Parasitoid Trichogramma Pretiosum Research Articles

Do releases of the mirid predator Macrolophus basicornis (Hemiptera: Miridae) together with the egg parasitoid Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) improve biological control of Tuta absoluta (Lepidoptera: Gelechiidae) in tomato?

During the past decade, the use of predatory mirids alone or combined with releases of egg parasitoids of the genus Trichogramma have been tested in Europe for biological control of the worldwide invasive pest, Tuta absoluta (Meyrick). Here, we evaluated the control of this pest by the release of the Neotropical mirid Macrolophus basicornis (Stal), the Neotropic/Nearctic parasitoid Trichogramma pretiosum Riley, and by combined releases of the predator and the parasitoid. Tests were conducted in greenhouse compartments during the summer and fall season. Each compartment contained 10 tomato plants in which only the pest was released or the pest with 1 or 2 natural enemies. Plant damage, and pest and natural enemy densities were checked weekly on one apical, medium, and bottom leaf of 5 plants. Both M. basicornis and T. pretiosum significantly reduced T. absoluta density when released alone. Combined releases resulted in a 10% higher reduction during the summer season, but not during the fall season. The damage caused by T. absoluta was significantly higher in control treatments than in all natural enemy treatments: at the end of the summer trial leaves were completely damaged in the control treatment, whereas only up to 25% leaf damage occurred in the natural enemy treatments. Combined releases did not result in lower damage than with releases of either M. basicornis or T. pretiosum. Practical aspects of single and combined releases are discussed.

Tomato plant defense induced by methyl jasmonate impacts on foraging behavior and parasitism of Trichogramma pretiosum

AbstractIndirect plant defense may be mediated by volatiles released after oviposition and/or herbivory or by exogenous application of plant hormones such as methyl jasmonate (MeJa), signaling host presence to parasitoids. There is still incipient information regarding phytohormone action on crop plant defense, especially among tomato plants (Solanum lycopersicum L., Solanaceae) and the parasitoid Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae). We aimed to evaluate T. pretiosum chemotaxis and parasitism in response to eggs and tomato plants exposed to Tuta absoluta (Meyrick) (Lepidoptera: Gelichiidae) oviposition and herbivory, with and without MeJa. We conducted laboratory (olfactometry and parasitism) and semi‐field (parasitism) bioassays with T. pretiosum in response to treatments with MeJa (0.5 mM) applied to tomato plants, and the interaction with its host, on plants with T. absoluta oviposition and herbivory. Methyl jasmonate presence directly on eggs did not affect T. pretiosum chemotaxis and parasitism. However, it did intensify this natural enemy's foraging behavior and parasitism when applied to the plant. Therefore, the use of MeJa in the T. absoluta and T. pretiosum tomato system may be beneficial, increasing parasitoid recognition and parasitism. Strategies aimed at improving biological control combined with environmentally friendly techniques, such as the use of phytohormones, are of utmost importance towards more sustainable agriculture.

Toxicidade de inseticidas utilizados na cultura do arroz sobre o parasitoide de ovos Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) em condições de campo

ABSTRACT: We evaluated under field conditions the toxicity of insecticides previously identified as harmful in laboratory and semifield bioassays on the parasitoid Trichogramma pretiosum (Hymenoptera: Trichogrammatidae). The experiments were conducted during the 2019/20 and 2020/21 harvests in rice fields. Following the recommendations of the International Organization for Biological and Integrated Control (IOBC), four insecticides were applied in 64 m2 experimental plots. Subsequently, T. pretiosum was released inundatively. To verify parasitism rates, at 1, 2, 4 and 6 days after release (DAR) of the parasitoids, eggs from the host Ephestia kuehniella (Lepidoptera: Pyralidae) were offered. After determining the number of parasitized eggs, the data were grouped into a reduction coefficient (Ex) to provide a single result for the effects of the insecticides on parasitoid. For both the 2019/20 and 2020/21 evaluated crops, it was found that at 2 DAR, the highest parasitism rates occurred. In contrast, in 6 DAR, no parasitism rates were observed. Lambda-cyhalothrin, thiamethoxam, and zeta-cypermethrin were classified as moderately harmful; thiamethoxam + lambda-cyhalothrin was classified as harmful. Following IOBC guidelines, the toxicity of these products under field conditions is lower than that obtained in the laboratory or semi-field for the T. pretiosum. However, these insecticides should be avoided, or used at times that do not coincide with the release or presence of the parasitoid in the field.

