A liquid larval diet for rearing Bactrocera invadens and Ceratitis fasciventris (Diptera:Tephritidae)

Authors: EKESI, SUNDAY - African Insect Science For Food And Health (ICIPE); MOHAMED, SAMIRA - African Insect Science For Food And Health (ICIPE); Chang, Chiou

Submitted to: International Journal of Tropical Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2013
Publication Date: 11/20/2014
Citation: Ekesi, S., Mohamed, S., Chang, C.L. 2014. A liquid larval diet for rearing Bactrocera invadens and Ceratitis fasciventris (Diptera:Tephritidae). International Journal of Tropical Insect Science. 34(S1):90-98.

Interpretive Summary: Increased awareness of the damage caused to the fruit industry by Bactrocera invadens and Ceratitis fasciventris has increased the demand for effective control measures against them. To conduct the prerequisite studies on insect biology and ecology, and on potential control agents against the target fruit flies, a regular supply of good quality insects of predetermined reproductive stages and ages is needed. In previous studies, Ekesi et al has demonstrated the adaptation and successful rearing of B.invadens on carrot-and wheat-based solid diet. C.fasciventris has also been reared in the laboraoty for over 100 generations on a carrot-based solid diet. In recent years, a liquid diet has been promoted as an excellent substitute for a solid-based diet. A liquid larval diet has been reported to have the following advantages over a solid larval diet: (1) total diet consumption by the flies if an accurate proportion of diet volume to egg density is established, thereby leaving a minimal amount of spent diet; (2) spent diet is water soluble, and can simply be rinsed off with a water gun; (3) larvae reared on a liquid diet can develop in the same environment controlled room without the necessity of moving trays around, thus providing more space for rearing; (4) flies can be reared in smaller and shallower trays than those used currently for a solid diet, but with each tray still producing the same number of pupae; and (5) the liquid diet includes using the most convenient inert bulking agent, the sponge cloth, which is composed maninly of natural cellulose and fibre. The sponge cloth has a low weight and high water absorbance and is reusable, recyclable, biodegradable, and environment-friendly. We evaluated the performance of B.invadens and C.fasciventris on a liquid diet for 5 generations. We also tested a local yeast and local oils as substitutes for expensive imported yeast and wheat germ oil, respectively, in the liquid diet of B.invadens.

Technical Abstract: Bactrocera invadens Drew, Tsuruta & White and Ceratitis fasciventris (Bezzi) are the major fruit fly pests of fruits and vegetables in Africa. The effects of two types of larval diet, liquid and solid (carrot based), on various quality control parameters (pupal recovery, pupal weight, adult emergence, flight ability, fecundity and fertility) of the two fruit fly species were investigated for five generations. The potential to replace two imported ingredients (yeast and wheat germ oil) with inexpensive and locally available alternatives was also explored. Most of the quality control parameters evaluated (pupal recovery, pupal weight, adult emergence and fecundity) for B.invadens reared on a liquid diet outperformed those reared on the carrot-based solid diet. In contrast, the quality control parameters evaluated (pupal recovery, pupal weight and fecundity) were significantly lower over the generations when compared with those from insects reared on a solid diet. Except for flight ability, the parameters of B.invadens reared on the diets substituted with the local yeast were of lower quality compared with those reared on the liquid diet containing the imported yeast. Corn (maize) and soybean oils were promising substitutes for wheat germ oil in the liquid larval diet of B.invadens without compromising any of the quality control parameters.