Jacquelyn L. Blackmer

Behavioral response of Lygus hesperus to conspecifics and headspace volatiles of alfalfa in a Y-tube olfactometer.

The western tarnished plant bug, Lygus hesperus Knight, feeds and develops on a variety of weeds in the spring, with later generations moving to alfalfa and cotton where severe damage to reproductive structures can occur. A synthetic attractant for monitoring or mass-trapping L. hesperus, or the identification of potential attractants for natural enemies, would be useful tools for integrated pest management programs. Studies investigated the response of naive and experienced fifth-instar and adult L. hesperus to odors associated with conspecifics and alfalfa, Medicago sativa L. Fifth-instar L. hesperus responded to all plant/insect combinations, whereas female L. hesperus only responded preferentially to vegetative and flowering alfalfa where conspecifics had fed for 24–72 hr, and to vegetative alfalfa where conspecifics were added approximately 30 min before the test began. Males were not attracted to headspace volatiles from any of the alfalfa treatments. Analysis of headspace volatiles showed that (E)-2-hexanal, (Z)-3-hexen-1-ol, α-pinene, (Z)-3-hexenyl acetate, (E)-2-hexenyl acetate, limonene, (Z)-ocimene, (E)-β-ocimene, linalool, (3E)-4,8-dimethyl-1,3,7-nonatriene, and (E, E)-α-farnesene are emitted from both vegetative and flowering alfalfa. Indole and (3E, 7E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene were only detected in flowering alfalfa. Damage to alfalfa by L. hesperus increased emissions of (Z)-ocimene, (E)-β-ocimene, (E)-β-caryophyllene, and (E, E)-α-farnesene, while β-pinene, myrcene, methyl salicylate, and (3E, 7E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene were only detected from damaged plants. Thus, individual or mixtures of these alfalfa volatiles may be useful as attractants for capturing nymphs and adult females of L. hesperus in the field.

Visual cues enhance the response of Lygus hesperus (Heteroptera: Miridae) to volatiles from host plants

Abstract Studies were conducted to examine the behavioral response of fifth-instar and adult Lygus hesperus Knight (Heteroptera: Miridae) to odors associated with a host plant (alfalfa) when presented singly or in combination with a visual plant cue (530 nm, green light-emitting diode [LED]). Bioassays were conducted in a modified Y-tube olfactometer, where incoming air was filtered and humidified before passing through chambers that held plant/conspecific treatments. A LED, placed behind an organdy screen at the end of one arm of the Y-tube, simulated a visual plant cue. In agreement with our previous findings, fifth-instar and adult female L. hesperus were attracted to plant/conspecific odor combinations, but adult males were not. Independently, the LED also was attractive to immature and adult female L. hesperus, and for all life stages, a much larger percentage of the bugs walked to the extreme end of the Y-tube when the visual cue was present. When visual and volatile cues were presented simultaneously, responses by both immature and adult (male and female) L. hesperus were significantly enhanced. Plant/conspecific treatments that had been marginally acceptable when only volatile stimuli were available showed the greatest enhancement in response with the addition of the visual cue. Presentation of visual and volatile cues together led to a mean increase in the percentage of bugs that walked to the extreme end of the Y-tube (nymphs, 36.6%; females, 23.4%; males, 26.1%). Results are discussed in terms of stage-specific responses and how these behavioral differences will likely play a role in developing effective trapping and monitoring systems for this important pest.

Comparative Dispersal of Homalodisca coagulata and Homalodisca liturata (Homoptera: Cicadellidae)

