Edison R. Sujii

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.

Inter and intra-guild interactions in egg parasitoid species of the soybean stink bug complex

Abstract – The objective of this research was to evaluate the parasitism behavior of Telenomus podisiAshmead, Trissolcus basalis (Wollaston) e Trissolcus urichi Crawford (Hymenoptera: Scelionidae) oneggs of Nezara viridula L., Euschistus heros F., Piezodorus guildinii Westwood and Acrosternumaseadum Rolston (Heteroptera: Pentatomidae), in no choice and multiple choice experiments. For allparasitoid species, the results demonstrated the existence of a main host species that maximizes thereproductive success. The competitive interactions among the parasitoid species were investigated inexperiments of sequential and simultaneous release of different combinations of parasitoid pairs on thehosts N. viridula, E. heros and A. aseadum. Exploitative competition was observed for egg batches atthe genus level ( Telenomus vs. Trissolcus) and interference competition at the species level ( T. basalisvs. T. urichi). Trissolcus urichi was the most aggressive species, interfering with the parasitism ofT. basalis. Generally, T. basalis showed an opportunistic behavior trying to parasitise eggs after T. urichihad abandoned the egg batch. The selection of parasitoid species for use in augmentative biologicalcontrol programs should take into account the diversity of pentatomids present in soybean in additionto the interactions among the different species of parasitoids.Index terms: parasitism, host-parasite relations, biological competition, pest control methods.Interacoes inter-guilda e intra-guilda entre especies de parasitoides de ovosque atacam o complexo de percevejos da sojaResumo – O objetivo desta pesquisa foi avaliar o comportamento de parasitismo de Telenomus podisiAshmead, Trissolcus basalis (Wollaston) e Trissolcus urichi Crawford (Hymenoptera: Scelionidae)em ovos de Nezara viridula L., Euschistus heros F., Piezodorus guildinii Westwood e Acrosternumaseadum Rolston (Heteroptera: Pentatomidae), em experimentos de multipla escolha e sem escolha dehospedeiros. Todas as especies de parasitoides testadas demonstraram possuir um hospedeiro quemaximizou a sua capacidade reprodutiva. As interacoes competitivas entre especies de parasitoidesforam investigadas mediante experimentos de liberacao sequencial e simultânea de diferentescombinacoes de pares de especies de parasitoides em N. viridula, E. heros e A. aseadum. Competicaopor exploracao foi observada a nivel de genero ( Telenomus vs. Trissolcus) e competicao por interferenciaa nivel de especie (T. basalis vs. T. urichi). A especie mais agressiva foi T. urichi, interferindo noparasitismo de T. basalis. Geralmente, T. basalis apresentou um comportamento oportunista tentandoparasitar os ovos apos T. urichi ter abandonado os lotes de ovos. A selecao de especies de parasitoidespara uso em programas de controle biologico aumentativo deve considerar a diversidade depentatomideos presentes na soja, alem das interacoes entre as especies de parasitoides que serao liberadas.Termos para indexacao: parasitismo, relacao parasita-hospedeiro, competicao biologica, metodos decombate as pragas.

Detection and decay rates of prey and prey symbionts in the gut of a predator through metagenomics

DNA methods are useful to identify ingested prey items from the gut of predators, but reliable detection is hampered by low amounts of degraded DNA. PCR‐based methods can retrieve minute amounts of starting material but suffer from amplification biases and cross‐reactions with the predator and related species genomes. Here, we use PCR‐free direct shotgun sequencing of total DNA isolated from the gut of the harlequin ladybird Harmonia axyridis at five time points after feeding on a single pea aphid Acyrthosiphon pisum. Sequence reads were matched to three reference databases: Insecta mitogenomes of 587 species, including H. axyridis sequenced here; A. pisum nuclear genome scaffolds; and scaffolds and complete genomes of 13 potential bacterial symbionts. Immediately after feeding, multicopy mtDNA of A. pisum was detected in tens of reads, while hundreds of matches to nuclear scaffolds were detected. Aphid nuclear DNA and mtDNA decayed at similar rates (0.281 and 0.11 h−1 respectively), and the detectability periods were 32.7 and 23.1 h. Metagenomic sequencing also revealed thousands of reads of the obligate Buchnera aphidicola and facultative Regiella insecticola aphid symbionts, which showed exponential decay rates significantly faster than aphid DNA (0.694 and 0.80 h−1, respectively). However, the facultative aphid symbionts Hamiltonella defensa, Arsenophonus spp. and Serratia symbiotica showed an unexpected temporary increase in population size by 1–2 orders of magnitude in the predator guts before declining. Metagenomics is a powerful tool that can reveal complex relationships and the dynamics of interactions among predators, prey and their symbionts.

