Effects of fatty acids and vitamin E in larval diets on development and performance of Queensland fruit fly.

Tephritid fruit flies are commonly reared on artificial larval diets for laboratory studies and for sterile insect technique pest management programs. While significant effort has been invested in developing artificial larval diets, surprisingly little is known about the specific nutritional requirements of tephritid flies. Recently developed gel larval diets have provided new opportunities for nutritional studies in Queensland fruit fly, Bactrocera tryoni ('Q-fly'). Wheat germ oil (WGO) is the main source of fatty acids and vitamin E in this diet, and is key for production of high-quality adults. To identify the importance of nutritional components of WGO for Q-fly productivity and quality, linoleic, linolenic, oleic and palmitic fatty acids as well as α-tocopherol (vitamin E) were included in the diet individually and in combination. Diets that included all of the tested fatty acids or just unsaturated fatty acids performed as well as diets containing WGO in most quality control parameters except fecundity, and addition of vitamin E reduced the pupal productivity. Considering individual fatty acids, larval diets containing only linolenic acid produced adults with higher percentage of fliers than did larval diets containing only palmitic acid or oleic acid. Compared with diets containing WGO, nutritional requirements for egg production in Q-fly were not entirely met by either grouped fatty acids or individual polyunsaturated, monounsaturated or saturated fatty acids, however, diets containing linoleic acid alone produced more eggs than any other fatty acid. The present study is a significant advance in understanding of the role of fatty acids as a component of WGO in larval diet in meeting the needs of developing Q-fly for somatic performance, but highlight also that other, untested, components of WGO appear to be important for reproduction.

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.

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 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.