Abstract California’s viticulture and ornamental industries have suffered significant losses since the introduction of Homalodisca coagulata (Say), an important vector of the Pierce’s disease bacterium. A better understanding of the factors that influence the dispersal of H. coagulata, as well as other native sharpshooters could enhance our ability to institute areawide management programs. Studies were conducted to establish the validity of an immunoglobulin G (IgG) protein marker for sharpshooter dispersal studies, to compare the dispersal of H. coagulata with that of a native sharpshooter Homalodisca liturata Ball, and to develop a better understanding of the factors that influence their dispersal. Field trials showed that the marker remained detectable for at least 19 d and did not affect sharpshooter survival. Four concentrations (0.04, 0.2, 1, and 5 mg/ml) and two different IgG markers (chicken and rabbit) were effective for marking sharpshooters. In mass-mark-recapture studies, ≈95% of the marked insects flew during the releases and the timing of flight initiation was similar for H. coagulata and H. liturata. Mean wind speeds >3 m s−1 were associated with a decline in flight initiation for both species. Most sharpshooters were trapped at heights below 4.2 m, and based on sex ratio comparisons, traps were equally attractive to males and females. Regression analyses of recapture data and a diffusion model were used to assess and compare sharpshooter dispersal. The majority (95%) of H. coagulata and H. liturata were recaptured within 90 and 155 m of the release site, respectively.

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)-β-ocimene, (E,E)-α-farnesene, (±)-linalool, and methyl salicylate. A dose dependent response was not observed for several terpenes (β-myrcene, β-caryophyllene, (+)-limonene, or both (R)-(+)- and (S)-(−)-α-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)-α-farnesene, and methyl salicylate. In contrast, female L. hesperus moved upwind towards (R)-(+)-α-pinene, (E)-β-ocimene, and (E,E)-α-farnesene, and showed a negative response towards (Z)-3-hexen-1-ol, (S)-(−)-α-pinene, and methyl salicylate. This study emphasizes the use of multiple approaches to better understand host plant finding in the generalist herbivore L. hesperus.

Tethered and Untethered Flight by Lygus hesperus and Lygus lineolaris (Heteroptera: Miridae)

Abstract We compared the flight behavior of Lygus hesperus Knight and Lygus lineolaris (Palisot de Beauvois) relative to age, sex, and time of day by using tethered (flight mills) and untethered flight (vertical flight chamber) assays. Both species and sexes initiated flights throughout the day, and flight mill assays recorded flights throughout the night. For both species and flight systems, most flights were <5 min in duration, with longest flights occurring from 1 to 3 wk of age. Number of flights and flight duration were influenced by age and sex for tethered individuals and by sex for untethered individuals. Species differences were less apparent, but tethered L. lineolaris had more sustained flights (individual flights >5 min) that were of longer cumulative duration compared with L. hesperus. The longest flights were obtained with flight mills and were 17–18 times longer than the longest flight (22 min) in the flight chamber. Determination of flight periodicity, throughout the day and night, was only possible for tethered insects, and females exhibited more distinct periodicities for sustained flights than males. For L. hesperus females, sustained flights followed a diurnal to crepuscular periodicity, whereas sustained flights by L. lineolaris females were nocturnal. No significant correlations were found between egg load and any of the flight parameters when grouped by species, but there was a positive correlation between the number of spermatophores and several of the flight parameters for female L. hesperus. In the vertical flight chamber, takeoffs began at low light levels and were always higher for L. lineolaris than L. hesperus. Rates of climb toward the skylight cue were ≈50 cm/s, indicating a capacity for strong, self-directed flight by both species.

Dispersal of Homalodisca vitripennis (Homoptera: Cicacellidae) from a Point Release Site in Citrus

Abstract The glassy-winged sharpshooter, Homalodisca vitripennis (Germar), is an important vector of Xylella fastidiosa Wells et al., a bacterium that has caused substantial losses in the viticulture and ornamental industries in California. Area-wide management programs have been implemented to reduce vector populations and limit the spread of this disease. However, there is still a lack of information on the factors that influence this insect’s movement within and between host crops. In this study, we used mark-release-recapture (MRR) to examine the dispersal of H. vitripennis in a mature orange grove, Citrus sinensis Osbeck. Insects were doubly marked with chicken or rabbit immunoglobulin G (IgG) proteins and fluorescent dusts to enable monitoring over several weeks. Our objectives were to examine the reliability of IgG protein markers relative to fluorescent dusts, determine how sharpshooter movement differed in this landscape relative to a previous study, and develop a better understanding of the biotic and abiotic factors that could influence sharpshooter dispersal. Linear regressions of recapture data with a diffusion model provided significant fits to the data in five of six releases. Recapture data were fitted to a diffusion model, and based on parameters generated with the model, estimated dispersal distances for H. vitripennis at 72 h showed 50 and 99% remained within annuli of 31 and 150 m from the release site, respectively. Flight activity was greatest between 1000 and 1400 hours, and no flights occurred between 2200 and 0600 hours. Only temperature explained a significant amount of the variability in recapture of H. vitripennis, with sharpshooters rarely trapped below 18°C.

