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

Larval Rearing and Nutrition of the Polyphagous Tephritid Pest Anastrepha ludens on Artificial Diets with Calcium Alginate, Agar, or Carrageenan as Gelling Agents at Various Concentrations and across Extreme Larval Density Conditions

Research on larval rearing and nutrition of tephritid flies on artificial diets is key for the sterile insect technique. Here, we examined the effects of the type of gel (calcium alginate, agar, or carrageenan), at varying percentages in artificial diets for the polyphagous pest Anastrepha ludens, on the physicochemical and nutritional traits of the diets, and the effects of the type of gel, the gel content and the larval density (larvae/g of diet) used in production, quality parameters for mass-reared tephritids, diet removal (an indirect estimation of diet consumption), and nutritional traits of flies. Regardless of the gel content, calcium alginate diets were firmer and more resistant to penetration than the agar and carrageenan diets. The larval recovery, pupation, pupal weight, and flight ability of A. ludens were lower in calcium alginate diets than in agar and carrageenan diets. Diet removal was higher in calcium alginate diets; however, low levels of ammonium and high levels of uric acid in excretions from larvae on these diets suggest an alteration in protein metabolism. The firmness and penetration resistance characteristics of calcium alginate diets may have limited movement and feeding of larvae, but this could be overcome by the collective feeding of large groups of larvae. Our findings provide insights into the mechanism governing gel-diet rearing systems for A. ludens.

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.

Wheat-Bran-Based Artificial Diet for Mass Culturing of the Fall Armyworm, Spodoptera frugiperda Smith (Lepidoptera: Noctuidae)

Spodoptera frugiperda Smith (fall armyworm (FAW)) has invaded many countries in Africa and Asia in recent years, considerably restricting global agricultural production. In this study, we assessed the rearing performance of four artificial diets (D₁: an artificial FAW diet based on wheat bran and soybean, maize, and yeast powders; D₂: an artificial diet developed for Helicoverpa armigera (Hübner), based on wheat bran and soybean and yeast powders; D₃: an artificial diet based on soybean powder; D₄: an artificial diet based on wheat bran) for FAWs. We designed D₄ based on a traditional diet (D₂) but substituted the wheat bran for soybean and yeast powders. At 25 ± 1 °C, 75% ± 5% RH, and a 16:8 h L:D photoperiod, the larval stage of FAWs fed on D₄ lasted 15.88 d, the pupal stage lasted 9.48 d, the pupal mass was 270.45 mg, the number of eggs deposited was 1364.78, and the mating rate was 89.53%. Most biological indicators of the larvae that were fed D₄ were basically consistent with those of the larvae fed on the traditional diet (D₂), but the intrinsic rate of increase (r), finite rate of increase (λ), and net reproduction rate (R₀) of the D₄ FAWs were lower than those of the D₂ FAWs. The flight capacity (flight distance, duration, and velocity were 19.73 km, 6.91 h, and 2.90 km/h, respectively) of the D₄ FAWs was comparable to that of the FAWs fed a traditional diet and maize leaves. Compared with the three other formulas, the cost of using D₄ was lower by 26.42% on average. These results show that using cheap wheat bran instead of soybean flour and yeast powder as the basic material for an artificial diet for FAWs is feasible, which will substantially reduce rearing costs and promote the development of new controlling measures for FAWs. In addition, this study also has a reference value for reducing the cost of artificial diets for other insects.

Life-History Traits and Flight Capacity of Grapholita molesta (Lepidoptera: Tortricidae) Using Artificial Diets With Varying Sugar Content

Successful application of the sterile insect technique (SIT), an environmentally friendly control technology, mainly depends on mass-rearing of high-quality and high-performance insects. For mass-rearing of insects, the development of artificial diets is a key component. For optimal insect growth and development, sugar is an essential nutrient as it provides energy for flight. To date, few studies have analyzed the effects of different sugar contents on the biological parameters, including the flight capacity of Grapholita molesta, a globally important economic pest. Artificial diets with different sucrose contents (0, 15, and 30 g) were evaluated in two consecutive generations. The insect flight mill was used to study the G. molesta flight capacity. The larval and pupal periods, adult longevity and pupal weight of the first-generation of G. molesta reared on artificial diets with different sucrose contents were significantly different. Insects of the second-generation had a shorter larval period, greater adult longevity, and heavier larvae and pupae in the treatment with 30 g of sucrose than using 15 g. Among the males, strong, medium, and weak flight capacities were recorded and the weakest one was observed in the diet without sucrose. Results showed that the proportion of insects with highest flight capacity increased with increasing sucrose content in insects of the second generation. It can be concluded that sucrose content is a key determinant in the biological traits, including flight capacity of G. molesta, and should be taken into consideration during the mass-rearing of the pest for SIT.

