Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) and Drosophila melanogaster Meigen (Diptera: Drosophilidae) are both important fruit pests. Drosophila suzukii is especially damaging to ripe cherries (Van der Linde et al. 2006). It's hard, serrated ovipositor can easily pierce the fruit skin, inserting eggs within intact fruits with little visible damage from oviposition on the fruit surface. The larvae hatching from eggs feed on the fruit, and cause it to soften, brown and completely rot. Many fruits are damaged by D. suzukii, including blueberry, blackberry, cherry, strawberry, plums, peaches, grapes, figs, kiwi fruit and pears (Dreves et al. 2009). In the United States, losses of strawberry, blueberry and raspberry caused by D. suzukii reached 80, 40, and 70%, respectively (Bolda et al. 2011). With increased planting of fruit trees in China, D. melanogaster has increased in importance as a pest of Chinese bayberry and cherries. In Tianshui, Gansu Province, some late-maturing varieties of cherries are especially susceptible to damage by D. melanogaster, and they suffer losses generally above 35%, and as high as 80% on some cultivars (Guo et al. 2007).

Fig. 1.

The ovipositional rhythms of Drosophila suzukii and Drosophila melanogaster. Data represent the mean values ± SEM (n = 4) for 4-h periods, and histograms with different letters indicate a significant difference (P = 0.05, Duncan's multiple range test), i.e., lower case letters show a significant difference for D. suzukii, and upper case letters C show a significant difference for D. melanogaster. Fecundity of D. melanogaster was much greater than that of D. suzukii. Lights were turned on at 4:30 am and off at 20:30 pm.

Daily biological rhythms are common in insects (Pittendrigh 1993; Takahashi 1995). Many life activities of insects, such as phototaxis, body color change, migration, feeding, hatching, eclosion, mating and oviposition exhibit a rhythm (Saunders 2002). It is helpful to determine the activity rhythms of populations of both beneficial and harmful insects as a basis for developing and improving methods for preventing or controlling the latter (Tu & Chen 2013). Applications of insect pheromones in pest control developed in recent decades, are based to some extent on studies of the timing of eclosion and rhythms of sexual activities insect pest species, and it may be possible to further improve pheromone-based control technology through better understanding of the circadian rhythms of pest species (Ran et al. 2013). There have been many studies on the behavioral rhythms of D. melanogaster, but few on those of D. suzukii. This study examines the rhythms of both species with respect to oviposition, egg hatch, pupation, adult eclosion, feeding and copulation. This information further understanding of the biological characteristics of D. suzukii and D. melanogaster these species, and may provide an important basis and technical guidance for their integrated control.

Materials and Methods

Experimental Insects

Both D. suzukii and D. melanogaster were obtained as larvae from infested fruit from cherry orchards in Tai'an, Shandong Province in May 2012, and flies were then raised in an insectary for about 11 generations at 25 ± 1 °C, 70 ± 5% RH, and 16:8 h (L:D) with the lights were turned on at 4:30 am and off at 20:30 pm. This light regime approximated the local natural photoperiod. The off light intensity was 10,000 lux. Table grapes (‘Kyoho' grape cultivar, Vitis vinifera L.; Vitales: Vitaceae), purchased from the market, were rinsed 3 times in distilled water and dried and cut into halves for adult oviposition and larval development. The average weight of each grape was 20.38 g.

Fig. 2.

The incubation rhythms of Drosophila suzukii and Drosophila melanogaster. Data represent the mean values ± SEM (n = 5) at 4 h, and significant differences at P = 0. 05 by Duncan multiple range test. Most D. suzukii eggs hatched with a single peak at 24–32 h after the eggs were laid, but D. melanogaster eggs hatched with two peaks, one at 4 h and the second at 32–36 h after eggs were laid. Error bars topped with different letters are significantly different.Lights were turned on at 4:30 am and off at 20:30 pm.

Oviposition Rhythm

Females 4–6 days after emergence were used for quantifying the oviposition rhythm. These females had mated and could have laid eggs for 2–3 days. Each group had 5 individual females with 4 replicates of either D. suzukii or D. melanogaster. They were placed into circular insectary bottles (2000 mL flat drum glass bottles) containing one fresh grape cut into halves. The grapes were replaced every four hours for 48 h, and the number of eggs laid was determined. The experiment was replicated 4 times.

