Taxonomy, Biology, Symbionts, Omics, and Management of Rhynchophorus Palm Weevils (Coleoptera: Curculionidae: Dryophthorinae)

Palm weevils, Rhynchophorus spp., are destructive pests of native, ornamental, and agricultural palm species. Of the 10 recognized species, two of the most injurious species, Rhynchophorus ferrugineus and Rhynchophorus palmarum, both of which have spread beyond their native range, are the best studied. Due to its greater global spread and damage to edible date industries in the Middle East, R. ferrugineus has received more research interest. Integrated pest management programs utilize traps baited with aggregation pheromone, removal of infested palms, and insecticides. However, weevil control is costly, development of resistance to insecticides is problematic, and program efficacy can be impaired because early detection of infestations is difficult. The genome of R. ferrugineus has been sequenced, and omics research is providing insight into pheromone communication and changes in volatile and metabolism profiles of weevil-infested palms. We outline how such developments could lead to new control strategies and early detection tools.

Effects of Temperature on the Developmental and Reproductive Biology of North American Bean Thrips, Caliothrips fasciatus (Pergande) (Thysanoptera: Thripidae: Panchaetothripinae)

North American bean thrips, Caliothrips fasciatus, native to California U.S., has been detected inside the navels of navel oranges exported from California for more than 120 years. Despite this long history of accidental movement into new areas, this thrips has failed to establish populations outside of its native range. The cold accumulation hypothesis postulates that increasing levels of cold stress experienced by thrips overwintering inside navels is compounded when harvested fruit is shipped under cold storage conditions. Consequently, the fitness of surviving thrips is compromised, which greatly diminishes invasion potential. At the time this study was conducted, the effects of temperature on C. fasciatus fitness were unknown. To address this shortcoming, the effects of nine fluctuating temperatures that averaged 8, 10, 15, 20, 25, 30, 32, 35, and 37 °C over a 24 h period on the developmental and reproductive biology of C. fasciatus were evaluated. One linear and five nonlinear regression functions were fit to egg-to-adult development rate data for parent and offspring thrips to characterize thermal performance curves. Estimates of minimum, optimal, and maximum temperature thresholds for development were in the ranges of -4.37-6.52 °C (i.e., T_min), 31.19-32.52 °C (i.e., T_opt), and 35.07-37.98 °C (i.e., T_max), respectively. Degree day accumulation to complete development, estimated from linear regression, ranged 370.37-384.61. Average development times for eggs, first and second instar larvae, propupae, pupae, and adult longevity, and mean lifetime fecundity of females were significantly affected by temperature. These biological responses to temperature may provide insight into how this abiotic variable affects the invasion potential of C. fasciatus.

Proactive classical biological control of Lycorma delicatula (Hemiptera: Fulgoridae) in California (U.S.): Host range testing of Anastatus orientalis (Hymenoptera: Eupelmidae)

Lycorma delicatula (Hemiptera: Fulgoridae), the spotted lanternfly, native to China, invaded and established in the northeast U.S. in 2014. Since this time, populations have grown and spread rapidly, and invasion bridgeheads have been detected in mid-western states (i.e., Indiana in 2021). This invasive pest presents a significant threat to Californian agriculture. Therefore, a proactive classical biological control program using Anastatus orientalis (Hymenoptera: Eupelmidae), a L. delicatula egg parasitoid native to China, was initiated in anticipation of eventual establishment of L. delicatula in California. In support of this proactive approach, the potential host range of A. orientalis was investigated. Eggs of 34 insect species either native or non-native to the southwestern U.S. were assessed for suitability for parasitism and development of A. orientalis. Of the native species tested, 10, 13, and one were Hemiptera, Lepidoptera, and Mantodea, respectively. Of the non-native species, eight Hemiptera and two Lepidoptera were evaluated. Host range tests conducted in a quarantine facility, exposed individually mated A. orientalis females (Haplotype C) to non-target and target (i.e., L. delicatula) eggs in sequential no-choice and static choice experiments to determine suitability for parasitization and development. Additionally, the sex ratio, fertility, and size of offspring obtained from non-target and target eggs were evaluated. Results of host range testing indicated that A. orientalis is likely polyphagous and can successfully parasitize and develop in host species belonging to at least two different orders (i.e., Hemiptera, Lepidoptera) and seven families (Coreidae, Erebidae, Fulgoridae, Lasiocampidae, Pentatomidae, Saturniidae and Sphingidae). Prospects for use of A. orientalis as a classical biological control agent of L. delicatula in the southwestern U.S. are discussed.

Effects of Freezing Lycorma delicatula Egg Masses on Nymph Emergence and Parasitization by Anastatus orientalis

Lycorma delicatula (White) (Hemiptera: Fulgoridae), native to China, was first detected in Pennsylvania, U.S. in 2014. This polyphagous pest can feed on over 70 plant species including agricultural crops, like grapes, that have high economic value. Anastatus orientalis Yang and Choi (Hymenoptera: Eupelmidae) is an egg parasitoid associated with L. delicatula egg masses in China that is being evaluated for possible introduction into the U.S. for classical biological control of L. delicatula. In support of this program, the suitability of frozen L. delicatula eggs for parasitization by A. orientalis was evaluated in a quarantine laboratory. Host egg masses held for four different cold storage periods (5°C for <1, 4, 8 and 11 months) were frozen at -40°C for 1 hour or 24 hours and exposed to female A. orientalis for parasitization for seven days. Following this experimental exposure period, rates of L. delicatula nymph emergence and A. orientalis parasitism were assessed for each of the eight different cold storage treatments. Host acceptance and suitability of frozen L. delicatula eggs by A. orientalis was assessed in terms of percentage parasitism, offspring sex ratio, and hind tibia length of emerged parasitoids. Results indicated that L. delicatula nymphs failed to emerge from eggs that were exposed to -40°C for 1 hour and 24 hours and A. orientalis could successfully parasitize L. delicatula eggs regardless of cold storage and freezing treatment. These results add a new tool for long term maintenance of L. delicatula egg masses and rearing methods for egg parasitoids of this pest. Additionally, it may be possible to field deploy sentinel eggs of L. delicatula frozen at -40°C to survey for resident natural enemy species capable of parasitizing eggs of this pest in advance of anticipated L. delicatula invasions into new areas.

Assessment of Age, Gender, Mating Status, and Size on Single and Repeat Flight Capabilities of Heilipus lauri Boheman (Coleoptera: Curculionidae)

Heilipus lauri Boheman (Coleoptera: Curculionidae) is a specialist pest of avocado fruit and is considered an incursion risk for U.S. avocado producers. At the time work reported here was undertaken the flight capabilities of H. lauri were unknown. Consequently, proactive studies were undertaken to quantify aspects of this pest's flight capabilities to inform potential future control efforts. Flight mill studies were conducted in a quarantine laboratory to measure the dispersal capacity of H. lauri with respect to gender, mating status, and size on the single and repeat flight capabilities of weevils. Gender, mating status, and size did not significantly affect measured flight parameters. Average total distances flown and flight velocity, and mean maximum flight bout distances and durations significantly declined as weevil age increased and when weevils engaged in repeat flights. Survivorship rates were significantly reduced as the number of successive flights undertaken increased. The distribution of total average flight distances flown and total cumulative flight distances flown was platykurtic. The implications of these findings are discussed in terms of developing incursion management plans.

