sampling-for-estimating-frankliniella-species-flower-thrips-orius

Sampling for Estimating <em>Frankliniella</em> Species Flower Thrips and <em>Orius</em> Species Predators in Field Experiments

The western flower thrips, Frankliniella occidentalis (Pergande), is a polyphagous pest that has been spread worldwide. The extensive use of insecticides ...

University of Florida

The redbay ambrosia beetle, Xyleborus glabratus, is an invasive wood-boring beetle that has become established in the southeastern United States. The beetle transmits the causal pathogen of lethal laurel wilt to susceptible host trees, which include redbay, an important forest community species, and avocado, a valuable food crop. By examining odors of redbay wood, we developed an artificial lure that captured X. glabratus in redbay forests. Eucalyptol was a critical component of the blend for beetle attraction, and eucalyptol alone in large quantities attracted X. glabratus. Furthermore, eucalyptol stimulated boring by X. glabratus into paper arenas. The results suggest that eucalyptol contributes to host selection behavior of X. glabratus and may be useful for management of this pathogen vector. 

Eucalyptol is an attractant of the Redbay ambrosia beetle, Xyleborus glabratus.

The redbay ambrosia beetle, Xyleborus glabratus, is an important pest of redbay (Persea borbonia) and swamp bay (P. palustris) trees in forests of the southeastern USA. It is also a threat to commercially grown avocado. The beetle is attracted to host wood volatiles, particularly sesquiterpenes. Contrary to other ambrosia beetles that attack stressed, possibly pathogen-infected, and dying trees, X. glabratus readily attacks healthy trees. To date little is known about the role of leaf volatiles in the host selection behavior and ecology of X. glabratus. To address this question, an olfactometer bioassay was developed to test the behavioral response of X. glabratus to plant leaf volatiles. We found that X. glabratus was attracted to the leaf odors of their hosts, redbay and swamp bay, with no attraction to a non-host tree tested (live oak, Quercus virginiana), which served as a negative control. Gas chromatography-mass spectrometry (GS/MS) analysis of leaves revealed the absence of sesquiterpenes known to be attractive to X. glabratus and present in host wood, suggesting that additional leaf-derived semiochemicals may serve as attractants for this beetle. An artificial blend of chemicals was developed based on GC/MS analyses of leaf volatiles and behavioral assays. This blend was attractive to X. glabratus at a level that rivaled currently used lures for practical monitoring of this pest. This synthetic redbay leaf blend also was tested in the field. Baited traps captured more X. glabratus than unbaited controls and equivalently to manuka oil lures. We hypothesize that leaf volatiles may be used by X. glabratus as an additional cue for host location. 

Attraction of Redbay Ambrosia Beetle, Xyleborus Glabratus, To Leaf Volatiles of its Host Plants in North America.

The spread of vector-transmitted pathogens relies on complex interactions between host, vector and pathogen. In sessile plant pathosystems, the spread of a pathogen highly depends on the movement and mobility of the vector. However, questions remain as to whether and how pathogen-induced vector manipulations may affect the spread of a plant pathogen. Here we report for the first time that infection with a bacterial plant pathogen increases the probability of vector dispersal, and that such movement of vectors is likely manipulated by a bacterial plant pathogen. We investigated how Candidatus Liberibacter asiaticus (CLas) affects dispersal behavior, flight capacity, and the sexual attraction of its vector, the Asian citrus psyllid (Diaphorina citri Kuwayama). CLas is the putative causal agent of huanglongbing (HLB), which is a disease that threatens the viability of commercial citrus production worldwide. When D. citri developed on CLas-infected plants, short distance dispersal of male D. citri was greater compared to counterparts reared on uninfected plants. Flight by CLas-infected D. citri was initiated earlier and long flight events were more common than by uninfected psyllids, as measured by a flight mill apparatus. Additionally, CLas titers were higher among psyllids that performed long flights than psyllid that performed short flights. Finally, attractiveness of female D. citri that developed on infected plants to male conspecifics increased proportionally with increasing CLas bacterial titers measured within female psyllids. Our study indicates that the phytopathogen, CLas, may manipulate movement and mate selection behavior of their vectors, which is a possible evolved mechanism to promote their own spread. These results have global implications for both current HLB models of disease spread and control strategies. 

