Plant volatiles influence electrophysiological and behavioral responses of Lygus hesperus.

Previous laboratory studies have shown that the mirid Lygus hesperus is attracted to volatiles emitted from alfalfa; feeding damage increases the amounts of several of these volatiles, and visual cues can enhance attraction further. The present study tested single plant volatiles in electrophysiological and behavioral trials with L. hesperus. Electroantennogram (EAG) analyses indicated that antennae responded to most plant volatiles included in the test, and that when gender differences were observed, males usually were more responsive than females. Antennal responses to the alcohols ((E)-3-hexenol, (Z)-3-hexenol, 1-hexanol), the acetate (E)-2-hexenyl acetate, and the aldehyde (E)-2-hexenal were among the strongest. Moderate responses were observed for (E)-beta-ocimene, (E,E)-alpha-farnesene, (+/-)-linalool, and methyl salicylate. A dose dependent response was not observed for several terpenes (beta-myrcene, beta-caryophyllene, (+)-limonene, or both (R)-(+)- and (S)-(-)-alpha-pinenes). EAG responses, however, were not always consistent with behavioral assays. In Y-tube bioassays, males did not exhibit a positive behavioral response to any of the compounds tested. Instead, males were repelled by (E)-2-hexenyl acetate, (+/-)-linalool, (E,E)-alpha-farnesene, and methyl salicylate. In contrast, female L. hesperus moved upwind towards (R)-(+)-alpha-pinene, (E)-beta-ocimene, and (E,E)-alpha-farnesene, and showed a negative response towards (Z)-3-hexen-1-ol, (S)-(-)-alpha-pinene, and methyl salicylate. This study emphasizes the use of multiple approaches to better understand host plant finding in the generalist herbivore L. hesperus.

Diet selection exhibited by juvenile and adult lifestages of the omnivores Western tarnished plant bug, Lygus hesperus and tarnished plant bug, Lygus lineolaris.

Lygus hesperus Knight and Lygus lineolaris (Palisot de Beauvois) (Heteroptera: Miridae) are economically important plant bugs on many crops worldwide. However, these omnivores are also facultative predators on a wide variety of insects. This study was conducted to quantify and compare herbivory and carnivory exhibited among different lifestages of these two insect pests. The feeding activity of a total of 422 individuals was observed for 1 h each in feeding arenas containing a cotton leaf disk and copious amounts of the sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) eggs, nymphs and adults. The L. hesperus and L. lineolaris lifestages examined included adults and 3rd, 4th and 5th instar nymphs. Plant feeding occupied the majority of both species' time budget, regardless of the species or lifestage examined. There was a tendency for L. lineolaris lifestages to feed more often and for longer duration on plant tissue than L. hesperus. All lifestages of both species rarely fed on B. tabaci, but when they did, they preferred nymphs > adults > eggs. There were only a few cases where there were significant differences in predation rates and prey handling times exhibited among lifestages and between species, but juvenile L. hesperus tended to be more predaceous than juvenile L. lineolaris on whitefly nymphs and adults and 5th instar and adult L. lineolaris were significantly more herbaceous than their L. hesperus counterparts. In addition, the younger individuals of both species tended to have greater prey handling times than their older counterparts. The significance of these findings is discussed.

Lygus spp. (Heteroptera: Miridae) host-plant interactions with Lesquerella fendleri (Brassicaceae), a new crop in the arid southwest.

