Female Parasitoids Research Articles

Radiation on Medfly Larvae of tsl Vienna-8 Genetic Sexing Strain Displays Reduced Parasitoid Encapsulation in Mass-Reared Diachasmimorpha longicaudata (Hymenoptera: Braconidae).

Improvements in the mass rearing of Diachasmimorpha longicaudata (Ashmead) on larvae of the Vienna-8 temperature-sensitive lethal genetic sexing strain of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) (= GSS Vienna-8) at the San Juan biofactory, Argentina, are currently under way. Lowering cost production is a key factor regarding parasitoid rearing. Thus, the variation in mass-reared parasitoid encapsulation levels and the incidence of superparasitism were determined; also, the gamma radiation dose-effect relation on host larvae and the influence of Mediterranean fruit fly strain were considered. Naked Mediterranean fruit fly larvae of both GSS Vienna-8 and a wild bisexual strain (= WBS) aged 6-d-old were irradiated at 0, 20, 40, 60, 80, 100, and 120 Gy, and exposed to parasitoid females. Melanization level was tested for encapsulated parasitoid larval first-instars (= L1). Non-irradiated and irradiated WBS larvae at 20-40 Gy displayed a significantly higher incidence of encapsulation when compared with GSS Vienna-8 larvae. The low melanized level in encapsulated parasitoid L1 was the most common melanization process at 72 h puparium dissection. A high melanized level was only found in non-irradiated WBS larvae. Irradiated GSS Vienna-8 larvae can neutralize the host immunological reactions over irradiated WBS larvae much more quickly. Superparasitism intensity in both Mediterranean fruit fly strains was not affected by radiation doses. High levels of superparasitism seemingly helped to overcome the host's immune reaction by the surviving parasitoid larva. Parasitoid emergence increased from 60 Gy onwards in both Mediterranean fruit fly strains. Radiation in GSS Vienna-8 larvae may favor host's antagonistic reactions decrease in relation with D. longicaudata development.

Alyssum (Lobularia maritima) selectively attracts and enhances the performance of Cotesia vestalis, a parasitoid of Plutella xylostella

The use of nectar-providing plants to nourish natural enemies of pest species has become a widely-used approach in conservation biological control to reduce pest damage without the indiscriminate use of insecticides. Choice of plant species is crucial to maximize benefits, but suitable species are yet to be identified for many important crop-pest systems. Here we explored the suitability of three candidate nectar plants for use in brassica vegetables to suppress the globally significant pest, Plutella xylostella L. (Lepidoptera: Plutellidae), using the widely-distributed parasitoid, Cotesia vestalis (Haliday) (Hymenoptera: Braconidae). Volatiles of alyssum (Lobularia maritima (L.) Desv) (Brassicaceae) were attractive to the parasitoid and access to flowering shoots increased adult longevity and realized fecundity of C. vestalis. Moreover, adult diamondback moth derived no benefit from this flower. In contrast, buckwheat (Fagopyrum esculentum Moench) (Polygonaceae), a species widely used in conservation biological control in other systems, increased the longevity and fecundity of both pest and parasitoid, rendering it less suitable. A third plant, heronsbill (Portulaca grandiflora Hook.) (Portulacaceae) denied benefit to the pest and promoted longevity of the parasitoid under no-choice conditions but did not improve fecundity and was repellent to female parasitoids under choice conditions. The contrasting effects of this set of plants illustrate the need to test multiple response variables and effects on both pest and natural enemy when seeking optimal nectar plants for use in a novel conservation biological control system.

Effects of exposure time and ratio of irradiated larvae from three medfly strains on progeny yield in Diachasmimorpha longicaudata (Hymenoptera: Braconidae) mass rearing