SELECTIVITY OF REGISTERED AGROCHEMICALS FOR SOYBEANS AIMING IMMATURE PHASES OF Trichogramma pretiosum

The aim of this study was to evaluate the effects of agrochemicals registered for soybean on parasitoid Trichogramma pretiosum in immature stages. Bioassays were conducted in the laboratory by exposing eggs parasited, using the methods proposed by the International Organization for Biological and Integrated Control of Noxious Animals and Plants (IOBC). The experimental design was completely randomized with eight replicates per treatment. The parameter for the classify agrochemical were based on the reduction of emergence of parasitoids (RE) evidenced by the number of parasitized eggs per female in the control. Based on the results obtained, all agrochemicals were innocuous to T. pretiosum in their immature stages.

Toxicity of essential oils and pure compounds of Lamiaceae species against Spodoptera frugiperda (Lepidoptera: Noctuidae) and their safety for the nontarget organism Trichogramma pretiosum (Hymenoptera: Trichogrammatidae)

The fall armyworm (FAW) Spodoptera frugiperda is a key pest of countless cultures of economic importance. FAW control is still mostly achieved by using synthetic chemicals and genetically modified plants, which can cause adverse effects on nontarget organisms. In this sense, secondary metabolites are an inexhaustible source of bioactive substances. Thus, this study investigated the insecticidal activity of essential oils (EOs) of plants of the Lamiaceae family against FAW. The EOs from Hyptis marrubioides (LD50 = 18.49 μg/larvae) and Ocimum basilicum (LD50 = 38.21 μg/larvae) were toxic to FAW in topical bioassays. The majority of compounds of H. marrubioides were identified as β-thujone (41.50%) and α-thujone (15.82%), while for O. basilicum, linalool (35.68%) and 1,8-cineole (16.03%) were the major substances. The pure compounds linalool (survival probability = 28.1%), α-thujone (survival probability = 24.5%) and 1,8-cineole (survival probability = 40.4%) were employed in a new bioassay; although all substances were toxic to FAW, the toxicity was less than that observed for EOs from H. marrubioides (survival probability = 9.5%) and O. basilicum (survival probability = 2.1%). These results suggest that there is more than one active substance in the EOs or else, there is synergism and/or an additive effect between the substances. With regard to the experiment conducted with the parasitoid Trichogramma pretiosum, the EOs from H. marrubioides and O. basilicum were classified as harmless according to the IOBC criteria, so they are safe for this parasitoid and have potential to be used in programs of integrated FAW pest management the natural enemy T. pretiosum.

Lethal, sublethal and transgenerational effects of insecticides labeled for cotton on immature Trichogramma pretiosum

The parasitoid Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) is often released to manage lepidopteran pests in cotton crops. However, growers rely on multiple insecticide applications to manage cotton pests. A harmonious integration of control tactics is required for proper pest management, and the use of selective insecticides (i.e., those promoting effective pest control while causing little impact on natural enemies) fits within this scope. This study aimed to assess the lethal, sublethal and transgenerational effects of insecticides from varying chemical groups on T. pretiosum. The insecticides were sprayed on parasitized host [Ephestia kuehniella (Zeller), Lepidoptera: Pyralidae] eggs with developing T. pretiosum stages (egg-larva, prepupa, and pupa), and biological traits were assessed following adult emergence. Overall, pupae were more susceptible to insecticides. We found thiodicarb and chlorfenapyr to reduce F0 adult emergence in rates comparable to the positive control (methomyl). Adult F0 deformation was the highest on flupyradifurone-treated organisms, and both the F0 parasitism rate and female survival were reduced by the insecticides (except for teflubenzuron). The sex ratio (proportion female) was affected by thiodicarb and flupyradifurone. Transgenerational effects occurred on adult emergence, which was reduced on the offspring (F1) of thiodicarb, chlorfenapyr, and flupyradifurone treated T. pretiosum. In addition, thiodicarb decreased the F1 sex ratio (≤ 0.33) compared to the other compounds (sex ratio ≥ 0.45). These results indicate that teflubenzuron is the safest insecticide; the other insecticides are non-selective to T. pretiosum. Field and semifield studies are required to confirm the harmfulness of chlorfenapyr, flupyradifurone and thiodicarb toward T. pretiosum.