Insights into the Interaction between the Monophagous Tephritid Fly Anastrepha acris and its Highly Toxic Host Hippomane mancinella (Euphorbiaceae)

Despite their enormous economic importance and the fact that there are almost 5000 tephritid (Diptera) species, fruit fly - host plant interactions are poorly understood from a chemical perspective. We analyzed the interactions among Anastrepha acris (a little studied monophagous tephritid) and its highly toxic host plant Hippomane mancinella from chemical, ecological and experimental perspectives, and also searched for toxicants from H. mancinella in the larval-pupal endoparasitoid Doryctobracon areolatus. We identified 18 phenolic compounds from H. mancinella pulp belonging to different chemical groups including phenylpropanoids, flavonoids, chalcones and coumarins. No traces of Hippomanin A were detected in larvae, pupae or A. acris adults, or in D. areolatus adults, implying that A. acris larvae can metabolize this toxicant, that as a result does not reach the third trophic level. We tested the "behavioral preference - lack of larval specialization-hypothesis" via feeding experiments with a larval rearing medium containing H. mancinella fruit (skin + pulp or pulp alone). The high toxicity of H. mancinella was confirmed as only two (out of 2520 in three experiments) A. ludens larvae (a polyphagous pest species that preferentially feeds on plants within the Rutaceae) survived without reaching the adult stage when fed on media containing H. mancinella, whereas A. acris larvae developed well and produced healthy adults. Together, these findings open a window of opportunity to study the detoxification mechanisms used by tephritid fruit flies.

Assessment of Bactrocera dorsalis (Diptera: Tephritidae) Diets on Adult Fecundity and Larval Development: Insights Into Employing the Sterile Insect Technique

Bactrocera dorsalis (Hendel) is a notorious insect pest that attacks diverse vegetables and fruits worldwide. The sterile insect technique has been developed as an environmentally friendly and effective control method that depends on the mass production of target flies. Because dietary yeast (protein) and sucrose (carbohydrate) are important in adult diets, yeast:sucrose (Y:S) mixtures are crucial for the mass-rearing of B. dorsalis. In this study, we found adult diets with different ratios of yeast to sucrose-influenced fecundity, and an extremely high or low Y:S ratios significantly decreased egg production of B. dorsalis. Additionally, the maximum oviposition efficiency was realized at dietary yeast to sucrose ratios of 1:1 and 1:3, suggesting their potential use to produce more eggs for the mass production of B. dorsalis. Here, new gel diets having different yeast concentrations (g/L water) were also assessed for rearing B. dorsalis larvae. Gel diets containing 20 g/L yeast led to a higher pupation, pupal weight and adult eclosion rate, and a shorter developmental time than other yeast concentrations. Moreover, the present gel diet also resulted in greater pupal production and adult emergence rates than previously used liquid and solid artificial diets, revealing that it is suitable for rearing B. dorsalis larvae. This research provides a useful reference on artificial diets mixtures for mass rearing B. dorsalis, which is critical for employing the sterile insect technique.