ABSTRACTAn augmentative biological control strategy against Ceratitis capitata (= medfly) in fruit-producing irrigated-valleys of San Juan, central-western Argentina, has been recently implemented by the San Juan Fruit Fly Control and Eradication Program. The Asian-native parasitoid Diachasmimorpha longicaudata is currently reared at the San Juan Medfly and Parasitoids Mass Rearing Facility for this purpose. In this regard, the objective of this study was to evaluate adult emergence and offspring sex ratio to improve parasitoid production. Three medfly strains at different host larvae densities and exposure times to female parasitoids were assessed. Prevalence of superparasitism was also considered. Three parasitoid population lines were used in the trials: one reared on medfly larvae of the Vienna-8 temperature-sensitive lethal (tsl) genetic sexing strain without inversion, and the other two on larvae of biparental medfly strains native to San Juan (central-western Argentina) and Tucumán (northwestern Argentina). Gamma-irradiated 6 d-old larvae (early third-instars) of each medfly strain were exposed to parasitoids for 30, 60, 90, and 120 min at 3:1, 6:1, and 9:1 host/parasitoid ratios. The Vienna-8 C. capitata strain was as efficient in producing parasitoids as both biparental native strains. Medfly larvae exposed to 10 female parasitoids for a relatively long time (1.30 hrs) at a high ratio (6–9:1) of host to parasitoid were enough to achieve the highest mean adult emergence (50–60%) and a female-biased offspring sex ratio. Superparasitism positively influenced female parasitoid production. These findings may be used to develop a more cost-effective mass rearing method for D. longicaudata.

Chemical Cues Induced from Fly-Oviposition Mediate the Host-Seeking Behaviour of Fopius arisanus (Hymenoptera: Braconidae), an Effective Egg Parasitoid of Bactrocera dorsalis (Diptera: Tephritidae), within a Tritrophic Context.

Fopius arisanus is a solitary endoparasitoid that parasitizes a variety of tephritid species. Native to the Indo-Australian region, it is currently exploited worldwide as a biological control agent due to its exceptional efficiency in reducing pest populations. The efficiency of any biological control program is affected by the host location ability of the parasitoids. The present study used a Y-tube olfactometer to test the behavioural responses of female F. arisanus to four fruit species which had undergone different types of damages: undamaged, damaged through Bactrocera dorsalis ovipositioning (i.e., infested), or different levels of mechanical damage. Our results suggest that F. arisanus females were significantly attracted to mangoes and pears (vs. purified air), regardless of their condition; however, whilst infested mangoes did not attract more female parasitoids compared to healthy or mechanically damaged fruits, infested pears attracted significantly more. For citrus fruits and peaches, oviposition damage caused them to be more attractive to parasitoid females. In terms of the longevity of the effects, infested mango fruits remained attractive for up to 5 days after infestation, whereas for infested peaches, pears, and citrus fruits, the attractiveness tended to decrease as time passed. Regarding mechanical damage, mango fruits that had undergone any intensity of damage were equally attractive to parasitoid females; however, peach and citrus fruits with high levels of mechanical damage were more attractive, and pears were found to be most attractive with slight mechanical damage. Additional to the above, we also tested the effect of insecticides on behavioural responses using mangoes. We found that the treatment of infested fruits with lambda-cyhalothrin and cypermethrin remained attractive to F. arisanus females, albeit to different extents, which is in contrast to spinosad, cyantraniliprole, and acetamiprid. Finally, we suggest that the host-searching behaviour of F. arisanus females is mainly mediated by oviposition-induced volatiles, either emitted from the fruit or left by the fruit fly.

Parasitism, host feeding, and transgenerational effects of three insecticides on the eulophid parasitoid Tamarixia triozae when exposed in the immature stages.

The ectoparasitoid Tamarixia triozae is a promising biological control agent of the tomato psyllid, Bactericera cockerelli, based on its high parasitism rates on different crops. The parasitism, host feeding, and transgenerational effects (in terms of sex ratio) of T. triozae females exposed to three insecticides (soybean oil, imidacloprid, and abamectin) as eggs, larvae, and pupae were evaluated when a mixture of second, third, fourth, and fifth instars of the host B. cockerelli was offered. The concentrations bioassayed of each insecticide corresponded to the minimum field-registered concentration [MiFRC] and one-half the MiFRC. No parasitism of B. cockerelli second instars was recorded when parasitoid's females were exposed in any of the three immature stages to any of the insecticides. In contrast, in some cases, parasitism of T. triozae females treated as eggs, larvae, or pupae with soybean oil and imidacloprid was reduced in third, fourth, or fifth instar. In most cases, the host feeding was reduced in second and third instar of the host B. cockerelli when T. triozae females were treated as eggs, larvae, or pupae. Any insecticide modified the sex ratio in the F2 generation. In conclusion, both parasitism and host feeding were affected by the insecticides depending on the concentration and on the nymphal instar of the host B. cockerelli offered.

Integrating sterile insect technique with the release of sterile classical biocontrol agents for eradication: is the Kamikaze Wasp Technique feasible?

