Effect of dietary components on larval life history characteristics in the medfly (Ceratitis capitata: Diptera, Tephritidae)

The maxillary palps of Tephritidae are selectively tuned to food volatiles and diverge with ecology

The maxillary palp is an auxiliary olfactory organ in insects, which, different from the antennae, is equipped with only a few olfactory sensory neuron (OSN) types. We postulated that these derived mouthpart structures, positioned at the base of the proboscis, may be particularly important in mediating feeding behaviors. As feeding is spatio-temporally segregated from oviposition in most Tephritidae, this taxonomic group appears quite suitable to parse out sensory breadth and potential functional divergence of palps and antennae. Scanning electron microscopy and anterograde staining underlined the limited palpal olfactory circuit in Tephritidae: only three morphological subtypes of basiconic sensilla were found, each with two neurons, and project to a total of six antennal lobe glomeruli in Bactrocera dorsalis. Accordingly, the palps detected only few volatiles from the headspace of food (fermentation and protein lures) and fruit (guava and mango) compared to the antennae (17 over 77, using gas-chromatography coupled electrophysiology). Interestingly, functionally the antennae were more tuned to fruit volatiles, detecting eight times more fruit than food volatiles (63 over 8), whereas the number of fruit and food volatile detection was more comparable in the palps (14 over 8). As tephritids diverge in oviposition preferences, but converge on food substrates, we postulated that the receptive ranges of palpal circuits would be more conserved compared to the antennae. However, palpal responses of three tephritid species that differed in phylogenetic relatedness and ecologically niche, diverged across ecological rather than phylogenetic rifts. Two species with strongly overlapping ecology, B. dorsalis and Ceratitis capitata, showed inseparable response profiles, whereas the cucurbit specialist Zeugodacus cucurbitae strongly diverged. As Z. cucurbitae is phylogenetically placed between B. dorsalis and C. capitata, the results indicate that ecology overrides phylogeny in the evolution of palpal tuning, in spite of being predisposed to detecting food volatiles.

Latitudinal variation in survival and immature development of Ceratitis capitata populations reared in two key overwintering hosts

Ceratitis capitata, a major agricultural pest, is currently expanding its geographic distribution to northern, temperate areas of Europe. Its seasonal biology and invasion success depend on temperature, humidity and host availability. In coastal warmer Mediterranean regions and cooler temperature areas, bitter oranges and apples serve as overwintering hosts during the larval stage. We assessed the overwintering capacity of C. capitata populations obtained from different areas of the northern hemisphere by studying the survival and development rates of immature stages in both fruits under laboratory conditions. Eggs from each population were artificially inserted in the flesh of the two hosts and kept at 15, 20, or 25 °C until pupation and adult emergence. Climatic analysis of the area of the population origin showed combined effects of latitude, host and macroclimatic variables on immature survival and development rates. Egg to adult survival rates and developmental duration were longer in apples than in bitter oranges. For populations originated from southern-warmer areas, egg to adult developmental duration was prolonged and adult emergence reduced at 15 °C compared to those populations obtained from northern regions. Our findings reveal varying plastic responses of medfly populations to different overwintering hosts and temperatures highlighting the differential overwintering potential as larvae within fruits. This study contributes towards better understanding the medfly invasion dynamics in temperate areas of Northern Europe and other parts of the globe with similar climates.

Optimization of Brewer's Yeast Quantity in Liquid and Gel Larval Diets for the Mediterranean Fruit Fly

Several artificial larval diets have been developed, evaluated and used for mass-rearing of the Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann) (Diptera: Teprhitidae). There are several efforts to reduce the cost of rearing and optimize the quality of the produced sterile males that are destined for release in sterile insect release programs. Survival, growth, longevity and reproductive capacity of sterile males are strongly connected with the most expensive ingredient, the brewer's yeast (protein), in the larval diet. The current study focused on settling the optimal content of brewer's yeast in a liquid diet and a gel diet. Egg hatch rates, developmental duration of immatures, pupation rate, pupae and adult survival were recorded as indicators of quantity and quality of the produced adults. Egg hatch was higher and larval developmental duration longer in the gel diet. In contrast to the liquid diet, an increase in brewer's yeast concentration was correlated with increased pupation rate and pupae survival in the gel diet. Reducing brewer's yeast up to 50% of its initial quantity had no significant effect on the survival of the emerging adults regardless of the diet type. Our findings may contribute to the production of low-cost and effective diets for use in mass-rearing facilities of medflies.

Feeding on the Fruit Waste Orange Bagasse Modifies Immature Protein Content, Body Weight, Scent Bouquet Composition, and Copula Duration in Males of a Tephritid Frugivorous Fly

Anastrepha ludens is a polyphagous frugivorous tephritid that infests citrus and mango. Here, we report the establishment of a laboratory colony of A. ludens reared on a larval medium that is a waste for the citrus industry, specifically, orange (Citrus × sinensis) fruit bagasse. After 24 generations of rearing on a nutritionally poor orange bagasse diet, pupae weighed 41.1% less than pupae from a colony reared on a nutritionally rich artificial diet. Larvae from the orange bagasse diet had 6.94% less protein content than larvae from the artificial diet, although their pupation rate was similar. Males from the orange bagasse diet produced a scent bouquet with 21 chemical compounds and were sexually competitive, but they had significantly shorter copulations when compared to males from the artificial diet and from the wild host, Casimiroa edulis, which had relatively simple scent bouquets. The chemical complexity in the odors of males from the orange bagasse diet might initially have attracted females to novel scent combinations, but, once in the copula, they may have been able to sense negative characteristics in males, leading them to terminate copulations soon after they began. We conclude that A. ludens can adjust morphological, life history, nutritional, and chemical traits when adapted to a larval environment consisting of fruit bagasse.