Influence of Holding Conditions and Storage Duration of Halyomorpha halys (Hemiptera: Pentatomidae) Eggs on Adventive and Quarantine Populations of Trissolcus japonicus (Hymenoptera: Scelionidae) Behavior and Parasitism Success

Halyomorpha halys (Stål) is an invasive pest in the United States and other countries. In its native range, H. halys eggs are parasitized by a co-evolved parasitoid, Trissolcus japonicus (Ashmead). In the United States, T. japonicus, a classical biological control candidate, is being redistributed in many states where adventive populations exist. To establish if H. halys egg holding conditions affect T. japonicus foraging behavior or successful parasitism, naïve, female parasitoids from an adventive population were allowed to forage in laboratory bioassay arenas with either fresh or frozen (-20 or -80°C) egg masses, the latter held for five durations ranging from 1 h to 112 d. Parasitoid movements were recorded for 1 h. Thereafter, parasitoids were transferred with the same egg mass for 23 h. Additionally, female parasitoids from a quarantine colony were exposed to: 1) pairs of fresh egg masses and egg masses frozen at -40°C (>24 h) or 2) a single fresh egg mass or egg mass frozen at -40°C (<1 h). All exposed egg masses were held to assess progeny emergence. In the foraging bioassay, holding temperature and storage duration appeared to influence host-finding and host quality. Egg masses held at -80°C and fresh egg masses resulted in significantly greater levels of parasitism and progeny emergence compared with eggs held at -20°C. No differences were recorded between egg masses held at -40°C for ≤1 h and fresh egg masses. These results will help refine methods for preparation of egg masses for sentinel monitoring and parasitoid mass rearing protocols.

Sex, males, and hermaphrodites in the scale insect Icerya purchasi

Androdioecy (the coexistence of males and hermaphrodites) is a rare mating system for which the evolutionary dynamics are poorly understood. Here, we investigate the cottony cushion scale, Icerya purchasi, one of only three reported cases of androdioecy in insects. In this species, female-like hermaphrodites have been shown to produce sperm and self-fertilize. However, males are ocassionally observed as well. In a large genetic analysis, we show for the first time that, although self-fertilization appears to be the primary mode of reproduction, rare outbreeding events do occur in natural populations, supporting the hypothesis that hermaphrodites mate with males and hence androdioecy is the mating system of I. purchasi. Thus, this globally invasive pest insect appears to enjoy the colonization advantages of a selfing organism while also benefitting from periodic reintroduction of genetic variation through outbreeding with males.

Quantification of the Life Time Flight Capabilities of the South American Palm Weevil, Rhynchophorus palmarum (L.) (Coleoptera: Curculionidae)

Simple Summary

The South American palm weevil, Rhynchophorus palmarum, is an invasive pest that has killed thousands of ornamental palms in San Diego County in California, USA. Emerging management plans for this pest need to consider the flight capabilities of this insect, which are not well understood. To address this shortcoming, flight mills, a type of computerized insect “merry-go round” that measures how far weevils can fly in the laboratory, were used to quantify the flight distances of 101 weevils that were flown repeatedly over the course of their lifetimes. The results indicate that weevils are strong flyers capable of flying numerous times before dying of natural causes. Over their lifetimes, weevils, on average, covered distances that cumulatively totaled >220 km. One female weevil flew an impressive cumulative distance of approximately 806 km over the course of nine consecutive flights before dying.

Abstract

The life time flight capabilities of an invasive palm pest, Rhynchophorus palmarum, were assessed using flight mill assays under controlled conditions in the laboratory. A total of 101 weevils were used for experiments and subjected to repeat flight assays. A total of 17 flight trials were run, of which the first 14 provided useful data prior to weevil death. Male and female weevils exhibited a strong capacity for repeat long distance flights. Flight metrics of interest were not affected by weevil sex or mating status. Cumulative lifetime flight distances for male and female R. palmarum averaged ~268 km and ~220 km, respectively. A maximum lifetime cumulative flight distance of ~758 km and ~806 km was recorded for one male of unknown mating status and one unmated female weevil, respectively. Dispersal data for individual flights (i.e., trials 1 through 9, 10–14 combined) and all flight trial data (i.e., flights 1–14 combined) exhibited platykurtic distributions. The results presented here may have important implications for modeling the spread of this invasive pest and for the development of monitoring and management plans.

Use of Digital Video Cameras to Determine the Efficacy of Two Trap Types for Capturing Rhynchophorus palmarum (Coleoptera: Curculionidae)

The efficacies of two trap types, bucket and Picusan traps, for capturing and retaining Rhynchophorus palmarum (L.), an invasive palm pest responsible for killing thousands of ornamental Canary Islands date palms (Phoenix canariensis Chabaud [Arecales: Arecaceae]) in San Diego County, CA, were compared. Digital video data were analyzed to determine how R. palmarum behavior toward each trap type affected capture and retention rates. Videography was conducted 24 h/d, 7 d/wk, for more than 7 mo resulting in 20,211 h of digital data for analysis. Weevil attraction to traps was observed only during daylight hours and no patterns in diel activity were found. Neither trap type tested captured 100% of weevils attracted to traps. Bucket traps suspended 1.5 m above the ground attracted 30% more weevils than ground deployed Picusan traps. Of those weevils attracted to bucket traps, 89% entered, 82% escaped, and 18% that entered traps were retained. Weevils that were not retained spent an average of 19 min 20 s entering and exiting entry holes and walking and flying around the bucket trap. By contrast, Picusan traps captured 89% of weevils that entered the trap. The time between weevils arriving (via walking or flight) on the sides of the Picusan trap and retention in the trap ranged between 90 and 376 s. These visual observations suggest that Picusan traps are more efficient than bucket traps for R. palmarum capture.

Effects of Food Bait and Trap Type on Captures of Rhynchophorus palmarum (Coleoptera: Curculionidae) and Trap Bycatch in Southern California

Rhynchophorus palmarum (L.) is an invasive pest responsible for killing thousands of ornamental Canary Islands date palms (Phoenix canariensis Chabaud) in San Diego County, CA. Two field experiments were conducted to compare the attractiveness of six different baits and two trap types. The tested baits were dates + water; dates + water + Saccharomyces cerevisiae; dates + water + S. bayanus; dates + water + S. pastorianus; 15% sugarcane molasses water solution mixed with 3% paraffinic oil, and a no bait control treatment. The two traps tested were white bucket traps (hanging 1.5 m above the ground and set on the ground) and black cone shaped Picusan traps (set on ground only). All traps were loaded with commercially available R. palmarum aggregation pheromone and the synergist ethyl acetate. Differences in weevil capture rates were observed across bait and trap types. Weevil captures were almost five times greater in Picusan traps compared to bucket traps that were hanging or placed on the ground. Adding dates and water alone or combined with S. cerevisiae to traps increased weevil captures compared to other baits and controls. Trap and bait types affected bycatch of nontarget arthropod species. In general, spiders, earwigs, and carabid beetles were most commonly recovered from Picusan traps, regardless of bait type. Scarab beetles, moths, and flies were found more frequently in bucket traps baited with molasses or dates mixed with S. bayanus. No effects of bait and trap type were associated with bycatch species richness.

How Far Can Rhynchophorus palmarum (Coleoptera: Curculionidae) Fly?

The palm weevil, Rhynchophorus palmarum (L.), was first recorded in San Diego County, CA in 2011 and breeding populations were recovered from infested Canary Islands date palms, Phoenix canariensis, in San Ysidro, San Diego County, in 2015. This palm pest presents a significant threat to California's edible date industry as Phoenix dactylifera is a recorded host for this weevil. The flight capabilities of R. palmarum are unknown which limits understanding of rates of natural dispersal. In response to this knowledge deficit, 24-h flight mill trials were conducted with field-collected male and female weevils. A total of 87 weevils (49 females and 38 males) were used in experiments, ~6% failed to fly >1 km in 24 h and were excluded from analyses. Of those 82 weevils flying >1 km in 24 h, the average distance flown by males and females was ~41 and ~53 km, respectively. Approximately 10% of females flew >100 km in 24 h, with two (~4%) females flying >140 km. The maximum recorded distance flown by a male weevil was 95 km. Flight activity was predominantly diurnal and flying weevils exhibited an average weight loss of ~18% while non-flying control weevils lost ~13% body weight in 24 h. The combined flight distances for male and female weevils exhibited a heavy-tailed platykurtic distribution. Flight mill data for R. palmarum are compared to similarly collected flight mill data for two other species of invasive palm weevil, Rhynchophorus ferrugineus (Olivier) and Rhynchophorus vulneratus (Panzer).