Lesquerella fendleri is a new crop being cultivated in the arid Southwest for the hydroxy fatty acids found in its seed oils; however, little is know about the agricultural pests that will affect the seed production of this crop or the role the crop may have as a possible source or sink for current agricultural pests in the Arizona landscape. In the early spring, lygus bugs, some of our most important agricultural pests, are normally found in relatively small numbers on weeds; however, as lesquerella production increases, it may serve as an important early-season host for lygus. Here we present results from olfactometer bioassays that showed a significant attraction by Lygus hesperus females to volatiles associated with flowering lesquerella. Headspace volatiles of flowering lesquerella were collected and identified by gas chromatography-mass spectrometry, and phenylacetaldehyde (PAA) was found to be the major component, followed by benzaldehyde and Z-3- hexenyl acetate. In the field, we examined the Lygus spp. complex, as well as the prevalence of other herbivores and select predators, and monitored their responses to unbaited sticky traps of various colors and PAA-baited green and blue sticky traps. Green, blue, and clear sticky traps captured significantly more Lygus spp. (L. elisus in particular) than opaque yellow and red traps, but PAA-baited blue and green traps did not capture more lygus than unbaited traps. Collops spp., however, were collected in higher numbers on PAA-baited traps, suggesting that this compound might provide a means of recruiting and/or retaining this particular natural enemy.

Oviposition preference of Neoleucinodes elegantalis (Guenée) (Lepidoptera: Crambidae) and rates of parasitism by Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) on Lycopersicon esculentum in São José de Ubá, RJ, Brazil / Preferência de oviposição de Neoleucinodes elegantalis (Guenée) (Lepidoptera: Crambidae) e taxas de parasitismo por Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) em Lycopersicon esculentum em São José de Ubá, RJ

Neoleucinodes elegantalis (Guenée) is one of the most important pests in several tomato growing regions of Brazil. The neonate larva enters the fruit shortly after eclosion, a characteristic that limits the effectiveness of insecticides and biological control agents. A better understanding of the cues that elicit or inhibit host-plant location and oviposition by N. elegantalis could lead to novel control strategies. Our findings indicate that N. elegantalis deposited 89 percent of its eggs on small fruits (23.1±0.95 mm), and that 76 percent of the eggs were placed on the first four basal fruits within the fruit cluster. The average number of eggs/egg mass was 2.9±0.17 (range 1-13), and approximately 70 percent of these were deposited in a single oviposition bout. The percentage of plants with one or more egg mass increased from 11.8 to 100 percent during a 10-wk monitoring period in 1996, and from 8.7 to 80 percent during a 9-wk period in 1997. At the end of the growing season in 1996, when the number of plants on which N. elegantalis eggs were found was increasing and pesticide applications were declining, the egg parasitoid Trichogramma pretiosum Riley, was observed and collected. During the last three sampling dates of 1996, parasitism rates increased from 2.4 to 28.7 percent. However, no egg parasitoids were found during the following autumn to winter growing season of 1997.

Neoleucinodes elegantalis (Guenée) é uma praga importante em diversas regiões tomaticultoras do Brasil. Logo após a eclosão, a larva penetra rapidamente no fruto, característica que limita a efetividade dos inseticidas e do controle biológico. O maior entendimento dos sinais que estimulam ou inibem a localização do hospedeiro e a oviposição por N. elegantalis permitiria o desenvolvimento de novas estratégias de controle. Observou-se que a mariposa depositou 89 por cento de seus ovos em frutos pequenos (23,1±0,95 mm) e que 76 por cento dos ovos foram colocados sobre os quatro primeiros frutos basais da penca de tomates. A média do número de ovos/massa de ovos foi de 2,9±0,17 (intervalo de 1 a 13) e aproximadamente 70 por cento desses ovos foram depositados de uma só vez. A percentagem de plantas com uma ou mais massas de ovos aumentou de 11,8 por cento para 100 por cento durante o período de dez semanas de monitoramento em 1996, e de 8,7 para 80 por cento durante o período de nove semanas de amostragem em 1997. No final da safra de 1996, quando o número de plantas contendo ovos de N. elegantalis estava aumentando e as aplicações de pesticidas estavam diminuindo, um parasitóide de ovos, Trichogramma pretiosum Riley, foi coletado. Durante as últimas três datas de amostragem de 1996, a taxa de parasitismo aumentou de 2,4 para 28,7 por cento. Entretanto, na passagem do outono para o inverno da safra de 1997, parasitóides de ovos não foram encontrados.

