Identification of neurons responsible for feeding behavior in the Drosophila brain

Drosophila melanogaster feeds mainly on rotten fruits,which contain many kinds of sugar.Thus,the sense of sweet taste has evolved to serve as a dominant regulator and driver of feeding behavior.Although several sugar receptors have been described,it remains poorly understood how the sensory input is transformed into an appetitive behavior.Here,we used a neural silencing approach to screen brain circuits,and identified neurons labeled by three Gal4 lines that modulate Drosophila feeding behavior.These three Gal4 lines labeled neurons mainly in the suboesophageal ganglia(SOG),which is considered to be the fly’s primary taste center.When we blocked the activity of these neurons,flies decreased their sugar consumption significantly.In contrast,activation of these neurons resulted in enhanced feeding behavior and increased food consumption not only towards sugar,but to an array of food sources.Moreover,upon neuronal activation,the flies demonstrated feeding behavior even in the absence of food,which suggests that neuronal activation can replace food as a stimulus for feeding behavior.These findings indicate that these Gal4-labeled neurons,which function downstream of sensory neurons and regulate feeding behavior towards different food sources is necessary in Drosophila feeding control.     

Aggression and courtship in Drosophila: pheromonal communication and sex recognition

Upon encountering a conspecific in the wild, males have to rapidly detect, integrate and process the most relevant signals to evoke an appropriate behavioral response. Courtship and aggression are the most important social behaviors in nature for procreation and survival: for males, making the right choice between the two depends on the ability to identify the sex of the other individual. In flies as in most species, males court females and attack other males. Although many sensory modalities are involved in sex recognition, chemosensory communication mediated by specific molecules that serve as pheromones plays a key role in helping males distinguish between courtship and aggression targets. The chemosensory signals used by flies include volatile and non-volatile compounds, detected by the olfactory and gustatory systems. Recently, several putative olfactory and gustatory receptors have been identified that play key roles in sex recognition, allowing investigators to begin to map the neuronal circuits that convey this sensory information to higher processing centers in the brain. Here, we describe how Drosophila melanogaster males use taste and smell to make correct behavioral choices.     

Dietary fatty acids promote sleep through a taste‐independent mechanism

Consumption of foods that are high in fat contribute to obesity and metabolism‐related disorders. Dietary lipids are comprised of triglycerides and fatty acids, and the highly palatable taste of dietary fatty acids promotes food consumption, activates reward centers in mammals and underlies hedonic feeding. Despite the central role of dietary fats in the regulation of food intake and the etiology of metabolic diseases, little is known about how fat consumption regulates sleep. The fruit fly, Drosophila melanogaster, provides a powerful model system for the study of sleep and metabolic traits, and flies potently regulate sleep in accordance with food availability. To investigate the effects of dietary fats on sleep regulation, we have supplemented fatty acids into the diet of Drosophila and measured their effects on sleep and activity. We found that flies fed a diet of hexanoic acid, a medium‐chain fatty acid that is a by‐product of yeast fermentation, slept more than flies starved on an agar diet. To assess whether dietary fatty acids regulate sleep through the taste system, we assessed sleep in flies with a mutation in the hexanoic acid receptor Ionotropic receptor 56D, which is required for fatty acid taste perception. We found that these flies also sleep more than agar‐fed flies when fed a hexanoic acid diet, suggesting the sleep promoting effect of hexanoic acid is not dependent on sensory perception. Taken together, these findings provide a platform to investigate the molecular and neural basis for fatty acid‐dependent modulation of sleep.     

