Understanding the movement and dispersal patterns of released Fopius arisanus (Hymenoptera: Braconidae) parasitoids in a papaya orchard

Implementation of augmentative biological control requires estimates of parasitoid dispersal from the release point to determine appropriate release density, spacing, and timing. This study evaluated the movement patterns of Fopius arisanus Sonan (Hymenoptera: Braconidae) parasitoids, which have historically been used to control invasive tephritid fruit flies. The wasps were released from the central point, and dispersal was monitored over time using parasitism in sentinel fruit and trap captures at 40 points radiating out from the center (15-240 m). The releases were conducted 4 times during June, July, September, and November 2006. The data showed that there were large declines in dispersal by distance. Parasitism was greatest closest to the release point, within 30 m. Parasitism was also greatest within the first 24 h of the release. After 1 wk, parasitism decreased from 41% to 1.5% within 30 m. These data correlated strongly with trap capture data, which also showed that parasitoid movement favored the SE region of our release site, roughly corresponding to the overall prevailing winds. Wind speed, relative humidity, and temperature all affected parasitoid movement during our trial, indicating the complex environmental factors that can affect release success. This is the first report of dispersal metrics for F. arisanus. Our findings are in agreement with other similar studies on braconid movement generally and suggest that frequent, high-density releases are most effective since the dispersal of F. arisanus is limited and retention in the environment is low. We discuss our results in the context of international augmentative biological control release programs.

Previously introduced braconid parasitoids target recent olive fruit fly (Bactrocera oleae) invaders in Hawai'i

The olive fruit fly Bactrocera oleae (Diptera: Tephritidae) was detected on Maui and Hawai'i Islands in 2019, affecting yields and quality of the state's emerging olive oil industry. Given previous parasitoid releases to control other invasive frugivorous tephritids in Hawai'i, we were interested in determining whether these parasitoids were naturally targeting recent olive fly invaders in field, if local olive cultivar differences affected parasitization rates, and if there was a seasonal pattern of parasitization that could inform future management decisions. To address these questions, we collected data from olive growing in Hawai'i during 2021 and 2022. During the fruiting season we collected monthly samples and reared out B. oleae in the lab. We detected two previously introduced braconid wasps: first Diachasmimorpha tryoni during 2021 and 2022 and later Fopius arisanus during the 2022 collection. Cultivar effects were limited to a single site in our study, where more D. tryoni were reared from 'Arbequina' olives. Seasonality of olive fruit fly and parasitoid activity was earlier in lower elevation sites, as expected based on tree phenology and temperature-dependent insect development. This represents the first report of D. tryoni parasitism activity against B. oleae and may reflect elevational effects combined with the ecological complexity in interactions between multiple invasive arthropod pests, their invasive and cultivated plant hosts, and introduced braconid parasitoids.

Physical, Chemical, and Sensory Properties of a Turmeric-Fortified Pineapple Juice Beverage

Beverage mixtures based on pineapple (Ananas comosus) and turmeric (Curcuma longa) juice as a ready-to-drink product were developed, and their physicochemical, nutritional, and sensory properties were evaluated. Four different concentrations of turmeric juice (5%, 10%, 15%, and 20% (v/v)) were added to pineapple juice to make turmeric-fortified pineapple (TFP) juice samples. Pineapple juice without turmeric was the control. The L*, a*, b*, titratable acidity (TA), total antioxidant capacity, and %DPPH scavenging values, as well as the concentrations of the phenolic compounds curcumin and demethoxycurcumin, were significantly increased with increasing turmeric concentration. Thirty volatile compounds were detected in the mixed juice samples with turmeric. Most of the turmeric-specific compounds, including monoterpenes, sesquiterpenes and turmerones, were detected in the TFP juice samples. While the antioxidant activity of the juice samples increased with increasing turmeric concentration, the pineapple juice fortified with 10% turmeric (10%T) had the best overall quality as determined by panelists. Greater concentrations of turmeric were associated with decreased palatability due to reduced mouthfeel and sweetness and increased aftertaste and sourness. These results suggest that the 10%T juice could be developed into a commercial functional beverage with increased overall flavor and nutritional quality.

