Factors Affecting Engorgement Behavior in the Salt Marsh Horse Fly, <Emphasis Type="Italic">Tabanus nigrovittatus</Emphasis> Macquart (Diptera: Tabanidae)

Female Tabanus nigrovittatus were field collected and used in laboratory experimentation to explore physiological and behavioral factors that affect engorgement. Previous studies showed sulfakinins act as feeding satiety factors in insects. This study demonstrates that sulfakinins have differing effects on engorgement that is dependent on the feeding technique used in the laboratory. The satiety effect of sulfakinin on flies engorging using the blood-soaked Kimwipe® feeding technique is not in agreement with previous experiments using an alternate feeding technique with artificial membranes. This study is the first to demonstrate that the temperature of blood is a significant factor for engorgement in this species. Also, the percentage of flies engorging is significantly different depending on the feeding technique used.     

Clonidine, octopaminergic receptor agonist, reduces protein feeding in the blow fly, Phormia regina (Meigen)

Results in this study are consistent with those of Murdock and his colleagues who clearly demonstrated that clonidine, an agonist of octopaminergic receptors in some insects, significantly increases sucrose feeding. Their studies, however, did not examine the effect of clonidine on protein feeding. Injection of a 20 microg/microl/fly dose of clonidine significantly reduces protein feeding in both sexes of Phormia regina, instead of stimulating feeding as is observed with carbohydrate feeding. The manner in which the flies are fed prior to starvation and the method of testing influences the amounts of diet consumed. It is proposed that the biogenic amines influence the state of hunger (i.e., protein versus carbohydrates) while other chemicals and neural mechanisms (i.e., such as sulfakinins and stretch receptors, respectively) affect satiety.     

Effects of diet and activity on lipid levels of adult Mediterranean fruit flies

Abstract. The objectives of this study were to determine whether adult Mediterranean fruit flies, Ceratitis capitata Wiedeman (Diptera: Tephritidae), are capable of synthesizing lipids, and whether adult diet affects this ability.Lipid levels in females fed protein and carbohydrate or carbohydrate alone declined significantly from emergence to the fourth day of life and then rose back to teneral levels on the fifth day, before oviposition took place on the sixth day.In males fed protein and carbohydrate, lipid levels initially declined as males aged and then stabilized.In carbohydrate-fed males lipid levels declined following emergence and recovered somewhat by the sixth day.Lipid levels declined significantly when flies underwent post-emergence starvation, but after substantial feeding on the above-mentioned diets they eventually (within 6–7 days) reached teneral levels in all experimental groups.Multivariate analysis of variance revealed that differences in lipid contents are primarily related to the flies' age, which corresponds to the various sex-specific activities these flies exhibit.Average lipid investment in eggs was found to equal teneral lipid levels in females.Without lipogenic abilities, oviposition would completely deplete female lipid reserves.We conclude that adult medflies are capaple of lipid synthesis, and that this capability is modulated by individual and sex-specific activity patterns.     

Nutritional status and the foraging behaviour of Bactrocera tryoni with particular reference to protein bait spray

Poisoned protein baits comprise a recognized method for controlling tephritid fruit flies in the form of a ‘lure‐and‐kill’ technique. However, little is known about how a fly's internal protein and carbohydrate levels (i.e. nutritional status) might influence the efficacy of this control. In the present study, the relationships between the internal levels of protein (as measured by total body nitrogen) and carbohydrate (as measured by total body carbon) of the fruit fly Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) are investigated, as well as its foraging behaviours in response to protein, fruit and cue‐lure (a male‐specific attractant) baits. Small cage behavioural experiments are conducted using flies from cultures of different nutritional status and wild flies sampled from the field during the fruiting cycle of a guava crop. For female flies, increasing total body nitrogen is correlated with decreased protein foraging and increased oviposition activity; increasing total body carbon levels generate the same behavioural changes except that the oviposition response is not significant. For males, there are no significant correlations between changes in total body nitrogen and total body carbon and protein or cue‐lure foraging. For wild flies from the guava orchard, almost all of them are sexually mature when entering the crop and, over the entire season, total body nitrogen and total body carbon levels are such that protein hunger is unlikely for most flies. The results infer strongly that the requirements of wild, sexually mature flies for protein are minimal and that flies can readily gain sufficient nutrients from wild sources for their physiological needs. The results offer a mechanistic explanation for the poor response of male and mature female fruit flies to protein bait spray.     