Innovative feedstocks for optimal mass production of the edible long-horned grasshopper, Ruspolia differens

The edible long-horned grasshopper Ruspolia differens Serville (Orthoptera:Tettigoniidae) is a highly nutritious food source consumed in over 20 African countries. Its occurrence is highly seasonal, and wild harvesting is carried out using locally designed and inefficient light traps, thus limiting sustainable utilization as an important food source. To ensure year-round production and availability of R. differens, we evaluated the effects of low-cost and affordable diets based on agricultural by-products on their growth performance, survival, fecundity, and longevity. A total of four diets with varying ratios of agricultural by-products were evaluated: Diet 1 [33.3% maize bran (MB) + 33.3% wheat bran (WB) + 33.3% Moringa oleifera leaf powder (MOLP)], Diet 2 [25% MB + 25% WB + 25% MOLP + 25% shrimp powder (SP)], Diet 3 [20% MB + 20% WB + 20% MOLP + 20% SP + 20% soya bean meal], and Diet 4 (“control”—routinely used diet). The grasshoppers were subjected to the diets from the 1st nymphal instar (24-h-old stages) through adult stages until death. Diet 3 had the highest crude protein content (28%) and digestibility (74.7%). R. differens fed Diet 3 had the shortest development time (57 days) [p < 0.001], highest survival (87%) [p < 0.001], and maximum longevity (89 days) [p = 0.015] and fecundity (247 eggs/female) [p = 0.549] across the various diets. Female survival rate (59%) on Diet 3 was significantly higher compared to the males (41%). The adult female weight gain was significantly higher compared to males fed on different diets. Percentage hatchability of eggs was not significantly different when females were fed Diet 3 and Diet 2. There was a significantly positive correlation between longevity and fecundity of R. differens reared on Diet 2 and 3. These diets could be further optimized and fine-tuned for improved cost-effective mass production of R. differens continent-wide to reduce dependence on erratic and poor seasonal harvest during swarms.

Effect of larval nutrition on the hemolymph protein composition during metamorphosis of Anastrepha obliqua

Few studies have focused on how nutrition affects the bioavailability and investment of protein during the metamorphosis of tephritids. Our study allowed us to observe how the type and particle size of the bulking agent affected the protein composition in the hemolymph of the larva and adult of Anastrepha obliqua. Results indicated that, true protein bioavailability and protein profile was greatly modified by the bulking agent and its particle size. The physical structure of the food matrix affected the content of crude fiber (F), crude protein (P), F/P ratio, non-protein nitrogen, ammoniacal nitrogen, and α-amylase and trypsin inhibitors. Results from SDS-PAGE revealed 45 fractions with well-defined bands ranging from ~28 to ~401 kDa in larvae and adults, we found the main differences between the samples from different food matrices within the 75-100 kDa range. Hemolymph of adults from the coarse coconut fiber food matrix treatment showed a single band with a molecular weight close to 250 kDa, probably associated with a storage protein such as lipophorins. The food matrix with a coarse bulking agent had a high concentration of ammoniacal nitrogen, suggesting high microbial activity. In conclusion, the particle size of the bulking agent of the food matrix changes the bioavailability of protein in hemolymph in the adult regardless of the total concentration of protein. Also, when the particle size of the bulking agent favored the F/P ratio, higher larval density resulted in higher individual larval weight, larval yield, and adult emergence.

Detection of Fruit Meals Within Laboratory-Raised and Field-Trapped Adult Drosophila suzukii (Diptera: Drosophilidae) Guts

The feeding habits of adult Brachycera are understudied and may provide important context for understanding invasive pest biology, as with the polyphagous small fruit pest Drosophila suzukii. We developed molecular methods to study adult D. suzukii gut content in order to understand its feeding habits. We designed and verified two primer pairs specific for either blueberries or blackberries and used a qPCR melt curve analysis to determine whether we can detect the presence or absence of berry feeding by adult flies. In a laboratory assay, the blueberry fly meal DNA can be detected for longer periods than the blackberry meal DNA. Generally, female gut contents are less variable than male gut contents. We also tested recently emerged flies that were not fed as adults but developed as larvae in either blueberries or blackberries. Some adult flies from each fruit had detectable fruit DNA in their gut, which could be due to pupal meconium feeding after emergence. Next, we aimed to test the primers in the field to develop techniques to track fruit feeding by D. suzukii in its natural field environment. First, to identify the most appropriate collection method, we determined how long we could detect fruit DNA, using previously developed primers within D. suzukii gut preserved in four types of trap fluid in the laboratory. The likelihood of detecting blackberry DNA differed by day, trap fluid, and between sexes. For the blueberry primer, the possibility of detecting blueberry DNA differed by trap fluid only. Based on those results, we used RV antifreeze with a Scentry SWD lure in field trials at two research station locations, one containing blackberries and one with blueberries. We established transects away from each fruit planting and collected up to 120 total flies at each point along transects. There were no significant differences in the number of flies containing berry DNA among collection points along the transect in both locations. These results suggest that adult flies move between crop and non-crop habitats and may not be highly dependent on fruit food resources.