Molecular and behavioral studies reveal differences in olfaction between winter and summer morphs of Drosophila suzukii

Spotted-wing drosophila, Drosophila suzukii (Matsumura), is a major economic pest of several fruit crops in Europe, North and South America, and other parts of the world because it oviposits in ripening thin-skinned fruits. This vinegar fly exhibits two distinct morphotypes: a summer and a winter morph. Although adaptations associated with the winter morph enhance this invasive pest's capacity to survive in cold climates, winter is still a natural population bottleneck. Since monitoring early spring populations is important for accurate population forecasts, understanding the winter morph's response to olfactory cues may improve current D. suzukii management programs. In this study, a comparative transcriptome analysis was conducted to assess gene expression differences between the female heads of the two D. suzukii morphs, which showed significant differences in 738 genes (p ≤ 0.0001). Out of twelve genes related to olfaction determined to be differentially expressed in the transcriptome, i.e., those related to location of food sources, chemosensory abilities, and mating behavior, nine genes were upregulated in the winter morph while three were downregulated. Three candidate olfactory-related genes that were most upregulated or downregulated in the winter morph were further validated using RT-qPCR. In addition, behavioral assays were performed at a range of temperatures to confirm a differing behavioral response of the two morphs to food odors. Our behavioral assays showed that, although winter morphs were more active at lower temperatures, the summer morphs were generally more attracted to food odors. This study provides new insights into the molecular and behavioral differences in response to olfactory cues between the two D. suzukii morphs that will assist in formulating more effective monitoring and physiological-based control tools.

Diet Hierarchies Guide Temporal-Spatial Variation in Drosophila suzukii Resource Use

Among insects, female oviposition preferences are critical to understanding the evolutionary dynamics between herbivores and hosts. Previous studies have shown Drosophila resource use has a strong genetic basis, although there is evidence that preferences are adaptable given isolation from ancestral hosts. Given the high degree of adaptability and behavioral plasticity of invasive species, we were interested in the mechanisms affecting host preferences of the invasive fruit fly, Drosophila suzukii, which in recent years has developed a nearly global range infesting small fruit crops. We studied the diet hierarchies of D. suzukii using a combination of laboratory and field assays designed to assess how female oviposition host choice differs given the availability of, and experience with, different fruit and non-fruit hosts. We found that host preferences did not shift over time and flies reared on two differential isolated diets up to F5 behaved and performed similarly regardless of diet lineage. Rather, female host choice appeared guided by a fixed hierarchical system of host preferences. Raspberry was more preferred to mushroom, which was more preferred to goose manure. However, if preferred resources were absent, the use of less-preferred resources was compensatory. We suggest that among niche specialists, such as D. suzukii, these hierarchies may support a bet-hedging strategy, rather than multiple-niche polymorphism, allowing for niche separation during periods of increased competition, while maintaining more diverse, ancestral feeding behaviors when preferred resources are scarce.

Does Habituation Affect the Efficacy of Semiochemical Oviposition Repellents Developed Against Drosophila suzukii?

The application of feeding and oviposition repellents is limited to arthropod systems in which habituation does not occur. Although several compounds appear to reduce Drosophila suzukii Matsumura (Dipetra: Drosophilidae) oviposition in berries, previous studies have yet to address whether habituation is a significant risk following preexposure. We tested the response of adult female D. suzukii to three previously identified semiochemical oviposition repellents, 1-octen-3-ol (octenol), ±-geosmin, and 2-n-pentylfuran, following adult and larval preexposure. Using a two-choice gated trap capture assay, we assessed captures in repellent-treated versus blank traps, female survival, and oviposition frequency in the selected trap. We did not find evidence of habituation to octenol or 2-pentylfuran in adult flies preexposed for 24, 48, or 72 hr. When exposed to each of the repellents as larvae, D. suzukii showed similar deterrence as those exposed as adults alone. However, mortality did decrease in F1 octenol treated flies. In contrast with previous investigations we did not observe repellent effects in response to geosmin. Our results suggest that neither exposure during the adult life stage nor during larval development inhibited the effectiveness of octenol and 2-pentylfuran. However, greater survivorship on octenol treated baits in F1 flies, combined with apparent neurotoxic effects of this compound, indicate that octenol may be less suited for field applications. For this reason, 2-pentylfuran appears to be a better candidate for ongoing research aimed at developing an effective push-pull system of behavioral management.