Serotonin Inhibits Protein Feeding in the Blow Fly, Phormia regina (Meigen)

Serotonin is an important signaling molecule involved in the control of feeding in flies and other animals. In this study, a potential neurohemal release site for serotonin and the effects of exogenous serotonin on protein feeding were examined in the black blow fly, Phormia regina. A dense network of varicose neural processes exhibiting serotonin-like immunoreactivity was identified on the dorsal region of the thoracico-abdominal ganglion in P. regina. This dorsal region of the central nervous system is a likely site for the release of serotonin into the hemolymph. Circulating serotonin may have multiple systemic effects on fly physiology, including modulating or regulating feeding related processes and diuresis. Injections of exogenous serotonin reduced protein meal size in female flies at all doses and at all time points examined within a 24 h period relative to control and saline injected flies. Similar results were observed in serotonin-injected males at 35 min post injection. The injection of 50 μg serotonin resulted in the greatest amount of protein feeding inhibition. Serotonin injected flies also experienced greater weight loss than control or saline-injected flies during the 24 h post-injection period, possibly due to increased diuresis.     

Sulfakinins reduce food intake in the desert locust, Schistocerca gregaria

In vertebrates, the peptides cholecystokinin (CCK), neuropeptide Y, galanin, and bombesin are known to be involved in the control of food intake. We report here that insect sulfakinins, peptides which display substantial sequence similarities with the vertebrate gastrin/CCK peptide family, significantly inhibit food uptake in fifth instar nymphs of the locust, Schistocerca gregaria. Upon injection of Lom-sulfakinin, a neuropeptide present in the corpus cardiacum of locusts, food intake was significantly reduced in a dose-dependent manner within a fixed 20 min time period. The induced effect ranged from 13% inhibition (10 pmol of injected peptide) to over 50% inhibition at 1 nmol. Other naturally occurring sulfakinins from different insect species also elicited this satiety effect. Analogous to the satiety effect of CCK in vertebrates, the sulfate group is required for activity. No effect on the palptip resistance was found after injection with sulfakinin. Therefore it seems unlikly that sulfakinins reduce food intake by decreasing the sensitivity of the taste receptors.     

Feeding and foraging of wild and sterile Mediterranean fruit flies (Diptera: Tephritidae) in the presence of spinosad bait

The sterile insect technique (SIT) is used to control wild Mediterranean fruit fly introductions in California and Florida in the U.S. In the past, bait sprays containing malathion proved invaluable in treating new outbreaks or large populations before the use of SIT. Recently, a spinosad protein bait spray, GF-120, has been developed as a possible alternative to malathion, the standard insecticide in protein bait sprays. In this study, protein-deficient and protein-fed Vienna-7 (sterile, mass-reared, "male-only" strain) flies and wild males and females were evaluated to determine the effectiveness of the GF-120 protein bait containing spinosad with respect to bait attraction, feeding, and toxicology. There were no effects of diet or fly type on feeding duration in small laboratory cages. Wild flies, however, registered more feeding events than Vienna-7 males. Flies that fed longer on fresh bait died faster. Protein-deficient flies were more active and found the bait more often than protein-fed flies. Data suggest that adding protein to the diet of SIT flies may decrease their response to baits, therefore, reduce mortality, and thus, allow the concurrent use of SIT and bait sprays in a management or eradication program.     

Is aggregated oviposition by the blow flies Lucilia sericata and Phormia regina (Diptera: Calliphoridae) really pheromone‐mediated?