Manipulation of Gut Symbionts for Improving the Sterile Insect Technique: Quality Parameters of Bactrocera dorsalis (Diptera: Tephritidae) Genetic Sexing Strain Males After Feeding on Bacteria-Enriched Diets

One environmentally friendly method used to manage Bactrocera dorsalis (Hendel), a key agricultural pest of substantial economic importance, is the sterile insect technique (SIT). Nevertheless, several deficiencies related to this strategy impair the success of the SIT, including the inferior performance of released sterile males compared with wild males, which could be partly solved by the utilization of gut symbionts as probiotic dietary components. In this study, a culture-dependent method was used to isolate and characterize gut-associated bacterial species in adult B. dorsalis genetic sexing strain (GSS) males. In addition, three bacterial isolates from the Enterobacteriaceae family, namely, Enterobacter sp., Morganella morganii, and Moellerella wisconsensis, were used as supplements in larval and adult diets to assess their effects on the life-history traits of irradiated males. Consistent with many previous studies, Enterobacter spp. was shown to be beneficial, with some quality control indices, such as adult size, pupal weight, survival rate under stress and nutritionally rich conditions, and mating competitiveness, being significantly increased, while slight nonsignificant increases in emergence rate and flight ability were observed. Conversely, the M. morganii and M. wisconsensis strains both had negative effects on irradiated male fitness and mating competitiveness. Our results, in combination with those of earlier studies, can contribute to improving the effectiveness of SIT application by enhancing the different aspects of augmentative rearing and biological traits of pests under laboratory rearing conditions.

Vertically Transmitted Gut Bacteria and Nutrition Influence the Immunity and Fitness of Bactrocera dorsalis Larvae

Symbiotic bacterial communities that colonize the digestive tract of tephritid fruit flies interact with nutrient intake to improve the flies' fitness and immunity. Some bacterial species consistently inhabit the tephritid guts and are transmitted to the next generation vertically. These species contribute significantly to some aspects of their host's physiology. In the current study, we examined the role of four vertically transmitted bacteria (Citrobacter, Enterobacter, Klebsiella, and Providencia) on the fitness parameters and immunity of Bactrocera dorsalis larvae that were fed a nutritionally manipulated diet. For this purpose, eggs were collected from axenic, gnotobiotic, and symbiotic adult flies, and larvae were reared on four types of diets in which carbohydrate and/or protein contents were reduced and then compared with larvae raised on a control diet. The diet and bacterial interactions significantly affected the fitness and immunity of B. dorsalis. Larvae of axenic flies grew slower and displayed weaker immune-based responses (PO activity, antibacterial activity, survival) than larvae of gnotobiotic and symbiotic flies. Overall, larvae reared on the low-protein diet grew slower than those reared on the control or low-carbohydrate diets. Survival, PO activity, and antibacterial activity were significantly lower in the hemolymph of larvae reared on low-protein diets. Our results also revealed that the levels of hemolymph protein, glucose, trehalose, and triglyceride in larvae from axenic flies were significantly lower than those in larvae of the symbiotic group after they fed on most of the tested diets. These results strongly infer that diet and vertically transmitted bacteria are both essential contributors to the fitness and immunity of B. dorsalis.

Fruit host-dependent fungal communities in the microbiome of wild Queensland fruit fly larvae

Bactrocera tryoni (Froggatt), the Queensland fruit fly (Qfly), is a highly polyphagous tephritid fly that is widespread in Eastern Australia. Qfly physiology is closely linked with its fungal associates, with particular relationship between Qfly nutrition and yeast or yeast-like fungi. Despite animal-associated fungi typically occurring in multi-species communities, Qfly studies have predominately involved the culture and characterisation of single fungal isolates. Further, only two studies have investigated the fungal communities associated with Qfly, and both have used culture-dependant techniques that overlook non-culturable fungi and hence under-represent, and provide a biased interpretation of, the overall fungal community. In order to explore a potentially hidden fungal diversity and complexity within the Qfly mycobiome, we used culture-independent, high-throughput Illumina sequencing techniques to comprehensively, and holistically characterized the fungal community of Qfly larvae and overcome the culture bias. We collected larvae from a range of fruit hosts along the east coast of Australia, and all had a mycobiome dominated by ascomycetes. The most abundant fungal taxa belonged to the genera Pichia (43%), Candida (20%), Hanseniaspora (10%), Zygosaccharomyces (11%) and Penicillium (7%). We also characterized the fungal communities of fruit hosts, and found a strong degree of overlap between larvae and fruit host communities, suggesting that these communities are intimately inter-connected. Our data suggests that larval fungal communities are acquired from surrounding fruit flesh. It is likely that the physiological benefits of Qfly exposure to fungal communities is primarily due to consumption of these fungi, not through syntrophy/symbiosis between fungi and insect ‘host’.