The Effects of Constant and Fluctuating Temperatures on Development of Diaphorina citri (Hemiptera: Liviidae), the Asian Citrus Psyllid

The effects of six average daily temperatures, 15, 20, 25, 30, 32, and 35°C, that were either constant or fluctuating over 24 h on development times of California-sourced Diaphorina citri Kuwayama nymphs were examined. Thermal performance curves for immature stages of D. citri were characterized using one linear and six nonlinear models (i.e., Ratkowsky, Lobry-Rosso-Flandrois, Lactin-2, Brière-2, Beta, and Performance-2). Daily thermal fluctuations had significant effects on development times of D. citri nymphs, which differed across experimental temperatures. Diaphorina citri nymphs reared at constant temperatures completed development faster than those reared under fluctuating profiles with equivalent temperature means. Linear model estimates of degree-days required for completion of cumulative development of D. citri were 25% lower for constant temperatures when compared with fluctuating temperature regimens. Nonlinear model estimations of optimum developmental temperature and upper theoretical temperature bounds for development were similar for individuals reared under constant and fluctuating temperatures. Nevertheless, the estimated values of lower theoretical temperature limits above which development occurred were lower under fluctuating than constant temperatures. A meta-analysis of published D. citri temperature-dependent development literature, synthesizing datasets of five globally distributed populations (Brazil, California, China, Florida, and Japan) reared under different constant temperatures on six different host plants (i.e., Citrus limonia, C. sinensis cv Natal, C. sinensis cv. Pêra, C. reticulata, Fortunella margarita, and Murraya paniculata), together with the results of this study (C. volkameriana), revealed convergence in estimates of developmental parameters. These results have implications for predicting D. citri invasion and establishment risk and subsequent population performance across various climactic gradients and geographic regions.

Invasion Biology, Ecology, and Management of Western Flower Thrips

Western flower thrips, Frankliniella occidentalis, first arose as an important invasive pest of many crops during the 1970s-1980s. The tremendous growth in international agricultural trade that developed then fostered the invasiveness of western flower thrips. We examine current knowledge regarding the biology of western flower thrips, with an emphasis on characteristics that contribute to its invasiveness and pest status. Efforts to control this pest and the tospoviruses that it vectors with intensive insecticide applications have been unsuccessful and have created significant problems because of the development of resistance to numerous insecticides and associated outbreaks of secondary pests. We synthesize information on effective integrated management approaches for western flower thrips that have developed through research on its biology, behavior, and ecology. We further highlight emerging topics regarding the species status of western flower thrips, as well as its genetics, biology, and ecology that facilitate its use as a model study organism and will guide development of appropriate management practices.

Population model for the decline of Homalodisca vitripennis (Hemiptera: Cicadellidae) over a ten-year period

The glassy-winged sharpshooter, Homalodisca vitripennis (Germar), is an invasive pest which presents a major economic threat to grape industries in California, because it spreads a disease-causing bacterium, Xylella fastidiosa. In this note we develop a time and temperature dependent mathematical model to analyze aggregate population data for H. vitripennis from a 10-year study consisting of biweekly monitoring of H. vitripennis populations on unsprayed citrus, during which H. vitripennis decreased significantly. This model was fitted to the aggregate H. vitripennis time series data using iterative reweighted weighted least squares (IRWLS) with assumed probability distributions for certain parameter values. Results indicate that the H. vitripennis model fits the phenological and temperature data reasonably well, but the observed population decrease may possibly be attributed to factors other than the abiotic effect of temperature. A key factor responsible for this decline but not analyzed here could be biotic, for example, potentially parasitism of H. vitripennis eggs by Cosmocomoidea ashmeadi. A biological control program targeting H. vitripennis utilizing the mymarid egg parasitoid Cosmocomoidea (formerly Gonatocerus) ashmeadi (Girault) is described.

The Influence of Temperature Variation on Life History Parameters and Thermal Performance Curves of Tamarixia radiata (Hymenoptera: Eulophidae), a Parasitoid of the Asian Citrus Psyllid (Hemiptera: Liviidae)

This study examined the effects of seven constant and fluctuating temperature profiles with corresponding averages of 12 to 38°C on the life history of the Punjab, Pakistan-sourced Tamarixia radiata (Waterston) released in California for biological control of Diaphorina citri Kuwayama. One linear and seven nonlinear regression functions were fit to egg-to-adult development rate data to characterize thermal performance curves. Temperature fluctuations significantly affected both development and longevity of T. radiata. Estimates of degree-days predicted by the linear model were 30% higher for the fluctuating regime than the constant regime. Nonlinear model estimations of theoretical minimum and maximum developmental thresholds were lower for the fluctuating regime when compared to the constant regime. These predictions align with experimental observations. Parasitoids reared under fluctuating profiles at low average temperatures developed faster (15°C) and survived longer (15-20°C) when compared to those reared under constant regimes with corresponding means. In contrast, high average fluctuating temperatures produced parasitoids with an extended developmental period (35°C) and reduced longevity (30-35°C). A meta-analysis of published T. radiata development datasets, together with the results of this study, indicated convergence in degree-days and theoretical minimum developmental thresholds among geographically distinct parasitoid populations. These findings demonstrate the significant effects of temperature on T. radiata life history and have important implications for optimization of mass-rearing and release efforts, improvement of predictions from climate modeling, and comparison of T. radiata population performance across climatic gradients and geographic regions.

Effects of Constant and Fluctuating Temperatures on Development Rates and Longevity of Diaphorencyrtus aligarhensis (Hymenoptera: Encyrtidae)

The effects of fluctuating and constant temperatures on the development and longevity of Diaphorencyrtus aligarhensis (Shafee, Alam, and Argarwal) (Hymenoptera: Encyrtidae), a parasitoid sourced from Pakistan and released in California for the classical biological control of Diaphorina citri Kuwayama (Hemiptera: Liviidae), were examined. The influence of six fluctuating temperatures that averaged 15, 20, 25, 30, 32, and 35°C, over 24 h on the development times and longevity of male and female D. aligarhensis were quantified and compared to six constant temperatures set at the same average temperatures. The development rates of immature stages of D. aligarhensis as a function of temperature were modeled using one linear and four nonlinear models. Fluctuating temperatures had significant effects on parasitoid development times and longevity which differed across experimental temperatures. Degree-days required for completion of cumulative development of D. aligarhensis were significantly different being 21% lower under fluctuating temperature regimens when compared with constant temperatures. The lower temperature threshold estimates above which development occurred were estimated to be lower under constant than fluctuating temperatures. The estimated values of upper and optimum temperature limits were similar for individuals reared under constant and fluctuating temperatures. Diaphorencyrtus aligarhensis lived longer at constant intermediate temperatures and for shorter times at constant lower temperature extremes when compared with their fluctuating temperature counterparts. Daily thermal fluctuations significantly influenced life history parameters of D. aligarhensis and should be considered when assessing likelihoods of establishment and impacts of this parasitoid on D. citri across diverse citrus-growing climates.

An assessment of interspecific competition between two introduced parasitoids of Diaphorina citri (Hemiptera: Liviidae) on caged citrus plants

Two parasitoids attacking nymphs of Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae) and Diaphorencyrtus aligarhensis (Shafee, Alam & Agarwal) (Hymenoptera: Encyrtidae) are being released in California, USA in a classical biological control program. To evaluate the effect of multiple parasitoid species on D. citri mortality, we conducted mesocosm experiments under controlled conditions using a complete block design with 6 treatments (D. citri nymphs exposed to: no parasitoids; D. aligarhensis or T. radiata alone; D. aligarhensis or T. radiata released first (by 48 h); and both species released simultaneously). Parasitism of D. citri nymphs by T. radiata exceeded 60% and was unchanged when D. aligarhensis were present. Parasitism by D. aligarhensis was greatest when T. radiata was absent (∼28%) and was reduced in all treatments with T. radiata present (<3%). D. citri mortality and parasitoid-related mortality of D. citri was consistent across parasitoid treatments. Laboratory results suggest that competition between D. aligarhensis and T. radiata is asymmetric and favors T. radiata. It may be difficult for D. aligarhensis to contribute significantly to D. citri biological control where T. radiata is present. However, results reported here suggest that competition between T. radiata and D. aligarhensis is not likely to reduce parasitism by T. radiata or reduce parasitoid-induced mortality of D. citri.