Alternative food sources and overwintering feeding behavior of the boll weevil, Anthonomus grandis boheman (coleoptera: curculionidae) underthe tropical conditions of central Brazil

The boll weevil causes serious damage to the cotton crop in South America. Several studies have been published on this pest, but its phenology and behavior under the tropical conditions prevailing in Brazil are not well-known. In this study the feeding behavior and main food sources of adult boll weevils throughout the year in Central Brazil was investigated. The digestive tract contents of insects captured in pheromone traps in two cotton fields and two areas of native vegetation (gallery forest and cerrado sensu stricto) were analyzed. The insect was captured all through the year only in the cerrado. It fed on pollen of 19 different plant families, on Pteridophyta and fungi spores and algae cysts. Simpson Index test showed that the cerrado provided greater diversity of pollen sources. In the beginning of the cotton cycle, the plant families used for pollen feeding were varied: in cotton area 1, the weevil fed on Poaceae(50%), Malvaceae and Smilacaceae (25% each); in cotton area 2 the pollen sources were Malvaceae (50%), Asteraceae (25%) and Fabaceae and Clusiaceae (25% each); in the cerrado they were Chenopodiaceae (67%) and Scheuchzeriaceae (33%). No weevils were collected in the gallery forest in this period. After cotton was harvested, the family Smilacaceae was predominant among the food plants exploited in all the study areas. These results help to explain the survivorship of adult boll weevil during cotton fallow season in Central Brazil and they are discussed in the context of behavioral adaptations to the prevailing tropical environmental conditions.

Effect of plant diversification on abundance of South American tomato pinworm and predators in two cropping systems

Several studies have demonstrated that the diversification of the agroecosystem may reduce insect pest infestation using the strategy of companion planting. We studied the effect of the presence of coriander and Gallant soldier as companion plants in the tomato crop under organic and conventional management on abundance of the tomato pests and predators. The experiment was carried out under field conditions, at Distrito Federal, Brazil, from July to October, 2004. The experimental design was of randomized blocks with three replicates in a 3 x 2 factorial arrangement [Three crop diversification levels: tomato in monoculture, tomato intercropped with coriander, and tomato intercropped with coriander and Gallant soldier; and two cropping systems: organic and conventional]. Each plot had 80 plants of the tomato and the pest-insects and predaceous arthropods were collected every week in five tomato plants/plot. Tuta absoluta (Meyr.) was the commonest pest species in both cropping systems. The tomato intercropped with coriander and Gallant soldier in organic cropping system had lower abundance and higher diversity of pests, and higher abundance and diversity of predaceous arthropods, mainly at 80 days after the tomato transplanting, coinciding with the population peak of T. absoluta (eggs and adults). The more abundant predators were spiders, lady beetles and ants. The spiders were abundant and uniformly distributed in both systems. The lady beetles appeared lately in the organic system, at the flowering season of the coriander. The ants were more abundant in the conventional systems.

The Environmental Effects of Genetically Modified Crops Resistant to Insects

Transgenic crops are currently being cultivated on a commercial scale in many countries. The area devoted to transgenic pest resistant varieties worldwide reached 13 million hectares in 2001. These varieties offer valuable benefits but also pose potential risks. Assessments of their impact on the environment are conducted before they are approved for commercial use, as required by the regulatory biosafety frameworks. In this review, we discuss the potential ecological consequences of the commercial use in agriculture of genetically modified insect resistant crops. We also discuss the impacts caused by the change in agricultural practices, and attempt to identify gaps and possible opportunities for research, considering this new technological tool. We based our analysis and comments on the current knowledge of the risks and benefits of these genetically modified insect resistant crops, within the context of traditional insect management strategies.

Dry-Season Embryonic Dormancy in Deois flavopicta (Homoptera: Cercopidae): Roles of Temperature and Moisture in Nature

Abstract A field-based experimental study examined the roles of temperature and moisture in the dry-season embryonic dormancy and postdormancy hatching of the spittlebug Deois flavopicta Stål from Brazil’s dry interior region. The results show that dormancy consists of two discrete parts: an initial period of diapause that persists from April to the beginning of July, followed by a period of postdiapause quiescence that prevails until the rainy season begins (usually October). Low temperatures during the early part of the diapause period accelerates diapause development, whereas contact with liquid water determines the timing of postdiapause hatching. Soil temperatures during June and July and the relative humidity of the soil during August and September strongly affect overwintering survival and thus are important in determining the size of the nymphal population after dormancy. The findings indicate that, like hibernation and aestivation in temperate-zone insects, dry-season dormancy in tropical insects is a dynamic state that is influenced by seasonal changes in key environmental factors.

