Effect of physiological and experiential state ofBactrocera tryoni flies on intra-tree foraging behavior for food (bacteria) and host fruit

Preferential Attraction of Oviposition-Ready Oriental Fruit Flies to Host Fruit Odor over Protein Food Odor

Simple Summary

Oriental fruit fly, Bactrocera dorsalis, is one of the most destructive invasive pests of tropical fruit and vegetable crops worldwide. Current oriental fruit fly quarantine programs focus heavily on the control and surveillance of male flies, which is less effective for mitigating the impact caused by female populations. We investigated the relationship between olfactory preference and oviposition outcome of oriental fruit flies. In laboratory bioassays using similarly aged (14–16 day old) cohorts of mated females, some females preferred host fruit odors over protein food odor (torula yeast), while some preferred protein odor. The females that preferred host fruit odor had 2.1 times greater egg load and laid 2.4 times more eggs than females that preferred protein odor. Our results suggest that mated female oriental fruit flies with a preference for host fruit odor are likely to be in an imminent oviposition-ready physiological status, while mated females that prefer torula yeast odor are likely more protein-hungry and need more protein to produce the critical egg load necessary for oviposition.

Abstract

Olfaction plays a key role in the location of food and oviposition resources by tephritid fruit flies. Adult females, including oriental fruit fly, Bactrocera dorsalis, can sustain egg production throughout their lives provided they obtain sufficient protein. Thus, preferential attraction to food or oviposition sites (host fruit) will depend on a fly’s particular physiological state. In this study, laboratory bioassays were conducted with mature, mated B. dorsalis (provisioned protein and sugar ad libitum) to evaluate attraction to traps baited with torula yeast versus six host fruit sources (guava, guava juice, mango, orange, Surinam cherry, or white sapote). Females that preferred fruit laid a significant number of eggs around the trap entrance (average 405 eggs/fly), while almost no eggs were laid by females that preferred yeast (0.5 and 1.3 eggs/fly on two occasions). Similar results were observed in a bioassay using headspace extracts of guava juice and torula yeast, supporting olfactory-mediated responses. When individual females were allowed to oviposit in guava juice traps 0–24 h after a choice test, 45.8% of females that chose guava juice laid eggs (average 14.7 eggs/fly), compared with 27.5% that chose yeast (average 6.5 eggs/fly). Dissections indicated that females with a preference for guava juice had an egg load 2.4 times greater than females that preferred yeast. These results suggest there is an olfactory-based behavioral switch in preference from protein to host odors when female B. dorsalis are oviposition-ready. We discuss the implications of our findings for practical behavioral management and detection programs for B. dorsalis.

Canopy distribution and microclimate preferences of sterile and wild Queensland fruit flies

Insects tend to live within well-defined habitats, and at smaller scales can have distinct microhabitat preferences. These preferences are important, but often overlooked, in applications of the sterile insect technique. Different microhabitat preferences of sterile and wild insects may reflect differences in environmental tolerance and may lead to spatial separation in the field, both of which may reduce the control program efficiency. In this study, we compared the diurnal microhabitat distributions of mass-reared (fertile and sterile) and wild Queensland fruit flies, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae). Flies were individually tagged and released into field cages containing citrus trees. We recorded their locations in the canopies (height from ground, distance from canopy center), behavior (resting, grooming, walking, feeding), and the abiotic conditions on occupied leaves (temperature, humidity, light intensity) throughout the day. Flies from all groups moved lower in the canopy when temperature and light intensity were high, and humidity was low; lower canopy regions provided shelter from these conditions. Fertile and sterile mass-reared flies of both sexes were generally lower in the canopies than wild flies. Flies generally fed from the top sides of leaves that were lower in the canopy, suggesting food sources in these locations. Our observations suggest that mass-reared and wild B. tryoni occupy different locations in tree canopies, which could indicate different tolerances to environmental extremes and may result in spatial separation of sterile and wild flies when assessed at a landscape scale.