Evaluation of Rearing Parameters of a Self-Limiting Strain of the Mediterranean Fruit Fly, Ceratitis capitata (Diptera: Tephritidae)

The Mediterranean fruit fly (medfly), Ceratitis capitata, is a significant pest of stone and pome fruit that causes considerable economic losses worldwide. Current control is primarily based on insecticides, which are often mixed with protein baits. Oxitec has developed a self-limiting medfly strain (OX3864A) that demonstrates conditional female-specific mortality in the early life stages. Sustained release of OX3864A males offers medfly control, which should lead to substantial economic benefits in area-wide programmes. In the current study, the optimum quantities of mature and immature stages of the strain are assessed under semi-mass production. Moreover, the rearing and quality control limitations related to the production of this strain are provided. The data here demonstrate that the egg hatch rate can reach >85% under optimum rearing conditions. However, this depends on the number of pupae loaded in a cage and their ages. The suggested pupal density ranges between 14,000 and 18,000 pupae per cage to provide optimum egg production. In parallel, the embryo densities of 1.25-1.5 mL/kg larval Tet+ diet are recommended for strain propagation, while embryo densities of 1.25-2.0 mL/kg larval Tet- diet are suggested for male-only pupal production.

Effect of host fruit, temperature and Wolbachia infection on survival and development of Ceratitis capitata immature stages

The Mediterranean fruit fly, Ceratitis capitata (Diptera: Tephritidae), holds an impressive record of successful invasions promoted by the growth and development of international fruit trade. Hence, survival of immatures within infested fruit that are subjected to various conditions during transportation seems to be a crucial feature that promotes invasion success. Wolbachia pipientis is a common endosymbiont of insects and other arthropods generating several biological effects on its hosts. Existing information report the influence of Wolbachia on the fitness traits of insect host species, including the Mediterranean fruit fly. However, little is known regarding effects of Wolbachia infection on immature development in different host fruits and temperatures. This study was conducted to determine the development and survival of immature stages of four different Mediterranean fruit fly populations, either infected or uninfected with Wolbachia, in two hosts (apples, bitter oranges) under three constant temperatures (15, 25 and 30°C), constant relative humidity (45-55 ± 5%), and a photoperiod of 14L:10D. Our findings demonstrate both differential response of two fruit fly lines to Wolbachia infection and differential effects of the two Wolbachia strains on the same Mediterranean fruit fly line. Larva-to-pupa and larva-to-adult survival followed similar patterns and varied a lot among the four medfly populations, the two host fruits and the different temperatures. Pupation rates and larval developmental time were higher for larvae implanted in apples compared to bitter oranges. The survival rates of wildish medflies were higher than those of the laboratory adapted ones, particularly in bitter oranges. The Wolbachia infected medflies, expressed lower survival rates and higher developmental times, especially the wCer4 infected line. High temperatures constrained immature development and were lethal for the Wolbachia infected wCer4 medfly line. Lower temperatures inferred longer developmental times to immature stages of all medfly populations tested, in both host fruits. Implications on the ecology and survival of the fly in nature are discussed.

Agar and Carrageenan as Cost-Effective Gelling Agents in Yeast-Reduced Artificial Diets for Mass-Rearing Fruit Flies and Their Parasitoids

The development of cost-effective diets for mass-rearing fruit flies (Diptera: Tephritidae) and their parasitoids in pest control programs based on the Sterile Insect Technique is a high priority worldwide. To this end, we tested carrageenan, agar, gelatin and two types of pregelatinized corn starches as gelling agents at varying percentages in a yeast-reduced liquid larval diet for rearing the Mexfly, Anastrepha ludens. Only diets with 0.234% (w/w) agar or 0.424% carrageenan were identified as diets with potential for mass-rearing A. ludens in terms of the number of pupae recovered from the diet, pupal weight, adult emergence, flight ability and diet cost. Comparative experiments showed that yeast-reduced agar and carrageenan gel diets produced heavier pupae and higher proportions of flying adults than the standard mass-rearing diet. The gel-agar and mass-rearing diets produced more pupae than the gel-carrageenan diet, but the latter produced more suitable larvae as hosts for rearing of Diachasmimorpha longicaudata (Hymenoptera: Braconidae) females, a widely used fruit fly biocontrol agent. Yeast-reduced agar and carrageenan gel diets could represent cost-effective fruit fly mass-rearing diets if a practical system for gel diet preparation and dispensation at fruit fly mass-rearing facilities is developed.

Effects of carbohydrate types on larval development and adult traits in a polyphagous fruit fly

Nutrition is a major mediator of insect life-history trait expression. While the role of macronutrient (carbohydrate and protein) balance on trait expression has received substantial attention, the implications of different classes of specific macronutrients remains virtually unexplored. Here, we addressed this gap by varying the type of carbohydrate in larval diets of the polyphagous fruit fly Bactrocera tryoni (aka 'Queensland fruit fly'). Sourcing insects from a colony maintained using larval diets that contain sucrose, we assessed the effects of sucrose, maltose, and lactose on larval development and adult traits. Replacement of sucrose with lactose resulted in slow larval growth, as well as decreases in pupation, adult emergence and adult body weight for both sexes, although adult lipid reserves were unaffected. Sucrose and maltose were equivalent in terms of larval growth, pupation, adult emergence and adult weight of both sexes. Surprisingly, adults from larvae reared on diets containing maltose had lower lipid reserves than adults from larvae reared on diets containing either lactose or sucrose. The sex ratio of adults at emergence from larvae reared on diets containing lactose and maltose was balanced, but was female-biased in adults from larvae reared on diets containing sucrose. Our results show that carbohydrate sources are not equivalent for development of the Queensland fruit fly, affecting both larval development and adult traits. These findings have implications for understanding the ecology of this highly polyphagous species which infests fruits with highly diverse carbohydrate contents, as well as for the rearing and management of this pest species.