Population genomics of Drosophila suzukii reveal longitudinal population structure and signals of migrations in and out of the continental United States

Drosophila suzukii, or spotted-wing drosophila, is now an established pest in many parts of the world, causing significant damage to numerous fruit crop industries. Native to East Asia, D. suzukii infestations started in the United States a decade ago, occupying a wide range of climates. To better understand invasion ecology of this pest, knowledge of past migration events, population structure, and genetic diversity is needed. In this study, we sequenced whole genomes of 237 individual flies collected across the continental United States, as well as several sites in Europe, Brazil, and Asia, to identify and analyze hundreds of thousands of genetic markers. We observed strong population structure between Western and Eastern US populations, but no evidence of any population structure between different latitudes within the continental United States, suggesting that there are no broad-scale adaptations occurring in response to differences in winter climates. We detect admixture from Hawaii to the Western United States and from the Eastern United States to Europe, in agreement with previously identified introduction routes inferred from microsatellite analysis. We also detect potential signals of admixture from the Western United States back to Asia, which could have important implications for shipping and quarantine policies for exported agriculture. We anticipate this large genomic dataset will spur future research into the genomic adaptations underlying D. suzukii pest activity and development of novel control methods for this agricultural pest.

Winter warm-up frequency and the degree of temperature fluctuations affect survival outcomes of spotted-wing drosophila winter morphotypes

Among overwintering Drosophila suzukii, discrete environmental changes in temperature and photoperiod induce a suite of biochemical changes conferring cold tolerance. However, little is known regarding how temperature fluctuations, which can influence metabolic and cellular repair activity, affect survival outcomes in this species. For that reason, we designed three experiments to test the effects of intermittent warm-up periods and the degree of temperature fluctuation on winter-morphotype (WM) D. suzukii survival. We found that at 5 °C, a temperature sufficient to induce reproductive diapause, but warm enough to allow foraging, increasing warm-up frequency (warmed to 25 °C at various interval schedules) was associated with decreased survival. In contrast, when the nightly low temperature was 0 °C, daily fluctuations that warmed the environment to temperatures above freezing (5, or 15 °C) appeared beneficial and resulted in improved survival compared to flies held at 0 °C during day and night. When we next evaluated cold tolerance using a 24-hour stress test assay (-5 °C), we found that again, thermal fluctuations improved survival compared to static freezing conditions. However, we also found that WM D. suzukii exposed to freezing temperatures during acclimation were less cold tolerant, regardless of the thermal fluctuation schedule, indicating that there may be tradeoffs between adequate acclimation temperature, which is required to induce cold tolerance, and the ensuing effects of incidental chill injury. Moving forward, these data, which account for the nuanced interactions between the thermal environment and in the internal physiology of D. suzukii, may help refine seasonal populations models, which aim to forecast pest pressure based on conditions the previous winter.

2-Pentylfuran: a novel repellent of Drosophila suzukii

BACKGROUND

Drosophila suzukii (Matsumura), spotted-wing drosophila (SWD), is a major invasive pest of soft-skinned fruits in North America and Europe. Although insecticides are currently the primary method of SWD control, it is imperative to develop alternative management approaches, such as behavioral control through the use of repellents and attractants. This study explores the repellent properties of 2-pentylfuran as an oviposition deterrent on raspberries.

RESULTS

2-Pentylfuran was found to be aversive to SWD in laboratory multiple-choice tests. When co-released from a vial (loaded as neat compound) with a synthetic SWD lure, 2-pentylfuran reduced SWD attraction to the SWD lure by 98% and the effect appeared 17% stronger compared to 1-octen-3-ol, a known SWD repellent. Releasing 50% 2-pentylfuran mixed with mineral oil from a vial located near ripe raspberries resulted in 30% reduction in SWD oviposition in the field. In laboratory no-choice assays, 2-pentylfuran reduced SWD oviposition on raspberries above 2.5 mg h^-1 with greater repellency achieved at higher release rates. A release rate of 10 mg h^-1 from a polyethylene sachet reduced egg-laying on raspberries by 60% in a semifield cage choice experiment. In a field experiment using fruiting raspberry clusters, 14 mg h^-1 release rate of 2-pentylfuran was effective at reducing SWD infestations by 56% compared to untreated plots.

CONCLUSION

2-Pentylfuran acts as a repellent for SWD and can significantly reduce fruit infestations under field conditions and high SWD pressure. Given that 2-pentylfuran is a registered food additive and generally regarded as safe, 2-pentylfuran has a potential use in behavioral control strategies against SWD. Published 2020. This article is a U.S. Government work and is in the public domain in the USA.