Evaluation of a Hydrogel Matrix for Baiting Western Yellowjacket (Vespidae: Hymenoptera)

Baiting is an effective method to manage Vespula spp. yellowjacket (Hymenoptera: Vespidae) populations without having to locate and treat nests. Here, we assessed the utility of a commercially available polyacrylamide hydrogel as an alternative bait material for yellowjacket baiting. The experimental bait (hereafter referred to as 'hydrogel bait') consisted of diluted chicken juice (from canned chicken meat) and fipronil (0.025%, wt/wt) absorbed into granular polyacrylamide hydrogel particles. Three separate 24-h baiting trials were conducted at two different field sites with the western yellowjacket, Vespula pensylvanica (Saussare), as the target species. The monitoring data from pre- and posttreatment periods indicated that baiting with polyacrylamide hydrogel baits provided ≈74-96% reduction in the foraging activity of V. pensylvanica during its active season. In addition to their ability to absorb large quantities of aqueous bait containing phagostimulants and toxicants, the hydrogels' tactile resemblance to fresh meat upon hydration makes them a promising option as a non-meat material for delivering small amounts of insecticides to yellowjacket populations in a highly targeted manner.

Modeling the Phenology of Asian Citrus Psyllid (Hemiptera: Liviidae) in Urban Southern California: Effects of Environment, Habitat, and Natural Enemies

Modeling can be used to characterize the effects of environmental drivers and biotic factors on the phenology of arthropod pests. From a biological control perspective, population dynamics models may provide insights as to when the most vulnerable pest life stages are available for natural enemies to attack. Analyses presented here used temperature and habitat dependent, instar-specific, discrete models to investigate the population dynamics of Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae). This pest is the target of a classical biological control program with the parasitoid Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae). The population trends of D. citri eggs, nymphs, and adults, citrus flush growth patterns, and T. radiata activity were monitored monthly on orange and lemon trees at 10 urban sites in southern California for a 2-yr period. Cumulative D. citri egg, nymph, and adult days recorded at each site, were regressed against accumulated degree-days (DDs) to model the population dynamics of each development stage in relation to temperature. Using a biofix point of 1 January, the model predicted that 10% and 90% of eggs were laid by 198 and 2,255 DD, respectively. Populations of small and large D. citri nymphs increased slowly with 90% of the population recorded by 2,389 and 2,436 DD, respectively. D. citri adults were present year round with 10 and 90% of the population recorded by 95 and 2,687 DD, respectively. The potential implications of using DD models for optimizing inoculative releases of natural enemies, such as T. radiata into citrus habitat infested with D. citri, are discussed.

Development of an alginate hydrogel to deliver aqueous bait for pest ant management

BACKGROUND

Insecticide sprays used for ant control cause environmental contamination. Liquid bait is a safe and effective alternative, but it requires bait stations to dispense the toxicant. We developed a biodegradable hydrogel to deliver liquid bait obviating the need for bait stations.

RESULTS

Alginate hydrogel beads with preferred rigidity and maximum hydration in 25% sucrose solution were engineered by optimizing a crosslinking process. The moisture content of the substrate on which the beads were placed and the relative atmospheric humidity significantly influenced water loss dynamics of the hydrated hydrogel beads. Laboratory choice studies indicated that hydrated hydrogel beads had reduced palatability to foraging ants when they lost ≥50% water. An enzyme-linked immunosorbent assay (ELISA) indicated that the insecticide thiamethoxam added to sucrose solution was absorbed into the hydrogel beads. Hydrogel beads conditioned in sucrose solution with 1 mg L^-1 thiamethoxam provided complete control of all castes of Argentine ant Linepithema humile (Mayr) colony by 14 days post treatment in the laboratory trial and provided a 79% reduction in ant activity after 8 weeks in the field trial.

CONCLUSION

Alginate hydrogel beads provided an effective delivery system for liquid baits laced with low concentrations of insecticide to control Argentine ants. © 2017 Society of Chemical Industry.

Assessment of Feeding Acceptance and Injury of Kerman Pistachios, Pistacia vera, by Brown Marmorated Stink Bug (Hemiptera: Pentatomidae)

In the United States, California (CA) is the primary commercial producer of pistachio nuts, Pistacia vera L. (Anacardiaceae). The brown marmorated stink bug (BMSB), Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), an invasive and polyphagous insect pest from Asia, has established in urban areas in several pistachio-growing counties in CA. Breeding BMSB populations have not been detected in commercial pistachio acreage. However, the detection of BMSB in Kern and Fresno counties, major Kerman pistachio producing areas in CA, underscored key knowledge gaps on BMSB ecology in CA and motivated investigations on the susceptibility of pistachio nuts to BMSB feeding. Laboratory feeding trials conducted in quarantine under permit indicated that adult BMSB stylets can penetrate developing pistachio shells and associated feeding was correlated with kernel necrosis for nuts collected mid to late season (June to August 2016). Feeding damage estimates indicated that higher levels of kernel injury were associated with female BMSB when compared to feeding by male BMSB. These results suggest that there is probable risk of feeding damage to field grown pistachios from BMSB. The implications of this study for BMSB pest management in the CA pistachio system and future research directions are discussed.

Assessing Flight Potential of the Invasive Asian Longhorned Beetle (Coleoptera: Cerambycidae) With Computerized Flight Mills

The Asian longhorned beetle, Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae: Lamiinae), is an invasive woodborer that poses a serious threat to urban and natural landscapes. In North America, this beetle is a quarantine pest, and populations are subject to eradication efforts that consist of the identification, removal, and destruction of infested host material, and removal or prophylactic treatment of high-risk host plant species. To enhance Asian longhorned beetle eradication protocols in landscapes with extensive host availability, we assessed the dispersal potential of male and female adults of varying age, mating, and nutritional status using computerized flight mills. In total, 162 individuals were tethered to computerized flight mills for a 24-h trial period to collect information on total distance flown, flight times and velocities, and number and duration of flight bouts. Adult Asian longhorned beetles (in all treatments) flew an average of 2,272 m within a 24-h period, but are capable of flying up to 13,667 m (8.5 miles). Nutrition and age had the greatest impacts on flight, with Asian longhorned beetle adults >5 d of age that had fed having greater overall flight performance than any other group. However, mating status, sex, and body size (pre-flight weight and elytron length) had a minimal effect on flight performance. This information will be useful for refining quarantine zones surrounding areas of infestation, and for providing greater specificity as to the risk the Asian longhorned beetle poses within invaded regions.

Spatial Dependence and Sampling of Phytoseiid Populations on Hass Avocados in Southern California

Research on phytoseiid mites has been critical for developing an effective biocontrol strategy for suppressing Oligonchus perseae Tuttle, Baker, and Abatiello (Acari: Tetranychidae) in California avocado orchards. However, basic understanding of the spatial ecology of natural populations of phytoseiids in relation to O. perseae infestations and the validation of research-based strategies for assessing densities of these predators has been limited. To address these shortcomings, cross-sectional and longitudinal observations consisting of >3,000 phytoseiids and 500,000 O. perseae counted on 11,341 leaves were collected across 10 avocado orchards during a 10-yr period. Subsets of these data were analyzed statistically to characterize the spatial distribution of phytoseiids in avocado orchards and to evaluate the merits of developing binomial and enumerative sampling strategies for these predators. Spatial correlation of phytoseiids between trees was detected at one site, and a strong association of phytoseiids with elevated O. perseae densities was detected at four sites. Sampling simulations revealed that enumeration-based sampling performed better than binomial sampling for estimating phytoseiid densities. The ecological implications of these findings and potential for developing a custom sampling plan to estimate densities of phytoseiids inhabiting sampled trees in avocado orchards in California are discussed.

How Far Can the Palm Weevil, Rhynchophorus vulneratus (Coleoptera: Curculionidae), Fly?