Infection of an Insect Vector with a Bacterial Plant Pathogen Increases Its Propensity for Dispersal.

The Asian citrus psyllid, Diaphorina citri Kuwayama, is the vector of the bacterial pathogen, Candidatus Liberibacter asiaticus, which is the causal agent of huanglongbing (HLB) in the United States. Both short-range and long-range dispersal of D. citri adults affect the spread of HLB; however, little is known about the long-range dispersal capabilities of D. citri in the field or the seasonality of flight behavior. In the present study, an in situ protein marking technique was used to determine the dispersal of D. citri by trapping marked adults under natural field conditions. D. citri movement from abandoned citrus groves to adjacent managed citrus groves was greatest during the spring and summer months and decreased significantly during the colder months (September-March). D. citri were able to traverse potential geographic barriers such as roads and fallow fields. In an experiment conducted to determine long-range dispersal capacity in the absence of severe weather events, D. citri were able to disperse at least 2 km within 12 d. Wind direction was not correlated with the number of marked psyllids captured, indicating substantial flight capability by D. citri. Finally, the number of marked psyllids captured increased with the density of emerging young leaves on surrounding trees. The results confirm that abandoned citrus groves in Florida serve as reservoirs for D. citri, which can disperse across long distances despite geographical barriers. 

Seasonal Movement Patterns and Long-Range Dispersal of Asian Citrus Psyllid in Florida Citrus.

Although specialist herbivorous insects are guided by innate responses to host plant cues, host plant preference may be influenced by experience and is not dictated by instinct alone. The effect of learning on host plant preference was examined in the Asian citrus psyllid, Diaphorina citri; vector of the causal agent of citrus greening disease or huanglongbing. We investigated: a) whether development on specific host plant species influenced host plant preference in mature D. citri; and b) the extent of associative learning in D. citri in the form of simple and compound conditioning. Learning was measured by cue selection in a 2-choice behavioral assay and compared to naïve controls. Our results showed that learned responses in D. citri are complex and diverse. The developmental host plant species influenced adult host plant preference, with female psyllids preferring the species on which they were reared. However, such preferences were subject to change with the introduction of an alternative host plant within 24-48 hrs, indicating a large degree of experience-dependent response plasticity. Additionally, learning occurred for multiple sensory modalities where novel olfactory and visual environmental cues were associated with the host plant. However, males and females displayed differing discriminatory abilities. In compound conditioning tasks, males exhibited recognition of a compound stimulus alone while females were capable of learning the individual components. These findings suggest D. citri are dynamic animals that demonstrate host plant preference based on developmental and adult experience and can learn to recognize olfactory and visual host plant stimuli in ways that may be sex specific. These experience-based associations are likely used by adults to locate and select suitable host plants for feeding and reproduction and may suggest the need for more tailored lures and traps, which reflect region-specific cultivars or predominate Rutaceae in the area being monitored. 

The Influence of Learning on Host Plant Preference in a Significant Phytopathogen Vector, Diaphorina citri.

Plant pathogens can manipulate the odor of their host; the odor of an infected plant is often attractive to the plant pathogen vector. It has been suggested that this odor-mediated manipulation attracts vectors and may contribute to spread of disease; however, this requires further broad demonstration among vector-pathogen systems. In addition, disruption of this indirect chemical communication between the pathogen and the vector has not been attempted. We present a model that demonstrates how a phytophathogen (Candidatus Liberibacter asiaticus) can increase its spread by indirectly manipulating the behavior of its vector (Asian citrus psyllid, Diaphorina citri Kuwayama). The model indicates that when vectors are attracted to pathogen-infected hosts, the proportion of infected vectors increases, as well as, the proportion of infected hosts. Additionally, the peak of infected host populations occurs earlier as compared with controls. These changes in disease dynamics were more important during scenarios with higher vector mortality. Subsequently, we conducted a series of experiments to disrupt the behavior of the Asian citrus psyllid. To do so, we exposed the vector to methyl salicylate, the major compound released following host infection with the pathogen. We observed that during exposure or after pre-exposure to methyl salicylate, the host preference can be altered; indeed, the Asian citrus psyllids were unable to select infected hosts over uninfected counterparts. We suggest mechanisms to explain these interactions and potential applications of disrupting herbivore host preference with plant volatiles for sustainable management of insect vectors. 