Response of Trichogramma pretiosum females (Hymenoptera: Trichogrammatidae) to herbivore-induced Bt maize volatiles

Parasitoids use herbivore-induced plant volatiles (HIPV´s) to locate their hosts. However, little is known about variations in HIPV´s production in genetically modified maize plants that are herbicide tolerant (singular event), insect resistant (Bt plants, singular event), or both herbicide tolerant and insect resistant, like staked events. We investigated the olfactory responses of the egg parasitoid Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) to HIPV´s produced in maize (Zea mays) herbicide-tolerant and insect-resistant plants or their stacked events in response to damage caused by Spodoptera frugiperda during nighttime and daytime infestations. Real-time reverse-transcription PCR was used to assess whether the presence of one or more Bacillus thuringiensis (Bt) proteins and the time of induction of HIPV’s affected the expression of genes in plants under herbivore attack. The results showed that compounds were released during both nocturnal and diurnal infestations. However, some HIPV´s were released exclusively in infestations that started during the night by non-Bt plants and they were highly attractive to parasitoids. HIPV´s produced by non-Bt plants were more attractive to parasitoids than those released by Bt plants in infestations that started during the night. However, glyphosate-tolerant maize plants were more attractive to parasitoids than isogenic plants. The expression of the analyzed genes TPS10, TPS23, LOX10, and STC1 was higher in infestations that started during the night. In this study, we discuss the possible causes of the unresponsiveness of T. pretiosum females to HIPV´s produced by Bt maize.

Pesticide selectivity to the parasitoid Trichogramma pretiosum: A pattern 10-year database and its implications for Integrated Pest Management

Trichogramma pretiosum is one of the main egg parasitoids used in the control of lepidopteran pests in Brazil. This natural enemy can be negatively affected by the use of insecticides, herbicides, and fungicides. The present work used a systematic review and meta-analysis to group information from multiple studies on the selectivity of pesticides (279 commercial products) in rice, corn, soybean, apple and peach crops for immature stages (egg-larva, pre-pupa, and pupa) and adult parasitoids. The selected studies used the International Organization for Biological and Integrated Control (IOBC) methodology with the same adaptations for T. pretiosum. The meta-analysis found that corn crops had the highest frequency of tests (2 0 7). The most frequently tested active ingredients (a.i.) were glyphosate, glyphosate isopropylamine salt, and sulfur at frequencies of 41, 32 and 24 tests, respectively. The pesticides registered for rice crops showed the greatest sublethal effects on T. pretiosum, with an approximately 47% reduction in parasitism (RP) or emergence (RE). The adult stage of the parasitoid showed greater sensitivity to the tested pesticides (65% RP), in comparison to the immature stages. In general, insecticides showed superior toxicity for all development stages of T. pretiosum, compared to herbicides and fungicides, regardless of the recommended dosage for the crop. The present study aggregates information related to selectivity for the four life stages of T. pretiosum, contributing significantly to the integration of biological control and chemical control in rice, corn, soybean, apple and peach crops in Brazil.