Eradication of new pests can avoid ongoing management costs. Although predominantly employed for suppression, classical biological control (CBC) may support eradication attempts, but also may cause non-target impacts in the long term. While CBC is potentially less costly than other approaches, complete eradication is difficult, especially when pests can sustain their populations at low levels. The sterile insect technique (SIT) involves the mass-rearing and release of sterilised insects to disrupt fecundity. This has proven to be synergistic with the release of biological control agents such as egg parasitoids. Here we describe a newly conceptualised tool, the ‘Kamikaze Wasp Technique’ (KWT), which uses a novel combination of CBC and SIT in an eradication to avoid impacts on non-target organisms. This technique proposes the release of sterile parasitoids, as irradiating mated female parasitoids can induce sterility without inhibiting their ability to kill the host. Future work should characterise the irradiation biology of parasitoids. Halyomorpha halys Stal (Hemiptera: Pentatomidae) and its natural enemy, Trissolcus japonicus Ashmead (Hymenoptera: Scelionidae), provide a model system for assessing the potential of the KWT.

Deterrent effects of intact plants on host-searching behavior of parasitoid wasps

Female parasitoids distinguish between host-infested and intact plants using chemical cues; however, the contribution of intact plants to host searching of parasitoids has not been investigated so far. Here, we tested how host-searching behavior of the parasitoid wasp, Cotesia kariyai (Watanabe) (Hymenoptera: Braconidae), was affected by intact maize plants in a wind tunnel. To determine the best color for material to create a plant model, we observed flight responses of female wasps to paper plant models of four different colors. Wasps tended to land more frequently on green models than other models. Therefore, a green paper model was used for subsequent experiments. In a no-choice test, female wasps showed higher landing rates on a paper plant model treated with herbivore-induced plant volatiles (HIPVs) than on an intact plant. Moreover, in two-choice tests, wasps preferred the plant model with HIPVs over an intact plant with HIPVs. Intact plants seem to deter C. kariyai females. Our findings suggest that information from intact plants also contributes to the host-searching behavior of females in the natural environment.

Interactions between Entomopathogenic Nematodes and Entomophagous Insects

The objective of this review article is to clarify the different interactions between entomopathogenic nematodes, as bio-control agents, against other bio-control agents (parasitoids and predators) proposed by the researchers. Thus, it gives clear information concerning the potential of combining them as a part of Integrated Pest Management (IPM) programs against insect pests. Some laboratory studies showed that the treatment of predacious insects by entomopathogenic nematodes (EPNs) at different concentrations can infect and kill the treated larva, nymphs and adults of predators. The percentages of mortality were found to be high (up to 100%), moderate (15% - 35%) or low (3% - 7%). Other studies revealed the resistant of treated predators to nematode-infection. Some predators that were offered infected prey avoid feeding on such prey and, in contrast, the soil predators (ants and mites) consumed the offered cadavers as well as the infective juvenile of the nematodes and did not show any detrimental effects. Mostly, parasitoids cannot complete their development inside or on nematode-infected hosts if parasitism occurs before or early after infection. The parasitoid females may avoid laying eggs in the infected hosts or cannot discriminate between healthy and infected hosts. A field study demonstrated that applying EPNs combined with the predator, Labidura riparia significantly reduced the population of the target pest compared to the nematode or the predator alone. Also, two field experiments indicated that the combination of parasitoids and nematodes can be successful for insect pest management.

Interactions between Entomopathogenic Fungi and Entomophagous Insects

Direct treatment of predators with entomopathogenic fungi (EPF) at different concentrations revealed that some species, like Beauveria bassiana and Metarhizium anisopliae, were found to have detrimental effects on all developmental stages of some predator species. Other species, like Numoraea rileyi and Paecilomycis fumosorosius, showed little or no effect on treated predators. Adult predators were found to avoid feeding on fungi-infected prey. EPF could be isolated from hibernating or field-collected coccinellids. Some studies indicated that combining a fungus with a predator could increase the rate of insect control in the field. As for parasitoids, this review indicates that the developmental stages of the egg parasitoids can develop successfully in host eggs treated with fungi. However, fungus-infected hosts negatively impact the development of larval parasitoids inside such hosts and this impact depends on the species and concentration of the fungus as well as the time between infection and parasitism. Some parasitoid females can discriminate between fungus-infected and uninfected hosts and do not parasitize the infected hosts. With appropriate timing, the parasitoids or predators could be combined with fungi for the biological control of insects in the field.