Disruption of Vector Host Preference with Plant Volatiles May Reduce Spread of Insect-Transmitted Plant Pathogens.

The Asian citrus psyllid, Diaphorina citri Kuwayama, is the insect vector of the pathogen causing huanglongbing. We selected three botanical oils to evaluate behavioral activity against D. citri. In laboratory olfactometer assays, fir oil was repellent to D. citri females, while litsea and citronella oils elicited no response from D. citri females. In choice settling experiments, D. citri settled almost completely on control plants rather than on plants treated with fir oil at a 9.5 mg/day release rate. Therefore, we conducted field trials to determine if fir oil reduced D. citri densities in citrus groves. We found no repellency of D. citri from sweet orange resets that were treated with fir oil dispensers releasing 10.4 g/day/tree as compared with control plots. However, we found a two-week decrease in populations of D. citri as compared with controls when the deployment rate of these dispensers was doubled. Our results suggest that treatment of citrus with fir oil may have limited activity as a stand-alone management tool for D. citri and would require integration with other management practices. 

Repellent Activity of Botanical Oils against Asian Citrus Psyllid, Diaphorina citri (Hemiptera: Liviidae).

In the Asian citrus psyllid,  Kuwayama, stimulatory cuticular hydrocarbons act as sex pheromone attractants. Male psyllids locate aggregations of females using those olfactory cues, as well as vibrational communication on the plant surface. Although previous research has indicated that learning plays a role in modulating female reproductive behaviors in psyllids, it is unknown whether males similarly use learning to increase the likelihood of copulatory success. We used an olfactometer-based bio-assay to study the effects of experience on male response to female odor. First, we compared male attraction to female odor in virgin and previously mated males. Second, we tested the effect of several modes of experience with a novel odor, vanillin, to determine whether mating, feeding, or general environmental exposure elicited a learned response. We found that male attraction to female odor significantly increased after mating experience. In addition, we found that males learn about odor specifically in the context of mating, rather than feeding or general exposure. Electrophysiological measurements of antennal response to odorants confirmed that mating status did not affect the sensitivity of the peripheral nervous system to volatile stimuli implicating learning at the level of the central nervous system. These results suggest that male response to female odor is not an entirely innate behavior. Males may require mating experience with female conspecifics to develop attraction to those olfactory cues produced by the female and in association with the female's habitat. This adaptive plasticity may allow males to detect females in an ever-changing environment and promote diversification and further specialization on different host genotypes.

Male Psyllids Differentially Learn in the Context of Copulation.

Predicting the emergence and arrival of insect pests is paramount for integrated pest management. To achieve this goal, it is important to understand how abiotic factors influence pest dispersal behavior. We investigated the effects of abiotic conditions on flight initiation by the Asian citrus psyllid, Diaphorina citri Kuwayama. We first explored the effect of barometric pressure changes on flight initiation. We used a custom-made barometric chamber and observed the activity of D. citri as measured by the number of psyllids captured on yellow cardboard panels coated with adhesive. We found that psyllid flight initiation changed in response to variations in barometric pressure rather than to differences in stable pressures. Diaphorina citri were equally active at 1,009 mbar and 1,022 mbar. However, D. citri dispersed more as barometric pressure increased, and less when barometric pressure decreased. In a subsequent experiment, we manipulated temperature and relative humidity and observed how D. citri dispersed between citrus plants. Psyllids dispersal increased linearly with temperature. Changes in humidity did not affect dispersal of D. citri. Less than 1% of psyllids dispersed at 15 °C, compared with 7.7% at 21 °C and 27% at 25 °C. The minimal threshold for D. citri to initiate flight is estimated to be 16.5 °C. Collectively, our results provide an initial step toward developing predictive models of D. citri movement as influenced by abiotic factors.