Combining sterile and incompatible insect techniques for the population suppression of Drosophila suzukii

The spotted wing Drosophila, Drosophila suzukii, has recently invaded Europe and the Americas, and it is a major threat for a wide variety of commercial soft fruits both in open field and greenhouse production systems. D. suzukii infests a wide range of ripening fruits, leading to substantial yield and revenue losses. As the application of insecticides close to the harvest period poses great concerns, the development of an efficient environment-friendly control approach to fight D. suzukii is necessary. In this study, we exploited the sterile insect technique (SIT) in combination with Wolbachia symbiosis as a population suppression approach that can constitute a potential component of an area-wide integrated pest management program. We aimed to establish a combined SIT/incompatible insect technique (IIT) protocol that would require lower irradiation doses as a complementary tool for D. suzukii management. Two D. suzukii lines trans-infected with the Wolbachia wHa and wTei strains were irradiated at doses four times less than usual (e.g., 45 Gy), and the egg hatching and adult emergence were determined. Our results indicated that wHa and wTei females as well as wHa males were sterile at this low dose. The longevity, adult emergence and flight ability of adults were evaluated, and no major effect caused by irradiation was detected. Our data indicate that a SIT/IIT protocol can be a competent approach for D. suzukii management.

Enterobacter sp. AA26 gut symbiont as a protein source for Mediterranean fruit fly mass-rearing and sterile insect technique applications

Background

Insect species have established sophisticated symbiotic associations with diverse groups of microorganisms including bacteria which have been shown to affect several aspects of their biology, physiology, ecology and evolution. In addition, recent studies have shown that insect symbionts, including those localized in the gastrointestinal tract, can be exploited for the enhancement of sterile insect technique (SIT) applications against major insect pests such as the Mediterranean fruit fly (medfly) Ceratitis capitata. We previously showed that Enterobacter sp. AA26 can be used as probiotic supplement in medfly larval diet improving the productivity and accelerating the development of the VIENNA 8 genetic sexing strain (GSS), which is currently used in large scale operational SIT programs worldwide.

Results

Enterobacter sp. AA26 was an adequate nutritional source for C. capitata larvae, comprising an effective substitute for brewer’s yeast. Incorporating inactive bacterial cells in the larval diet conferred a number of substantial beneficial effects on medfly biology. The consumption of bacteria-based diet (either as full or partial yeast replacement) resulted in decreased immature stages mortality, accelerated immature development, increased pupal weight, and elongated the survival under stress conditions. Moreover, neither the partial nor the complete replacement of yeast with Enterobacter sp. AA26 had significant impact on adult sex ratio, females’ fecundity, adults’ flight ability and males’ mating competitiveness. The absence of both yeast and Enterobacter sp. AA26 (deprivation of protein source and possible other important nutrients) from the larval diet detrimentally affected the larval development, survival and elongated the immature developmental duration.

Conclusions

Enterobacter sp. AA26 dry biomass can fully replace the brewer’s yeast as a protein source in medfly larval diet without any effect on the productivity and the biological quality of reared medfly of VIENNA 8 GSS as assessed by the FAO/IAEA/USDA standard quality control tests. We discuss this finding in the context of mass-rearing and SIT applications.

Mate choice and gene expression signatures associated with nutritional adaptation in the medfly (Ceratitis capitata)

Evolutionary responses to nutrition are key to understanding host shifts and the resulting potential for reproductive isolation. Experimental evolution has previously been used to describe the responses of the medfly (Ceratitis capitata) to larval diets with different nutritional properties. Within 30 generations this led to divergence in larval development time, egg to adult survival and adaptation in adult body size. Here we used mRNA-seq to identify differences in gene expression patterns in these same populations, using males from the 60^th generation of nutritional selection. We validated differential expression by using qRT-PCR and found that genes linked to metabolism, oxidative phosphorylation and proteolysis were significantly over-represented among the differentially expressed genes. The results provide the first genome-wide survey of the putative mechanisms underpinning evolved responses to nutritional adaptation. In addition, we tested the hypothesis that nutritional adaptation can alter mating patterns. We found evidence for assortative mating by diet at generation 60, but not 90. Hence, the pattern was variable across generations and there was no evidence overall for any isolating mating divergence between the lines. Overall, the results provide insight into the mechanisms underpinning dietary adaptation and extend our knowledge of which traits represent core responses to nutritional selection.

