China.     

Conséquences de l'élevage continu deLixophaga diatraeae [Dipt. Tachinidae] sur l'hote de remplacement:Galleria mellonella [Lep. Galleriidae]

Résumé L. diatraeae, parasite naturel des foreurs du genreDiatraea a été élevé au laboratoire en permanence surG. mellonella utilisé comme h?te de remplacement. Cet élevage a été comparé à celui effectué parallèlement surChilo sacchariphagus qui peut être considéré comme un h?te convenable pour le développement de cette Tachinaire. Les conséquences de l'exploitation deGalleria parLixophaga se sont traduites chez la tachinaire par une incapacité progressive des màles à s'accoupler et une fertilité moindre des femelles. Ces réactions ont eu pour conséquence de faire disparaitre, dès la 6^e génération, la souche deLixophaga élevée surGalleria. D'une fa?on plus générale ce mode d'action ?à long terme? contribe à expliquer les modalités de la spécificité parasitaire au même titre que les réactions ?à court terme? qui sont habituellement mieux connues parce qu'elles correspondent à des effets immédiats sur le parasite.

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Summary L. diatraeae, a natural parasite of the American borers from the genusDiatraea, has been reared continuously in the laboratory onG. mellonella. The results have been compared with those obtained on the Asian borer,C. sacchariphagus, which is a suitable host for the development of this Tachnid. Under these conditions, it became evident thatL. diatraeae could not maintain itself for more than 6 generations onG. mellonella. Indeed, the effect of adverse physiological factors onLixophaga during its larval stage is to reduce progressively both female fertility and the ability of the males to mate, even if there is no visible effect on the development of the larval and pupal stages. This phenomenon must be recognized because it affects the use of laboratory hosts for production of parasites for biological control. In this test the defensive reactions ofGalleria appeared progressively, generation after generation, but only on the adults (particularly on males) by widely known, that either prevent the parasite from penetrating into the host, or inhibit its subsequent development. In general, these results contribute to a better explanation of host specificity.

     

Thermal tolerance of potential <Emphasis Type="Italic">Trichogramma</Emphasis> strains for mass-production and paddy field release in the Greater Mekong Subregion

In order to identify suitable Trichogramma strains for mass production and successful control of key lepidopteran pests in paddy fields in the Greater Mekong Subregion, the effects of high temperatures on wasp life history traits were compared among three strains of Trichogramma chilonis Ishii and two strains of Trichogramma ostriniae Pang et Chen, collected from paddy fields in the region. At a rearing temperature of 25 °C, life history traits differed significantly among the five strains tested and the three T. chilonis strains and a T. ostriniae strain were of high performance. When female wasps were exposed to higher temperatures commonly encountered in the region, negative effects were observed on key life history parameters of adult females and their offspring at 34 °C, which became even more serious at 37 °C. In particular, the two T. ostriniae strains were not able to successfully develop to adulthood at all at 37 °C while for the T. chilonis strains adult emergence was significantly reduced. In addition, the emerged offspring females lived only around one day and no parasitism was observed. When the three T. chilonis strains were exposed to 37 °C for 4 to 12 h at prepupal and pupal stages, reflecting heat shocks that the released Trichogramma may experience in the field, adult emergence was significantly reduced after an exposure time of 12 h. In summary, the three T. chilonis strains show a relatively high potential for incorporation in a biological control program in the target region. Our results also highlight that tests at both rearing and field temperatures are necessary in selection of potential Trichogramma strains for an inundative release program where there is significant difference between rearing and field temperatures.     

Effects of host age on the performance of >Diadromus collaris, a pupal parasitoid of >Plutella xylostella

The ichneumonid >Diadromus collaris(Gravenhorst) (Hymenoptera: Ichneumonidae) is amajor solitary, pupal endoparasitoid of thediamondback moth, >Plutella xylostella(Linnaeus) (Lepidoptera: Plutellidae).Experiments to examine parasitism of the hostpupae of different ages by the parasitoid wereconducted in the laboratory. >Diadromuscollaris preferred host pupae that were in thefirst half of their pupal development. Survivalfrom larva to adult, and size and parasitizingcapacity of the resultant female adultsdecreased dramatically as host pupal ageincreased. When ovipositions were made intohost pupae that were in the last quarter oftheir development, all parasitoids died beforeadult emergence. The performance of >D.collaris, as affected by host pupal age,agrees with the simple diet theory thatpredicts female wasps should select hosts ofhigher nutritional quality for oviposition.     

Age and parasitism status of Tuta absoluta eggs alter the foraging responses of the predator Nabis pseudoferus

We studied the effect of Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae) parasitism of Tuta absoluta Meyrick (Lepidoptera: Gelechiidae) eggs on the foraging behavior of Nabis pseudoferus Remane (Hemiptera: Nabidae) feeding on T. absoluta eggs of different ages. Older parasitized eggs (48–72 h old) were rejected after probing with the probosis. A separate experiment showed that probing did not harm developing parasitoids. Bugs greatly reduced their feeding times on older parasitized eggs and spent more time grooming and probing eggs and leaves. Predators exhibited a type III functional response to 24 h-old eggs, but a type II response to older eggs, whether parasitized or not. 24 h-old eggs suffered higher attack rates, and required less handling time than older eggs. Although the predatory efficiency of N. pseudoferus was reduced in the presence of parasitized eggs, the partial refuge enjoyed by T. brassicae in older eggs may permit an additive impact on the pest, and should facilitate the joint augmentation of both species against T. absoluta.