Compatibilidade de inseticidas com o fungo entomopatogênico Metarhizium rileyi (Ascomycota)

Atualmente existem no mercado inúmeras substâncias químicas empregadas no controle de insetos-praga. Entre eles, os inseticidas são um grupo numeroso e destacado. Este trabalho teve como objetivo avaliar a compatibilidade “in vitro” entre os inseticidas Permetrina (Pounce®) e Acefato (Orthene®) e os isolados UFMS 06 e UFMS 07 do fungo Metarhizium rileyi. Para tanto, o crescimento micelial, produção e germinação dos esporos foram avaliados. Ao solidificar o meio de cultura contendo os inseticidas, foram inoculados o fungo M. rileyi e incubados por 7 dias, em câmara climatizada a 25±1 ºC, umidade relativa 70±10% e fotoperíodo de 12 horas. Para germinação dos esporos o período de incubação foi de 20 horas, nas mesmas condições citados anteriormente O índice biológico foi utilizada para o estabelecimento da classificação toxicológica dos inseticidas sobre o fungo. Os resultados mostraram que os produtos testados foram compatíveis com o fungo, podendo ser, portanto, utilizados no manejo integrado de pragas agrícolas por não afetarem o desenvolvimento do agente de controle biológico M. rileyi.

Thromboxane Mobilizes Insect Blood Cells to Infection Foci

Innate immune responses are effective for insect survival to defend against entomopathogens including a fungal pathogen, Metarhizium rileyi, that infects a lepidopteran Spodoptera exigua. In particular, the fungal virulence was attenuated by cellular immune responses, in which the conidia were phagocytosed by hemocytes (insect blood cells) and hyphal growth was inhibited by hemocyte encapsulation. However, the chemokine signal to drive hemocytes to the infection foci was little understood. The hemocyte behaviors appeared to be guided by a Ca2+ signal stimulating cell aggregation to the infection foci. The induction of the Ca2+ signal was significantly inhibited by the cyclooxygenase (COX) inhibitor. Under the inhibitory condition, the addition of thromboxane A2 or B2 (TXA2 or TXB2) among COX products was the most effective to recover the Ca2+ signal and hemocyte aggregation. TXB2 alone induced a microaggregation behavior of hemocytes under in vitro conditions. Indeed, TXB2 titer was significantly increased in the plasma of the infected larvae. The elevated TXB2 level was further supported by the induction of phospholipase A2 (PLA2) activity in the hemocytes and subsequent up-regulation of COX-like peroxinectins (SePOX-F and SePOX-H) in response to the fungal infection. Finally, the expression of a thromboxane synthase (Se-TXAS) gene was highly expressed in the hemocytes. RNA interference (RNAi) of Se-TXAS expression inhibited the Ca2+ signal and hemocyte aggregation around fungal hyphae, which were rescued by the addition of TXB2. Without any ortholog to mammalian thromboxane receptors, a prostaglandin receptor was essential to mediate TXB2 signal to elevate the Ca2+ signal and mediate hemocyte aggregation behavior. Specific inhibitor assays suggest that the downstream signal after binding TXB2 to the receptor follows the Ca2+-induced Ca2+ release pathway from the endoplasmic reticulum of the hemocytes. These results suggest that hemocyte aggregation induced by the fungal infection is triggered by TXB2via a Ca2+ signal through a PG receptor.

Contact Toxicity of Insecticides and Biopesticides to Trichogramma Chilonis Ishii. (Hymenoptera: Trichogrammatidae) under Laboratory Condition

Integration of insecticides and biological controls is an important tactic of Integrated Pest Management (IPM). Trichogramma chilonis is a promising natural enemy of many lepidopteran insect pests. However, this hymenopteran egg parasitoid is adversely affected by most insecticides. Contact toxicity of nineteen insecticides and three biopesticides on adults of T. chilonis was investigated by using dry film residue bioassays under laboratory conditions. Profenofos and chlorpyrifos were highly lethal to the adults even at sublethal doses followed by dimethoate, spinosad, indoxacarb and acephate + imidacloprid. Diafenthiuron, nimbecidine and flubendiamide were categorised as less toxic. The biopesticides viz., Metarhizium anisopliae, Beauveria bassiana and Metarhizium rileyi were found innocuous to T. chilonis. The studysuggests that the insecticides with less toxicity and biopesticides with apparently no harmful effects on the parasitoid can be used in conjunction with parasitoids in IPM programmes. This will also advice the plant protectionists in avoiding the one with detrimental effects on this hymenopteran wasp with appropriate timing of application that controls the pests without adversely affecting their natural enemies

Evaluation of Metarhizium rileyi Farlow (Samson) impregnated with azadirachtin and indoxacarb against Helicoverpa armigera (Hubner)

