P. H. B. Togni

Odour masking of tomato volatiles by coriander volatiles in host plant selection of Bemisia tabaci biotype B

The silverleaf whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), is one of the most important pest insects in tomato crop systems worldwide. It has been previously demonstrated that intercropping tomato [Solanum lycopersicum L. Mill. (Solanaceae)] with coriander [Coriandrum sativum L. (Apiaceae)] reduces the incidence and severity of damage caused by B. tabaci. However, it is not yet known how coriander affects the insect′s behaviour. We evaluated the attractiveness of tomato constitutive volatiles to B. tabaci and what effect coriander constitutive volatiles have on the insect′s behaviour. To this end, we conducted three bioassays in a multiple‐choice four‐arm olfactometer (‘×’ type), measuring B. tabaci behaviour when offered tomato and coriander constitutive volatiles presented alone as well as together. We also evaluated the colonisation and establishment of B. tabaci in experimental plots with only single tomato plants and tomatoes intercropped with coriander in a greenhouse. Bemisia tabaci males and females recognised tomato constitutive volatiles as a positive stimulus (kairomonal effect), indicating that semiochemicals from this plant can play an important role in the insect’s host plant selection. Coriander constitutive volatiles reduced the attractiveness of tomato volatiles but no repellency to these volatiles was observed. Greater numbers of adults and nymphs of B. tabaci per plant were observed in tomato monoculture plots than in tomato intercropped with coriander. We suggest that coriander constitutive volatiles have an odour masking effect on tomato volatiles, thus interfering in the host plant selection of B. tabaci.

Field Evaluation of Bt Cotton Crop Impact on Nontarget Pests: Cotton Aphid and Boll Weevil

Bt cotton plants expressing Cry1Ac protein have high specificity for the control of lepidopteran larvae. However, studies conducted in several countries have shown these plants have a differential impact on nontarget herbivores. The aim of this study was to compare the colonization rates and population abundance of the cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae) and the boll weevil, Anthonomus grandis Boheman (Coleoptera: Curculionidae), in plots of Bt (Nuopal) and non-Bt cotton (Delta Opal) in an experimental field in Brasilia, DF, Brazil. No difference was observed in the preference and colonization by winged aphids to plants from the two treatments. There was no significant difference in abundance of wingless aphids or in the production of winged aphids between treatments. Apparently, the parameters that control factors such as fecundity, survival, and dispersal were similar on both Bt and non-Bt plants. Monitoring of plants for coccinellids, a specialist predator of aphids, and ants that act on the dispersal of aphids among plants showed no significant difference between Bt and non-Bt plants, supporting the inference above. Regarding the effect on boll weevil, there was also no significant difference between treatments in the total number of fruiting structures attacked in each plot, the percentage of fruiting structures attacked per plant or on the number of weevils emerging from fruits with boll weevil damage from egg-laying, when damaged fruit samples were held in the laboratory. Based on these results, we conclude that there is no impact of Bt cotton crop expressing Cry1Ac on the nontarget herbivores tested under field conditions.

The role of integrating agroforestry and vegetable planting in structuring communities of herbivorous insects and their natural enemies in the Neotropical region

Abstract The integration of agroforestry plots with ephemeral crops such as vegetables on the farm scale can probably serve as a refuge and source of beneficial insects. Therefore, agroforestry systems possibly represent an alternative that favors ecosystem services and help growers in the transition process from conventional to agro-ecological agriculture. This study aimed to understand the role of introducing agroforestry systems in structuring insect communities, with consequences for the abundance of herbivore and natural enemies, contributing to farm management and favoring biological control as an ecosystem service. Field surveys showed that agroforestry systems can harbor more species than horticultural crops, independent of the functional group. They also contain a greater diversity of herbivores and an even greater diversity profile of natural enemy communities. Agroforestry systems served as a source of natural enemies that can colonize horticultural crops when herbivores are present. As a consequence, natural enemies can establish a numerical response to herbivore abundance, but their communities are also affected by stochastic factors related to climatic conditions. Thus, agroforestry systems and agro-ecological practices might favor an agriculture based on the maintenance and conservation of ecosystem services.