Effects of monosodium glutamate on food acceptance and toxicity of selenium in rats

Food acceptance and toxic effects of feeding sodium selenite (Se) alone and in combination with monosodium glutamate (MSG), a taste enhancer were studied in the laboratory rat. Dose-dependent stimulation of daily food intake was observed with MSG offered in no-choice or bi-choice with the plain food. Consumption of pellets containing 0.05, 0.5 and 1.0% Se was significantly low than the plain or MSG containing pellets but their active ingredient was sufficient to cause mortality of rats. Food pellets containing both MSG and Se in no-choice feeding trial were not preferred by the rats, as their consumption remained low as compared to pellets containing only MSG. However, prior feeding on MSG containing pellets for two days increased the amount of intake of Se-containing pellets. No mortality of rats feeding on pellets containing different concentrations of MSG was recorded. Feeding on Se-containing pellets caused dose-dependent mortality on the third day of the trial. As compared to rats feeding on Se-containing pellets, the mortality rate was reduced in those provided Se in combination with MSG but the intake of active ingredient of Se in both these trials did not differ significantly. Decrease in death rate of rats feeding on Se in combination with MSG containing pellets suggested that addition of MSG to seleniferous food probably provide protection to some extent from the toxic effects of selenium. However, combination of excess doses of MSG and Se in food pellets caused mortality of all experimental animals.     

Induction of Salivary Proteins Modifies Measures of Both Orosensory and Postingestive Feedback during Exposure to a Tannic Acid Diet

There are hundreds of proteins in saliva. Although it has long been hypothesized that these proteins modulate taste by interacting with taste receptors or taste stimuli, the functional impact of these proteins on feeding remains relatively unexplored. We have developed a new technique for saliva collection that does not interfere with daily behavioral testing and allows us to explore the relationship between feeding behavior and salivary protein expression. First, we monitored the alterations in salivary protein expression while simultaneously monitoring the animals'' feeding behavior and meal patterns on a custom control diet or on the same diet mixed with 3% tannic acid. We demonstrated that six protein bands increased in density with dietary tannic acid exposure. Several of these bands were significantly correlated with behaviors thought to represent both orosensory and postingestive signaling. In a follow-up experiment, unconditioned licking to 0.01–3% tannic acid solutions was measured during a brief-access taste test before and after exposure to the tannic acid diet. In this experiment, rats with salivary proteins upregulated found the tannin solution less aversive (i.e., licked more) than those in the control condition. These data suggest a role for salivary proteins in mediating changes in both orosensory and postingestive feedback.     

The similarity between odors and their binary mixtures in Drosophila

How are odor mixtures perceived? We take a behavioral approach toward this question, using associative odor-recognition experiments in Drosophila. We test how strongly flies avoid a binary mixture after punishment training with one of its constituent elements and how much, in turn, flies avoid an odor element if it had been a component of a previously punished binary mixture. A distinguishing feature of our approach is that we first adjust odors for task-relevant behavioral potency, that is, for equal learnability. Doing so, we find that 1) generalization between mixture and elements is symmetrical and partial, 2) elements are equally similar to all mixtures containing it and that 3) mixtures are equally similar to both their constituent elements. As boundary conditions for the applicability of these rules, we note that first, although variations in learnability are small and remain below statistical cut-off, these variations nevertheless correlate with the elements' perceptual "weight" in the mixture; thus, even small differences in learnability between the elements have the potential to feign mixture asymmetries. Second, the more distant the elements of a mixture are to each other in terms of their physicochemical properties, the more distant the flies regard the elements from the mixture. Thus, titrating for task-relevant behavioral potency and taking into account physicochemical relatedness of odors reveals rules of mixture perception that, maybe surprisingly, appear to be fairly simple.     

Choosing between good and better: optimal oviposition drives host plant selection when parents and offspring agree on best resources

Insect preferences for particular plant species might be subjected to trade-offs among several selective forces. Here, we evaluated, through laboratory and field experiments, the feeding and ovipositing preferences of the polyphagous leafminer Liriomyza?huidobrensis (Diptera: Agromyzidae) in relation to adult and offspring performance and enemy-free space. Female leafminers preferred laying their eggs on Vicia?faba (Fabaceae) over Beta?vulgaris var. cicla (Chenopodiaceae), in both laboratory and field choice experiments, although no oviposition preference was observed in no-choice tests. Females fed more often on B.?v.?var.?cicla (no-choice test) or showed no feeding preference (choice test), even when their realized fecundity was remarkably higher on V.?faba. Offspring developed faster, tended to survive better, and attained bigger adult size on the preferred host plant. Also, a field experiment showed higher overall parasitism rates for leafminers developing on B.?v.?var.?cicla, with a nonsignificant similar tendency in field surveys. According to these results, host plant selection by L.?huidobrensis appears to be driven mainly by variation in host quality. Moreover, the consistent oviposition choices for the best host and the labile feeding preferences observed here, suggest that host plant selection might be driven by maximization of offspring fitness even without a conflict of interest between parents and offspring. Overall, these results highlight the complexity of decisions performed by phytophagous insects regarding their host plants, and the importance of simultaneous evaluation of the various driving forces involved, in order to unravel the adaptive significance of female choices.     