Background Entomopathogenic fungi are the most versatile having a wide host range, capable of infecting insects at different developmental stages. In the present study, Metarhizium rileyi, at the concentrations of 102, 103, 104, 105, 106, 107 and 108 conidia/ml and sub-lethal concentrations of azadirachtin (1.02 and 1.53 ppm) and indoxacarb (0.72 ppm) were evaluated against the 1st, 2nd, 3rd, 4th and 5th larval instars of Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) under laboratory conditions. Results M. rileyi applied at 106 conidia/ml caused a maximum mortality of 83.33 and 80.00% of 1st and 2nd larval instars of H. armigera, respectively. The maximum mortality of 3rd, 4th and 5th larval instars of H. armigera with 108 conidia/ml of M. rileyi was 83.33, 76.67 and 53.33%, respectively. When M. rileyi blended with azadirachtin at 1.02 ppm, the highest mortality rate of 86.21% at 106 conidia/ml against 2nd instar larvae was resulted. Similarly, M. rileyi applied at 108 conidia /ml mixed with azadirachtin (1.53 ppm) showed 89.66% mortality of 3rd instar larvae. The 2nd instar larvae treated with M. rileyi at 106 conidia/ml, mixed with indoxacarb (0.72 ppm), the corrected mortality rate was 82.14%. Concentration mortality response of 3rd instar larvae to M. rileyi blended with indoxacarb (0.72 ppm) was 85.71% at 108 conidia/ml. The median lethal concentration (LC50) values were 5.51 × 103, 1.86 × 104, 2.81 × 105 and 5.55 × 105 conidia/ml for 1st, 2nd, 3rd and 4th larval instars, respectively, after 7 days of treatment. M. rileyi when mixed with sub-lethal concentrations of azadirachtin (1.02 ppm) and indoxacarb (0.72 ppm) resulted LC50 values of 1.09 × 104 conidia/ml and 1.37 × 104 conidia/ml against 2nd instar larvae, respectively, after 24 hours. Similarly, M. rileyi mixed with sub-lethal concentrations of azadirachtin (1.53 ppm) and indoxacarb (0.72 ppm) resulted LC50 values of 3.12 × 108 and 3.06 × 105 conidia/ml against 3rd instar larvae, respectively, after 24 hours. The study revealed that the susceptibility of larvae decreased in case of large larval instars. Conclusions M. rileyi can be utilized as one of the component of Integrated Pest Management Program for the eco-friendly management of H. armigera. As the application of M. rileyi @ 107 conidia/ml alone or in combination with azadirachtin (1.02 and 1.53 ppm) or indoxacarb (0.72 ppm) resulted to the highest mortality.

Efeito de fungicidas ao fungo entomopatogênico Metarhizium rileyi

O fungo entomopatogênico Metarhizium rileyi é conhecido como agente de controle biológico de vários lepidópteros entre eles destaca-se a família Noctuidae. O objetivo deste trabalho foi avaliar o efeito dos fungicidas sobre o desenvolvimento de dois isolados de M. rileyi em condições de laboratório. Foi estudado o efeito in vitro de cinco fungicidas sobre os isolados UFMS 06 e UFMS 07 do fungo M. rileyi. Os produtos foram colocados em placas de Petri contendo o meio de cultura Batata-Dextrose-Ágar (BDA), nas concentrações recomendadas para a aplicação do produto em campo. Após ter incubado o fungo no meio de cultura as placas foram vedadas com filme de PVC e colocadas em câmara climatizada (tipo B.O.D.) a 25 ± 1 °C, umidade relativa de 70 ± 10 % e fotoperíodo de 12 horas por um período de 7 dias, foram avaliados o crescimento micelial e concentração de esporos. Para quantificar a porcentagem de germinação foi utilizada uma suspensão de 1,0 × 106 con.mL-1, sendo mantida em repouso por duas horas nos diferentes fungicidas. Logo após este período foi plaqueado 1,0 mL da suspensão com o auxílio de uma pipeta graduada (1mL) em placas de Petri e espalhada com alça de Drigalsky no meio nutritivo, após a inoculação as placas foram identificadas e vedadas com filme PVC, e incubadas por 20 horas em câmara climatizadas tipo B.O.D. a 25 ± 1 °C, umidade relativa de 70 ± 10 % e fotoperíodo de 12 horas. Os fungicidas testados neste trabalho todos eles interferiram no crescimento vegetativo, na produção de conídios e na germinação dos dois isolados do fungo, no teste de índice biológico todos os produtos foram classificados como tóxicos.

Comparative effectiveness of Metarhizium rileyi, novaluron, and glyphosate on immune system, development, and redox metabolism of Anticarsia gemmatalis

Anticarsia gemmatalis is one of the most important pests in world soybean crop. The most common intervention is the application of agrochemicals, such as novaluron and glyphosate. Among biological control agents, much attention has been drawn to entomopathogenic fungi, as Metarhizium rileyi. Here, we examined the changes that occur in the immune system (total and differential hemocyte count), secondary effects (caterpillar morphology), and oxidative metabolism after the caterpillars were exposed to M. rileyi, novaluron or glyphosate. M. rileyi was able to induce changes in the width, length, and weight of A. gemmatalis pupae, along with an increased in the number of defense cells. Novaluron prompt changes the insect’s immunity, and glyphosate caused milder immunological effects. However, it caused significant secondary effects including malformations in pupae and adults, and an increase in nitric oxide (NO) levels. Mortality observed when treating insects with novaluron and malformations due to glyphosate treatments did not occur due to oxidative stress. However, when insects were exposed to M. rileyi, we verified significantly increased levels of NO and concluded that these insects died due to oxidative stress. Our data provide evidence that contributes to better understanding the mechanism of herbicide-fungus interaction in the management of Anticarsia gemmatalis.