The palm weevil, Rhynchophorus vulneratus, is native to Southeast Asia and was recovered from an infested Canary Islands date palm in Laguna Beach, California, USA, in 2010. The detection of this potentially destructive palm pest initiated a detection, containment, and eradication program that was reliant, in part, on the deployment of bucket traps loaded with aggregation pheromone and baited with fermenting fruit. A key question that pertained to the deployment of traps was “how far can R. vulneratus fly?” This question could not be answered and in response to this knowledge deficit, computerized flight mill studies were conducted with field-captured R. vulneratus in an outdoor screen house in Sumatra, Indonesia. Of the 63 weevils tethered to flight mills, ∼27% failed to fly >1 km in 24 h and were excluded from analyses. In total, 46 weevils (35 females and 11 males) flew >1 km on flight mills and of these adults, the average total distance flown in 24 h was significantly greater for females (∼32 km) when compared with males (∼15 km). A small proportion of females (∼16%) flew 50-80 km, and one female flew 100.1 km in 24 h. Flying weevils exhibited an average weight loss of ∼13–17% and non-flying control weevils (n=27) lost 10–13% body weight in 24 h. The distribution of flight distances for female and male weevils combined was leptokurtic, which suggests that faster than expected spread by R. vulneratus may be possible in invaded areas.

Sampling method evaluation and empirical model fitting for count data to estimate densities of Oligonychus perseae (Acari: Tetranychidae) on 'Hass' avocado leaves in southern California

Oligonychus perseae (Acari: Tetranychidae) is an important foliar spider mite pest of 'Hass' avocados in several commercial production areas of the world. In California (USA), O. perseae densities in orchards can exceed more than 100 mites per leaf and this makes enumerative counting prohibitive for field sampling. In this study, partial enumerative mite counts along half a vein on an avocado leaf, an industry recommended practice known as the "half-vein method", was evaluated for accuracy using four data sets with a combined total of more than 485,913 motile O. perseae counted on 3849 leaves. Sampling simulations indicated that the half-vein method underestimated mite densities in a range of 15-60 %. This problem may adversely affect management of this pest in orchards and potentially compromise the results of field research requiring accurate mite density estimation. To address this limitation, four negative binomial regression models were fit to count data in an attempt to rescue the half-vein method for estimating mite densities. These models were incorporated into sampling plans and evaluated for their ability to estimate mite densities on whole leaves within 30-tree blocks of avocados. Model 3, a revised version of the original half-vein model, showed improvement in providing reliable estimates of O. perseae densities for making assessments of general leaf infestation densities across orchards in southern California. The implications of these results for customizing the revised half-vein method as a potential field sampling tool and for experimental research in avocado production in California are discussed.

Phenology of Asian Citrus Psyllid (Hemiptera: Liviidae), With Special Reference to Biological Control by Tamarixia radiata , in the Residential Landscape of Southern California

Since its discovery in 2008, the pestiferous Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), has become widely established in residential citrus trees throughout southern California. In 2011, Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae), a host-specific parasitoid of D. citri , sourced from Punjab Pakistan, was introduced into California as part of a classical biological program aimed at suppressing D. citri populations in urban areas. Despite these release efforts, little is known about the population dynamics of D. citri in urban citrus or the efficacy of T. radiata in controlling psyllid populations in urban-grown citrus. To address this shortcoming, the population phenology of D. citri was monitored biweekly for 2-3 yr on five different host plants (Rutaceae) at 11 residential sites across Riverside and Los Angeles Counties in southern California. Citrus flush growth patterns and parasitoid activity levels were also assessed. Urban D. citri populations were present year round at each site, with highest densities occurring over July through November. Temperature was an important indicator of overall D. citri densities with positive correlations across all life stages. Regularly flushing lime trees consistently supported the highest densities of psyllid eggs and nymphs, while equally vigorous flushing curry leaf plants supported the highest adult densities. While T. radiata activity was detected at all sites, average year-round percent parasitism was low throughout the study, averaging <5% in 2012, 2013, and 2014.

The Scirtothrips perseae species-group (Thysanoptera), with one new species from avocado, Persea americana

Following recent molecular studies on avocado thrips, a new species is described from Costa Rica, Ecuador, and Colombia from the young leaves of avocado, Persea americana. Scirtothrips hansoni sp.n. is closely related to the Californian pest, S. perseae, and also to S. astrictus from Costa Rica that remains known from a single female. An illustrated key to these three species is provided.

How Far Can the Red Palm Weevil (Coleoptera: Curculionidae) Fly?: Computerized Flight Mill Studies With Field-Captured Weevils

Adult Rhynchophorus ferrugineus (Olivier) captured in pheromone-baited traps in commercial date palm orchards in the Al Ahsaa Directorate, Kingdom of Saudi Arabia, were used in computerized flight mill studies to determine the flight characteristics of this highly invasive and destructive palm pest. Flight mill studies were run at three different time periods, winter (December), spring (March), and summer (May). Of the 192 weevils tethered to flight mills ∼30% failed to fly > 1 km. Of those weevils flying > 1 km (n = 139), 55% flew > 10 km, and of these flyers 5% flew > 50 km in 24 h. Flying weevils exhibited an average weight loss of 20-30% and nonflying control weevils lost ∼9-13% body weight in 24 h. Male and female weevils flying in summer (average laboratory temperature was ∼27°C) flew the longest average distances (∼25-35 km), exhibited highest weight reductions (∼30%), and greatest mortality rates (∼80%). Consequently, time of year not weevil sex or color morph had a consistent and significant effect on flight activity, weight loss, and survivorship rates. Flight activity was predominantly diurnal commencing around 5:00 a.m. and peaking between 9-11:00 a.m. before tapering off. The distribution of flight distances combined across season and sex was mesokurtic (i.e., normally distributed).

Comparison and Field Validation of Binomial Sampling Plans for Oligonychus perseae (Acari: Tetranychidae) on Hass Avocado in Southern California

Oligonychus perseae Tuttle, Baker, & Abatiello is a foliar pest of 'Hass' avocados [Persea americana Miller (Lauraceae)]. The recommended action threshold is 50-100 motile mites per leaf, but this count range and other ecological factors associated with O. perseae infestations limit the application of enumerative sampling plans in the field. Consequently, a comprehensive modeling approach was implemented to compare the practical application of various binomial sampling models for decision-making of O. perseae in California. An initial set of sequential binomial sampling models were developed using three mean-proportion modeling techniques (i.e., Taylor's power law, maximum likelihood, and an empirical model) in combination with two-leaf infestation tally thresholds of either one or two mites. Model performance was evaluated using a robust mite count database consisting of >20,000 Hass avocado leaves infested with varying densities of O. perseae and collected from multiple locations. Operating characteristic and average sample number results for sequential binomial models were used as the basis to develop and validate a standardized fixed-size binomial sampling model with guidelines on sample tree and leaf selection within blocks of avocado trees. This final validated model requires a leaf sampling cost of 30 leaves and takes into account the spatial dynamics of O. perseae to make reliable mite density classifications for a 50-mite action threshold. Recommendations for implementing this fixed-size binomial sampling plan to assess densities of O. perseae in commercial California avocado orchards are discussed.

Host Range Testing of Diaphorencyrtus aligarhensis (Hymenoptera: Encyrtidae) for Use in Classical Biological Control of Diaphorina citri (Hemiptera: Liviidae) in California

Host range tests for Diaphorencyrtus aligarhensis (Shafee, Alam, & Agarwal) (Hymenoptera: Encyrtidae), an endoparasitoid of Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), sourced from Punjab Pakistan, were conducted in quarantine at the University of California, Riverside, CA. Seven nontarget psyllid species representing four psyllid families were exposed to mated D. aligarhensis females in four different treatment types: 1) short sequential no-choice treatments, 2) prolonged sequential no-choice treatments, 3) prolonged no-choice static treatments, and 4) choice treatments. Selection of nontarget psyllid species was based on phylogenetic proximity to D. citri, likelihood of being encountered by D. aligarhensis in the prospective release areas in California, and psyllid species in biological control of invasive weeds. D. aligarhensis exhibited high host affinity to D. citri, and only parasitized one nontarget species, the pestiferous potato psyllid, Bactericera cockerelli (Sulc), at low levels (<14%). Based on the results of this study, we conclude that D. aligarhensis has a narrow host range and exhibits a high level of host specificity, as it shows a significant attack preference for the target pest, D. citri. Results presented here suggest D. aligarhensis poses minimal risk to nontarget psyllid species in California.