Comparison of Gel Larval Diet With Traditional Lucerne Chaff and Carrot Solid Diets for Rearing of Queensland Fruit Fly (Diptera: Tephritidae)

Sterile insect technique (SIT) for Queensland fruit fly, Bactrocera tryoni Froggatt, Australia's most economically damaging fruit fly species, is currently undergoing a major renewal and expansion. SIT relies on efficient and economical mass-rearing procedures that produce high-quality flies. Two solid larval diets, carrot and lucerne chaff, have traditionally been used to rear Queensland fruit fly. Recently, a gel larval diet has been developed to eliminate biological bulking agents from the mass-rearing process, but to date, there has been no direct comparison of gel larval diet with traditional solid diets. In the present study, the performance of flies reared on gel larval diet was compared with the performance of flies reared on carrot and lucerne chaff diets. In addition, to investigate whether the performance of reared flies depends on ancestral diet as well as tested diet, we sourced eggs from a colony maintained on carrot diet and from a colony maintained on a lucerne chaff diet. Overall, the gel diet was as good or better than the solid diets in all quality control parameters, including, egg-larval duration, pupal number, pupal recovery, adult emergence, percentage of fliers, and rate of fliers. Of note, larvae developed faster and pupated more synchronously on the gel diet than on either of the solid diets. At the loading densities used, gel and carrot diets produced less waste than lucerne chaff diet. Gel diets offer a rearing solution for Queensland fruit fly that eliminates biological bulking agents and yields faster and more synchronous larval development without compromising productivity or quality.

A Novel, Low-Cost Coconut Fiber Larval Diet for Mass Rearing Anastrepha (Diptera: Tephritidae)

Mass rearing fruit flies of the genus Anastrepha for the sterile insect technique involves the use of artificial larval diets that commonly contain corn cob powder as a bulking agent. Corn cob powder varies in quality, and larval diets that contain it can be reaching at high temperatures (>34°C), which subsequently has a negative effect on pupal weight and adult survival. In addition, corn cob powder is susceptible to contamination by mycotoxins, which can inhibit larval development and cause high larval mortality. The objective of this work was to develop a low-cost artificial larval diet for mass rearing Anastrepha spp. fruit flies using coconut fiber, a nonconventional bulking agent, and to evaluate its effects on the quality parameters for A. ludens wild-type, A. ludens Tap-7 GS-strain, A. obliqua, A. serpentina, and A. striata. The coconut fiber diet resulted in an increase in the larval and pupal weight of A. ludens Tap-7 GS-strain and A. obliqua, an increase in the larval weight of A. ludens wild-type, an increase in the flight ability of A. obliqua and A. serpentina and an increase in adult eclosion in A. ludens Tap-7 GS-strain. The coconut fiber diet resulted in increased production and quality of the mass-reared flies, reduced the cost of the diet by 15 and 20% for A. ludens and A. obliqua, respectively, and led to further cost savings through reduced labor processes.

Yeast derivatives and wheat germ in the adult diet modulates fecundity in a tephritid pest

Anastrepha fraterculus (Wiedemann), a pest of great economic importance in South America, needs urgently to be controlled by environmentally friendly methods such as the sterile insect technique for which mass rearing of insects is required. Because oogenesis takes place during the adult stage, mass-rearing facilities should provide the females a diet that maximizes egg production at the lowest cost. Accordingly, we investigated the effect of artificial protein sources in the adult diet (yeast derivatives of different cost but with similar amino acids profiles, and the addition of wheat germ) on fecundity. Additionally, we evaluated different ratios of yeast derivatives or wheat germ on ovary maturation, fecundity, and fertility as well as their association with the nutrient content of females. Females fed hydrolyzed yeast and yeast extract attained the highest fecundity level, and those fed brewer's yeast the lowest. Reducing the amount of hydrolyzed yeast, an expensive protein source, in the diet negatively affected fecundity and ovary maturation. Increasing the amount of brewer's yeast, a low-cost protein source, did not favor fecundity. The addition of wheat germ in the adult diet improved fecundity regardless of the yeast derivate considered. Percentage of egg hatch was not affected by the diet. Nutrient content of A. fraterculus females varied according to the adult diet provided and mating status. Our findings provide novel baseline information to understand the role of nutrition on reproductive performance of A. fraterculus females and are discussed in the context of resource allocation. They also provide valuable advances in the search for cost-effective adult diets at fruit fly mass rearing facilities.

