ABSTRACT
The insect immune system includes several mechanisms responsible for defending against pathogens, parasites, and parasitoids. Some botanical insecticides, such as Azadirachta indica oil, cause changes in the immune system of various insect species. Spodoptera frugiperda is an important agricultural pest; thus, knowledge about the effect of neem oil on the immune system of this species can assist in its management. This study aimed to evaluate the effect of A. indica oil on the immune system of S. frugiperda. Caterpillars (2-3 mg) were placed individually in containers (50 ml) with approximately 10 g of diet, containing 125, 250, and 500 ppm of neem oil with propanone; the control group received only the propanone diet. In four experiments, the total number of hemocytes, the phagocytic activity, the activity of lysozyme-like enzymes, and phenoloxidase activity were measured in caterpillars at the end of the sixth instar. The total number of hemocytes in insects exposed to neem oil was 21% lower than in the control group. The percentage of cells that phagocyted the latex beads was similar among the caterpillars that ingested the different concentrations. The mean diameter of cell lysis halos was reduced only at concentrations of 125 and 250 ppm. Absorbance did not differ between treatments. Knowing that this oil reduces the number of circulation cells and the activity of lysozyme-like enzymes is of great importance to design control strategies, once the neem oil could be added to other biological agents for mortality reducing the chances of this insect surviving in the environment.
Subject(s)
Azadirachta/chemistry , Glycerides/pharmacology , Insecticides/pharmacology , Larva/drug effects , Spodoptera/drug effects , Terpenes/pharmacology , Animals , Immune System/drug effects , Larva/immunology , Spodoptera/immunologyABSTRACT
ABSTRACT: The innate immune system of honeybees mainly consists in antimicrobial peptides, cellular immunity and melanisation. In order to investigate the immune response of honeybees to immune stressors, three stress degrees were tested. Newly emerged bees naturally DWV-infected were collected from a Varroa mite-free apiary and divided into three experimental groups: naturally DWV infected bees, PBS injected bees, and artificially DWV super infected bees. Phenoloxidase activity and haemolymph cellular subtype count were investigated. Phenoloxidase activity was highest (P<0.05) in DWV-superinfected bees, and the haemocyte population differed within the three observed groups. Although, immune responses following DWV infection have still not been completely clarified, this investigation sheds light on the relation between cell immunity and the phenoloxidase activity of DWV-naturally infected honeybees exposed to additional stress such as injury and viral superinfection.
RESUMO: O sistema imune inato das abelhas consiste principalmente em peptídeos antimicrobianos, imunidade celular e melanização. Para investigar a resposta imune das abelhas a estressores imunológicos, foram testados três graus de estresse. Abelhas recém-emergidas naturalmente infectadas por DWV foram coletadas de um apiário livre de Varroa e divididas em três grupos experimentais: abelhas naturalmente infectadas por DWV, abelhas injetadas com PBS e abelhas superinfectadas artificialmente com DWV. A atividade de fenoloxidase e a contagem de subtipos celulares de hemolinfa foram investigadas. A atividade da fenoloxidase foi maior (P<0,05) nas abelhas super-infectadas com DWV, e a população de hemócitos diferiu entre os três grupos observados. Embora as respostas imunes após a infecção pelo DWV ainda não tenham sido completamente esclarecidas, esta investigação lança luz sobre a relação entre a imunidade celular e a atividade da fenoloxidase das abelhas infectadas naturalmente pelo DWV, expostas a estresse adicional, como lesão e superinfecção viral.
ABSTRACT
Fenoloxidase é considerada um importante mediador no sistema de defesa dos insetos contra patógenos e parasitóides. Essa enzima está presente na hemolinfa da maioria dos insetos estudados como uma proenzima inativa chamada profenoloxidase. Em Acheta domesticus (L.) a atividade da enzima foi estudada na presença de Bacillus subtilis. Injeções de bactéria na hemocele de ninfas desse inseto elevaram o nível de atividade da phenoloxidase. A taxa de aumento foi semelhante à observada nos insetos injetados com laminarin, um ativador da proenzima. A incubação de células de B. subtilis em soro com fenoloxidase ativada in vitro, e posterior injeção nos insetos, acelerou a remoção das bactérias da hemolinfa. A concentração das bactérias foi menor do que a observada nas ninfas injetadas apenas com bactéria em solução tampão. Por outro lado, ninfas injetadas com suspensão de bactéria incubada em soro com fenoloxidase inativada in vitro apresentaram alta concentração de bactéria na hemolinfa. Esses resultados indicam que B. subtilis é sensível à cascata de profenoloxidase de A. domesticus. Sugere-se que a fenoloxidase ativada adere à superfície das bactérias e aumenta a fixação dos hemócitos em torno das bactérias. Isso contribui para acelerar sua remoção da hemolinfa através da formação de nódulos.
Insect phenoloxidase is considered an important mediator in defense reaction against pathogens and parasites. It is present in the hemolymph of most insects as an inactive proenzyme, called prophenoloxidase. In Acheta domesticus (L.) the phenoloxidase activity was studied in the presence of Bacillus subtilis. The bacteria induced the activation of the prophenoloxidase and increased the level of phenoloxidase activity when injected into the hemocoel of A. domesticus nymphs. The level of increase was comparable to those observed in nymphs injected with laminarin, an activator of the proenzyme. Incubating B. subtilis in serum with phenoloxidase activated in vitro and then injecting into the insects accelerated the removal of the bacteria from the hemolymph in vivo. The concentration of bacteria was lower than those observed in nymphs injected with Mes buffer alone. In control insects, injection of soybean trypsin inhibitor lowered phenoloxidase activity and the removal of bacteria from the hemolymph. These results indicate that B. subtilis is sensitive to the prophenoloxidase cascade of A. domesticus. It is suggested that activated phenoloxidase could bind to the surface of bacteria and increase the adhesion of hemocytes to bacteria, and thus accelerating their removal by nodule formation.