When female blow flies Lucilia sericata and Phormia regina (Diptera: Calliphoridae) oviposit in aggregations on carrion, even‐aged larval offspring reportedly develop faster, and fewer are parasitized or preyed upon. The benefits of aggregated oviposition equally affect con‐ and heterospecific larvae sharing a resource. The benefits imply that female blow flies engage in coordinated, pheromone‐mediated oviposition behavior. Yet, repeated attempts to identify oviposition pheromones have failed invoking doubt that they exist. Simply by regurgitating and feeding on carrion, flies may produce attractive semiochemicals. If flies were to aggregate in response to feeding flies rather than ovipositing flies, then the semiochemical cue(s) may be associated with the salivary gland. Working with L. sericata and P. regina and using liver as a surrogate oviposition medium, we test the hypotheses, and present data in their support, that (i) gravid or nongravid females ovipositing and/or feeding on liver enhance its attractiveness to gravid and nongravid females; (ii) females respond to semiochemicals from feeding heterospecific females; (iii) females respond equally well to semiochemicals from feeding con‐ and heterospecific females; (iv) macerated head tissues of females applied to liver enhance its attractiveness; and (v) females in direct contact with and feeding on liver, but not when next to yet physically separated from liver, enhance attraction of flies. We conclude that oviposition site‐seeking females do not respond to an oviposition pheromone. Instead, they appear to coopt semiochemicals associated with feeding flies as resource indicators, taking chances that resources are suitable for oviposition, and that ovipositing flies are present.     

How female caterpillars accumulate their nutrient reserves

Female Lepidoptera are often heavier than males. We examined the importance of consumption and post-ingestive processing as mechanisms for female Heliothis virescens larvae to meet the protein and carbohydrate requirements. In experiments in which caterpillars had a choice of diets, enabling them to select an appropriate protein and carbohydrate intake, females caterpillars ate more carbohydrate than males, but only on the heavily carbohydrate biased treatment. Overall, the sexes were not distinguished according to the selective feeding behavior, but females accumulated more protein and carbohydrate over the whole instar than the males did. Additionally, when given no choice, females ate more than males and accumulated more protein provided the diet contained a high proportion of protein. If they were reared on a high carbohydrate diet, there were no differences between the sexes. Our results indicate that female H. virescens larvae accumulate protein by regulating both intake and post-ingestive processing on high protein foods. In the field, late instar H. virescens feed on anthers, which are protein-rich and have the highest amino acid content relative to other cotton floral tissues.     

Effect of enterostatin given intravenously and intracerebroventricularly on high-fat feeding in rats.

The effect of enterostatin, the amino-terminal pentapeptide of pancreatic procolipase, on high-fat food intake has been investigated after intracerebroventricular as well as after intravenous injection. After an overnight fast enterostatin given i.c.v. at doses of 167 pmol and 333 pmol produced a significant and dose-dependent reduction in high-fat food intake, while a higher dose of 667 pmol had no effect. Following intravenous injection of enterostatin the intake of high-fat food was suppressed at doses of 8.3 nmol and 16.7 nmol, while no effect was observed at higher doses. The inhibition of feeding started 3 h after the initiation of feeding and persisted to the end of the test period (6 h). Enterostatin at a dose of 16.7 nmol gave no sign of aversion in an aversion test comparing the effect of enterostatin, lithium chloride and saline on liquid intake. The data suggest that enterostatin may exert its satiety effect on high-fat feeding by being absorbed into the bloodstream.     

Female access and diet affect insemination success,senescence and the cost of reproduction in the male Mexican fruit fly Anastrepha ludens

Hypotheses exploring the influence of dietary conditions on the life‐history trade‐off between survival and reproductive success are extensively tested in female insects but only rarely explored in males. The present study examines the impact of dietary quality and female access on age‐specific reproduction and survival of the male Mexican fruit fly Anastrepha ludens Loew (Diptera: Tephritidae). There is a clear cost of female access for males with access to dietary protein, measurable as a decrease in life expectancy, which is further influenced by the age when females are introduced. A protein deficient diet reduces the lifespan benefit of virginity and masks the detrimental effect of female access on male life expectancy. Dietary protein is not necessary for reproductive success, although access to protein at eclosion improves the lifetime reproductive success of males compared to when it is delayed. Overall, reproductive success diminishes as the male flies age, regardless of the dietary conditions, providing evidence for reproductive senescence in males. Delaying the males' access to a protein source fails to influence the negative effect of age on reproductive ability. Because age‐specific reproductive rates decline with age, regardless of diet, male fitness does not benefit from lifespan extension. Therefore, males can be expected to allocate available resources towards reproductive effort in favour of an extended lifespan, regardless of mate and protein availability.     