Canola Oil as an Economical Lipid Source in Gel Larval Diet for Queensland Fruit Fly

A new sterile insect technique (SIT) program is currently being developed for management of the Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), the most costly challenge to Australian horticulture in the eastern states. SIT relies on cost-effective mass production of millions of high-quality flies. A recently developed gel larval diet has proven effective, enabling production of large numbers of high-quality flies, but includes some costly ingredients. With a basic diet now available, current research focuses on refining the formulation to deliver a more economical diet. Wheat germ oil (WGO) is the main lipid source in the current Queensland fruit fly gel diet, but is a particularly expensive ingredient and has limited availability. To identify an oil that maintains high productivity and fly quality at reduced cost, the present study assessed production and performance of Queensland fruit flies reared on gel larval diets containing the WGO that was used in previous studies (WGO/M), an alternative WGO (WGO/A), sunflower oil, rice bran oil, and canola oil. Diets containing canola oil ($5.24/liter) performed as well as diets with WGO/M ($116/liter) in terms of parental egg hatch, pupal number, pupal weight, adult emergence, percentage and rate of fliers, sex ratio, fecundity, and fertility (F1 egg hatch), offering a remarkably cost-effective alternative. Costs of oil in Queensland fruit fly production are reduced by ca. 95% per 1,000 flight capable adults ('fliers'). Substantial savings may be made in Queensland fruit fly mass rearing by substituting WGO/M with canola oil in gel larval diets without compromising productivity.

Effects of Larval Density and Support Substrate in Liquid Diet on Productivity and Quality of Artificially Reared Anastrepha ludens (Diptera: Tephritidae)

The larval developmental environment can affect the quality of artificially reared insects used in pest control programs that apply the sterile insect technique. We used a liquid larval diet lacking corncob fractions (an ingredient which may be contaminated by toxins that inhibit larval development and drastically reduce insect production in mass-rearing facilities) to examine quality indicators of Anastrepha ludens (Loew) (Diptera: Tephritidae) as a function of larval density (1-5 larvae per ml of diet) and on two types of supporting materials (synthetic sponge and carpet felt) compared with a standard solid diet with corncob fractions inoculated with a fixed quantity of A. ludens eggs. Pupal weight and adult emergence of A. ludens reared on a liquid artificial diet were negatively and positively density dependent, respectively. One tray of solid diet produced an average (95% CI) of 689.5 (594.4, 794.3) pupae, whereas one tray of liquid diet with synthetic sponge and carpet felt produced an average of 266.0 (208.7, 332.9) and 43.7 (23.2, 73.9) pupae, respectively. Pupal weight and adult emergence of flies reared on the solid diet were atypically low probably due to the type of rearing tray used, whereas pupal weight and adult emergence on liquid diet were equal to, or exceeded 20 mg and a proportion of 0.93, respectively. The highest proportion of adults capable of flight was observed in the liquid diet with carpet felt. The potential causes by which larval density and support substrate affected productivity and quality of A. ludens reared on liquid diet are discussed.

Effects of Wheat Germ Oil Concentration in Gel Larval Diets on Production and Quality of Queensland Fruit Fly, Bactrocera tryoni (Diptera: Tephritidae)

Queensland fruit fly ('Q-fly'), Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), is the most destructive insect pest of horticultural crops in Australia. The sterile insect technique (SIT) has attracted significant interest for sustainable management of Q-fly through the mass rearing and release of sterile flies. Cost-effective diets are required to rear Q-flies for SIT. Wheat germ oil (WGO) is the main source of fatty acids and vitamins in gel larval diets that are used to rear Q-fly but is an expensive ingredient. With the aim of reducing WGO cost in gel larval diet, we assessed performance of Q-flies reared on diets that varied in WGO content. Q-fly larvae were reared on two diets that differed mainly in yeast composition ('gel diet 2006' and 'gel diet 2009') and contained 0, 0.03, 0.07, 0.11, 0.15, or 1% WGO to identify reduced concentrations of WGO (and hence cost) without compromising productivity or quality. Diets containing WGO outperformed diets without WGO in development rate, pupal number, adult emergence, percentage of fliers, rate of fliers, and fecundity. Concentrations of 0.11% and above provided full benefit in gel diet 2006 (original formulation 0.15%), and concentrations of 0.15% (original formulation 1.0%) and above provided full benefit in gel diet 2009, and for both diets, a concentration-dependent decline in fly performance resulted from lower doses. Savings can be made in gel diets for mass rearing of Q-fly without compromising productivity by reducing WGO concentration.