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

Neoleucinodes elegantalis (Guenee) 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% of its eggs on small fruits (23.1±0.95 mm), and that 76% 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% 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% during a 10-wk monitoring period in 1996, and from 8.7 to 80% 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%. However, no egg parasitoids were found during the following autumn to winter growing season of 1997.

Eclosion time and larval behavior of the tomato fruit borer, Neoleucinodes elegantalis (Guenée) (Lepidoptera: Crambidae)

In several regions of Brazil, Neoleucinodes elegantalis (Guenee) is one of the most serious tomato pests. The moth lays eggs on the calyx or developing fruit, and shortly after eclosion larvae penetrate into the fruit, where they remain until pupation. Once larvae have entered the fruits, insecticides and biological control agents are relatively ineffective. Because N. elegantalis is most susceptible to conventional treatments when the larvae are outside the host tissues (or fruit), it would be advantageous to know the time required for egg development and the length of time that the larvae spend on the surface of the fruit. To answer these questions detailed behavioral studies were untaken. Eggs were collected from the field and maintained in an environmental chamber at 20°C, 75 ± 5% R.H., and a 12L:12D photoperiod. The time of egg eclosion was recorded with a video camera, whereas larval behavior and time required to enter the fruit were determined by direct observations. The majority of eggs (93%) hatched within the first two hours after the beginning of photophase. Larvae spent 51.1 ± 31.1 (mean ± SEM) min on the surface of the fruits. Once a suitable site was identified, larvae required an additional 23.8 ± 19.4 min to completely enter the fruit. Eighty-six percent of the larvae were successful in penetrating the fruit. Of the larvae that bored into the fruit, 42% selected the upper portion, 18% selected the middle portion, and 40% selected the lower portion.

Lygus spp. (Heteroptera: Miridae) Host–Plant Interactions with Lesquerella fendleri (Brassicaceae), a New Crop in the Arid Southwest

ABSTRACT 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.

Factors Affecting Egg Hatch, Development, and Survival of Bemisia argentifolii (Homoptera: Aleyrodidae) Reared on an Artificial Feeding System

Abstract Improvements in the way Bemisia argentifolii Bellows & Perring is managed have led to reduced whitefly populations in the southwest United States. However, the potential of the silverleaf whitefly to develop new biotypes, as well as its apparently increasing role in virus transmission, makes it a persistent threat in many parts of the world. Characteristics such as biotype formation and vector competency are at least partially explained by the host range of B. argentifolii. Consequently, a better understanding of the factors that play a role in the host acceptance process and subsequent development of this pest could lead to novel control strategies. Here we used a newly developed artificial feeding system that consists of a polycarbonate chamber, equipped with a Teflon membrane, and filled with a sterilized artificial diet, to determine how biotic and abiotic factors influenced egg hatch, crawler establishment, and development of B. argentifolii. Egg age significantly influenced hatch rates, and to a lesser extent survival and development of nymphs reared on the artificial diet. Five- to six-day-old eggs had higher hatch rates, and nymphs survived longer and developed faster than nymphs from younger or older eggs. There were negative associations between the number of eggs placed on the membranes and both hatch rate and establishment of crawlers. Eggs oviposited on and then subsequently removed from plants held under long-day conditions (14:10 [L:D] h) or high light intensity (≈36,000 lux) had higher hatch rates than eggs oviposited under short-day conditions (10:14 [L:D] h) or low light intensity (≈11,000 lux). Long-day conditions during oviposition also significantly enhanced survival of nymphs through day 20 and developmental rate for day 6 counts. Light intensity, at least for the range tested here, did not significantly affect development or survival of whitefly nymphs.