Estímulos Olfativos Envolvidos na Localização de Presas pelo Acaro Predador Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) em Macieiras e Plantas Hospedeiras Alternativas / Olfactory Stimuli Involved in Prey Location by Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) on Apple and Alternate Host Plants

The phytophagous mites Panonychus ulmi (Koch) and Tetranychus urticae Koch (Tetranychidae) cause severe losses in apples in southern Brazil. An alternate means of managing both species, currently under way in orchards in Fraiburgo, SC, is the use of the predatory mite Neoseiulus californicus (McGregor). To understand how this predator interacts at the olfactive level with both prey on their host plants, we studied the responses of N. californicus on apple, Malus domestica (Borkham), as well as on three of the predator's alternate winter hosts (Sida rhombifolia L., Plantago tomentosa Lamarck and Taraxacum officinale Weber), in a Y-tube olfactometer. On apple, the tests demonstrated that N. californicus responded significantly to allelochemicals associated with previously-infested leaves with or without P. ulmi or T. urticae or their associated byproducts (feces, eggs, exuviae, and webs), as well as to those associated with previously-uninfested leaves + prey and its byproducts. The predator also responded to a mixture of volatile odors from previously-uninfested apple leaves with T. urticae byproducts. In relation to the location of T. urticae by N. californicus on its alternate winter host plants, we observed that the prey byproducts are more attractive to the predator on S. rhombifolia and P. tomentosa, whereas infested leaves of T. officinale with or without prey and its byproducts did not elicit any response. These results indicate that the volatiles from the host plant, as well as those from the prey and its byproducts, serve as cues in the prey location by N. californicus. Additionally, volatiles from the flowers of the three alternate host plants were highly attractive to the predator, which suggests that this stimuli could be involved in locating pollen, another of its food sources.

Os ácaros fitófagos Panonychus ulmi (Koch) e Tetranychus urticae Koch (Tetranychidae) causam sérios prejuízos à cultura da maçã no Sul do Brasil. Uma alternativa de manejo dessas espécies, atualmente em uso em pomares de macieira de Fraiburgo, SC, é o controle biológico com o ácaro predador Neoseiulus californicus (McGregor). Visando compreender como as interações do predador com ambas as presas em suas plantas hospedeiras são intermediadas ao nível olfativo, estudaram-se as respostas do predador tanto em macieira, Malus domestica (Borkham), como em algumas plantas invasoras de pomares: Sida rhombifolia L., Plantago tomentosa Lamarck e Taraxacum officinale Weber, hospedeiras alternativas de T. urticae no inverno. As respostas foram investigadas em olfatômetro em tubo na forma de Y. Em macieira, para ambas as presas, N. californicus respondeu significativamente aos aleloquímicos emanados de folhas atacadas isoladamente ou em conjunto com a presa e/ou seus subprodutos (fezes, ovos, teias e exúvias), assim como àqueles emanados de folhas sadias com a presa e seus subprodutos. N. californicus também foi atraído por folhas sadias de macieira contendo os subprodutos de T. urticae. Em relação à localização de T. urticae nas plantas hospedeiras alternativas, verificou-se que, em S. rhombifolia e P. tomentosa, os voláteis dos subprodutos do ácaro aparentemente exercem papel atrativo preponderante, enquanto não houve resposta a nenhum dos estímulos olfativos relacionados a T. officinale. Assim, no processo de localização de P. ulmi e T. urticae por N. californicus, tanto os estímulos olfativos da presa e de seus subprodutos como aqueles emitidos pela planta atacada por estes podem funcionar como sinalizadores para o predador localizar as colônias de ácaros fitófagos. Além disto, voláteis das flores das três plantas invasoras exerceram forte atratividade ao predador, o que sugere que este estímulo está envolvido na localização de pólen, outra de ...