Performance of Newly Described Native Edible Cricket Scapsipedus icipe (Orthoptera: Gryllidae) on Various Diets of Relevance for Farming

A new native edible cricket species, Scapsipedus icipe Hugel and Tanga, has been described in Kenya for the first time. However, there is lack of information on suitable diets and their effects on the developmental time, survival, weight gain, body length, growth index, preoviposition, oviposition, postoviposition, fecundity, egg eclosion period, adult emergence, and longevity of this species, which are prerequisite for large-scale production. In this study, six diets (wheat bran, soybean, fish offal, pumpkin leaf, carrot, and maize meals) selected to vary in protein, carbohydrate, and fat content were evaluated. The developmental time and survival rate of the different life stages varied considerably on the various diets, with the shortest development and highest survival rate recorded when fed wheat bran diet. Preoviposition duration was significantly longer on maize and carrot diets (>10 d) compared with that recorded on the other diets (<8 d). Body weight and body length were significantly influenced by the different diets tested. Females of S. icipe fed on protein-rich diets (fish offal, soybean, and wheat bran) had significantly higher lifetime fecundity and fertility. Female-biased sex ratio was recorded on wheat bran and soybean diets, whereas male-biased sex ratio was recorded on maize and carrot diets. Our findings reveal that the impact of diet quality on the biological fitness parameters of S. icipe and the implication of the results are discussed in light of effective mass rearing of this species.

Composition and Toxicity of a Mixture of Essential Oils Against Mediterranean Fruit Fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae)

A natural insecticide developed from the mixture of the essential oils (EOs) of Cymbopogon citratus (DC.) Stapf (Poaceae), Cedrus atlantica (Endl.) Manetti ex Carriére (Pinaceae), and Corymbia citriodora (Hook.) K.D. Hill & L.A.S. Johnson (Myrtaceae) was studied. The mixture of oils caused high mortality (LD50 = 0.018 μl/insect) to the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), a globally important pest, after topical application on adults. Based on the chemical characterization of biopesticide using gas chromatography-mass spectrometry (GC-MS) analysis, many of the constituents had known insecticidal properties (the monoterpenes α-citronellal and E-citral and the sesquiterpernes α-himachalene and β-himachalene, all at concentrations above 15%). Phytotoxicity tests on orange trees demonstrated that this natural product was harmless when the mixture was applied diluted in water with a surfactant. The mixture of EOs was also harmless (1, IOBC category) to the biological control agent responsible for reducing populations of tephritids, the parasitoid Psyttalia concolor (Hymenoptera: Braconidae), following exposure to treated orange trees in a semifield assay within a greenhouse, but killed 46.2% of C. capitata (Szépligeti) adults after 72 h. Our results suggest that mixture of EOs has potential for use as an adulticide against medfly, although the production price was exceedingly high compared with that of commercial synthetic insecticides. Therefore, we discuss the advantages and disadvantages related to the potential use of this natural insecticide.

Contribution of maternal effects to dietary selection in Mediterranean fruit flies

Individual responses to dietary variation represent a fundamental component of fitness, and nutritional adaptation can occur over just a few generations. Maternal effects can show marked proximate responses to nutrition, but whether they contribute to longer term dietary adaptation is unclear. Here, we tested the hypotheses that maternal effects: (i) contribute to dietary adaptation, (ii) diminish when dietary conditions are constant between generations, (iii) are trait-specific and (iv) interact with high- and low-quality food. We used experimental evolution regimes in the medfly (Ceratitis capitata) to test these predictions by subjecting an outbred laboratory-adapted population to replicated experimental evolution on either constant high calorie sugar ('A') or low-calorie starch ('S') larval diets, with a standard adult diet across both regimes. We measured the contribution of maternal effects by comparing developmental and adult phenotypes of individuals reared on their own diet with those swapped onto the opposite diet for either one or two generations (high and low maternal effect conditions, respectively), both at the start and after 30 generations of selection. Initially, there were strong maternal effects on female body mass and male mating success but not larval survival. Interestingly, the initial maternal effects observed in female body mass and male mating success showed sex-specific interactions when individuals from high calorie regimes were tested on low calorie diets. However, as populations responded to selection, the effects of maternal provisioning on all traits diminished. The results broadly supported the predictions. They show how the contribution of maternal effects to dietary responses evolves in a context-dependent manner, with significant variation across different fitness-related traits. We conclude that maternal effects can evolve during nutritional adaptation and hence may be an important life history trait to measure, rather than to routinely minimize.

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.

Linking developmental diet to adult foraging choice in Drosophila melanogaster

Rather than maximizing intake of available macronutrients, insects increase intake of some nutrients and restrict intake of others. This selective consumption influences, and potentially optimizes, developmental time, reproduction and lifespan of the organism. Studies so far have focused on discriminating between protein and carbohydrate uptake and the consequences on fitness components at different life stages. However, it is largely unknown whether and how the developmental diets, which may entail habitat-specific nutrient restrictions, affect selective consumption in adults. We show that adult female D. melanogaster opt for the same protein to carbohydrate (P:C) ratio regardless of their developmental diet (P:C ratio of 1:1, 1:4 or 1:8). In contrast, males choose a diet that makes up for deficiencies; when protein is low during development, males increase protein consumption despite this being detrimental to starvation resistance. The sexual dimorphism in foraging choice could be due to the different energetic requirements of males and females. To investigate the effect of developmental diet on lifespan once an adult nutritional environment has been established, we also conducted a no-choice experiment. Here, adult lifespan increased as P:C ratio decreased, irrespective of developmental diet, thus demonstrating a 'cancelling out' effect of the nutritional environment experienced during early life stages. Our study provides novel insights into how developmental diet is linked to adult diet by presenting evidence for sexual dimorphism in foraging choice as well as life-stage dependency of diet on lifespan.