The Scirtothrips dorsalis Species Complex: Endemism and Invasion in a Global Pest

Invasive arthropods pose unique management challenges in various environments, the first of which is correct identification. This apparently mundane task is particularly difficult if multiple species are morphologically indistinguishable but accurate identification can be determined with DNA barcoding provided an adequate reference set is available. Scirtothrips dorsalis is a highly polyphagous plant pest with a rapidly expanding global distribution and this species, as currently recognized, may be comprised of cryptic species. Here we report the development of a comprehensive DNA barcode library for S. dorsalis and seven nuclear markers via next-generation sequencing for identification use within the complex. We also report the delimitation of nine cryptic species and two morphologically distinguishable species comprising the S. dorsalis species complex using histogram analysis of DNA barcodes, Bayesian phylogenetics, and the multi-species coalescent. One member of the complex, here designated the South Asia 1 cryptic species, is highly invasive, polyphagous, and likely the species implicated in tospovirus transmission. Two other species, South Asia 2, and East Asia 1 are also highly polyphagous and appear to be at an earlier stage of global invasion. The remaining members of the complex are regionally endemic, varying in their pest status and degree of polyphagy. In addition to patterns of invasion and endemism, our results provide a framework both for identifying members of the complex based on their DNA barcode, and for future species delimiting efforts.

Classical Biological Control of Invasive Legacy Crop Pests: New Technologies Offer Opportunities to Revisit Old Pest Problems in Perennial Tree Crops

Advances in scientific disciplines that support classical biological control have provided "new tools" that could have important applications for biocontrol programs for some long-established invasive arthropod pests. We suggest that these previously unavailable tools should be used in biological control programs targeting "legacy pests", even if they have been targets of previously unsuccessful biocontrol projects. Examples of "new tools" include molecular analyses to verify species identities and likely geographic area of origin, climate matching and ecological niche modeling, preservation of natural enemy genetic diversity in quarantine, the use of theory from invasion biology to maximize establishment likelihoods for natural enemies, and improved understanding of the interactions between natural enemy and target pest microbiomes. This review suggests that opportunities exist for revisiting old pest problems and funding research programs using "new tools" for developing biological control programs for "legacy pests" could provide permanent suppression of some seemingly intractable pest problems. As a case study, we use citricola scale, Coccus pseudomagnoliarum, an invasive legacy pest of California citrus, to demonstrate the potential of new tools to support a new classical biological control program targeting this insect.

Exposure of Brown Recluse and Brown Widow Spiders (Araneae: Sicariidae, Theridiidae) to a Commercial Sulfuryl Fluoride Fumigation

The body of pesticide research on spiders is sparse with most studies using topical or residual applications to assess efficacy. Data on the effects of fumigation on spider survivorship are scarce in the scientific literature. In this study, we exposed adult male and female brown recluse spiders, Loxosceles reclusa Gertsch & Mulaik, and female brown widow spiders, Latrodectus geometricus C. L. Koch, to a commercial fumigation event using sulfuryl fluoride directed at termite control. General consensus from the pest control industry is that fumigation is not always effective for control of spiders for a variety of reasons, including insufficient fumigant dosage, particularly, for contents of egg sacs that require a higher fumigant dosage for control. We demonstrated that a sulfuryl fluoride fumigation with an accumulated dosage of 162 oz-h per 1,000 ft(3) at 21°C over 25 h (≈1.7 × the drywood termite dosage) directed at termites was sufficient to kill adult brown recluse and brown widow spiders. The effectiveness of commercial fumigation practices to control spiders, and particularly their egg sacs, warrants further study.

Phenology of Asian citrus psyllid (Hemiptera: Liviidae) and associated parasitoids on two species of Citrus, kinnow mandarin and sweet orange, in Punjab Pakistan

The population phenology of Asian citrus psyllid, Diaphorina citri Kuwayama, was monitored weekly for 110 wk on two species of Citrus, kinnow mandarin and sweet orange, at two different research sites in Faisalabad, Punjab Pakistan. Citrus flush growth patterns were monitored and natural enemy surveys were conducted weekly. Flush patterns were similar for kinnow and sweet orange. However, flush on sweet orange was consistently more heavily infested with Asian citrus psyllid than kinnow flush; densities of Asian citrus psyllid eggs, nymphs, and adults were higher on sweet orange when compared with kinnow. When measured in terms of mean cumulative insect or Asian citrus psyllid days, eggs, nymphs, and adults were significantly higher on sweet orange than kinnow. Two parasitoids were recorded attacking Asian citrus psyllid nymphs, Tamarixia radiata (Waterston) and Diaphorencyrtus aligarhensis (Shafee, Alam and Agarwal). The dominant parasitoid species attacking Asian citrus psyllid nymphs on kinnow and sweet orange was T. radiata, with parasitism averaging 26%. D. aligarhensis parasitism averaged 17%. Generalist predators such as coccinellids and chrysopids were collected infrequently and were likely not important natural enemies at these study sites. Immature spiders, in particular, salticids and yellow sac spiders, were common and may be important predators of all Asian citrus psyllid life stages. Low year round Asian citrus psyllid densities on kinnow and possibly high summer temperatures, may, in part, contribute to the success of this cultivar in Punjab where Candidatus Liberibacter asiaticus, the putative causative agent of huanglongbing, a debilitating citrus disease, is widespread and vectored by Asian citrus psyllid.

Assessing the flight capabilities of the goldspotted oak borer (Coleoptera: Buprestidae) with computerized flight mills

The goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), is native to southern Arizona and is an invasive wood-boring beetle that has caused considerable mortality to native oak species in southern California. Assessing the dispersal capabilities of this woodborer may help to determine its potential environmental and economic risk within the invaded region, and possibly assist with the development of species-specific management strategies. The flight performance of A. auroguttatus adults under different age, mating, and nutritional status was assessed by tethering individuals to computerized flight mills for a 24-h trial period to collect information on total distance flown, flight times and velocities, number and duration of flight bouts, and postflight weight. The nutritional status and body size (i.e., elytron length) of A. auroguttatus adults had a significant influence on overall flight performance. Mating status and gender had no significant influence on total flight distance, duration, velocity, and flight bout time. Significant interactions between nutritional status and age were observed in the overall flight performance of A. auroguttatus, with decreased flight activity in old (approximately 6 d of age) starved individuals during a 24-h trial period. Overall, results of these flight mill assays indicate that A. auroguttatus is unable to disperse long distances across habitats that lack suitable oak hosts. This work supports the hypothesis that human-aided transportation via infested oak firewood from southern Arizona across the Sonoran desert likely caused the initial introduction, and subsequent satellite infestations of A. auroguttatus within southern California's native oak woodlands.

Host range testing of Tamarixia radiata (Hymenoptera: Eulophidae) sourced from the Punjab of Pakistan for classical biological control of Diaphorina citri (Hemiptera: Liviidae: Euphyllurinae: Diaphorinini) in California

ABSTRACT Tests evaluating the host range of Tamarixia radiata (Waterson) (Hymenoptera: Eulophidae), a parasitoid of the pestiferous Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), sourced from the Punjab of Pakistan, were conducted in quarantine at the University of California, Riverside, CA. Seven nontarget psyllid species (five native and two self-introduced species) representing five families were exposed to T radiata under the following three different exposure scenarios: 1) sequential no-choice tests, 2) static no-choice tests, and 3) choice tests. Nontarget species were selected for testing based on the following criteria: 1) taxonomic relatedness to the target, D. citri; 2) native psyllids inhabiting native host plants related to citrus that could release volatiles attractive to T. radiata; 3) native psyllids with a high probability of occurrence in native vegetation surrounding commercial citrus groves that could be encountered by T. radiata emigrating from D. citri-infested citrus orchards; 4) a common native pest psyllid species; and 5) a beneficial psyllid attacking a noxious weed. The results of host range testing were unambiguous; T radiata exhibited a narrow host range and high host specificity, with just one species of nontarget psyllid, the abundant native pest Bactericera cockerelli Sulc, being parasitized at low levels (< 5%). These results suggest that the likelihood of significant nontarget impacts is low, and the establishment of T. radiata in southern California for the classical biological control of D. citri poses negligible environmental risk.