Effects of peripheral CCK receptor blockade on feeding responses to duodenal nutrient infusions in rats

Type A cholecystokinin receptor (CCKAR) antagonists differing in blood-brain barrier permeability were used to test the hypothesis that duodenal delivery of protein, carbohydrate, and fat produces satiety in part by an essential CCK action at CCKARs located peripheral to the blood-brain barrier. Fasted rats with open gastric fistulas received devazepide (1 mg/kg iv) or A-70104 (700 nmol. kg(-1). h(-1) iv) and either a 30-min intravenous infusion of CCK-8 (10 nmol. kg(-1). h(-1)) or duodenal infusion of peptone, maltose, or Intralipid beginning 10 min before 30-min access to 15% sucrose. Devazepide penetrates the blood-brain barrier; A-70104, the dicyclohexylammonium salt of Nalpha-3-quinolinoyl-d-Glu-N,N-dipentylamide, does not. CCK-8 inhibited sham feeding by approximately 50%, and both A-70104 and devazepide abolished this response. Duodenal infusion of each of the macronutrients dose dependently inhibited sham feeding. A-70104 and devazepide attenuated inhibitory responses to each macronutrient. Thus endogenous CCK appears to act in part at CCKARs peripheral to the blood-brain barrier to inhibit food intake.     

Post-teneral protein feeding enhances sexual performance of Queensland fruit flies

Abstract.  Adult diet is an important determinant of sexual activity in many tephritid fruit flies. Whether availability of protein (hydrolysed yeast) in addition to sucrose influences sexual activity or longevity of male and female Queensland fruit flies ( Bactrocera tryoni Froggatt, 'Q-flies'), and whether irradiation of flies as pupae modifies their dietary needs, is investigated. Previous studies on groups of flies suggest that protein is required for sexual maturation of females but not males. By contrast, this study of individual flies demonstrates that protein in the adult diet provides a massive boost to sexual activity of both males and females. Mating probability increases with age from 4-14 days as the flies began to mature. However, mating probability reaches much higher levels when the flies are provided with protein. Although males and females mate at similar rates when provided with protein, females suffer a greater reduction in mating probability than males when deprived of protein. In addition to increased mating probability, access to dietary protein is also associated with reduced latency from onset of dusk until copulation. Furthermore, young male flies with access to dietary protein have longer copula duration than males fed only sucrose. Irradiation of flies as pupae has no apparent effect on mating probability, the latency to copulate or copula duration. However, when deprived of protein, sterile flies (especially males) suffer a greater reduction in longevity compared with fertile flies. Overall, access to dietary protein increases longevity for both males and females, although females live longer than males on both diets. These findings suggest that prerelease provision of dietary protein has the potential to greatly enhance the efficacy of Q-flies used in the sterile insect technique.     