Resistance of maize landraces from Brazil to fall armyworm (Lepidoptera: Noctuidae) in the winter and summer seasons

ABSTRACT The fall armyworm (Spodoptera frugiperda) is a major maize (Zea mays L.) pest in Brazil, whose larvae cause losses from plant emergence to harvesting stage. This pest has been controlled almost exclusively with chemical insecticides and Bt plants (transgenics); however, resistance evolution has been detected to these two control tactics. Therefore, alternative control tactics are needed for management and control of the fall armyworm. Thus, this study aimed to evaluate the resistance of maize landraces from Brazil to larvae of this herbivore in the winter and summer seasons, studying also the occurrence of the predator Doru luteipes (Dermaptera: Forficulidae). The variety Perola had the highest resistance levels to fall armyworm in the summer season, with lower values of leaf injury, number of infested plants, and number of larvae. Conversely, this variety did not express resistance to the pest in winter. Doru luteipes was found abundantly in the summer season, showing no differences between varieties. This is the first study to evaluate the resistance of maize landraces from Brazil to fall armyworm in the winter and summer seasons. The next step is the molecular characterization of the variety Perola, as well as evaluating its effects on the most common natural enemies of the pest in Brazil, such as the predator D. luteipes and the egg parasitoid Trichogramma pretiosum (Hymenoptera: Trichogrammatidae). These results may assist future maize breeding programs aimed at developing cultivars and hybrids resistant to the pest, and hence reducing agriculture’s dependence on chemical insecticides and transgenic plants.

Is Isaria fumosorosea selective to Trichogramma pretiosum (Hymenoptera: Trichogrammatidae)?

Entomopathogenic fungi and the egg parasitoid Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) might be used together in biological control. However, the effects of these fungi on T. pretiosum are not known. Thus, this study aimed to determine the effect of the entomopathogenic fungus Isaria fumosorosea, on the biological parameters of T. pretiosum. Two isolates of I. fumosorosea (IBCB 367 and IBCB 394) were used for this purpose. (1) In a free choice test: cards (1.0 × 5.0 cm) with non-parasitized eggs of Anagasta kuehniella Zeller (Lepidoptera: Pyralidae) were either sprayed with 0.2 mL of the fungus suspension (1.0 × 109 conidia.mL-1) or with sterile distilled water containing Tween® 80 (0.01%), which were then offered to females of T. pretiosum. (2) No choice test: the isolates were sprayed at a concentration of 1.0 × 109 conidia.mL-1 on cards (1.0 × 5.0 cm) with A. kuehniella eggs. The control consisted of spraying sterile distilled water containing Tween® 80 (0.01%). Individual females of T. pretiosum were confined for 24 h with the cards. The number of eggs parasitized, percentage of emergence, longevity, duration of the egg-adult period and sex ratio were evaluated, as well as the longevity of the females that parasitized the eggs and the mortality of the emerging adults evaluated. IBCB 367 isolate repelled T. pretiosum. The pre-parasitism and post-parasitism sprays did not affect the number of eggs parasitized or the sex ratio, however, the pre-parasitism IBCB 394 treatment the females and males survived for longer, whereas the survival of females in post-parasitism treatment with the same isolate was reduced.The presence of conidia on and mycelium of the fungus in T. pretiosum was confirmed using Scanning Electron Microscopy and a histological analysis. Isolates IBCB 367 and IBCB 394 from I. fumosorosea are selective to T. pretiosum in the laboratory.

Performance of Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) on eggs of Helicoverpa armigera (H\xfcbner) (Lepidoptera: Noctuidae)

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a polyphagous pest with a wide geographic distribution. This pest first arrived in Brazil in 2013, and since then studies on possible control methods for it have been necessary. A possible method for the control of H. armigera is using the egg parasitoid Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae). Therefore, the objective of this study was to evaluate the performance of T. pretiosum on H. armigera eggs, which are known to represent suitable hosts for the development of this parasitoid species in the laboratory. Parasitism and emergence rates and the duration of the egg-to-adult period of T. pretiosum were investigated following 24- and 48-h exposures of this parasitoid to H. armigera and Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae) eggs. The longevity of offspring after the 24-h exposure was studied, as well as the frequency of parasitism and emergence, host preference, and the emergence of offspring from eggs of different ages or oviposited by lepidopterans on different days. Parasitism was 14.4 and 34.9% more frequent on C. cephalonica than on H. armigera after 24 and 48 h of exposure, respectively. In C. cephalonica, parasitism was 27.2% higher after 48 h. Parasitism was more frequent on C. cephalonica eggs collected on the second day of oviposition (76.2%), and on H. armigera on the third day of oviposition (71.1%). Parasitism frequency was lower on 2-day-old C. cephalonica eggs (63.3%) and on 3-day-old H. armigera eggs (41.3%). When tested with a chance of choice between hosts, T. pretiosum preferred H. armigera, while in the test with no chance of choice there was no difference in preference. Thus, T. pretiosum may be considered a tool for the Integrated Pest Management (IPM) of H. armigera.