Influence of Abiotic Factors on Flight Initiation by Asian Citrus Psyllid (Hemiptera: Liviidae).

The redbay ambrosia beetle Xyleborus glabratus is the vector of the symbiotic fungus, Raffaelea lauricola that causes laurel wilt, a highly lethal disease to members of the Lauraceae family. Pioneer X. glabratus beetles infect live trees with R. lauricola, and only when tree health starts declining more X. glabratus are attracted to the infected tree. Until now this sequence of events was not well understood. In this study, we investigated the temporal patterns of host volatiles and phytohormone production and vector attraction in relation to laurel wilt symptomology. Following inoculations with R. lauricola, volatile collections and behavioral tests were performed at different time points. Three days after infection (DAI), we found significant repellency of X. glabratus by leaf odors of infected swamp bay Persea palustris as compared with controls. However, at 10 and 20 DAI, X. glabratus were more attracted to leaf odors from infected than non-infected host plants. GC-MS analysis revealed an increase in methyl salicylate (MeSA) 3 DAI, whereas an increase of sesquiterpenes and leaf aldehydes was observed 10 and 20 DAI in leaf volatiles. MeSA was the only behaviorally active repellent of X. glabratus in laboratory bioassays. In contrast, X. glabratus did not prefer infected wood over healthy wood, and there was no associated significant difference in their volatile profiles. Analyses of phytohormone profiles revealed an initial increase in the amount of salicylic acid (SA) in leaf tissues following fungal infection, suggesting that the SA pathway was activated by R. lauricola infection, and this activation caused increased release of MeSA. Overall, our findings provide a better understanding of X. glabratus ecology and underline chemical interactions with its symbiotic fungus. Our work also demonstrates how the laurel wilt pathosystem alters host defenses to impact vector behavior and suggests manipulation of host odor by the fungus that attract more vectors.

The Fungus Raffaelea lauricola Modifies Behavior of Its Symbiont and Vector, the Redbay Ambrosia Beetle (Xyleborus Glabratus), by Altering Host Plant Volatile Production.

We compared the flight activity of Xyleborus glabratus Eichhoff, vector and symbiont of the causal agent of laurel wilt disease (Raffaelea lauricola), with a native species Monarthrum mali (Fitch) using flight mills. Flight mills were operated either for 24 h or for three 3-h time intervals. During the 3-h interval experiment, the shortest time to flight initiation for X. glabratus occurred at 1600-1900 hours. The average flight time and total flying distance during 1600-2100 hours were also higher than those quantified during the other two recording times investigated. However, total flight duration and proportion of fliers was highest at 1000-1300 hours. We compared several flight parameters. About 64.0% of tested X. glabratus flew <20 m. During 24-h recording periods, M. mali flew longer distances than X. glabratus. Over 50.0% of M. mali flew over 100 m on the flight mill. Xyleborus glabratus flight activity was greatest between 1200 and 1800 hours, while M. mali flew most frequently between 1500 and 2100 hours. Monarthrum mali flew more than five times more frequently than X. glabratus, and their longest single flight distance (37.5 ± 12.5 m) and total flight distance (213.7 ± 85.5 m) were greater than those of X. glabratus. These data will be useful for development of species-specific control and monitoring protocols for these ambrosia beetles based on greater understanding of their flight capacities and associated invasion distance.

Flight Capacities and Diurnal Flight Patterns of the Ambrosia Beetles, Xyleborus glabratus and Monarthrum mali (Coleoptera: Curculionidae).