OXIDIZED LIPIDS DID NOT REDUCE LIFESPAN IN THE FRUIT FLY,Drosophila melanogaster

Aging is often associated with accumulation of oxidative damage in proteins and lipids. However, some studies do not support this view, raising the question of whether high levels of oxidative damage are associated with lifespan. In the current investigation, Drosophila melanogaster flies were kept on diets with 2 or 10% of either glucose or fructose. The lifespan, fecundity, and feeding as well as amounts of protein carbonyls (PC) and lipid peroxides (LOOH), activities of superoxide dismutase (SOD), catalase, glutathione‐S‐transferase (GST), and glutathione reductase activity of thioredoxin reductase (TrxR) were measured in “young” (10‐day old) and “aged” (50‐day old) flies. Flies maintained on diets with 10% carbohydrate lived longer than those on the 2% diets. However, neither lifespan nor fecundity was affected by the type of carbohydrate. The amount of PC was unaffected by diet and age, whereas flies fed on diets with 10% carbohydrate had about fivefold higher amounts of LOOH compared to flies maintained on the 2% carbohydrate diets. Catalase activity was significantly lower in flies fed on diets with 10% carbohydrates compared to flies on 2% carbohydrate diets. The activities of SOD, GST, and TrxR were not affected by the diet or age of the flies. The higher levels of LOOH in flies maintained on 10% carbohydrate did not reduce their lifespan, from which we infer that oxidative damage to only one class of biomolecules, particularly lipids, is not sufficient to influence lifespan.     

Ecological significance of male attractant in the defence and mating strategies of the fruit fly, Bactrocera papayae

After being acclimatized to feeding on fruit flies, the Asian house gecko, Hemidactylus frenatus Duméril & Bibron (Gekkonidae:Squamata), consumed fewer methyl eugenol (ME) fed male fruit flies, Bactrocera papayae Drew & Hancock (Tephritidae: Diptera) than when offered ME-deprived males. After one-day exposure to only ME-fed males, the geckos avoided feeding on female flies when in the presence of ME-fed males. When mechanically disturbed, the ME-fed males spontaneously ejaculated a rectal secretion which contains phenyl propanoids that deter the predator.The ME-fed males also competed significantly better than normal (ME-deprived) males for virgin females. Male B. papayae converts ME to three other phenyl propanoids which act in concert as a sex pheromone to attract females during courtship and as an allomone to the gecko.     

Sex-specific differences in nutrient regulation in a capital breeding caterpillar, Spodoptera litura (Fabricius)

Nutrient requirements by male and female insects are likely to differ, but relatively little is known regarding how sexes differ in their regulation of macronutrient acquisition. The present study reports the results from a laboratory experiment in which behavioural and physiological components of nutrient regulation were compared between male and female caterpillars of Spodoptera litura (Fabricius). When provided with choices between two nutritionally complementary foods (one is a protein-biased diet and the other a carbohydrate-biased diet), both males and females adjusted their food selection to defend an intake target. However, the composition of diet preferred by the two differed, with females selecting significantly more protein than males with no difference in carbohydrate intake between the two. When confined to single diets with varying mixtures of protein and carbohydrate [P:C ratios, expressed as the percentage of diet by dry mass: protein 42%:carbohydrate 0% (p42:c0), p35:c7, p28:c14, p21:c21, p14:c28, p7:c35], females consumed more macronutrients than did males across on all P:C diets except the extremely carbohydrate-biased diet (p7:c35). Under both choice and no-choice feeding condition, such sex differences in nutrient intake were not expressed until late in the feeding stage of the final stadium. Sexes also differed in post-ingestive utilization of ingested nutrients. Females utilized ingested protein for body growth with greater efficiency compared to males, presumably reflecting provisioning their adult needs for protein to develop eggs, whereas males were more efficient at depositing lipids from carbohydrate intake than females.     

Cost of reproduction in the Queensland fruit fly: Y-model versus lethal protein hypothesis

The trade-off between lifespan and reproduction is commonly explained by differential allocation of limited resources. Recent research has shown that the ratio of protein to carbohydrate (P : C) of a fly''s diet mediates the lifespan–reproduction trade-off, with higher P : C diets increasing egg production but decreasing lifespan. To test whether this P : C effect is because of changing allocation strategies (Y-model hypothesis) or detrimental effects of protein ingestion on lifespan (lethal protein hypothesis), we measured lifespan and egg production in Queensland fruit flies varying in reproductive status (mated, virgin and sterilized females, virgin males) that were fed one of 18 diets varying in protein and carbohydrate amounts. The Y-model predicts that for sterilized females and for males, which require little protein for reproduction, there will be no effect of P : C ratio on lifespan; the lethal protein hypothesis predicts that the effect of P : C ratio should be similar in all groups. In support of the lethal protein hypothesis, and counter to the Y-model, the P : C ratio of the ingested diets had similar effects for all groups. We conclude that the trade-off between lifespan and reproduction is mediated by the detrimental side-effects of protein ingestion on lifespan.     