Functional response of Trichogramma pretiosum on Trichoplusia ni eggs at different temperatures and egg densities

Abstract: The objective of this work was to determine the functional response of the parasitoid Trichogramma pretiosum on Trichoplusia ni eggs at different temperatures (20, 25, and 30ºC) and egg densities (5, 10, 15, 20, 25, and 30 eggs). The logistic regression showed a type-II functional response for all temperatures. The search efficiency of T. pretiosum was reported as 0.049±0.0019, 0.069±0.0042 and 0.068±0.0033 per hour, and the estimated handling times were 1.82±0.0424, 1.69±0.0398, and 1.54±0.0498 hour at 20, 25 and 30ºC, respectively. Females of Trichogramma pretiosum show greater efficiency at 30ºC and a type-II functional response. The parasitism rate decreases, when host density increases.

Morphometry, allometry, and fluctuating asymmetry of egg parasitoid Trichogramma pretiosum under insecticide influence

AbstractThe morphometric analysis of parasitoids may contribute to biological control programs by providing information on development of insects and relationships among sizes of morphological characters. Furthermore, it can infer about the impact of insecticides on morphological characters and fitness. We evaluate the morphometry, allometry, and fluctuating asymmetry of the egg parasitoid Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) with and without influence of the growth‐regulating insecticides teflubenzuron and lufenuron. Trichogramma pretiosum had significantly larger wings and tibiae in treatments with insecticides. We found no effects of insecticides on asymmetry in T. pretiosum and conclude that this insect is very close to isometry. This study emphasizes the importance of evaluating the size of parasitoids destined to biological control programs.

Selectivity of plant extracts for Trichogramma pretiosum Riley (Hym.: Trichogrammatidae)

We evaluated the selectivity of three plant extracts with potential insecticidal effects for the parasitoid Trichogramma pretiosum Riley, which is commonly used in biological pest control. The plant extracts assayed were an acetone extract of Toona ciliata M. Roem., commercial neem oil, and a nanoencapsulated formulation of neem oil (NC40). The toxicity of the plant extracts to T. pretiosum was evaluated according to the recommendations of the International Organization for Biological Control- IOBC Working Group. We assessed the susceptibility of adults of the maternal and F1 generations and immature stages of T. pretiosum to the extracts. Females exposed to egg cards treated with commercial neem oil parasitized almost 70% fewer eggs than control eggs treated with water; and this extract was therefore classified as slightly harmful. When the eggs were offered to females 24h after treatment with neem oil and aqueous NC40, the parasitism rate also decreased, and the two extracts were classified as slightly harmful. Adult emergence was lower for parasitoids that fed on host eggs offered 24h after the treatment with the T. ciliata extract, which was considered slightly harmful. The emergence of T. pretiosum from eggs, larvae and pupae treated with the different plant extracts, did not decrease compared to development stages treated with the water control. The use of T. pretiosum, combined with the application of an ethanol extract of T. ciliata and a nanoencapsulated formulation of neem, appears to be feasible in view of these low toxicity indices.