Competition between honeydew producers in an ant-hemipteran interaction may enhance biological control of an invasive pest

Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), is an invasive citrus pest in southern California, which secretes honeydew and has the potential to spread a lethal bacterial disease, huanglongbing, of citrus. In urban citrus, Argentine ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae), also an invasive pest, tends honeydew-producing hemipterans. We used field data to determine whether the mutualistic relationship between L. humile and six established species of honeydew producers may hinder or favor the establishment of D. citri and its biological control with Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae) in citrus via competition or mutualism for ants, respectively. In the field, L. humile and D. citri are engaged in a mutualistic relationship. Ants harvest solid honeydew secreted by psyllid nymphs and tended more than 55% of observed D. citri colonies. Linepithema humile displayed a preference hierarchy when tending honeydew producers infesting citrus. It responded equally or less intensively to D. citri than to other honeydew-producing species. Consequently, the mutualism between L. humile and D. citri was affected by the presence of other honeydew-producing species, and the percentage of D. citri colonies tended by L. humile. The number of ants per D. citri colony also decreased as the number of other honeydew producers increased. Diaphorina citri density was also affected by the presence of other honeydew producers. Both colony size and the number of D. citri nymphs counted per tree decreased as the number of other honeydew producers increased. Our results indicate that competition between honeydew producers for the mutualist ant L. humile may hinder the establishment of D. citri by possibly facilitating increased biological control.

The lesser of two weevils: molecular-genetics of pest palm weevil populations confirm Rhynchophorus vulneratus (Panzer 1798) as a valid species distinct from R. ferrugineus (Olivier 1790), and reveal the global extent of both

The red palm weevil (RPW) is a major pest of palms. It is native to southeast Asia and Melanesia, but in recent decades has vastly expanded its range as the result of multiple accidental anthropogenic introductions into the Middle East, Mediterranean Basin, Caribbean, and U.S.A. Currently regarded as a single species, Rhynchophorus ferrugineus (Olivier), RPW displays remarkable color variation across its range, and consequently has a taxonomic history littered with new species descriptions and synonymization. We compared DNA sequences of the mitochondrial cytochrome oxidase subunit I (COI) gene from RPW populations throughout the native and invaded ranges, to investigate the specific status and invasion history of this serious economic pest, and to identify possible common routes of entry. Analyses of COI haplotype data provide conclusive support, corroborated by sequences of additional nuclear gene regions, for the existence of at least two predominantly allopatric species. The true R. ferrugineus is native only to the northern and western parts of continental southeast Asia, Sri Lanka and the Philippines, and is responsible for almost all invasive populations worldwide. In contrast, the second species, which is currently synonymized under R. ferrugineus and should be resurrected under the name R. vulneratus (Panzer), has a more southern distribution across Indonesia, and is responsible for only one invasive population; that in California, U.S.A. The distribution of COI haplotypes is used to discuss the possible existence of further cryptic species, sources and routes of entry of different invasive populations, and the implications of our findings for current control methods.

Phylogeographic structure, outbreeding depression, and reluctant virgin oviposition in the bean thrips, Caliothrips fasciatus (Pergande) (Thysanoptera: Thripidae), in California

Bean thrips, Caliothrips fasciatus, is native to western North America. Once considered a pest of several crops in its native area, its pest status has waned over recent decades. However, due to its habit of aggregating in the navel of navel oranges, bean thrips remains economically important because some countries importing oranges from California have designated it a quarantine pest. Despite continued propagule pressure, bean thrips has never established outside North America. We examined genetic variation in mitochondrial DNA among Californian populations of C. fasciatus and found that potentially two cryptic species are present (supported by Kimura 2-P distances): a common widespread form B and a rarer form A with a very limited distribution. Form B showed strong phylogeographic structure, with many haplotypes having a limited geographic distribution. Inter-population crossing experiments between three geographically isolated populations of form B resulted in the production of some female offspring, indicating a degree of compatibility between these populations of this haplodiploid species. However, substantial outbreeding depression was also detected. A low frequency of offspring production by hetero-population pairs was evidence of pre-mating isolation, while post-mating isolation was also evident in the elevated mortality of fertilized eggs in successful hetero-population crosses. One surprising finding was the total lack of offspring production by virgin females when isolated individually. However, virgin females did produce sons in the presence of other virgin females. A test for the presence of Wolbachia showed that form B was not infected, but that some populations of the rarer form A were.

Surveys for Stenoma catenifer (Lepidoptera: Elachistidae) and associated parasitoids infesting avocados in Perú

Surveys for Stenoma catenifer Walsingham, the avocado seed moth, and its associated larval parasitoids were conducted in the Departments of Junín, Huánuco, Cusco, and Madre de Dios in Perú. Fruit infestation levels in some areas ranged from 0 to 58%, and parasitism of S. catenifer larvae in Junín and Huánuco was 23%. Five species of hymenopteran parasitoid in two families, Braconidae (Apanteles sp., Hypomicrogaster sp., and Chelonus sp.) and Ichneumonidae (Pristeromerus sp. and Xiphosomella sp.), were reared from larvae, and one species of tachinid fly (Chrysodoria sp.) emerged from pupae. The dominant larval parasitoid, a gregarious Apanteles sp., accounted for 55% of parasitized hosts. Branch and twig tunneling by S. catenifer larvae in a commercial Hass avocado orchard was observed in Cusco. The field attractiveness of the sex pheromone of S. catenifer was demonstrated with 73% of monitoring traps deployed in three departments (Junín, Huánuco, and Cusco) catching male moths. Approximately 55% of avocado fruit sourced from the Province of Chanchamayo (Junin) and purchased at the Mercado Modelo de Frutas in La Victoria, in central Lima were infested with larvae of S. catenifer. Infested avocado fruit sold at this market could represent a potential incursion threat to coastal Hass avocado production regions in Perú that are reportedly free of this pest.

Field optimization of the sex pheromone of Stenoma catenifer (Lepidoptera: Elachistidae): evaluation of lure types, trap height, male flight distances, and number of traps needed per avocado orchard for detection

The sex pheromone of Stenoma catenifer was evaluated in commercial avocado orchards in Guatemala to determine operational parameters, such as optimal lure type, trap height, trap density and estimates of the distances that male moths fly. Of four pheromone dispensers tested, gray and white rubber septa were of equal efficacy, whereas 1-ml low-density polyethylene vials and 2×3-cm polyethylene ziplock bags were least efficacious. The height at which wing traps were hung did not significantly affect the number of adult male S. catenifer captured. For monitoring S. catenifer, these data suggest that the pheromone should be dispensed from gray rubber septa in wing traps hung inside the tree canopy at 1.75 m, a height convenient for trap placement and monitoring. Mark-recapture studies of male S. catenifer indicated that, on average, males flew 67 m in one night. However, it is likely that this is an underestimate of the distance that male moths are capable of flying in a single night. Probabilistic modeling of S. catenifer capture data from different numbers of pheromone traps deployed in seven commercial avocado orchards of varying sizes and infestation levels suggested that 10-13 randomly deployed traps per orchard for a 7-day period are needed to detect at least one male S. catenifer with 90% confidence. These data provide sufficient information to develop effective protocols for using the S. catenifer pheromone to detect and monitor this pest in countries with endemic populations that are exporting fresh avocados, and for quarantine detection and incursion monitoring in countries receiving avocado imports from high risk areas.

