Reciprocal intraguild predation and predator coexistence.

Intraguild predation is a mix of competition and predation and occurs when one species feeds on another species that uses similar resources. Theory predicts that intraguild predation hampers coexistence of species involved, but it is common in nature. It has been suggested that increasing habitat complexity and the presence of alternative food may promote coexistence. Reciprocal intraguild predation limits possibilities for coexistence even further. Habitat complexity and the presence of alternative food are believed to promote coexistence. We investigated this using two species of predatory mites, Iphiseiodes zuluagai and Euseius concordis, by assessing co-occurrence in the field and on arenas differing in spatial structure in the laboratory. The predators co-occured on the same plants in the field. In the laboratory, adults of the two mites fed on juveniles of the other species, both in the presence and the absence of a shared food source, showing that the two species are involved in reciprocal intraguild predation. Adults of I. zuluagai also attacked adults of E. concordis. This suggests limited possibilities for coexistence of the two species. Indeed, E. concordis invariably went extinct extremely rapidly on arenas without spatial structure with populations consisting of all stages of the two predators and with a shared resource. Coexistence was prolonged on host plant leaves with extra food sources, but E. concordis still went extinct. On small, intact plants, coexistence of the two species was much longer, and ended with the other species, I. zuluagai, often going extinct. These results suggest that spatial structure and the presence of alternative food increase the coexistence period of intraguild predators.

Spatial-temporal distribution of phytophagous and predatory mites in the canopy of Jatropha curcas L / Distribuição espaço-temporal de ácaros fitófagos e predadores no dossel de plantas de pinhão-manso

The aim of the present study was to evaluate the spatial-temporal distribution of phytophagous and predatory mites in the canopy of Jatropha curcas L. Mite richness, diversity, and abundance were determined, and higher values were observed primarily in the top stratum. Mite population in J. curcas was higher during the rainy season. Phytophagous mites were mostly concentrated in the top stratum, and Brevipalpus sp. was the most abundant. Predatory mites from the family Phytoseiidae presented the highest richness and diversity, and Amblydromalus zannoui was the most abundant species. The present results indicate seasonal population dynamics for both predatory and phytophagous mites on J. curcas.(AU)

O presente estudo teve por objetivo avaliar a distribuição espaço-temporal de ácaros fitófagos e predadores no dossel de plantas de pinhão-manso. Parâmetros de riqueza, diversidade e abundância de ácaros foram determinados. Os resultados deste estudo demonstram que maiores valores de riqueza, diversidade e abundância de ácaros foram observados principalmente no estrato apical e que os níveis populacionais desses artrópodes em plantas de pinhão-manso são mais expressivos na estação chuvosa. Os ácaros fitófagos concentram-se distribuídos principalmente no estrato apical, sendo Brevipalpus sp. a espécie mais abundante. Ácaros predadores da família Phytoseiidae foram aqueles de maior riqueza e diversidade, sendo o ácaro predador Amblydromalus zannoui o mais abundante. Os resultados obtidos neste trabalho sugerem uma dinâmica sazonal tanto para populações de ácaros predadores quanto para ácaros fitófagos em pinhão-manso.(AU)

Glyphosate sub-lethal toxicity to non-target organisms occurring in Jatropha curcas plantations in Brazil.

Weed management in physic nut plantations has generally been performed by spraying the herbicide glyphosate. However, the effects of glyphosate on non-target organisms present in the crop system are unknown. Here, we evaluated the toxicity of glyphosate (Roundup Transorb(®)) against the pest species Polyphagotarsonemus latus (Acari: Tarsonemidae) and Tetranychus bastosi (Acari: Tetranychidae) which can be exposed by drift. These mites are considered pests of the physic nut; however, they can also feed and reside on weeds associated with the crop, serving as food sources for predatory mites. When subjected to residue (by ingestion of sap of treated plants), and direct contact to glyphosate, P. latus reproduction was affected but T. bastosi was affected only by the residual effect. Although the herbicide caused a reduction in the number of eggs laid by the females of both pest mites, it is suggested that sublethal effects of glyphosate stimulates oviposition of P. latus and T. bastosi: both species displayed higher reproductive rates when exposed to 0.36 kg ha(-1) of the herbicide. We conclude that glyphosate negatively affects the arthropod herbivores studied and we discuss possible implications on their biological control in Jatropha curcas plantations.