The Potential of Telenomus remus Nixon (Hymenoptera: Scelinoidae) as Biocontrol Agent for the New Fall Armyworm S. frugiperda (Lepidoptera: Noctuidae) in Indonesia

The fall armyworm Spodoptera frugiperda is an emerging new pest species in several Asian countries including Indonesia. This pest can be a threat to Indonesian agriculture because this pest has been reported to cause many losses in other countries. As a preemptive and ecofriendly control strategy, a research to study the performance of Telenomus remus as potential biocontrol agent of this pest was done in laboratory scale. Research was done by exposing an adult female to 50 eggs of S. frugiperda in a cluster. We also exposed the female parasitoid to another 50 eggs of S. litura in a cluster for comparison since this parasitoid had been reported as S. litura egg parasitoid in Indonesia previously. Results showed that there are no difference in the numbers of parasitized eggs, parasitism rate, survival rates and percent females of T. remus reared from both S. frugiperda and S litura, which implies the effectiveness of T. remus as a candidate for bio control agent for S. frugiperda.

Walking patterns of Trichogramma chilonis and Trichogrammatoidea bactrae upon vegetable leaf surfaces

AbstractTrichogramma chilonis Ishii (Hymenoptera: Trichogrammatidae) and Trichogrammatoidea bactrae Nagaraja (Hymenoptera: Trichogrammatidae) are egg parasitoids of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae). We observed and recorded the walking patterns of T. chilonis and T. bactrae females on leaves of Raphanus sativus L., Brassica juncea (L.) Czern. et Coss., Brassica campestris L. ssp. chinensis var. utilis Tsen et Lee, and Brassica oleracea L. Our analysis indicated that Trichogramma females spent more time and moved more slowly on R. sativus leaf surface, compared with the other vegetable leaf surfaces. In addition, Trichogramma females were more likely to walk in straight line on B. oleracea leaf surfaces than R. sativus, B. juncea, and B. campestris leaf surface. Compared to T. bactrae females, T. chilonis females spent significantly less time on the leaf surface, and the walking path of T. chilonis was less affected by leaf surface characters (e.g., trichomes, wrinkle, and waxes). During the period of residence on the leaf surface, parasitoid females spent more than 87.8% of their time moving. This study demonstrates that vegetable leaf surface can influence Trichogramma's walking pattern while they are foraging for hosts.

Effects of parasitoid and host age on the parasitism of Trichogramma pretiosum on eggs of Anticarsia gemmatalis

Abstract The ages of parasitoid females and their hosts can have substantial effects on parasitism and parasitoid efficacy. This relationship has been investigated over the last few decades and found to vary among species. To our knowledge, it was virtually unknown for Trichogramma pretiosum wasps that parasitize Anticarsia gemmatalis eggs. Therefore, the influence of parasitoid and host age on the parasitism of T. pretiosum on eggs of A. gemmatalis was here evaluated in three independent bioassays. Neither the number of parasitized eggs nor that of emerged parasitoids differed between T. pretiosum females of different age. The number of parasitoids per egg and the sex ratio were higher for 5-day-old females. Regarding host age, the number of parasitized eggs was highest for A. gemmatalis eggs aged 24 h (9.60), followed by eggs aged 48 h (1.00), while no parasitism was observed for eggs aged 72 h. The number of parasitoids per egg and sex ratio were not influenced by host age. Preference was significantly higher for host eggs aged 24 h (79.67%), followed by eggs aged 48 h (16.99%) and 72 h (3.33%). Accordingly to these results, the key challenge for a successful T. pretiosum release to control A. gemmatalis in the field is to synchronize the presence of up to 5-day-old adults with the most susceptible phase of the host eggs (1 day).

The Biology of Trissolcus semistriatus Nees and Trissolcus grandis Thomson (Hymenoptera: Scelionidae) in the eggs of Eurygaster maura (Hemiptera: Scutelleridae)

