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Todd E. Shelly, Donald O. McInnis
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Using field-caged host trees, this study investigated the influence of adult diet on the mating success and survival of male Mediterranean fruit flies, Ceratitis capitata (Wied.), from two mass-rearing strains. Upon emergence, males from a genetic sexing (temperature sensitive lethal) strain and a bisexual strain were given either a sugar-protein diet (protein-fed) or a sugar-only diet (protein-deprived). Mating trials were conducted using field-caged host trees, and 100 males of a given strain and diet competed with 100 wild males for matings with 100 wild females (all wild flies were given the sugar-protein diet). There was no apparent effect of diet on male mating success for either mass-reared strain. Wild males obtained significantly more matings per replicate than males from either strain on either diet, and the mean number of matings per replicate was similar between protein-fed and protein-deprived males for both strains. In addition, the survival of protein-fed and protein-deprived males was compared over 2- and 4-day intervals on field-caged host trees. Within each mass-reared strain, there was no apparent effect of adult diet on male survival for either test interval. The present findings are compared with similar studies on other mass-reared strains.

In a series of recent articles, Yuval and his colleagues have demonstrated the importance of adult diet, specifically the inclusion of protein (yeast hydrolysate), on the mating success and longevity of male Mediterranean fruit flies, Ceratitis capitata (Wied.). In the initial study, Blay and Yuval (1997) worked with mass-reared flies and found that, in no-choice tests, females mated more readily with protein-fed males than protein-deprived males and that remating frequency was lower for females that first mated with protein-fed males than protein-deprived males. Subsequently, Kaspi et al. (2000) observed wild flies on field-caged host trees and found that protein-fed males signaled (pheromone-called) and mated more frequently than protein-deprived males. In another laboratory study, Kaspi and Yuval (2000) investigated the influence of adult diet on mating competition among mass-reared males for wild females and found that protein-fed males had a mating advantage over protein-deprived males. However, protein-fed males were found to have lower longevity than protein-deprived males.

These findings potentially have great importance for sterile male release programs against the Mediterranean fruit fly. While the pre-release diet in current use is a sugar agar gel, the above studies suggest that the addition of protein may significantly enhance the mating competitiveness of mass-reared males and hence the effectiveness of sterile release programs. Before widespread adoption of this dietary change, however, data on other pairwise combinations of mass-reared and wild strains should be gathered to determine the generality and strength of protein-mediated effects on the mating success and longevity of male Mediterranean fruit flies.

The present study investigates the effect of dietary protein on the mating success and longevity of Mediterranean fruit fly males from two mass-reared strains (Vienna-7/Tol-99 and Maui Med-93) in field-caged host trees in Hawaii. This research expands upon an earlier project (Shelly & Kennelly 2002) in which the mating success and longevity of males from one of these strains (Maui Med-93) were measured under laboratory conditions. This earlier study showed that, in trials with wild flies, protein-fed males had a significant mating advantage over protein-deprived males. However, the addition of protein to the diet did not boost the mating success of mass-reared males in competition with wild males or mass-reared males for wild females. In addition, no difference was found in the survival probability of protein-fed versus protein-deprived males from the mass-reared strain. The present study was undertaken 1) to verify these trends under more natural conditions (field-cages) and 2) to gather comparable data for males from a genetic sexing strain (Vienna-7/Tol-99) used widely (e.g., in California and Guatemala) in ongoing sterile insect release programs.

Materials and Methods

Study Insects

Wild flies were reared from infested coffee, Coffea arabica L., berries collected on the island of Kauai. Fruits were held over vermiculite at 23-25°C, and larval development proceeded in situ. Puparia were sifted from the vermiculite 7-9 days after fruit collection, and adults were separated by sex within 2 days of eclosion, well before reaching sexual maturity at 7-10 days of age. Adults were held in plastic buckets covered with nylon screening (volume 5 liters; 100-125 flies per bucket). Wild flies were provided with a mixture (3:1 v/v) of sugar (sucrose) and protein (yeast hydrolysate) and water ad libitum, held at 20-24°C and 65-85% RH, and received both natural and artificial light in a 12:12 (L:D) photoperiod.

Sterile males from two mass-reared strains were used in the mating and survival trials. One was a temperature sensitive lethal (or tsl) strain (Vienna-7/Tol-99, hereafter referred to as Vienna-7), a type of genetic sexing strain in which females are selectively killed in the egg stage by exposure to high temperature (Franz et al. 1994), obtained from the California Department of Food and Agriculture Fruit Fly Rearing Facility, Waimanalo, Oahu. The other was a bisexual strain (Maui Med-93) produced by the USDA-APHIS Hawaii Fruit Fly Rearing Facility, Waimanalo. Larvae of both strains were reared on standard larval medium (Tanaka et al. 1969), and males from both strains received an absorbed dose of 150 Gy of gamma radiation from a 137Cs source 2 days before emergence and then delivered to the laboratory. For the Maui Med-93 strain, males were collected within 12 h of emergence (males of this strain become sexually mature at 2-4 days of age). Mass-reared males were separated into 2 dietary regimes: “protein-fed” males were given the same sugar-protein mixture as wild flies plus water, and “protein-deprived” males were given only sugar plus water. Aside from this dietary difference, mass-reared males were maintained in the same manner as wild flies.

Mating Trials

Mating tests were conducted at the Agricultural Experiment Station of the University of Hawaii, Waimanalo. Groups of 100 irradiated, mass-reared males (from the same strain and diet), 100 wild males (10-15 days old), and 100 wild females (10-17 days old) were released between 0800-0830 h in field-cages (2.5 m in height, 3.0 m in diameter) that contained a single rooted guava, Psidium guajava L., tree. For a given trial, we marked only males from one group (i.e., mass-reared or wild) and alternated the identity of the marked group between successive trials. Males were marked 1 day before testing by cooling them for several minutes and placing a dot of e