Seasonal variation in the populations of Polyphagotarsonemus latus and Tetranychus bastosi in physic nut (Jatropha curcas) plantations.

Studies on the seasonal variation of agricultural pest species are important for the establishment of integrated pest control programs. The seasonality of pest attacks on crops is affected by biotic and abiotic factors, for example, climate and natural enemies. Besides that, characteristics of the host plant, crop management, location and the pests' bioecology also affect this seasonality. The mites Polyphagotarsonemus latus (Prostigmata: Tarsonemidae) and Tetranychus bastosi (Prostigmata: Tetranychidae) are the most important pests in the cultivation of physic nut, Jatropha curcas (Euphorbiaceae). All parts of J. curcas can be used for a wide range of purposes. In addition many researchers have studied its potential for use as neat oil, as transesterified oil (biodiesel), or as a blend with diesel. However studies about physic nut pests have been little known. The objective of this study was to assess the seasonal variation of P. latus and T. bastosi in physic nut. This study was conducted at three sites in the state of Tocantins, Brazil. We monitored climatic elements and the densities of the two mite species and of their natural enemies for a period of 2 years. Attack by P. latus occurred during rainy seasons, when the photoperiod was short and the physic nut had new leaves. In contrast, attack by T. bastosi occurred during warmer seasons with longer photoperiods and stronger winds. Populations of both mites and their natural enemies were greater in sites with greater plant diversity adjacent to the plantations. The predators found in association with P. latus and T. bastosi were Euseius concordis (Acari: Phytoseiidae), spiders, Stethorus sp. (Coleoptera: Coccinellidae) and Chrysoperla sp. (Neuroptera: Chrysopidae).

Weed management practices affect the diversity and relative abundance of physic nut mites.

Crop management practices determine weed community, which in turn may influence patterns of diversity and abundance of associated arthropods. This study aimed to evaluate whether local weed management practices influence the diversity and relative abundance of phytophagous and predatory mites, as well as mites with undefined feeding habits--of the families Oribatidae and Acaridae--in a physic nut (Jatropha curcas L.) plantation subjected to (1) within-row herbicide spraying and between-row mowing; (2) within-row herbicide spraying and no between-row mowing; (3) within-row weeding and between-row mowing; (4) within-row weeding and no between-row mowing; and (5) unmanaged (control). The herbicide used was glyphosate. Herbicide treatments resulted in higher diversity and relative abundance of predatory mites and mites with undefined feeding habit on physic nut shrubs. This was probably due to the toxic effects of the herbicide on mites or to removal of weeds. Within-row herbicide spraying combined with between-row mowing was the treatment that most contributed to this effect. Our results show that within-row weeds harbor important species of predatory mites and mites with undefined feeding habit. However, the dynamics of such mites in the system can be changed according to the weed management practice applied. Among the predatory mites of the family Phytoseiidae Amblydromalus sp. was the most abundant, whereas Brevipalpus phoenicis was the most frequent phytophagous mite and an unidentified oribatid species was the most frequent mite with undefined feeding habit.

Population dynamics of Aceodromus convolvuli (Acari: Mesostigmata: Blattisociidae) on spontaneous plants associated with Jatropha curcas in central Brazil.