Organic products selectivity for Trichogramma pretiosum (Hymenoptera: Trichogrammatidae)

ABSTRACT: The selectivity of different insecticides, fungicides and fertilizers used in organic soybean cropping was evaluated according to the protocols proposed by the Pesticides and Beneficial Organisms Working Group of the International Organization for Biological Control (IOBC) concerning adults and pupae of the egg parasitoid Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) under laboratory conditions. Treatments 1) baculovirus anticarsia 140 x 109 cpi; 2) Bacillus thuringiensis 16.8 g; 3) azadirachtin-A, azadirachtin-B, nimbina and salamina 9.6 ppm; 4) rotenoids 4% 4 L; 5) nitrogen 1.3%, phosphorus 3.0% and total organic carbon 8.0% 3 L; 6) sodium silicate 2% 4 L; 7) copper 7% + calcium 3.3% 1.8 L; 8) sulfur 20% + quicklime 10% 1.8 L were in general safe (class 1) to both adults and pupae of T. pretiosum . Differently, chlorpyrifos (control treatment) was harmful to this parasitoid. Therefore, the utilization of the tested natural derived products in the production of organic soybean is viable, without impairing the natural biological control allowed by T. pretiosum . Furthermore, both management techniques can indeed be used together in organic cropping aiming at reaching increasing or complementary control of target pests. Chlorpyrifos use, on the other hand, whenever possible, should be replaced by other products more compatible with biological control preservation.

English

The aim of this study was to evaluate the effects of fungicides registered for soybean on the parasitoid Trichogramma pretiosum Riley, 1879 (Hymenoptera: Trichogrammatidae). Bioassays wereconducted in laboratory exposing adult insects to dried residues of fungicides, using the methodology proposed by the International Organization for Biological and Integrated Control of Noxious Animals and Plants (IOBC). The experimental design was completely randomized with four replications per treatment. The parameter used for classification of fungicides was based on the reduced parasitism (RP) evidenced by the number of parasitized eggs per female in the control treatment. Based on these results, we found that fungicides are classified in different classes of selectivity to adults of T. pretiosum regarding the tested fungicides. The fungicides cyproconazole, epoxyconazole + kresoxim-methyl, metconazole, thiophanatemethyl (CS), pyraclostrobin, difenoconazole, were classified as harmless (Class 1); carbendazim, carbendazim + thiram, tetraconazole, tetraconazole+ azoxystrobin, epoxyconazol + pyraclostrobin, tebuconazole, prothioconazole + trifloxystrobin, tebuconazole + trifloxystrobin, azoxystrobin, azoxystrobin + cyproconazole, and thiophanate methyl (WG) were slightly harmful (Class 2); flutriafol, thiophanate methyl (WP), epoxyconazole + pyraclostrobin, and cyproconazole+ trifloxystrobin were moderately harmful (Class 3); and Kumulus DF was harmful (Class 4) to the adult parasitoids. Keywords: Chemical control, integrated pest management (IPM), parasitoid eggs, pesticide, International Organization for biological and integrated control of noxious animals and plants (IOBC) methodology, soybean.

Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) Parasitism of Trichoplusia ni (Lepidoptera: Noctuidae) Eggs Under Different Temperatures

Abstract A study of the biological characteristics and thermal requirements of the parasitoid Trichogramma pretiosum Riley, 1879 (Hymenoptera: Trichogrammatidae) on eggs of Trichoplusia ni (Hübner, 1802) (Lepidoptera: Noctuidae) at several different temperatures was performed in this work. Eggs of T. ni were exposed to T. pretiosum strain Tspd parasitism for 5 hr and then transferred to environmentally controlled growth chambers set at the temperatures of 18, 21, 24, 27, 30, and 33 ± 1°C. The duration of the T. pretiosum egg-to-adult period was affected by temperature, varying from 6 to 18 d over the range of the studied temperatures. The number of individuals emerged per egg and the sex ratio also were affected by temperature variations, but regression analysis did not find correlation between the increase of temperature and the observed variation of these biological parameters. Similarly, parasitism viability (percentage) was influenced by temperature variation, but always exceeded 80% at all tested temperatures. The thermal lower limit of development (Tbase) and the thermal constant (K) for T. pretiosum were 11.84°C and 128.37 DD, respectively. These results here reported indicate that T. pretiosum was impacted by the temperature, however, this parasitoid had a satisfactory performance on T. ni eggs at all studied temperature (from 18 to 33°C), showing potential to be used successfully as a biological control agent of this pest in different regions that fit in this tested temperature range. Also, the rearing temperature of this parasitoid might be changed from 18 to 33°C, according to commercial demands for accelerating or retarding mass production for field releases without damages to the parasitoid development.