Citrus production worldwide is currently threatened by Huanglongbing, or citrus greening disease. The associated pathogen, Candidatus Liberibacter asiaticus (CLas), is transmitted by the Asian citrus psyllid, Diaphorina citri. Annotation of the D. citri genome revealed a reduced innate immune system lacking a number of antimicrobial peptides and the Imd pathway associated with defense against Gram-negative bacteria. We characterized this apparent immune reduction in survival assays in which D. citri were exposed to Gram-negative or Gram-positive bacteria. D. citri experienced significant mortality when exposed to Serratia marcescens (Gram-negative) through oral ingestion or by septic injury. Escherichia coli (Gram-negative) also caused significant D. citri mortality, but only when inoculated at high concentrations through oral ingestion or by septic injury. Neither Micrococcus luteus (Gram-positive) or Bacillus subtilis (Gram-positive) caused significant mortality as compared to controls in any experiment. E. coli titers increased rapidly following exposure, while M. luteus titer remained stable for 72 h. We demonstrate that D. citri is capable of defending against E. coli, a Gram-negative bacterium, despite lacking the Imd defense pathway. The tolerance of D. citri to M. luteus infection, yet inability to effectively clear infections, presents questions to efficacy of D. citri immune response to effectively clear Gram-positive infections.

Innate immune system capabilities of the Asian citrus psyllid, Diaphorina citri.

Plants can defend themselves against herbivores through activation of defensive pathways and attraction of third-trophic-level predators and parasites. Trophic cascades that mediate interactions in the phytobiome are part of a larger dynamic including the pathogens of the plant itself, which are known to greatly influence plant defenses. As such, we investigated the impact of a phloem-limited bacterial pathogen,  Liberibacter asiaticus (Las), in cultivated citrus rootstock on a well-studied belowground tritrophic interaction involving the attraction of an entomopathogenic nematode (EPN), , to their root-feeding insect hosts,  larvae. Using belowground olfactometers, we show how Las infection interferes with this belowground interaction by similarly inducing the release of a C12 terpene, pregeijerene, and disconnecting the association of the terpene with insect presence.  larvae that were not feeding but in the presence of a Las-infected plant were more likely to be infected by EPN than those near uninfected plants. Furthermore, nonfeeding larvae associated with Las-infected plants were just as likely to be infected by EPN as those near noninfected plants with  larval damage. Larvae of two weevil species,  and , were also more attracted to plants with infection than to uninfected plants.  larvae were most active when exposed to pregeijerene at a concentration of 0.1 μg/μl. We attribute this attraction to Las-infected plants to the same signal previously thought to be a herbivore-induced plant volatile specifically induced by root-feeding insects, pregeijerene, by assessing volatiles collected from the roots of infected plants and uninfected plants with and without feeding . . Phytopathogens can influence the structuring of soil communities extending to the third trophic level. Field populations of EPN may be less effective at host-finding using pregeijerene as a cue in citrus grove agroecosystems with high presence of Las infection.

Bacterial phytopathogen infection disrupts belowground plant indirect defense mediated by tritrophic cascade.

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), is the vector of the bacterium responsible for huanglongbing, a deadly plant disease affecting citrus worldwide. We investigated the effects of wind direction and speed on flight duration and direction of D. citri, as well as the effects of temperature and barometric pressure on sustained flight duration of D. citri. Experiments were performed with laboratory flight mills and wind tunnels. Flight activity of D. citri increased with increasing temperature. Of the few insects that flew at 18°C, most performed short duration flights (<60 s). When exposed to temperatures between 21 and 28°C, D. citri performed long duration flights (>60 s). In addition, the distance covered increased with temperature. Interestingly, males were more sensitive to cold temperature and flew significantly shorter distances than females at 21 and 25°C. Barometric pressure recorded before and during the flight mill experiment suggested that decreasing pressure reduced distance flown by D. citri. Flight direction was strongly influenced by wind. In wind tunnel experiments where psyllids were challenged to reach citrus leaf flush positioned either downwind or upwind, most D. citri moved downwind when exposed to continuous airflow. In a subsequent experiment, we challenged psyllids to pulsed wind blowing at higher speeds. In this case, most psyllids progressed upwind, suggesting upwind movement by psyllids during pauses within pulsed airflow. Collectively, the results indicate that D. citri are able to modify their flight behavior in response to abiotic factors.