Influence of Supplemental Protein on the Life Expectancy and Reproduction of the Chinese Citrus Fruit Fly, Bactrocera minax (Enderlein) (Tetradacus minax) (Diptera: Tephritidae)

Bactrocera minax (Enderlein) (Diptera: Tephritidae) is a major citrus pest in China, whose artificial rearing technology of the adult is not well documented to date. In this study, we tried to determine if supplementing proteins to the adult diet could result in the enhancement of some fitness parameters of B. minax. Four feeds with varying protein source were provided as F0 (water), F1 (sucrose), F2 (sucrose + yeast), and F3 (sucrose + peptone). F0 and F1 being the control, F2 and F3 were protein food types. The results showed that adults fed by F2 and F3 lived longer with 40.1 d and 32.8 d, respectively, had reduced death rates (death peaks were delayed for 5.6 d and 4.1 d, respectively), increased mating frequencies (8.1 and 5.3 per females, 4.7 and 7.3 per males, respectively), and longer mating durations (with 42 d and 34 d). In addition, females recorded an increased adult ovary development, more egg load (with 94.8 and 77.3 brood eggs per ovary) and to greater oviposition rates of 63.2 eggs/female and 19.3 eggs/female. Based on our results, protein supplements enhanced B. minax survival, mating, and fecundity. This study does not only provide basic knowledge to implement artificial rearing of B. minax, but also deepens our understanding on its physiology that could be used to enhance the management of the pest.

The Impact of Diet Protein and Carbohydrate on Select Life-History Traits of The Black Soldier Fly Hermetia illucens (L.) (Diptera: Stratiomyidae)

This study examined the impact of diet protein and carbohydrate percentages as well as moisture on the immature development, survivorship, and resulting adult longevity and egg production of the black soldier fly, Hermetiaillucens (L.) (Diptera: Stratiomyidae). Moisture impacted development and corresponding life-history traits more than protein:carbohydrate content; larvae were unable to develop on diets at 40% moisture. Larvae fed diets at 70% moisture developed faster, grew larger, and required less food than those reared on diets at 55% moisture. Larvae reared on the balanced diet (21% protein:21% carbohydrate) at 70% moisture developed the fastest on the least amount of food and had the greatest survivorship to the prepupal stage. Adult emergence and longevity were similar across treatments, indicating immature life-history traits were impacted the most. The control (Gainesville house fly) diet was superior to the artificial diets for all parameters tested. These differences could indicate that other constituents (e.g., associated microbes) serve a role in black soldier fly development. These data are valuable for industrialization of this insect as a "green" technology for recycling organic waste, which can be highly variable, to produce protein for use as feed in the livestock, poultry, and aquaculture industries, as well as for bioenergy production.

Adaptation to divergent larval diets in the medfly, Ceratitis capitata

Variation in diet can influence the timing of major life-history events and can drive population diversification and ultimately speciation. Proximate responses of life histories to diet have been well studied. However, there are scant experimental data on how organisms adapt to divergent diets over the longer term. We focused on this omission by testing the responses of a global pest, the Mediterranean fruitfly, to divergent selection on larval diets of different nutritional profiles. Tests conducted before and after 30 generations of nutritional selection revealed a complex interplay between the effects of novel larval dietary conditions on both plastic and evolved responses. There were proximate-only responses to the larval diet in adult male courtship and the frequency of copulation. Males on higher calorie larval diets consistently engaged in more bouts of energetic courtship. In contrast, following selection, larval development time, and egg to adult survival showed evidence of evolved divergence between diet regimes. Adult body size showed evidence for adaptation, with flies being significantly heavier when reared on their "own" diet. The results show the multifaceted responses of individuals to dietary selection and are important in understanding the extreme generalism exhibited by the medfly.

Host plant range of a fruit fly community (Diptera: Tephritidae): does fruit composition influence larval performance?

Background

Phytophagous insects differ in their degree of specialisation on host plants, and range from strictly monophagous species that can develop on only one host plant to extremely polyphagous species that can develop on hundreds of plant species in many families. Nutritional compounds in host fruits affect several larval traits that may be related to adult fitness. In this study, we determined the relationship between fruit nutrient composition and the degree of host specialisation of seven of the eight tephritid species present in La Réunion; these species are known to have very different host ranges in natura. In the laboratory, larval survival, larval developmental time, and pupal weight were assessed on 22 fruit species occurring in La Réunion. In addition, data on fruit nutritional composition were obtained from existing databases.

Results

For each tephritid, the three larval traits were significantly affected by fruit species and the effects of fruits on larval traits differed among tephritids. As expected, the polyphagous species Bactrocera zonata, Ceratitis catoirii, C. rosa, and C. capitata were able to survive on a larger range of fruits than the oligophagous species Zeugodacus cucurbitae, Dacus demmerezi, and Neoceratitis cyanescens. Pupal weight was positively correlated with larval survival and was negatively correlated with developmental time for polyphagous species. Canonical correspondence analysis of the relationship between fruit nutrient composition and tephritid survival showed that polyphagous species survived better than oligophagous ones in fruits containing higher concentrations of carbohydrate, fibre, and lipid.

Conclusion

Nutrient composition of host fruit at least partly explains the suitability of host fruits for larvae. Completed with female preferences experiments these results will increase our understanding of factors affecting tephritid host range.

Electronic supplementary material

The online version of this article (doi:10.1186/s12898-016-0094-8) contains supplementary material, which is available to authorized users.