Çalışma konukçu olarak Eurygaster maura (Hemiptera: Scutelleridae) yumurtaları kullanılarak, doğa koşullarında yumurta parazitoiti Trissolcus semistriatus Nees ve T. grandis Thomson (Hymenoptera: Scelionidae)’in biyolojilerini belirlemek amacıyla yürütülmüştür. Parazitoitler ölene kadar her gün 42 adet konukçu yumurtası verilmiştir. T. semistriatus, verilen yumurtaların T. semistriatus ortalama 79.70 adedini, T. grandis ise 75.50 adedini parazitlemişlerdir. Bu yumurtalardan parazitoitlerin çıkış oranı T. semistriatus’ta %11.42 ile 62.85 arasında, T. grandis’te ise %10.28 ile 67.50 arasında değişmiştir. Eşey oranı T. semistriatus’ta 0.81, T. grandis’te ise 0.82 olarak kaydedilmiştir. Aynı konukçuda, parazitoitlerin gelişme süreleri, dişi T. semistriatus’ta 27.05 gün ve T. grandis’te ise 26.69 gün ve erkek bireylerde bu süreler sırasıyla 25.07 ve 22.56 gün olarak saptanmıştır. İstatistiki analiz sonucu, iki parazitoit arasında ovipozisyon süreleri yönünden fark önemli bulunmuş olup, postovipozisyon ve ömür yönünden fark önemli bulunmamıştır.

Trichopria drosophilae parasitizes Drosophila suzukii in seven common non-crop fruits

The invasive vinegar fly Drosophila suzukii not only infests and damages numerous fruit crops but also develops in many wild fruit species in semi-natural habitats. Biological control in these refuges could reduce D. suzukii populations and minimize their dispersal into fruit crops. We investigated parasitization of D. suzukii by the pupal parasitoid Trichopria drosophilae in seven common wild fruit species. Development and nutrient content of D. suzukii differed among the fruit species. Nevertheless, T. drosophilae significantly reduced D. suzukii numbers in all fruits. The development of T. drosophilae was affected by both the fruit species and the quality of the pupal host (size, nutrient content). In olfactometer assays, parasitoid females preferred infested fruits to an empty control and to most non-infested fruits, but spent an equal amount of time on the walking arena above the infested and non-infested fruits of Rhamnus cathartica and Viscum album. Our results show that T. drosophilae can utilize D. suzukii hosts from a variety of wild fruit species and therefore has the potential to be used as a control agent of D. suzukii in semi-natural habitats.

Impacts of seven insecticides on Cotesia flavipes (Cameron) (Hymenoptera: Braconidae).

The endoparasitoid wasp Cotesia flavipes (Cameron) (Hymenoptera: Braconidae) is inundatively released in Brazilian sugarcane plantations to control the sugarcane borers Diatraea saccharalis (Fabricius) and Diatraea flavipennella (Box) (Lepidoptera: Crambidae). In conjunction with these releases, several synthetic insecticides are used to control the neonate larvae of these pests. We assessed the lethal and transgenerational sublethal effects of seven of these insecticides on C. flavipes. Leaf discs were sprayed at the highest field concentrations of chlorantraniliprole, lambda-cyhalothrin + chlorantraniliprole, chlorfluazuron, triflumuron, lambda-cyhalothrin + thiamethoxam, tebufenozide, and novaluron. Distilled water was used as a negative control. Newly emerged females (24 h old) were placed in Petri dishes containing the treated leaves, and the lethal and transgenerational sublethal effects were assessed for the next two generations. Lambda-cyhalothrin + chlorantraniliprole and lambda-cyhalothrin + thiamethoxam caused 100% mortality of the parasitoid and were highly persistent, causing more than 30% mortality at 30 days after spraying. Chlorantraniliprole, chlorfluazuron, novaluron, and triflumuron did not cause significant mortality compared to the negative control, but did have transgenerational sublethal effects. The length of the tibia of the right posterior leg, used as a growth measurement, was reduced in the progeny (F1 generation) of exposed female parasitoids. In addition, chlorantraniliprole increased and chlorfluazuron reduced the proportion of females in the F1 generation, whereas novaluron reduced the proportion of females in the F2 generation. Overall, only tebufenozide was considered harmless to C. flavipes. The results of this study suggest that lambda-cyhalothrin + chlorantraniliprole and lambda-cyhalothrin + thiamethoxam are harmful to C. flavipes, although field studies are needed to obtain results for actual sugarcane crops.

Food or host: do physiological state and flower type affect foraging decisions of parasitoids?