Spontaneously growing plants are commonly considered competitors of cultivated plants. Owing to the lack of specificity of many arthropods, spontaneous plants may be attacked by the same arthropods that attack cultivated plants and they may also harbor natural enemies of organisms harmful to cultivated plants. Aceodromus convolvuli Muma (Blattisociidae) has been reported recently in relatively large numbers in Tocantins state, central Brazil, mostly on Helicteres guazumifolia Kunth (Malvaceae). Very little has been reported about the population dynamics of blattisociid mites under field conditions. The objective of this work was to study the population dynamics of A. convolvuli in Gurupi, Tocantins state, to evaluate its possible interaction with associated mites. Monthly samples were taken from leaves of the 11 most abundant and frequent spontaneous plants in a Jatropha curcas L. (Euphorbiaceae) plantation. About 96.5 % of the specimens of A. convolvuli were collected in the rainy season. The patterns of variation of the population of A. convolvuli and of predators belonging to the family Phytoseiidae were similar, but A. convolvuli was much more numerous than all phytoseiid specimens combined. Highly significant correlations were observed between A. convolvuli densities and relative humidity or diversity of spontaneous plants. When only mites on H. guazumifolia were considered, highly significant correlation was also observed between densities of A. convolvuli and of mites of the family Tetranychidae. The results suggested that A. convolvuli could be a predator of tenuipalpid and/or tetranychid mites. Studies about its biology are needed to determine its preferred food sources and potential as biological control agent.

Functional response of Euseius concordis to densities of different developmental stages of the cassava green mite.

Both prey density and developmental stage of pests and natural enemies are known to influence the effectiveness of biological control. However, little is known about the interaction between prey density and population structure on predation and fecundity of generalist predatory mites. Here, we evaluated the functional response (number of prey eaten by predator in relation to prey density) of adult females and nymphs of the generalist predatory mite Euseius concordis to densities of different developmental stages of the cassava green mite Mononychellus tanajoa, as well as the fecundity of adult females of the predator. We further assessed the instantaneous rate of increase, based on fecundity and mortality, of E. concordis fed on eggs, immatures and adults of M. tanajoa. Overall, nymphs and adults of E. concordis feeding on eggs, immatures and females of M. tanajoa had a type III functional response curve suggesting that the predator increased prey consumption rate as prey density increased. Both nymphs and adult females of the predator consumed more eggs than immatures of M. tanajoa from the density of 20 items per leaf disc onwards, revealing an interaction between prey density and developmental stage in the predatory activity of E. concordis. In addition, population growth rate was higher when the predator fed on eggs and immatures in comparison with females. Altogether our results suggest that E. concordis may be a good candidate for the biological control of M. tanajoa populations. However, the efficiency of E. concordis as a biological control agent of M. tanajoa is contingent on prey density and population structure.

Sampling plans for pest mites on physic nut.

The starting point for generating a pest control decision-making system is a conventional sampling plan. Because the mites Polyphagotarsonemus latus and Tetranychus bastosi are among the most important pests of the physic nut (Jatropha curcas), in the present study, we aimed to establish sampling plans for these mite species on physic nut. Mite densities were monitored in 12 physic nut crops. Based on the obtained results, sampling of P. latus and T. bastosi should be performed by assessing the number of mites per cm(2) in 160 samples using a handheld 20× magnifying glass. The optimal sampling region for T. bastosi is the abaxial surface of the 4th most apical leaf on the branch of the middle third of the canopy. On the abaxial surface, T. bastosi should then be observed on the side parts of the middle portion of the leaf, near its edge. As for P. latus, the optimal sampling region is the abaxial surface of the 4th most apical leaf on the branch of the apical third of the canopy on the abaxial surface. Polyphagotarsonemus latus should then be assessed on the side parts of the leaf's petiole insertion. Each sampling procedure requires 4 h and costs US$ 7.31.

Life history of Amblyseius herbicolus (Chant) (Acari: Phytoseiidae) on coffee plants.