Prey preference and egg production of the carabid beetleAgonum dorsale

In order to elucidate whether the aphidRhopalosiphum padi is low quality food for the carabid beetleAgonum dorsale, as it has previously been found to be for cereal spiders, we performed a series of experiments using fruit fliesDrosophila melanogaster as a standard alternative prey (‘control prey’): 1) Prey preference, 2) Aphid consumption for satiated and starved beetles, 3) Egg production on different diets and 4) Preference experiments with fruit flies coated with a taste of different prey types. Other alternative prey types used were earthworms and sciarid midges, all potential prey in the field.A. dorsale has a low preference for aphids compared to fruit flies. Apparently there is an upper limit to the consumption of aphids independent of hunger and much below the beetles' total food demand. Egg production on a pure diet of aphids is lower than on a pure diet of fruit flies; it is extremely low on a pure diet of earthworms; the highest fecundity is found on a mixed diet. As fruit flies coated with a taste of aphids or sciarid midges are less prefered than flies covered with a taste of fruit flies there may be a chemical factor, acting through taste, involved in determining prey preference.     

Consumption of sugars by Anastrepha suspensa (Diptera: Tephritidae)

We were interested in determining the feeding response of the Caribbean fruit fly, Anastrepha suspensa Loew (Diptera: Tephritidae), to various sugar concentrations to develop an improved bait for adults. We compared the consumption of 0.01-1.00 M concentrations of glucose, fructose, raffinose, and sucrose in no-choice tests for 24-h- and 6-d-old male and female flies. Sucrose was the most consumed sugar or within the most consumed group of sugars at 0.02-0.20 M concentrations. There were no differences in consumption among sugars at 0.01, 0.40, and 1.00 M. Consumption generally increased with increasing sugar concentration except that sucrose consumption peaked at 0.20 M. Twenty-four-hour females consumed less fructose than other sugars; 24-h males consumed more sucrose than fructose or raffinose, with an intermediate response to glucose. Females in the 6-d group consumed more sucrose than the other three sugars, whereas 6-d males exhibited no difference in consumption among sugars. In choice tests, flies consumed more sugar solution than water, but the difference between 0.20 M fructose and water was not significant for 24-h males or 24-h females. In choice tests between 0.20 M fructose and 0.20 M sucrose, both 24-h and 6-d females showed a preference for fructose. Males of both age classes showed no preference. These results indicate that the responses of flies to different sugars can vary by sugar, gender, and age.     

House fly (Diptera: Muscidae) activity near baits containing (Z)-9-tricosene and efficacy of commercial toxic fly baits on a southern California dairy

Sticky card captures of house flies, Musca domestica L. (Diptera: Muscidae), were used to compare efficacy of screen-covered baits containing sugar, sugar and 0.1% (Z)-9-tricosene, sugar and 1.0% (Z)-9-tricosene, Golden Malrin [1.1% methomyl and 0.049% (Z)-9-tricosene], and Quick-Bayt [0.5% imidacloprid and 0.1% (Z)-9-tricosene]. The QuickBayt treatment caught more flies per hour (mean = 116.5) than sugar alone (mean = 81.0), but the addition of (Z)-9-tricosene to sugar did not increase fly capture compared with sugar alone. More males (65% of total) than females were collected on the sticky cards for all treatments. Fly kill by plain sugar (control) and the commercial baits Golden Malrin, QuikStrike Fly Abatement strips (1.0% nithiazine), and QuickBayt was tested over a 90-min period. An average of 1.4, 5.6, 363.0, and 1,266.0 flies were killed using sugar, Golden Malrin, QuikStrike, and QuickBayt, respectively. The similarity between Golden Malrin and plain sugar reflects severe resistance to this once effective methomyl bait. A no-choice feeding assay using lab-reared methomyl-susceptible and methomyl-resistant house flies was conducted with and without (Z)-9-tricosene. Adult mortality was significantly higher in the methomyl-susceptible strain exposed to treatments containing methomyl. Lower consumption of the methomyl treatments by resistant flies suggested resistance was behavioral and mortality was not influenced by (Z)-9-tricosene for either fly strain.     