Within the optimal foraging theory framework, parasitoids constitute ideal models to elucidate combined physiological and environmental determinism of foraging behavior between current and future fitness gains. Parasitoid females need hosts to lay eggs for their reproduction (immediate gain), but also sugar food resources for their survival (future gain). According to theoretical models and previous empirical studies, fed females should favor host foraging, whereas females with lower energetic reserves should search for food. Surprisingly, the influence of mating status and food quality has not been considered, whereas they may both constitute major factors altering animals’ choices between reproducing and feeding. We tested decision-making on Aphidius rhopalosiphi parasitoid females with different life expectancy levels (as set by recent feeding history) and mating status, using two flower species with contrasted attractiveness and nectar suitability. Interestingly, all fed and unfed females with different expected lifetime levels favored reproduction over nutrition since they are mated. This could be explained by their reproductive status that appeared to be the main determinant of their foraging decisions. For a given expected lifetime, mated females favored more reproduction whereas unmated ones favored food. Physiological status of females (mating and lifetime expectancy) did not interact with flower species on their foraging decisions nor did it modify their preferences, as they always favored the most attractive flower, which does not have the best nectar. These results highlight the need for more empirical studies to evaluate the interactions between different intrinsic factors and to carefully consider the mating status in model assumptions, as it influences foraging behavior between immediate and future fitness gains. Parasitic wasps need hosts to lay eggs for their reproduction (immediate fitness gain) and sugar resources for their survival (future fitness gain). Empirical studies and related theoretical models about foraging decisions of parasitic wasps between current and future gains included influences of energetic and resource availability constrains. We examined assumptions used by those mathematical models by empirically testing two new factors, food qualities provided by two nectar provisioning flower species with contrasted functional traits, which had surprisingly no impact on decision-making, and mating status which we showed to play a decisive role on decision-making between food or host resources. These factors should henceforth be considered in model assumptions or in models themselves to realize accurate predictions and to provide a better understanding of foraging decisions made by female parasitic wasps.

Lethal and parasitism effects of selected novel pesticides on adult Trichogramma chilonis (Hymenoptera: Trichogrammatidae)

Integration of chemical and biological controls is an important tactic of integrated pest management. Trichogramma chilonis (Ishii) is an important natural enemy of lepidopteran pests. However, the minute parasitoids are adversely affected by most pesticides. Effects of acute mortality and parasitism of selected novel pesticides on adults of T. chilonis exposed to the dried residues of field doses for 24 h on glass surface were evaluated. Acetamiprid, spinetoram and fipronil induced mortality of > 95%, followed by abamectin (ranged 71.3–83.5%) in four residual-age treatments. Spiromesifen, haloxyfop-p-methyl, mixture of pyraclostrobin + metiram and mixture of trifloxystrobin + tebuconazole revealed mortality of ≤ 36.4% in all treatments (when female parasitoids were exposed to 1 day, 5 days, 10 days and 15 days after treatments). Bispyribac sodium induced mortality of ranged 51.1–54.9% in 1- and 5-day treatments, and approximately ≤ 10% in others (10-day and 15-day treatment). Eggs of Sitotroga cerealella in acetamiprid, spinetoram, fipronil and abamectin treatments showed ≤ 36% parasitism relative to controls in all treatments. Spirotetramat, bispyribac sodium, nicosulfuron, trifloxystrobin + tebuconazole and pyraclostrobin + metiram resulted in parasitism rates of 49.2–71.2% and 81.5–93.8% in 1-day and 15-day treatment, respectively. Helicoverpa armigera nucleopolyhedrovirus, chlorantraniprole, spiromesifen haloxyfop-p-methyl, chlorothalonil + procymidone and myclobutanil showed ≥ 80.6% parasitism in all treatments. Thus, acetamiprid, spinetoram, fipronil and abamectin were the most harmful among the pesticides used for both emergence and parasitism, while remaining pesticides demonstrated relatively compatibility with the emergence as well as parasitism by the minute parasitoids, and can be integrated with the minute parasitoid in agroecosystem.

Compatibility between the endoparasitoid Hyposoter didymator and the entomopathogenic fungus Metarhizium brunneum: a laboratory simulation for the simultaneous use to control Spodoptera littoralis.

