Does Bacillus thuringiensis have adverse effects on the host egg location by parasitoid wasps?

ABSTRACT This study investigated the interaction between two pest biological control agents, the parasitoid wasp Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) and the entomopathogen Bacillus thuringiensis (Bacillales: Bacillacea) (Bt). The aim of this study was to evaluate if the presence of Bt (formulated products Agree®, Dipel® and HD1 and HD11 strains) interferes in the oviposition preference of T. pretiosum to eggs of Helicoverpa zea (Lepidoptera: Noctuidae). Using an olfactometry test, the eggs of H. zea were bathed with the commercial formulations, with the Bt suspensions or distilled water, and offered to the parasitoid wasps in order to evaluate parasitism. The results showed that H. zea eggs sprayed with commercial formulations and Bt strains did not interfere in the choice made by the parasitoid. The parasitoid wasp is not able to distinguish between eggs with or without B. thuringiensis treatment, independently of strains suspension or commercial formulations. Therefore, these two control agents may be used together without negative interaction.

Response of the predatory mite Phytoseiulus macropilis (Banks) to volatiles produced by strawberry plants in response to attack by Tetranychid mites (Acari: Phytoseiidae: Tetranychidae)

The attack of phytophagous mites may induce plants to produce volatiles, which in turn may attract predators. The occurrence of multiple phytophagous infestations on plants may influence predator response. In this paper, we investigated whether the attraction of the predatory mite Phytoseiulus macropilis (Banks) to phytophagous-infested plants would change with the simultaneous presence of two tetranichid mites Oligonychus ilicis (McGregor) and Tetranychus urticae Koch. While the former species is rarely found on strawberry plants and is only occasionally found in association with P. macropilis, the latter is commonly found on strawberry plants and is frequently found in association with P. macropilis. Y-tube olfactometer test assays demonstrated that the predator preferred plants infested with T. urticae, avoided plants infested with O. ilicis, and had no preference for plants infested with both phytophagous mite species. These results indicated that the presence of a non-prey species (O. ilicis) on a given plant can alter the response of the predator to one of its prey (T. urticae). The consequences of the predatory behavior determined in this study on the predator ability to control T. urticae population on strawberry plants are discussed.

Distribuição espacial de ácaros fitófagos (Acari: Tetranychidae) em morangueiro / Spatial distribution of phytophagous mites (Acari: Tetranychidae) on strawberry plants

O morangueiro, Fragaria x ananassa, pode ser atacado por diferentes espécies de ácaros fitófagos, dentre elas o ácaro-vermelho, Oligonychus ilicis McGregor, e o ácaro-rajado, Tetranychus urticae Kock. Essas espécies são encontradas juntas, alimentando-se, com maior freqüência, sobre a epiderme adaxial e abaxial das folhas, respectivamente. Neste trabalho estudou-se o padrão de escolha de O. ilicis e T. urticae por sítio de alimentação em plantas de morangueiro. Duas hipóteses foram formuladas: a primeira, que a escolha por sítios de alimentação estaria relacionada à aptidão das espécies; a segunda, que esta escolha seria determinada pela presença do heteroespecífico. Com o objetivo de testar tais hipóteses, avaliou-se a preferência, biologia e sucesso reprodutivo de O. ilicis e T. urticae sobre a face abaxial e adaxial de folhas de morangueiro infestadas ou não pelo heteroespecífico. O. ilicis preferiu permanecer sobre a face adaxial enquanto T. urticae preferiu permanecer sobre a face abaxial de folhas de morangueiro. A preferência pelas faces foliares correlacionou-se com o sucesso reprodutivo das espécies, avaliado pela taxa intrínseca de crescimento populacional (r m). O padrão de escolha não se alterou quando as espécies foram submetidas ao teste de escolha entre as faces foliares previamente infestadas pelo heteroespecífico. É discutida a possibilidade de T. urticae induzir defesas da planta capazes de reduzir a aptidão de O. ilicis e vice-versa. A possibilidade dessas espécies permanecerem juntas sobre plantas de morangueiro aumenta a capacidade de dano à cultura.