Genetic structure of Graphocephala atropunctata (Hemiptera: Cicadellidae) populations across its natural range in California reveals isolation by distance

The genetic structure of 23 populations of Graphocephala atropunctata (Signoret) (Hemiptera: Cicadellidae: Cicadellinae), a vector of the plant pathogenic bacterium Xylellafastidiosa Wells et al., was investigated using ribosomal 28S and mitochondrial cytochrome C oxidase I gene sequences. The 28S sequences were identical across all G. atropunctata specimens and populations, but 16 mitochondrial haplotypes were detected and significant interpopulation differences were found in the distribution of these haplotypes. Pairwise estimates of Fst correlated positively with geographical distance between populations, a phenomenon known as genetic isolation by distance. Thus, despite potential for widespread movement of G. atropunctata through nursery and agricultural industries, isolated populations of G. atropunctata have remained genetically distinct, suggesting that negligible numbers of G. atropunctata are actually transported or population interbreeding rarely occurs. The phylogenetic relationship between G. atropunctata and two additional congeners, Graphocephala cythura Baker and Graphocephala flavovittata Metcalf, which have overlapping distributions with G. atropunctata, also was investigated. Although 28S sequences of G. flavovittata were strikingly similar to those of G. atropunctata, mitochondrial DNA (mtDNA) suggests that both species are genetically distinct from G. atropunctata.

Field evaluation of systemic imidacloprid for the management of avocado thrips and avocado lace bug in California avocado groves

BACKGROUND

The efficacy of systemic applications of imidacloprid for the management of avocado thrips and avocado lace bug was determined in field trials. Following insecticide treatment by chemigation, leaves of appropriate age for each insect were sampled over a 6 month period and used for bioassays. Imidacloprid residues were measured by ELISA in leaves used for bioassays to determine concentrations of insecticide that were toxic to both pests.

RESULTS

The uptake of imidacloprid into treated trees was extremely slow, peaking in the current year's leaf flush at only 8 ng cm(-2) leaf tissue after 15 weeks. Avocado thrips mortality in bioassays with young flush leaves, the preferred feeding substrate for this insect, was minimal, indicating that imidacloprid concentrations were below threshold levels needed for effective control. Residues present in older leaves, which are preferred by the avocado lace bug, were higher than in young flush leaves, and provided good control of this pest. Probit analysis of bioassay data showed that the avocado lace bug (LC(50) = 6.1 ng imidacloprid cm(-2) leaf tissue) was more susceptible to imidacloprid than the avocado thrips (LC(50) = 73 ng imidacloprid cm(-2) leaf tissue).

CONCLUSIONS

In spite of the slow uptake of imidacloprid into avocado trees, the levels of imidacloprid would be sufficient to control avocado lace bug infestations. In contrast, the slow uptake would be problematic for avocado thrips control because inadequate levels of insecticide accumulate in new flush foliage and would allow avocado thrips populations to build to levels that would subsequently damage developing avocado fruit.

Nuclear-mitochondrial barcoding exposes the global pest Western flower thrips (Thysanoptera: Thripidae) as two sympatric cryptic species in its native California

Over the past three decades, Western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), has become a major worldwide pest of many agricultural and horticultural crops. In response, much time, money, and effort have been put into pure and applied research focusing on the biology and control of this pest. Western flower thrips is native to Western North America and widespread in California. High levels of variation in basic biology, pest status, and resistance to insecticides bring into question the specific status of Western flower thrips. We used nuclear-mitochondrial barcoding to compare DNA sequences of nuclear and mitochondrial genes between Western flower thrips populations across California, looking for association between these unlinked loci. Sequences of D2 domain of 28S and cytochrome c oxidase I gene revealed the existence of two distinct but sympatric genetic entities, and we describe a simple polymerase chain reaction-based method for diagnosing these entities. The complete association of these nuclear and mitochondrial loci in areas of sympatry is indicative of reproductive isolation and the existence of two cryptic species, both of which key out to Western flower thrips by using morphological characters. The finding that Western flower thrips is a complex of two species has important implications for past, current, and most importantly future research on these pests.

Synthesis and field evaluation of the sex pheromone of Stenoma catenifer (Lepidoptera: Elachistidae)

Field trials of the sex pheromone of an important and potentially invasive pest of avocados, Persea americana Miller (Lauraceae), Stenoma catenifer Walsingham (Lepidoptera: Elachistidae), were carried out in commercial avocado orchards in Guatemala. The results indicated that the pheromone consists of a single component, (9Z)-9,13-tetradecadien-1-ynal; blends of this compound with a range of ratios of the corresponding alcohol and acetate, or with (6Z,9Z)-tricosadiene, which was present in pheromone gland extracts, were equally or less attractive to male moths than the single component. A range of doses from 10 microg to 1 mg were equally attractive, and lures remained attractive for periods of several weeks. Male moth flight activity peaked between 0230 and 0430 hours. Overall, trap catches were relatively low, similar to what was reported for the congeneric Stenoma cecropia Meyrick, suggesting that this species may use other signals in addition to pheromones during mate location. Nevertheless, the pheromone will be useful for detection of S. catenifer, particularly in areas where there is a risk of the moth invading and establishing due to increased commerce in fresh avocados, and for certifying export orchards as being free of S. catenifer.

Lepidoptera and associated parasitoids attacking Hass and non-Hass avocados in Guatemala

A 5-mo survey for fruit feeding Lepidoptera attacking Hass and non-Hass avocados (Persea americana Miller [Lauraceae]) was conducted in Guatemala from 1 November 2006 to 1 April 2007. In total, 6,740 fruit were collected from 22 different areas in Guatemala. Eight species of Lepidoptera, of which at least two are species new to science, were reared from avocado fruit. Reared Lepidoptera were Amorbia santamaria Phillips and Powell, Cryptaspasma sp. nr. lugubris, Euxoa sorella Schaus, Histura n. sp., Holcocera n. sp., Micrathetis triplex Walker, Netechma pyrrhodelta (Meyrick), and Stenoma catenifer Walsingham. Hymenopteran parasitoids were reared from larvae of C. sp. nr. lugubris and S. catenifer. One species of parasitoid, Pseudophanerotoma sp., was reared from field collected C. sp. nr. lugubris larvae. The dominant parasitoid reared from S. catenifer was a gregarious Apanteles sp. Other parasitoid species reared from S. catenifer larvae were Brachycyrtus sp., Macrocentrus sp., and Pristomerus sp. The oviposition preference of C. sp. nr. lugubris for avocado fruit hanging in trees, dropped fruit on the ground, or exposed avocado seeds was investigated by studying the oviposition preferences of adult female moths and determining egg hatch times in the laboratory, and by investigating the longevity of avocado fruit on the ground under prevailing field conditions. Together, data from these studies suggested that C. sp. nr. lugubris may be an unrecognized pest of avocados that causes hanging fruit to drop to the ground prematurely. The influence of season and altitude on the phenology and distribution of avocado feeding Lepidoptera in Guatemala is discussed.

Bioecology of Stenoma catenifer (Lepidoptera: Elachistidae) and associated larval parasitoids reared from Hass avocados in Guatemala

A 10-wk study of the avocado seed-feeding moth Stenoma catenifer Walsingham (Lepidoptera: Elachistidae), was conducted in a commercial 'Hass' avocado (Persea americana Miller [Lauraceae]) orchard in Guatemala. Up to 45% of fruit in the orchard were damaged by larval S. catenifer. Larval-to-adult survivorship for 1,881 S. catenifer larvae in Hass fruit was 37%, and adult sex ratio was 51% female. Four species of larval parasitoid were reared from field-collected S. catenifer larvae. The most common parasitoid reared was a gregarious Apanteles sp., which parasitized 53% of larvae and produced on average eight to nine cocoons per host. Apanteles sp. sex ratio was 47% female and 87% of parasitoids emerged successfully from cocoons. Apanteles sp. longevity was approximately equal to 1.5 d in the absence of food, and when provisioned with honey, parasitoids survived for 5-7 d. The mean number of cocoons produced by Apanteles sp. per host, and larval parasitism rates were not significantly affected by the number of S. catenifer larvae inhabiting seeds. Oviposition studies conducted with S. catenifer in the laboratory indicated that this moth lays significantly more eggs on the branch to which the fruit pedicel is attached than on avocado fruit. When given a choice between Hass and non-Hass avocados, S. catenifer lays up to 2.69 times more eggs on Hass.