Rearing Larvae of the Avian Nest Parasite, Philornis downsi (Diptera: Muscidae), on Chicken Blood-Based Diets

Captive rearing of insect pests is necessary to understand their biology and to develop control methods. The avian nest fly, Philornis downsi Dodge and Aitken, is a blood-sucking parasite during its larval stage and a serious threat to endemic birds in the Galapagos Islands where it is considered invasive. In order to procure large numbers of flies for biological studies, rearing media and diets were trialed for rearing the larval stage of P. downsi under controlled conditions in the absence of its avian host. P. downsi eggs were obtained from field-caught female flies, and once eggs hatched they were reared on chicken blood for the first 3 d. Following this, three diets were tested on second- and third-instar larvae: 1) chicken blood only; 2) chicken blood, hydrolyzed protein and dried milk powder; and 3) chicken blood, hydrolyzed protein and brewer's yeast. Out of 385 P. downsi larvae tested, we were able to rear 50 larvae to the adult stage. The highest level of mortality was found in the first-instar larvae. Survivorship of second- and third-instar larvae was similar irrespective of diet and diet did not significantly influence larval or pupal development times; though larvae fed the diet with brewer's yeast developed marginally faster. Pupal weights were similar to those of larvae that had developed on bird hosts in the field. To our knowledge, this is the first effective protocol for rearing a hematophagous parasitic avian fly from egg to adult in the absence of a living host.

Exploitation of the Medfly Gut Microbiota for the Enhancement of Sterile Insect Technique: Use of Enterobacter sp. in Larval Diet-Based Probiotic Applications

The Mediterranean fruit fly (medfly), Ceratitis capitata, is a pest of worldwide substantial economic importance, as well as a Tephritidae model for sterile insect technique (SIT) applications. The latter is partially due to the development and utilization of genetic sexing strains (GSS) for this species, such as the Vienna 8 strain, which is currently used in mass rearing facilities worldwide. Improving the performance of such a strain both in mass rearing facilities and in the field could significantly enhance the efficacy of SIT and reduce operational costs. Recent studies have suggested that the manipulation of gut symbionts can have a significant positive effect on the overall fitness of insect strains. We used culture-based approaches to isolate and characterize gut-associated bacterial species of the Vienna 8 strain under mass rearing conditions. We also exploited one of the isolated bacterial species, Enterobacter sp., as dietary supplement (probiotic) to the larval diet, and we assessed its effects on fitness parameters under the standard operating procedures used in SIT operational programs. Probiotic application of Enterobacter sp. resulted in improvement of both pupal and adult productivity, as well as reduced rearing duration, particularly for males, without affecting pupal weight, sex ratio, male mating competitiveness, flight ability and longevity under starvation.

Costly Nutritious Diets do not Necessarily Translate into Better Performance of Artificially Reared Fruit Flies (Diptera: Tephritidae)

Protein, lipid, carbohydrate, and energy contents of three artificial diets (Xal2, Met1, and Met2) used for laboratory-rearing and mass-rearing the Mexican fruit fly, Anastrepha ludens (Loew), for a sterile insect technique program were measured. The larval survival, pupation, pupal weight, adult emergence, sex ratio, and flight capacity of the flies reared on each of these diets were also quantified. The diet with the highest nutrient and energy content was Xal2 followed by Met2 and Met1, but larval recovery and percent pupation was significantly higher in flies reared on either the Met1 or Met2 diets. A. ludens reared on Xal2 exhibited the highest proportion of adults capable of flight. No other response variable differed significantly among the three diets tested. This suggests that a high content of nutrients and multiple sources of protein (dried yeast and wheat germ in the case of the Xal2 diet) do not necessarily improve overall performance or fly quality. We conclude that nutritious diets for A. ludens can be modified to reduce their cost without compromising the performance of artificially reared flies.

Conserved metallomics in two insect families evolving separately for a hundred million years

Μetal cofactors are required for enzymatic catalysis and structural stability of many proteins. Physiological metal requirements underpin the evolution of cellular and systemic regulatory mechanisms for metal uptake, storage and excretion. Considering the role of metal biology in animal evolution, this paper asks whether metal content is conserved between different fruit flies. A similar metal homeostasis was previously observed in Drosophilidae flies cultivated on the same larval medium. Each species accumulated in the order of 200 µg iron and zinc and approximately ten-fold less manganese and copper per gram dry weight of the adult insect. In this paper, data on the metal content in fourteen species of Tephritidae, which are major agricultural pests worldwide, are presented. These fruit flies can be polyphagous (e.g., Ceratitis capitata) or strictly monophagous (e.g., Bactrocera oleae) or oligophagous (e.g., Anastrepha grandis) and were maintained in the laboratory on five distinct diets based on olive oil, carrot, wheat bran, zucchini and molasses, respectively. The data indicate that overall metal content and distribution between the Tephritidae and Drosophilidae species was similar. Reduced metal concentration was observed in B. oleae. Feeding the polyphagous C. capitata with the diet of B. oleae resulted in a significant quantitative reduction of all metals. Thus, dietary components affect metal content in some Tephritidae. Nevertheless, although the evidence suggests some fruit fly species evolved preferences in the use or storage of particular metals, no metal concentration varied in order of magnitude between these two families of Diptera that evolved independently for over 100 million years.