Effects of Wind, Temperature, and Barometric Pressure on Asian Citrus Psyllid (Hemiptera: Liviidae) flight behavior.

Dung beetles are important to ecosystems as they aid in nutrient recycling and waste removal. In North Florida, there is a high diversity of dung beetles due to the intentional and accidental introduction of non-native species. Understanding patterns and processes on local scales is important for conservational planning. The aim of this study was to evaluate how dung beetle communities respond to different dung sources, forage composition, and habitat types. We surveyed for the presence and distribution of dung beetles in an open field and forest as well as in three types of pasture forage designs. In the first experiment, four transects with pitfall traps from forest to open field were established with either horse, pig, or cow feces bait. In the second experiment, three cattle grazing systems with different forage species were tested with only cow feces. In the first experiment, 16 species were identified between the field and forest sites including native and exotic species. Although the dung type had little effect on beetle distribution, a significantly different distribution of dung beetles between the field and forest was observed. Only one species, Onthophagus hecate Panzer (Coleoptera: Scarabaeidae) showed no preference between open field and forest habitat. During this second experiment, no difference in dung beetle distribution was found between the three types of pasture assemblages. This study supports habitat type as a driver of interspecies distribution and diversity of dung beetles in North Florida.

Article	Year
Eucalyptol is an attractant of the Redbay ambrosia beetle, Xyleborus glabratus. Journal of chemical ecology\| PubMed ID: 24752857	2014
Attraction of Redbay Ambrosia Beetle, Xyleborus Glabratus, To Leaf Volatiles of its Host Plants in North America. Journal of chemical ecology\| PubMed ID: 26070721	2015
Infection of an Insect Vector with a Bacterial Plant Pathogen Increases Its Propensity for Dispersal. PloS one\| PubMed ID: 26083763	2015
Seasonal Movement Patterns and Long-Range Dispersal of Asian Citrus Psyllid in Florida Citrus. Journal of economic entomology\| PubMed ID: 26470097	2015
The Influence of Learning on Host Plant Preference in a Significant Phytopathogen Vector, Diaphorina citri. PloS one\| PubMed ID: 26930355	2016
Disruption of Vector Host Preference with Plant Volatiles May Reduce Spread of Insect-Transmitted Plant Pathogens. Journal of chemical ecology\| PubMed ID: 27193763	2016
Repellent Activity of Botanical Oils against Asian Citrus Psyllid, Diaphorina citri (Hemiptera: Liviidae). Insects\| PubMed ID: 27429006	2016
Male Psyllids Differentially Learn in the Context of Copulation. Insects\| PubMed ID: 28178203	2017
Influence of Abiotic Factors on Flight Initiation by Asian Citrus Psyllid (Hemiptera: Liviidae). Environmental entomology\| PubMed ID: 28334135	2017
The Fungus Raffaelea lauricola Modifies Behavior of Its Symbiont and Vector, the Redbay Ambrosia Beetle (Xyleborus Glabratus), by Altering Host Plant Volatile Production. Journal of chemical ecology\| PubMed ID: 28455797	2017
Flight Capacities and Diurnal Flight Patterns of the Ambrosia Beetles, Xyleborus glabratus and Monarthrum mali (Coleoptera: Curculionidae). Environmental entomology\| PubMed ID: 28459955	2017
Innate immune system capabilities of the Asian citrus psyllid, Diaphorina citri. Journal of invertebrate pathology\| PubMed ID: 28624621	2017
Bacterial phytopathogen infection disrupts belowground plant indirect defense mediated by tritrophic cascade. Ecology and evolution\| PubMed ID: 28690813	2017
Effects of Wind, Temperature, and Barometric Pressure on Asian Citrus Psyllid (Hemiptera: Liviidae) flight behavior. Journal of economic entomology\| PubMed ID: 30137351	2018
Phenology, Distribution, and Diversity of Dung Beetles (Coleoptera: Scarabaeidae) in North Florida's Pastures and Forests. Environmental entomology\| PubMed ID: 31188428	2019

Xavier Martini

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