Automated aerosol puffers effectively deliver 1-OCTEN-3-OL, an oviposition antagonist useful against spotted-wing drosophila

BACKGROUND

Automated aerosol puffers releasing behaviorally active volatile organic compounds can deter insect pests in crops. During 2016, we tested the efficacy of aerosol puffer arrays emitting 1-octen-3-ol at reducing Drosophila suzukii oviposition in fall-bearing raspberries in Western New York State. During 2017, we compared the performance of aerosol puffers with a passive diffusion release method (vial dispensers), as well as puffer timing and placement within the field.

RESULTS

During 2016, we found that octenol application in the field via aerosol puffer systems resulted in a 20% decrease in D. suzukii oviposition compared to control plots. During 2017, we found that aerosol puffers releasing octenol were 42-55% more effective than vial dispensers at deterring oviposition. We also found that a discontinuous application of octenol during dawn and dusk was sufficient to deter D. suzukii oviposition equivalent to continuous applications throughout the day. Although we observed no differences in infestation depending on puffer placement, low fly populations at the time of the trial may have affected the data.

CONCLUSIONS

Our data indicate that automated aerosol puffer systems may reduce D. suzukii infestation to a greater extent than vial dispensers. If adopted, a discontinuous puffer release schedule may protect both economic and ecological interests by reducing the amount of material required to achieve efficacy. Further research on puffer placement is needed to determine whether perimeter applications are effective in larger scale field research and in combination with attractants as part of a push-pull management system.

Seasonal polyphenism of spotted-wing Drosophila is affected by variation in local abiotic conditions within its invaded range, likely influencing survival and regional population dynamics

Overwintering Drosophila often display adaptive phenotypic differences beneficial for survival at low temperatures. However, it is unclear which morphological traits are the best estimators of abiotic conditions, how those traits are correlated with functional outcomes in cold tolerance, and whether there are regional differences in trait expression.We used a combination of controlled laboratory assays, and collaborative field collections of invasive Drosophila suzukii in different areas of the United States, to study the factors affecting phenotype variability of this temperate fruit pest now found globally.Laboratory studies demonstrated that winter morph (WM) trait expression is continuous within the developmental temperature niche of this species (10-25°C) and that wing length and abdominal melanization are the best predictors of the larval abiotic environment.However, the duration and timing of cold exposure also produced significant variation in development time, morphology, and survival at cold temperatures. During a stress test assay conducted at -5°C, although cold tolerance was greater among WM flies, long-term exposure to cold temperatures as adults significantly improved summer morph (SM) survival, indicating that these traits are not controlled by a single mechanism.Among wild D. suzukii populations, we found that regional variation in abiotic conditions differentially affects the expression of morphological traits, although further research is needed to determine whether these differences are genetic or environmental in origin and whether thermal susceptibility thresholds differ among populations within its invaded range.

Induced Preference Improves Offspring Fitness in a Phytopathogen Vector

In the Asian citrus psyllid (Diaphorina citri Kuwayama), learning facilitates host recognition and mate preference; however, it is unclear whether induced female oviposition preference occurs in this species. We investigated the influence of natal host experience on adult oviposition preference when reared on either 'Valencia' orange (Citrus x sinesis) or orange jasmine (Murraya paniculata). Psyllids reared on 'Valencia' orange preferred 'Valencia' orange as an oviposition host compared with orange jasmine, whereas there was no difference in oviposition between the two hosts in orange jasmine reared psyllids. Nymphs transferred from 'Valencia' orange to orange jasmine were smaller in adult size and required more time for development. These findings were reversed in orange jasmine reared psyllids, which increased in size and displayed shorter development times when transferred from orange jasmine to 'Valencia' orange. However, mortality increased in nymphs transferred to the non-natal host species in both treatment groups compared with nymphs transferred to the same host. These results indicate an association between host plant preference and performance in this species. Maternal host experience appeared to influence the oviposition preference in this species. Juvenile psyllid performance appeared negatively affected by orange jasmine plants such that fitness was reduced, suggesting benefits for maternal host fidelity in those insects not acclimated to feeding on orange jasmine. Induced oviposition preference may provide an important mechanism of adaptive plasticity in D. citri reproductive strategies, allowing females to discriminate among potential host species in favor of those to which her offspring are best adapted.