Genetic dimorphism in the taste sensitivity to trehalose inDrosophila melanogaster

Summary A quantitative behavioral assay was developed for the measurement of taste responses to sugars inDrosophila. The amount of the intake of a sugar solution was measured colorimetrically after homogenization of flies which had consumed sugar solutions mixed with a food-dye. A two-choice method was utilized to determine the taste sensitivity to sugars. Two kinds of sugar solutions were marked with either blue or red food-dye and placed alternately in the wells of a micro test plate. Flies were allowed to choose between the two sugar solutions. By classifying and counting the coloured flies, the relative taste sensitivity could be determined. Employing these methods, a genetic dimorphism in the taste sensitivity to trehalose was found among some laboratory strains ofDrosophila melanogaster. No difference in the taste sensitivity to glucose, fructose and sucrose was found between the trehalose high-sensitivity (T-1) and the low-sensitivity (Oregon-R) strains. Trehalose concentration equivalent to 2 mmol/1 sucrose, in terms of stimulating activity, was 57 mmol/1 inOregon-R and was 10 mmol/1 inT-1. Genetic analysis showed that theTre gene, whose locus is closely linked tocx (13.6) on theX chromosome, is responsible for the difference in the taste sensitivity to trehalose.     

A simple vision-based algorithm for decision making in flying Drosophila

Animals must quickly recognize objects in their environment and act accordingly. Previous studies indicate that looming visual objects trigger avoidance reflexes in many species [1-5]; however, such reflexes operate over a close range and might not detect a threatening stimulus at a safe distance. We analyzed how fruit flies (Drosophila melanogaster) respond to simple visual stimuli both in free flight and in a tethered-flight simulator. Whereas Drosophila, like many other insects, are attracted toward long vertical objects [6-10], we found that smaller visual stimuli elicit not weak attraction but rather strong repulsion. Because aversion to small spots depends on the vertical size of a moving object, and not on looming, it can function at a much greater distance than expansion-dependent reflexes. The opposing responses to long stripes and small spots reflect a simple but effective object classification system. Attraction toward long stripes would lead flies toward vegetative perches or feeding sites, whereas repulsion from small spots would help them avoid aerial predators or collisions with other insects. The motion of flying Drosophila depends on a balance of these two systems, providing a foundation for studying the neural basis of behavioral choice in a genetic model organism.     

Efficacy of cyromazine to control immature stable flies (Diptera: Muscidae) developing in winter hay feeding sites

Hay mixed with manure and urine residues at sites where hay has been provided as supplemental winter feed for cattle provide an excellent substrate for the development of immature stable flies, Stomoxys calcitrans (L.). Such sites are primary sources of early summer stable flies in the central United States and no effective measures are currently available to control fly development in them. A single application of granular cyromazine in May provided 97% reduction in the number of adult stable flies emerging from hay feeding sites. Stable fly control did not decline during the 12 wk season. A small decline in control was observed relative to anthomyiid, sarcophagid, and syrphid flies developing in the hay feeding sites. However, none of those flies are considered to be pests and > or = 50% control of those flies was maintained for 65 d after application. Cyromazine offers a safe and affordable option for the control of immature stable flies developing in winter hay feeding sites. Controlling those flies should reduce the estimated $2 billion per year of lost production in U.S. cattle industries attributable to stable flies.     