Many phytophagous mites can attack strawberry plants, Fragaria x ananassa, among them the southern red mite, Oligonychus ilicis McGregor, and the two-spotted spider mite, Tetranychus urticae Koch. They are found together feeding on the same plant on the upper and underside of the leaves, respectively. Here we studied the choice for feeding sites of O. ilicis and T. urticae on strawberry plants. The first hypothesis tested whether the feeding site choice would be related to the fitness of the species. The second hypothesis dealt whether the feeding site would be determined by the presence of a heterospecific mite. We evaluated the preference, biology and reproductive success of O. ilicis and T. urticae on the under and upper side surface of strawberry leaves infested or not by the heterospecific. O. ilicis preferred to stay on the upper side surface while T. urticae preferred the underside. The preference for the leaf surface correlated with the reproductive success of the species (measured by the intrinsic growth rate). The choice pattern of feeding sites did not alter when the choice test was applied using sites previously infested by heterospecific. Although O. ilicis and T. urticae, apparently, do not interact directly for feeding sites, there is a chance that the first species induces defenses in strawberry plant enabling to reduce the fitness of the second species. The possibility of those species stay together on strawberry plant increases the damage capacity to the culture.

Herbivoria de Tetranychus urticae Koch (Acari: Tetranychidae) induz defesa direta em morangueiro? / Does herbivory of Tetranychus urticae Koch (Acari: Tetranychidae) induce direct defense in strawberry?

Plants of strawberry Fragaria x ananassa may present mechanisms of direct and indirect defenses against herbivores. Such defenses may influence behaviour and development ofphythophagous mites and their natural enemies, thereby reducing herbivory rate. We tested the effect of pre-infestation of strawberry plants by Tetranychus urticae Koch on the development and reproduction of the mite species. Strawberry plants (cultivar IAC Campinas) were divided into two groups: plants without and plants with pre-infestation of T. urticae. The length of immature phases, thenumber of eggs per female and the survival of mites were not altered by the pre-infestation. These results may be associated to either the absence or low level of induced resistance of the cultivar IAC Campinas or perhaps the pre-infestation was insufficient to induce defenses. The reported resistanceof this cultivar to T. urticae could be related to indirect defenses.

Plantas de morangueiro Fragaria x ananassa podem apresentar mecanismos de defesa direta e indireta contra herbívoros. Tais defesas podem alterar o comportamento e o desenvolvimento dos ácaros fitófagos e seus inimigos naturais, reduzindo a taxa de herbivoria. Testou-se o efeito da préinfestação de plantas de morangueiro por Tetranychus urticae Koch sobre o seu desenvolvimento ereprodução. Plantas de morangueiro cultivar IAC Campinas foram divididas em dois grupos: plantas limpas e plantas pré-infestadas por T. urticae. A infestação prévia de plantas de morangueiro por T. urticae não alterou a duração das fases imaturas, a fecundidade e a sobrevivência das fêmeas do ácaro. Tais resultados podem estar associados à inexistência ou baixo nível de resistência induzida da cultivarIAC Campinas, ou ainda, ao fato de a pré-infestação ter sido insuficiente para induzir defesa. Assim, a resistência relatada na cultivar IAC Campinas a T. urticae pode estar relacionada às defesas indiretas.

Efeito da profundidade de aplicação e da distribuição de inseticidas líquidos no controle de cupins de montículo em pastagens (Isoptera: Termitidae) / The effects of depth and distribution of liquid insecticides for the control of mound termites in pastures (Isoptera: Termitidae)

Foi testada a eficiência de duas profundidades de aplicação de cupinicidas líquidos para o controle de cupins de montículo Cornitermes sp. (Isoptera: Termitidae) em pastagens na região Sul de Minas Gerais. Estes aplicadores diferiam basicamente quanto à profundidade e distribuição da calda cupinicida dentro do ninho, sendo um aplicador de tubo curto e outro de tubo longo e perfurado. Os resultados mostram que, o aplicador e tubo longo e perfurado apresenta maior eficiência de controle de cupins de montículo em pastagem e que a profundidade e distribuição de aplicação da calda cupinicida interfere na taxa de mortalidade das colônias. O uso de um aplicador com tubo longo, pode ser uma estratégia adequada para o efetivo controle de cupins de montículo, quando se utilizam inseticidas em formulação líquida.

The efficacy of two depths was tested for the control of mound termites, Cornitermes sp. (Isoptera: Termitidae) using liquid a formulation of imidacloprid. Both devices were funnels constructed so as to differ only in the depth and distribution of the liquid within the termite nest. One of the devices was a standard funnel, whereas the other presented a longer tube perforated along its extension and closed in the outer end. Termites in mounds treated with the long funnel died faster than termites treated with the short funnel. It seems that the depth and distribution of the insecticide within termite nest was crucial for the efficacy of the control. We therefore recommend that control methods of termite in mounds should favor the use of applying devices which distribute better the insecticide within the nest.