Fatores de mortalidade na fase de ovo de Tuta absoluta em sistemas de produção orgânica e convencional de tomate

A traca-do-tomateiro Tuta absoluta (Meyrick) (Lep.: Gelechiidae) esta sujeita a fatores de mortalidade bioticos como predadores e parasitoides e fatores abioticos como agua da irrigacao e da chuva que influenciam sua dinâmica populacional. O objetivo deste trabalho foi quantificar a importância desses fatores na sobrevivencia de ovos da traca-do-tomateiro. Os experimentos foram desenvolvidos na Embrapa Hortalicas, de 1/8/2004 a 7/11/2005, em plantio de tomate e tomate consorciado em sistema orgânico e tomate em sistema convencional. As avaliacoes consistiram em: 1) coleta de ovos no campo em diferentes epocas do ciclo da cultura e sua incubacao em laboratorio ate a emergencia do parasitoide ou eclosao da lagarta; 2) exposicao de ovos sentinelas no campo por 72 horas; 3) ovos marcados e acompanhados a cada 24 horas ate eclosao das lagartas em campo. Ovos coletados no campo e incubados em laboratorio mostraram que a mortalidade por Trichogramma sp. foi de 32%. A mortalidade dos ovos que permaneceram no campo (metodologia 2 e 3), evidenciaram que o parasitismo por Trichogramma sp. foi de 12% e que os predadores e o efeito mecânico da agua produziram 36% de mortalidade dos ovos. Essa diferenca revela que a permanencia dos ovos no campo os expoe a competicao com predadores e a mortalidade causada pelo efeito mecânico da agua reduzindo o recrutamento de Trichogramma sp. Parasitoides de ovos, predadores generalistas associados a acao da agua acarretaram maior mortalidade de T. absoluta em sistemas de producao orgânica de tomate.

Movimentos de migração e dispersão de adultos da cigarrinha-das-pastagens

The effect of adults of the spittlebug (Deois flavopicta Stal) movement in their population dynamics was evaluated in pastures of Brachiaria ruziziensis in Brasilia, DF, Brazil. Plastic panels containing adesive trap were used to monitorate the movement rates. The data suggest a lack of pattern related to the geographical position of the traps. Vegetation landscapes similar to pastures fields around the study area seemed to favour the dispersion, whilst Cerrados or wood vegetation in the neighborhood inhibted insect dispersion toward this direction and increased return rate of spittlebugs to the pasture. Spittlebugs moved mainly by short, low jumping flights (bellow 1 m). A proportion of 4:1 male:female was captured in the traps, indicating that males move more than females. The movement of marked and recaptured populations was monitored with non-toxic fluorescent powder. Speed rates lower than 5 m/day was observed. Adult dispersion movement, apparently, does not contribute significantly to the loss or recruitment of individuals to populations of D. flavopicta. Consequently, there is no need to consider this movement in modeling this insect population dynamics. Migration may have a role in this dynamics except in some cases, such as outbreaks and local extinction.O efeito do movimento de adultos da cigarrinha-das-pastagens (Deois flavopicta Stal) em sua dinâmica populacional foi avaliado em pastagens de Brachiaria ruziziensis na regiao do Distrito Federal, Brasil. Foram utilizados paineis de plastico com cola adesiva para monitorar as taxas de movimentacao. Os dados sugerem a ausencia de um padrao predominante de movimentacao em relacao a posicao geografica das armadilhas. A ocorrencia de vegetacao baixa, semelhante as pastagens em volta da area estudada, aparentemente favoreceu a dispersao, ao passo que a ocorrencia de cerrados ou matas na vizinhanca inibiu o movimento nesta direcao e aumentou a taxa de retorno da cigarrinha as pastagens. O inseto se deslocou principalmente mediante saltos ou voos curtos e baixos (abaixo de 1 m). Uma proporcao aproximada de 4:1 (macho:femea) foi capturada nas armadilhas, indicando que os machos movimentam-se mais que as femeas. A velocidade media de movimentacao, de populacoes marcadas com po fluorescente atoxico e recapturadas apos periodos variaveis de liberacao, foi inferior a 5 m por dia. O movimento de dispersao de adultos nao contribui significativamente para a perda ou recrutamento de adultos em populacoes de D. flavopicta, a nao ser em casos de explosoes populacionais ou extincao local.

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.