Preference of the cabbage root fly, Delia radicum (L.), for coloured traps: influence of sex and physiological status of the flies, trap background and experimental design

Abstract. Catches of Delia rudicum (L.) (Diptera: Anthomyiidae) were compared in water traps that reflected predominantly wavelengths shorter (violet and blue traps) and longer (green and yellow traps) than 500 nm.Traps were positioned in choice and no-choice situations against backgrounds of bare soil and weeds in the field and against backgrounds of brown and green paper in the laboratory.The physiological status of the flies was modified in the laboratory by denying them access to food sources and oviposition sites.
Males discriminated significantly more clearly than females between yellow and blue traps.The discrimination between yellow and blue traps was significantly more pronounced when the traps were presented in the choice than in the no-choice situation in both sexes.Green background (weeds and green paper) was highly preferred for landing and thus competed with the traps to such an extent that few flies were caught when non-preferred violet and blue traps were sited on green backgrounds.Flies seldom landed on the brown background (soil and brown paper) which resulted in the relative increase of catches in the non-preferred violet and blue traps.The preference for yellow traps was innate even in young flies with immature egg-follicles.Females that were ready to lay eggs, even those deprived of an oviposition site till the age of 8 days, also preferred yellow traps.In the no-choice situation, flies deprived of food landed with the same frequency in yellow and blue traps.Food deprivation, however, did not affect preference for yellow traps over the blue traps presented in a choice situation.     

Oviposition preferences and antennal size in carrion flies

Carrion-feeding flies use odours emanating from the decomposing corpse as cues for oviposition and are described as generalists because the larvae feed on the corpses of diverse species. Whereas several features of the corpse may influence the oviposition choices of these flies, it is not known whether there is a preference for a particular species of corpse. We provided carrion flies with ovipositional (and feeding) choices in a field experiment, in which various odour sources were presented simultaneously. We found novel evidence of broadly consistent choices of carrion by flies from four families. Traps baited with decaying fish flesh captured the greatest number of individuals, whereas traps baited with decaying pig liver typically attracted the least. We also asked whether individuals captured in the various baits vary in antennal size, perhaps reflecting different capacities for odour detection. There was a trend for individuals of Lucilia sericata Meigen (Diptera: Calliphoridae) and the platystomatid collected from the traps baited with pig liver to have significantly larger antennae, whereas individuals of Muscina stabulans (Fallen) (Diptera: Muscidae) captured in traps baited with marine fish flesh had relatively longer antennae for their body size. Our data reveal a more nuanced pattern of oviposition behaviour in these generalist carrion flies, which may reflect differences in their preference of carrion with different nutrients, and in their capacity to detect particular odours.     

Drosophila Fatty Acid Taste Signals through the PLC Pathway in Sugar-Sensing Neurons

Taste is the primary sensory system for detecting food quality and palatability. Drosophila detects five distinct taste modalities that include sweet, bitter, salt, water, and the taste of carbonation. Of these, sweet-sensing neurons appear to have utility for the detection of nutritionally rich food while bitter-sensing neurons signal toxicity and confer repulsion. Growing evidence in mammals suggests that taste for fatty acids (FAs) signals the presence of dietary lipids and promotes feeding. While flies appear to be attracted to fatty acids, the neural basis for fatty acid detection and attraction are unclear. Here, we demonstrate that a range of FAs are detected by the fly gustatory system and elicit a robust feeding response. Flies lacking olfactory organs respond robustly to FAs, confirming that FA attraction is mediated through the gustatory system. Furthermore, flies detect FAs independent of pH, suggesting the molecular basis for FA taste is not due to acidity. We show that low and medium concentrations of FAs serve as an appetitive signal and they are detected exclusively through the same subset of neurons that sense appetitive sweet substances, including most sugars. In mammals, taste perception of sweet and bitter substances is dependent on phospholipase C (PLC) signaling in specialized taste buds. We find that flies mutant for norpA, a Drosophila ortholog of PLC, fail to respond to FAs. Intriguingly, norpA mutants respond normally to other tastants, including sucrose and yeast. The defect of norpA mutants can be rescued by selectively restoring norpA expression in sweet-sensing neurons, corroborating that FAs signal through sweet-sensing neurons, and suggesting PLC signaling in the gustatory system is specifically involved in FA taste. Taken together, these findings reveal that PLC function in Drosophila sweet-sensing neurons is a conserved molecular signaling pathway that confers attraction to fatty acids.     