The predaceous mite Amblyseius herbicolus (Chant) is the second most abundant phytoseiid on coffee plants (Coffea arabica L), after Euseius alatus DeLeon, in Lavras, MG, Brazil, associated to the vector of the coffee ring spot virus, Brevipalpus phoenicis (Geijskes) (Acari: Tenuipalpidae). Its life history was studied taking into account biological aspects, life table, predatory activity and functional and numerical responses in relation to the density of the prey. The adult female has longevity of 38 days when supplied with B. phoenicis. The intrinsic rate of population increase (r m) was 0.150 and the mean generation time (T) 25.3 days. The population doubles every 4.6 days. Thirty mites B. phoenicis /3-cm diameter coffee leaf arenas were separately offered to one specimen of each predator phase. Adult females were more efficient in killing all developmental phases of B. phoenicis, followed by the nymph stages. For the functional and numerical responses studies, from 0.14 to 42.3 immature specimens of the prey /cm(2) of arena were submitted to the predator, the preferred phase for predation. Predation and the oviposition of A. herbicolus increased with increasing prey density, with a positive and highly significant correlation. Regression analysis suggests a functional type II response, with a maximum daily predation near 35 B. phoenicis /cm(2) /one adult female.

Life history of Amblyseius herbicolus (Chant) (Acari: Phytoseiidae) on coffee plants

The predaceous mite Amblyseius herbicolus (Chant) is the second most abundant phytoseiid on coffee plants (Coffea arabica L), after Euseius alatus DeLeon, in Lavras, MG, Brazil, associated to the vector of the coffee ring spot virus, Brevipalpus phoenicis (Geijskes) (Acari: Tenuipalpidae). Its life history was studied taking into account biological aspects, life table, predatory activity and functional and numerical responses in relation to the density of the prey. The adult female has longevity of 38 days when supplied with B. phoenicis. The intrinsic rate of population increase (r m) was 0.150 and the mean generation time (T) 25.3 days. The population doubles every 4.6 days. Thirty mites B. phoenicis /3-cm diameter coffee leaf arenas were separately offered to one specimen of each predator phase. Adult females were more efficient in killing all developmental phases of B. phoenicis, followed by the nymph stages. For the functional and numerical responses studies, from 0.14 to 42.3 immature specimens of the prey /cm² of arena were submitted to the predator, the preferred phase for predation. Predation and the oviposition of A. herbicolus increased with increasing prey density, with a positive and highly significant correlation. Regression analysis suggests a functional type II response, with a maximum daily predation near 35 B. phoenicis /cm² /one adult female.

O ácaro predador Amblyseius herbicolus (Chant) é o segundo fitoseídeo mais abundante em cafeeiro (Coffea arabica L.), após Euseius alatus DeLeon, na região de Lavras, MG, associado ao vetor do vírus da mancha-anular, Brevipalpus phoenicis (Geijskes) (Acari: Tenuipalpidae). Sua história de vida foi estudada levando em conta aspectos biológicos, tabela de vida, atividade predatória e respostas funcional e numérica em função da densidade de presa. Foi constatada longevidade de 38 dias para fêmeas adultas quando alimentadas com B. phoenicis. A estimativa da capacidade inata de crescimento da população (r m) foi 0,150 e a duração média de uma geração (T) 25,3 dias. A população dobrou a cada 4,6 dias. Trinta ácaros B. phoenicis /arena de folha de cafeeiro (3 cm de diâmetro) foram oferecidos separadamente para um espécime de cada fase do ácaro predador. Fêmeas adultas foram mais eficientes na predação de todas as fases do desenvolvimento do ácaro-presa, seguidas das fases ninfais. Para o estudo das respostas funcional e numérica, a presa foi oferecida nas densidades de 0,14 a 42,3 formas imaturas de B. phoenicis /cm² de arena, por serem preferidas para predação. A predação e oviposição de A. herbicolus aumentam com o aumento da densidade de presa, com uma correlação positiva e altamente significativa. A análise de regressão realizada sugere uma resposta funcional do tipo II, com uma predação máxima diária de aproximadamente 35 B. phoenicis /cm² /fêmea adulta.