Bitrophic toxicity of Cry1Ac to Cycloneda sanguinea, a predator in Brazilian cotton

Insect predators are exposed to the Cry1Ac toxin in Bt cotton fields through several pathways. In this study, we investigated the effects of activated Cry1Ac added to a diet on Cycloneda sanguinea (L.) (Coleoptera: Coccinellidae), which is one of the main predators of non‐target pests in Brazilian cotton. Direct bitrophic exposure of C. sanguinea to Cry1Ac was done by feeding beetles with Aphis gossypii (Glover) (Hemiptera: Aphidae) sprayed with 500 μg per ml Cry1Ac solution. Larval and pupal survival, development time, aphid consumption, and adult longevity were recorded daily. Couples within the same experimental treatment were paired and numbers of eggs laid and hatched per female were recorded daily. Net replacement rate was calculated for each female. During development, a C. sanguinea larva consumed on average 1.8 μg of activated Cry1Ac. No significant differences due to Cry1Ac were observed for any of the response variables, except aphid consumption. Larvae receiving Cry1Ac consumed more aphids than larvae receiving distilled water alone. Additional statistical analyses were conducted to evaluate independence of responses, and for the independent responses, a simple meta‐analysis was conducted to test the null hypothesis that all responses were zero. Nearly all of the response variables were statistically independent. Two pairs of responses were not independent, but the associated multivariate tests were not significant. The meta‐analysis suggested that all effects were not different from random variation around zero and no cumulative effects could be detected. Our results indicated that bitrophic exposure to activated Cry1Ac is likely to have little or no adverse ecological effect on C. sanguinea.

Seasonal fluctuation in the population of Harmonia axyridis (Pallas, 1773) (Coleoptera: Coccinellidae) and co-occurrence with other Coccinellids in the Federal District of Brazil

A joaninha asiatica, Harmonia axyridis (Pallas, 1773), foi primeiramente registrada no Brasil em 2002 no Estado do Parana, sendo posteriormente registrada nos estados de Sao Paulo e Minas Gerais. Essa especie pode colonizar novas areas e tornar-se dominante na comunidade local, reduzindo a densidade e diversidade de especies nativas, principalmente de coccinelideos. O objetivo deste trabalho foi registrar a presenca de H. axyridis no Distrito Federal, a flutuacao populacional e a sua co-ocorrencia com outros coccinelideos. As coletas foram realizadas em uma propriedade rural particular em Taguatinga e no campo experimental da Embrapa Hortalicas no Gama, Distrito Federal, entre agosto/2008-janeiro/2010, utilizando coleta direta dos individuos sobre as plantas. Foram coletados 881 coccinelideos, sendo que destes 110 pertencem a especie H. axyridis exclusivamente do grupo succinea, nas seguintes plantas: tomate, coentro, milho verde, repolho, couve, couve-flor, brocolis, pepino. Tambem foi observada a sua co-ocorrencia com outras especies de joaninhas: Cycloneda sanguinea (Linnaeus, 1763), Hippodamia convergens (Guerin-Meneville 1842), Eriopis connexa (German, 1824), Scymnus sp., Nephaspis sp., Azya luteipes (Mulsant, 1850), Hyperaspis festiva (Mulsant, 1850), Olla v-nigrum (Mulsant, 1866), Psyllobora sp. e Coleomegilla maculata (De Geer, 1775). Ate o momento, nao foram registradas interacoes negativas de H. axyridis com essas especies no Distrito Federal. Alem disso, esta regiao foi apontado anteriormente como tendo uma baixa probabilidade de ocorrencia para esta especie, refletindo H. axyridis grande plasticidade adaptativa para novos habitats.

Coccinellidae Parasitoids in Brazil: Neglected Species in a Mega-Diverse Country

Current knowledge on coccinellids is primarily focused on their role as natural enemies of soft-bodied insects. However, there is a great diversity of coccinellid parasitoid species that are less studied. Here, we describe new records of coccinellid parasitoids with emphasis on new host–parasitoid interactions in 11 sample sites in Brazil. We collected 122 coccinellid individuals parasitized by six species of parasitoids in the Cerrado and in the Atlantic Rainforest biomes. New records of coccinellid parasitoids and host associations, expansion of habitat ranges and interactions are discussed focusing on the lack of basic information on these interactions in Brazil.

Biodiversity provides whitefly biological control based on farm management

Management of the whitefly Bemisia tabaci biotype B (Hemiptera: Aleyrodidae) has challenged scientists and famers worldwide because this insect is highly polyphagous and resistant to traditional control methods. Innovative management tools, such as the use of the ecosystem service of biological control, are necessary, especially in a century in which sustainable crop systems are emerging. We investigated how management practices and farm diversity within the property limits affect the relationship between biodiversity conservation and the biological control of B. tabaci. We determined the mortality factors of whitefly nymph cohorts on 33 small farms growing tomatoes. The sampled farms formed a gradient of increasing farm diversity and decreasing management intensity. The diversity of natural enemies increased from conventional to agroecological farms, and predation was identified as the key mortality factor of B. tabaci nymphs on all farm types except the conventional farms. Biological control provided by biodiversity components (predators, parasitoids and pathogens) was enhanced on more diverse and less intensively managed farms. Higher predator richness and abundance resulted in more effective biological control and made it less variable among farms. Different components of natural enemy biodiversity were conserved and acted in a complementary way on agroecological farms, and the enhanced ecosystem services reduced the need for insecticides.