Sex differences in insect immune function: a consequence of diet choice?

Males often have reduced immune function compared to females but the proximate mechanisms underlying this taxonomically widespread pattern are unclear. Because immune function is resource-dependent and sexes may have different nutritional requirements, we hypothesized that sexual dimorphism in immune function may arise from differential nutrient intake (acquisition hypothesis). To test this hypothesis, we examined patterns of phenoloxidase (PO) activity in relation to nutrient consumption in Queensland fruit flies (Q-flies). In the first experiment, flies were allowed to choose their preferred nutrient intake. Compared with males, female Q-flies had higher PO activity, consumed more calories, and preferred a higher protein:carbohydrate (P:C) diet, suggesting that differential acquisition could explain sex differences. In the second experiment, we restricted flies to one of 12 diets varying in protein and carbohydrate concentrations and mapped PO activity for each sex onto a nutritional landscape. Counter to our hypothesis, females had higher PO activity than males at any given level of nutrient intake. Both carbohydrate and protein intake affected PO activity in females but only protein affected PO activity in males. Our results indicate that sex differences in Q-fly immune function are not solely explained by sex differences in nutrient intake, although nutrition does contribute to the magnitude of these sex differences.     

Adult diet and male-female contact effects on female reproductive potential in Mexican fruit fly (Anastrepha ludens Loew) (Diptera tephritidae)

Wild strains of fruit flies (Diptera: Tephritidae) placed into laboratory rearing conditions are subjected to selection pressures caused by the diet, cages, density of flies, and other factors. Selection that changes mating behavior of the strain may result in less effective males released in sterile insect programs. Tests were performed to examine the effects of protein in diet and adult interactions on egg production and mating during sexual maturation of the Mexican fruit fly (Anastrepha ludens Loew) in laboratory cages. Flies were offspring of wild flies collected from Chiapas or Nuevo Leon, Mexico, and reared on Valencia oranges. Experiments demonstrated effects of yeast hydrolysate protein in adult diet and pairing with males on production of mature and immature eggs, numbers of females producing eggs, and mating with females aged 15 d. Addition of protein to 4% fructose in the adult diet approximately tripled mature egg production in females maintained for the total maturation period with an equal number of males. Females that matured without males produced approximately 33% more-mature eggs when fed protein than those fed no protein. Total egg production of females matured without males and fed sugar only or sugar with protein was more than twice that of females matured with males. Tests to examine the effects of male and female diet separately on female egg production showed slightly higher egg production in females fed protein, or females paired with males fed protein, but these differences were not significant. The most definitive effects were that combining wild strain females and males in cages during maturation reduced egg production. This effect was greatest when flies were not fed protein.     

Insulin receptor regulates food intake through sulfakinin signaling in the red flour beetle,Tribolium castaneum

Insects obtain energy and nutrients via feeding to support growth and development. The insulin signaling pathway is involved in the regulation of feeding; however, the underlying mechanisms are not fully understood. Here, we show that insulin signaling regulates food intake via crosstalk with neuropeptide sulfakinin in the red flour beetle, Tribolium castaneum. Silencing of the insulin receptor (InR) decreased the food intake in the penultimate and final instar stages, leading to a decrease of weight gain and mortality during larval-pupal metamorphosis. Interestingly, the knockdown of InR co-occurred with an increased expression of sulfakinin (sk), a gene encoding neuropeptide SK functioning as a satiety signal. In parallel, double silencing of sk and InR eliminated the inhibitory effect on food intake as induced by silencing of InR and the larvae died as prepupae. In conclusion, this study shows, for the first time, that the insulin/InR signaling regulates food intake through the sulfakinin signaling pathway in the larval stages of this important model and pest insect, indicating a novel target for pest control.