Effect of prey density on the functional and numerical responses of two species of predaceous mites (Acari: Phytoseiidae) / Efeito da densidade de presa nas respostas funcional e numérica de duas espécies de ácaros predadores (Acari: Phytoseiidae)

Ácaros da família Phytoseiidae são os inimigos naturais de ácaros-praga mais importantes e estudados. Uma questão freqüentemente levantada é se os fitoseídeos podem reduzir altas densidades de ácaros fitófagos a baixos níveis. Os estudos da resposta funcional e numérica podem contribuir para responder essa pergunta. O objetivo deste trabalho foi avaliar o potencial de predação de Iphiseiodes zuluagai Denmark e Muma e Euseius alatus DeLeon (Acari: Phytoseiidae) como agentes de controle biológico do ácaro fitófago Brevipalpus phoenicis (Geijskes) (Acari: Tenuipalpidae), vetor do vírus da leprose-dos-citros e da mancha-anular do cafeeiro. Bioensaios foram realizados em laboratório. Fêmeasadultas de cada predador foram individualizadas em arenas de folha de citros com 3 cm de diâmetro. Fases imaturas de B. phoenicis foram oferecidas, como presas, nas seguintes quantidades/arena: 1, 2, 5, 10, 20, 30 e 35 (com sete repetições), 45 (quatro repetições), 55 (três repetições) e 70, 100, 125, 200 e 300 (duas repetições). O número de presas mortas e de ovos colocados pelo predador foram avaliadosa cada 24h, durante oito dias. As presas mortas foram diariamente substituídas por novas presas. Para ambos os ácaros predadores foi constatada uma correlação positiva e altamente significativa entre o número de presas oferecidas e mortas. A oviposição média diária também aumentou em função donúmero de presas mortas. Nas densidades mais baixas, E. alatus matou mais B. phoenicis do que I. zuluagai, e o contrário foi observado nas densidades mais altas. É possível que E. alatus possa reduzir a população de B. phoenicis mesmo em baixas densidades do ácaro fitófago, e que I. zuluagai possafazer o mesmo nas mais altas. O fato de E. alatus necessitar de menos presas que I. zuluagai sugere que sua sobrevivência possa ser maior do que a de I. zuluagai sob baixa densidade de presa.

Phytoseiidae mites are the most important and studied natural enemies of pest mites. A question frequently raised is whether phytoseiid may reduce high densities of phytophagous mites.Studies of functional and numerical responses may help to answer this question. The aim of this work was to evaluate the potential predation success of Iphiseiodes zuluagai Denmark and Muma and Euseius alatus DeLeon (Acari: Phytoseiidae) on Brevipalpus phoenicis (Geijskes) (Acari: Tnuipalpidae), vectorof the citrus leprosis and the coffee ringspot viruses. Bioassays were performed in the laboratory. Adult females of each predator were isolated in arenas made with citrus leaves (3-cm diameter). Immature stages of B. phoenicis were offered as prey, at the following numbers/arena: 1, 2, 5, 10, 20, 30 and 35 (seven replicates), 45 (four replicates), 55 (three replicates) and 70, 100, 125, 200 and 300 (tworeplicates). The number of killed prey and of eggs laid by the predators was evaluated every 24h, during eight days. Killed prey was replaced daily by new prey. For both predatory mites, a positive and highly significant correlation was found between the numbers of prey offered and killed. The average daily oviposition rate also increased with the number of killed prey. At the lower densities, E. alatuskilled and ate more B. phoenicis than I. zuluagai. The opposite was observed at the highest densities. It is possible that E. alatus can reduce B. phoenicis population even at low prey densities, and I. zuluagai can do the same also at high densities. The fact that E. alatus requires less prey than I. zuluagai suggests that its survivorship may be higher than that of I. zuluagai at low prey densities.