Recording lifetime behavior and movement in an invertebrate model

Characterization of lifetime behavioral changes is essential for understanding aging and aging-related diseases. However, such studies are scarce partly due to the lack of efficient tools. Here we describe and provide proof of concept for a stereo vision system that classifies and sequentially records at an extremely fine scale six different behaviors (resting, micro-movement, walking, flying, feeding and drinking) and the within-cage (3D) location of individual tephritid fruit flies by time-of-day throughout their lives. Using flies fed on two different diets, full sugar-yeast and sugar-only diets, we report for the first time their behavioral changes throughout their lives at a high resolution. We have found that the daily activity peaks at the age of 15-20 days and then gradually declines with age for flies on both diets. However, the overall daily activity is higher for flies on sugar-only diet than those on the full diet. Flies on sugar-only diet show a stronger diurnal localization pattern with higher preference to staying on the top of the cage during the period of light-off when compared to flies on the full diet. Clustering analyses of age-specific behavior patterns reveal three distinct young, middle-aged and old clusters for flies on each of the two diets. The middle-aged groups for flies on sugar-only diet consist of much younger age groups when compared to flies on full diet. This technology provides research opportunities for using a behavioral informatics approach for understanding different ways in which behavior, movement, and aging in model organisms are mutually affecting.     

The effects of simultaneous variation in protein, digestible carbohydrate and tannic acid on the feeding behaviour of larval Locusta migratoria (L.) and Schistocerca gregaria (Forskal). I. Short-term studies

ABSTRACT The influence of simultaneously varying the levels in artificial diets of protein, digestible carbohydrate (14% or 28%) and tannic acid (absent or 10%) on the feeding behaviour of the oligophagous Locusta migratoria (L.) and the polyphagous Schistocerca gregaria (Forskal) (Acrididae) was investigated. Total consumption and detailed feeding behaviour were recorded over a 12 h period in choice and no-choice experiments. In addition, amounts eaten by Schistocerca of the 14% protein, 14% carbohydrate diet with and without tannic acid were measured at regular intervals throughout the fifth stadium, and insect growth over this period was recorded. There were no interactive effects of nutrient levels and tannic acid, despite the fact that both species compensated for dilution of dietary protein by increasing consumption. Only male Locusta compensated for dilution of dietary carbohydrates, and this compensation was much less marked than for protein. Tannic acid did influence feeding as a main effect, however. It caused an increase in amounts eaten by Schistocerca in both choice and no-choice experiments. This increased consumption was due to an increase in the number of meals taken. A shorter latency period before and a longer duration of the first meal by naive insects suggested a phagostimulatory rather than a post-ingestive effect of tannic acid. The stimulatory effect was only apparent for the first 24 h of continuous exposure, but this temporary enhancement none the less resulted in the insects being heavier at adult ecdysis. Stadium duration was also somewhat reduced. In a no-choice situation, no effect of tannic acid on the feeding behaviour of Locusta was observed. When given a choice, however, this species took significantly more meals on the tannic acid-free diet, these being of similar average size to meals taken on the tannic acid diet. Significantly more insects took their first meals on the tannic acid-free diet in the choice test, indicating a deterrent effect of tannic acid in Locusta.     

Gustatory receptor 22e is essential for sensing chloroquine and strychnine in Drosophila melanogaster

Chloroquine, an amino quinolone derivative commonly used as an anti-malarial drug, is known to impart an unpleasant taste. Little research has been done to study chloroquine taste in insects, therefore, we examined both the deterrant properties and mechanisms underlying chloroquine perception in fruit flies. We identified the antifeedant effect of chloroquine by screening 21 gustatory receptor (Grs) mutants through behavioral feeding assays and electrophysiology experiments. We discovered that two molecular sensors, GR22e and GR33a, act as chloroquine receptors, and found that chloroquine-mediated activation of GRNs occurs through S-type sensilla. At the same time, we successfully recapitulated the chloroquine receptor by expressing GR22e in ectopic gustatory receptor neurons. We also found that GR22e forms a part of the strychnine receptor. We suggest that the Drosophila strychnine receptor might have a very complex structure since five different GRs are required for strychnine-induced action potentials.