Sub-lethal effects of a Bt-based bioinsecticide on the biological conditioning of Anticarsia gemmatalis.

Bioinsecticides based on Bacillus thuringiensis (Bt) Berliner, 1915 are widely used to control lepidopteran in several crops. However, surviving insects exposed to the sub-lethal concentration of Bt-based bioinsecticides can suffer a multitude of effects on the biological conditioning known as hormesis. Here, we aimed to provide a clearer understanding of the biological conditioning of Anticarsia gemmatalis (Hübner, 1818), exposed to different concentrations of a Bt-based bioinsecticide, by assessing life table parameters over three generations. We defined five sub-lethal concentrations (LC5, LC10, LC15, LC20, and LC25) from the response curve estimate of A. gemmatalis. Deionized water was used as a control. We assessed the parameters of eggs-viability and the duration of the stages, incubation, larval, pre-pupal, pupal, adult, pre-oviposition and total biological cycle. Data were used to construct the fertility life table using the two-sex program. The survival curves showed greater variation in the proportion of individuals at each development stage using the LC25. The sub-lethal concentrations did not influence the incubation-eggs period, pre-pupal and pupal. However, the larval and adult stages using LC25 and LC10 were the most affected. Changes in sex ratio were observed using LC20 and LC5. The toxic effect of Bt-based bioinsecticide interfered mainly in the parameters of fertility, sex ratio, net reproduction rate (R0), and gross reproduction rate (GRR).

Development of Helicoverpa armigera (Hübner, 1805) and Spodoptera frugiperda (SMITH, 1797) in winter forages / Desenvolvimento de Helicoverpa armigera (Hübner, 1805) e Spodoptera frugiperda (SMITH, 1797) em forragens de inverno

Helicoverpa armigera Hübner, 1805 and Spodoptera frugiperda Smith, 1797 are polyphagous pests of great agricultural importance in subtropical and temperate climate regions. The usual management of production areas in the southern region of Brazil occurs after the harvesting of summer crops, and the areas are sown with pasture. Thus, forages recommended for grazing are azevém (Lolium multiflorumLam.) and cornichão (Lotus corniculatus L.) due to their nutritional benefits, good palatability, regrowth, and hardiness. Considering the high degree of polyphagia of H. armigera and S. frugiperda, and the impact of maintaining continuous feeding areas (green bridges) in the management of these species, this work aimed to evaluate the development of H. armigera and S. frugiperda fed leaves of azevém and cornichão under laboratory conditions. The insects were collected in the city of Capão do Leão/RS in corn and soybean plantations. For each forage species, 130 newly hatched caterpillars were each placed in autoclaved glass tubes, with one-third of the tube length containing forage. The tubes were capped with waterproof cotton and placed in a climate-controlled room at 25 ± 1°C, 70 ± 10% relative humidity, and a 12-h photophase. The food was replenished daily until the caterpillars entered the pupae stage. The pupae were sexed and weighed, and the newly emerged adults were placed in pairs in PVC cages, lined with white A4 sulfite paper. The papers used as a laying substrate were removed and changed daily, and eggs were counted. The number of instars was determined by the linearized Dyar rule model. The complete randomization design was employed for the variables biological cycle length and viability of egg, caterpillar, pre-pupa, pupa, adult, and pre-oviposition phases and weight of caterpillars on the 14th day and pupae after 24 h. Based on the results obtained, a fertility life table was prepared. H. armigera did not complete the cycle, with only three instars and a duration of 22.1 and 24.6 days in azevém and cornichão, respectively. When evaluated in S. frugiperda caterpillars, development in forage species was observed, with five and six instars and duration of 51.7 and 45.1 days in azevém and cornichão, respectively. The azevém was distinguished by interference in the development cycle of the species, reducing the effect of the green bridge. In addition, surviving insects were susceptible to the effects of the agroecosystem due to the low-quality food source.