Persistência de agrotóxicos utilizados na cultura do milho ao parasitoide Trichogramma pretiosum Riley, 1879 (Hymenoptera: Trichogrammatidae)

As altas produtividades na cultura do milho têm sido alcançadas em função de vários fatores técnicos, sendo o controle de pragas um dos mais importantes. Nesse sentido, o objetivo deste trabalho foi avaliar a persistência de agrotóxicos utilizados na cultura do milho ao parasitoide Trichogramma pretiosum. Foram avaliadas as persistências de sete inseticidas e três fungicidas, os quais foram diluídos separadamente em 200L de água e pulverizados sobre folhas de videira. Essas folhas foram levadas ao laboratório e utilizadas dentro de gaiolas aos 3, 10, 17, 24 e 31 dias, onde permaneceram confinados os adultos do parasitoide para contaminação. A mortalidade dos adultos de T. pretiosum foi mensurada indiretamente em função do menor número de ovos parasitados do hospedeiro alternativo Anagasta kuehniella. Os resultados foram comparados com o tratamento testemunha e os agrotóxicos classificados conforme categorização da IOBC. Foram utilizadas quatro repetições para cada tratamento. Os fungicidas Opera, Priori Xtra e Folicur 200 EC foram de vida curta (classe 1). Os inseticidas Match EC e Sumithion 500 CE foram de vida curta (classe 1); Lorsban 480 BR e Safety foram moderadamente persistentes (classe 3) e Engeo Pleno, Karate Zeon 50 CS e Tracer foram persistentes (classe 4) aos adultos de T. pretiosum.

Trichogramma pretiosumparasitism and dispersal capacity: a basis for developing biological control programs for soybean caterpillars

In order to succeed in biological control programs, not only is it crucial to understand the number of natural enemies to be released but also on how many sites per area this releasing must be performed. These variables might differ deeply among egg parasitoid species and crops worked. Therefore, these trials were carried out to evaluate the parasitism (%) in eggs of Anticarsia gemmatalis and Pseudoplusia includens after the release of different densities of the egg parasitoid Trichogramma pretiosum. Field dispersal was also studied, in order to determine appropriate recommendations for the release of this parasitoid in soybean fields. The regression analysis between parasitism (%) and densities of the parasitoid indicated a quadratic effect for both A. gemmatalis and P. includens. The maximum parasitism within 24 h after the release was reached with densities of 25.6 and 51.2 parasitoids per host egg, respectively, for the two pests. Parasitism of T. pretiosum in eggs of P. includens decreased linearly as the distance of the pest eggs from the parasitoid release sites increased. For P. includens, the mean radius of T. pretiosum action and the area of parasitoid dispersal in the soybean crop were 8.01 m and 85.18 m2, respectively. We conclude that for a successful biological control program of lepidopteran pests using T. pretiosum in soybean fields, a density of 25.6 parasitoids per host egg, divided into 117 sites per hectare, should be used.

Trichogramma pretiosum attraction due to the Elasmopalpus lignosellus damage in maize

The objective of this work was to evaluate if corn plants damaged by the lesser cornstalk borer (Elasmopalpus lignosellus) larvae release volatile organic compounds capable of attracting the egg parasitoid Trichogramma pretiosum. The treatments consisted of plants subjected to harm caused by E. lignosellus larvae, plants subjected to mechanical damage, and undamaged plants. The parasitoid was more attracted by the volatiles released by the insect damaged plants than to those released by undamaged corn plants, after 24 and 72 hours. The volatiles (Z)-3-hexenyl acetate, β-pinene, β-myrcene, (E)-4,8-dimethylnona-1,3,7-triene, and benzothiazole were released in significantly larger quantities by damaged plants. Volatiles released by corn plants damaged by E. lignosellus larvae may act as an indirect defense, attracting by T. pretiosum.