The cotton leafworm, Spodoptera littoralis, is one of the most destructive pests in the Mediterranean basin, being predominantly controlled using synthetic chemical pesticides. Strain EAMa 01/58-Su of the fungus Metarhizium brunneum and the parasitoid Hyposoter didymator are promising biological control agents for this pest. In this study, we assessed the compatibility between these two agents to control S. littoralis under joint attack scenarios. Firstly, the direct and indirect effects of the fungus towards parasitoid adults were studied. The fungus significantly decreased life expectancy of the parasitoid (mortality=62.5%; mean lethal concentration=1.85 × 106 conidia ml-1 ; average survival time=92.2h) when applied at high concentrations (108 conidia ml-1 ), whereas it did not affect the reproductive potential of the parasitoid females during the 3 days after treatment. Secondly, the combinations between the two agents to control S. littoralis under different simultaneous use scenarios (inoculation of S. littoralis larvae with the fungus before being exposed to parasitoid females and vice versa) were investigated, with additive effect in all cases. A significant effect on fitness (preimaginal development time and reproductive potential) of the F1 parasitoid generation were detected. Moreover, parasitization significantly reduced the total hemocytes in S. littoralis hemolymph compared with the control, promoting fungal infection. Finally, parasitoids showed a significant preference for non-inoculated S. littoralis larvae. We demonstrated compatibility (additive effect) between fungus and parasitoid under different joint attack scenarios to control S. littoralis in laboratory conditions. However, this will be supported by our ongoing greenhouse and field studies. © 2019 Society of Chemical Industry.

Functional Responses of Three Candidate Asian Larval Parasitoids Evaluated for Classical Biological Control of Drosophila suzukii (Diptera: Drosophilidae).

Drosophila suzukii has become a key invasive pest of soft- and thin-skinned fruit crops in its invaded regions in Europe and Americas, where naturally occurring natural enemies are generally not effective for the suppression of this pest or largely absent such as larval-attacking parasitoids. As a part of systematic evaluations of candidate agents for classical biological control of this invasive pest, we evaluated the functional responses of three Asian-native larval hymenopteran parasitoids, Asobara japonica (Braconidae), Ganaspis brasiliensis, and Leptopilina japonica (both Figitidae) to D. suzukii or Drosophila melanogaster (A. japonica only) larvae. Host larval densities were 5, 10, 15, 20, 25, 30, 35, or 40 larvae per test for A. japonica and 3, 6, 9, 12, 18, 24, 30, 36, or 42 larvae per test for G. brasiliensis or L. japonica. Host larvae were provided in standard artificial diet in tubes for a 24-h exposure to individual female parasitoids under the quarantine conditions (23°C). All three parasitoids showed a linear (type I) functional response to the tested host densities. Host species (for A. japonica only) did not affect the number of hosts parasitized or the functional response. Asobara japonica was more efficient than either figitid in terms of the searching efficiency while L. japonica preformed slightly better than G. brasiliensis under the tested conditions. The results are discussed with respect to the selection of parasitoid species to be released in North America and Europe to suppress D. suzukii.

Telenomus remus (Hymenoptera: Platygastridae) parasitism on Spodoptera frugiperda (Lepidoptera: Noctuidae) eggs: different parasitoid and host egg ages

Abstract: Release of egg parasitoids for biological control of pests is a promising technique in integrated pest management (IPM). However, there is a lack of information on the performance of parasitoid females of different ages, and specifically on the behavior of the parasitoid Telenomus remus towards pest eggs at different stages of embryonic development. Thus, the relationships between host age, parasitoid age, and parasitism by T. remus on Spodoptera frugiperda eggs were evaluated. Three separate bioassays were performed, each in a completely randomized design. In the first bioassay, T. remus females grouped by age in days (ranging from 1 to 10 days old) were offered 100 ± 20 eggs of S. frugiperda for 24 hours. In the second bioassay, 100 ± 20 eggs of S. frugiperda (24, 48 or 72 hours old) were offered to females of T. remus for 24 hours. In the third bioassay, 24, 48- and 72-hour-old host eggs of S. frugiperda were offered to T. remus females in a choice test. The variables evaluated were: number of parasitized eggs, parasitoid emergence (%), and sex ratio of progeny in bioassays 1 and 2, and the number of eggs parasitized in bioassay 3. The age of T. remus females did not affect the number of S. frugiperda eggs parasitized or emergence of the progeny. However, the sex ratio was more male-biased in the progeny of 1- and 2-day-old females compared to older wasps. In bioassay 2, the highest parasitism was observed in 24- and 48-hour-old eggs. Percentage emergence and sex ratios were not influenced by the ages of the eggs tested. Telenomus remus preferred to parasitize 24-hour-old eggs in bioassays 3. Overall, the age of T. remus females tested did not affect the parasitism of S. frugiperda eggs, but the number of eggs parasitized decreased with increasing host age.