Response of Male Queensland Fruit Fly (Diptera: Tephritidae) to Host Fruit Odors

The surveillance and management of Dacini fruit fly pests are commonly split by fly gender: male trapping focuses on the dacine 'male-lures', whereas female trapping focuses on lures based on host-fruit volatiles. Although the males of several Dacini species have been reported to be attracted to host fruit volatiles, the option of using host-fruit traps for males has, to date, been ignored. Males of the cue-lure responsive fruit fly Bactrocera tryoni (Froggatt) have been recorded as responding to host-fruit volatile blends, but it is not known how frequently this happens, if it is age-dependent, or the strength of the response relative to cue-lure throughout the year. Here, we conducted an olfactometer experiment to test the lifetime (weeks 1-15) response of B. tryoni males to the odor of tomato, a known host of this fly, and compare catches of wild males to tomato-based traps and cue-lure traps in the field. Bactrocera tryoni males started to respond to tomato odor as they sexually matured (2 to 3 wk olds) and thereafter showed consistent olfactory response until advanced age (15 wk). In the field, wild males were captured by tomato-based traps throughout the year at a level not significantly different from cue-lure traps. The reason for the consistent B. tryoni male response to host fruit odor at this stage is not known, but it certainly occurs at a level greater than can be continued to be ignored for both basic and applied research.

Intestinal bacteria modulate the foraging behavior of the oriental fruit fly Bactrocera dorsalis (Diptera: Tephritidae)

The gut microbiome of insects directly or indirectly affects the metabolism, immune status, sensory perception and feeding behavior of its host. Here, we examine the hypothesis that in the oriental fruit fly (Bactrocera dorsalis, Diptera: Tephritidae), the presence or absence of gut symbionts affects foraging behavior and nutrient ingestion. We offered protein-starved flies, symbiotic or aposymbiotic, a choice between diets containing all amino acids or only the non-essential ones. The different diets were presented in a foraging arena as drops that varied in their size and density, creating an imbalanced foraging environment. Suppressing the microbiome resulted in significant changes of the foraging behavior of both male and female flies. Aposymbiotic flies responded faster to the diets offered in experimental arenas, spent more time feeding, ingested more drops of food, and were constrained to feed on time-consuming patches (containing small drops of food), when these offered the full complement of amino acids. We discuss these results in the context of previous studies on the effect of the gut microbiome on host behavior, and suggest that these be extended to the life history dimension.

Cage study of spinosad-based bait efficacy on Bactrocera cucurbitae, Dacus ciliatus, and Dacus demmerezi (Diptera: Tephritidae) in Reunion Island

On Reunion Island, Bactrocera cucurbitae (Coquillett), Dacus ciliatus (Loew), and Dacus demmerezi (Bezzi) cause severe damage to Cucurbit crops. The aim of the study was to test in field cages the effectiveness of Synéis-appât (Dow AgroSciences), a spinosad-based bait (0.02% of spinosad) on both attraction and mortality of young adults (6-9 d old) of these three species. The effects of gender were also evaluated for all species whereas the effects of protein deprivation were tested with B. cucurbitae only. For the first 15 min after application, significantly more B. cucurbitae adults (21.7 +/- 1.8%) were attracted to the bait than D. demmerezi (7.6 +/- 2.4%) and D. ciliatus (2.7 +/- 1.4%); the subsequent response (30-75 min after bait application) of D. demmerezi was statistically similar to that recorded for B. cucurbitae; whereas the response ofD. ciliatus to the bait was consistently significantly lower. Adult mortality was significantly higher for B. cucurbitae (94.6 +/- 0.7%) than for D. demmerezi (85.7 +/- 2.1%), and was significantly higher for the latter than for D. ciliatus (60.4 +/- 4.4%). Sex had no significant effect on the mortality rate for each species. The efficiency of the bait was the same for B. cucurbitae adults regardless whether or not the diet included proteins. Overall, Synéis-appât appears to be more effective against B. cucurbitae and B. demmerezi than against D. ciliatus. In Reunion Island, this bait could constitute a useful component in the framework of Integrated Pest Management.

Morphological features of the ovaries during oogenesis of the Oriental fruit fly, Bactrocera dorsalis, in relation to the physiological state

Determination of physiological state in insects is useful in furthering the understanding of how insect behavior changes with age. Central to this determination is the identification of characters that allow assessment of physiological age. While non-destructive measures produce the most desired outcomes, internal markers may be more diagnostic and reliable. In this study, key morphological characters during previtellogenesis through vitellogenesis and ovulation were assessed as markers to determine physiological states of the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae). Ovary length and width, ovarian index (length × width), and egg load of laboratory-reared B. dorsalis females recorded daily from eclosion up to 80 days old suggested significant differences in the ovarian index and egg load between females from each oogenesis stage. Parity status determined by the presence of follicular relics was found to provide high-accuracy classifications for B. dorsalis females. The presence of follicular relics with distinct morphological features provides a reliable identification tool to determine the physiological state of wild female oriental fruit fly. The potential applications of this technique to identify the physiological age of female fruit flies to study behavioral attributes in their natural habitat, and also the potential applications in relation to field control, are discussed.