Helicoverpa armigera Hübner, 1805 e Spodoptera frugiperda Smith, 1797 são pragas polífagas de grande importância agrícola, em regiões de clima subtropical e temperado. Após a colheita das culturas de verão no sul do Brasil, as áreas são utilizadas como pastagem. Com isso, as forrageiras recomendadas ao pastoreio são cornichão (Lotuscorniculatus L.) e azevém (Loliummultiflorum Lam.) por apresentarem benefícios nutricional, palatabilidade, rebrota e rusticidade. Devido ao alto grau de polifagia de H. armigera e S. frugiperda e o impacto de áreas continuas de alimento (pontes verdes) no manejo destas espécies, este trabalho objetivou-se avaliar o desenvolvimento de H. armigera e S. frugiperda alimentadas com azevém e cornichão em condições de laboratório. Os insetos foram coletados no município de Capão do Leão/RS em plantios de milho e soja. Para cada espécie forrageira foram individualizadas 130 lagartas recém-eclodidas em tubos de vidro autoclavados, com um terço (1/3) do seu comprimento contendo a respectiva forrageira. Os tubos foram tampados com algodão hidrófugo e levados para a sala climatizada a 25 ± 1°C, UR de 70 ± 10% e 12 horas de fotofase. Diariamente, o alimento foi reposto até que as lagartas entrarem em estágio de pupa. As pupas foram sexadas e pesadas e os adultos recém-emergidos foram individualizados em casais em gaiolas de PVC, forradas com papel sulfite A4 branco no seu interior. Os papéis utilizados como substrato de postura foram retirados e trocados diariamente e os ovos foram contabilizados. O número de instares foi determinado pelo modelo linearizado da regra de Dyar. O delineamento utilizado foi inteiramente casualizado (DIC) para as variáveis duração do ciclo biológico e viabilidade das fases de ovo, lagarta, pré-pupa, pupa, adultos e pré-oviposição, peso de lagartas ao decimo quarto (14°) dia e pupas após 24 horas. Com base nos resultados obtidos, foi elaborada tabela de vida de fertilidade. H. armigera não completou o ciclo, com apenas três instares e duração de 22,1 e 24,6 dias em azevém e cornichão, respectivamente. Quando avaliado em lagartas de S. frugiperda observou o desenvolvimento nas espécies forrageiras, com 5 e 6 instares e duração de 51,7 e 45,1 dias em azevém e cornichão, respectivamente. Contudo, considerando o critério que evite a formação de ponte verde, azevém destacou-se por interferir no ciclo de desenvolvimento das espécies. Onde, mesmos os que sobrevivem, estão suscetíveis aos efeitos do agroecossitema devido a fonte alimentar ser de baixa qualidade.

Immune response and susceptibility to Cotesia flavipes parasitizing Diatraea saccharalis larvae exposed to and surviving an LC25 dosage of Bacillus thuringiensis.

Biological control using entomopathogens and natural enemies is an ecofriendly method for pest management in agriculture. Biological control agents often can be simultaneously employed and compatibility between agents may improve pest suppression. We investigated the influence of the entomopathogen Bacillus thuringiensis (Bt) on the immune system of the sugarcane borer Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae) to determine if such changes impact parasitization by Cotesia flavipes Cameron, 1891 (Hymenoptera: Braconidae). The immune response of surviving D. saccharalis larvae fed with an LC25 dosage of a Bt-based biopesticide (Dipel®) was analyzed (total hemocyte count, hemocyte adhesion, and activities of phenoloxidase and lysozyme). Furthermore, the suitability of surviving Bt-fed larvae as hosts for C. flavipes was assessed by measuring parasitoid attributes such as number and size of teratocytes, weight of pupae, length of adult female tibia and number of emerged adults. Total hemocyte count, but not hemocyte adhesion, total protein content and phenoloxidase activity increased in the hemolymph of non-parasitized Bt-fed larvae (Bt-NP) compared to control larvae (NBt-NP). Lysozyme activity increased only after parasitization without Bt exposure (NBt-P). After parasitization, the immunological parameters activated in Bt-NP larvae decreased to levels at or below those observed in control larvae, showing that C. flavipes can regulate the activated immune response of Bt-fed larvae. The development of C. flavipes was not impaired in Bt-fed larval hosts (Bt-P); no changes were observed for teratocyte size, weight of pupal mass, length of hind tibia and number of adults emerged.