Midgut Protease Activity During Larval Development of Anastrepha obliqua (Diptera: Tephritidae) Fed With Natural and Artificial Diet

In this study, we examined the activity of two serine proteases (chymotrypsin and trypsin) and two metalloproteases (carboxypeptidases A and B) during larval development in Anastrepha obliqua fed natural (mango fruit) and artificial (formulation used in mass-rearing) diets. Proteolytic activity of chymotrypsin, trypsin, carboxypeptidase A, and carboxypeptidase B was detected in the midgut of different instars of A. obliqua and was strongly affected by the pH and diet type. The protein content of the natural and artificial diets was similar. Enzymatic activity was higher in the midgut of the larvae fed the natural diet than in larvae fed the artificial diet. The activity of the endopeptidases (chymotrypsin and trypsin) was lower than those of the exopeptidases (carboxypeptidases A and B). The pH of the midgut varied from acidic to neutral. The results indicate that in the midgut of the larvae reared on both types of diet, the level of carboxypeptidase activity was approximately 100-fold greater than the level of chymotrypsin activity and 10,000-fold greater than the level of trypsin. In conclusion, carboxypeptidase A and B are the main proteases involved in the digestion of proteins in the larvae of A. obliqua. The natural diet showed a high bioaccessibility. A clear tendency to express high activities of chymotrypsin and trypsin was observed by the third instar. Our research contributes to the planning and development of novel bioaccessibility assays to understand the nutrition processing of A. obliqua larvae under mass-rearing conditions for sterile insect technique.

Modeling the cost-effectiveness of insect rearing on artificial diets: A test with a tephritid fly used in the sterile insect technique

We modeled the cost-effectiveness of rearing Anastrepha ludens, a major fruit fly pest currently mass reared for sterilization and release in pest control programs implementing the sterile insect technique (SIT). An optimization model was generated by combining response surface models of artificial diet cost savings with models of A. ludens pupation, pupal weight, larval development time and adult emergence as a function of mixtures of yeast, a costly ingredient, with corn flour and corncob fractions in the diet. Our model revealed several yeast-reduced mixtures that could be used to prepare diets that were considerably cheaper than a standard diet used for mass rearing. Models predicted a similar production of insects (pupation and adult emergence), with statistically similar pupal weights and larval development times between yeast-reduced diets and the standard mass rearing diet formulation. Annual savings from using the modified diets could be up to 5.9% of the annual cost of yeast, corn flour and corncob fractions used in the standard diet, representing a potential saving of US $27.45 per ton of diet (US $47,496 in the case of the mean annual production of 1,730.29 tons of artificial diet in the Moscafrut mass rearing facility at Metapa, Chiapas, Mexico). Implementation of the yeast-reduced diet on an experimental scale at mass rearing facilities is still required to confirm the suitability of new mixtures of artificial diet for rearing A. ludens for use in SIT. This should include the examination of critical quality control parameters of flies such as adult flight ability, starvation resistance and male sexual competitiveness across various generations. The method used here could be useful for improving the cost-effectiveness of invertebrate or vertebrate mass rearing diets worldwide.

Nutritional and non-nutritional food components modulate phenotypic variation but not physiological trade-offs in an insect

Our understanding of how food modulates animal phenotypes and mediate trade-offs between life-history traits has benefited greatly from the study of combinations of nutritional and non-nutritional food components, such as plant secondary metabolites. We used a fruit fly pest, Anastrepha ludens, to examine phenotypic variation across larval, pupal and adult stages as a function of larval food with varying nutrient balance and content of chlorogenic acid, a secondary metabolite. Larval insects that fed on carbohydrate-biased diets relative to protein exhibited longer larval and pupal developmental periods, were often heavier as pupae and resisted desiccation and starvation for longer periods in the adult stage than insects fed on highly protein-biased diets. Except for a potential conflict between pupal development time and adult desiccation and starvation resistance, we did not detect physiological trade-offs mediated by the nutritional balance in larval food. Chlorogenic acid affected A. ludens development in a concentration and nutrient-dependent manner. Nutrients and host plant secondary metabolites in the larval diet induced changes in A. ludens phenotype and could influence fruit fly ecological interactions. We provide a unique experimental and modelling approach useful in generating predictive models of life history traits in a variety of organisms.