Fig. 3.

The pupation rhythms of Drosophila suzukii and Drosophila melanogaster. Data represent values ± SEM (n = 5) in 4 h observation periods, at 4 h, and histograms with different letters indicate a significant difference (P = 0.05, Duncan's multiple range test). Most D. suzukii larvae pupated with a single peak between 8:00 to 16:00, but most D. melanogaster larvae pupated with two peaks, one at 4:00–8:00 and the second at 12:00–20:00. Error bars topped with different letters are significantly different. Lights were turned on at 4:30 am and off at 20:30 pm.

Results

Oviposition Rhythm

In this experiment, Drosophila suzukii females laid a total of 1,297 eggs, with the egg-laying peak extending from 20:00–24:00. In this peak each female laid an average of 33 eggs, which accounted for 50.9% of the eggs one female laid in a single light cycle. Likewise D. melanogaster females laid a total of 2,743 eggs, with the egg-laying peak extending across 16:00–4:00 (the next day). During this protracted peak each female laid and average of 128.06 eggs, which accounted for 93.4% of the total per female in a single circadian period (Fig. 1).

Fig. 4.

The eclosion rhythms of Drosophila suzukii males and females. Most adults emerged during the hours that correspond to dawn. The number of females was larger than the number of males. Error bars topped with different letters are significantly different. Lights were turned on at 4:30 am and off at 20:30 pm.

Egg Hatching Rhythm

In total, 132 D. suzukii eggs and 130 D. melanogaster eggs were observed to hatch per 5-female replicate; i.e., an average of 26.4 and 26.0 per female, respectively. Per replicate an average 19.8 D. suzukii eggs of hatched 24∼32 h after the eggs were laid; i.e., 75% of the eggs that hatched. Hatching of D. melanogaster occurred in 2 peaks, the first at 0∼4 h and the second 32∼36 h after oviposition. In the first peak 7.0 eggs hatched, and in the second peak, 11.0 eggs hatched. These two peaks accounted for 26.9% and 42.3% of the total eggs that hatched, respectively (Fig. 2). No photoperiodic rhythm of egg hatching was found in either species.

Fig. 5.

The eclosion rhythms of Drosophila melanogaster males and females. Most adults emerged during the hours that correspond to dawn. The number of females was larger than the number of males. Error bars topped with different letters are significantly different. Lights were turned on at 4:30 am and off at 20:30 pm.

Discussion

Reports on the ovipositional rhythms of insects began to appear in the 1950s and have gradually increased in recent years (Haddow & Gillett 1957; Pittendrigh & Minis 1964; Minis 1965). These reports included research on Ostrinia nubilalis and Rhodnius prolixus (Skopik & Takeda 1980; Ampleford & Davey 1989). Several studies on the ovipositional rhythms of fruit flies have involved D. melanogaster, other Drosophila spp. and Zaprionus spp. (Rensing & Hardeland 1967; Gruwez et al. 1972; David & Fouillet 1973; Allemand 1974, 1976a, 1976b, 1976c, 1977). Fleugel (1978) studied the egg production of D. melanogaster individuals in weak light of the light-dark cycle, and found an oviposition rhythm under 12:12 h L:D conditions, which he held to be the hourglass timing mechanism, not an endogenous rhythm. Many recent studies, however, have found that wild and mutant varieties of fruit flies also display rhythmic oviposition (McCabe & Birley 1998; Sheeba et al. 2001). This study found the oviposition of both D. suzukii and D. melanogaster followed a circadian rhythm, with the effects of light having a greater effect on D. suzukii, which showed two oviposition peaks compared to one peak by D. melanogaster.

Fig. 6.

The copulation rhythms of Drosophila suzukii and Drosophila melanogaster. Data represent the mean values ± SEM (n = 4) in 4 h observation periods. Few matings of either species were observed between 12:00 and 20:00. Error bars topped with different letters are significantly different. Lights were turned on at 4:30 am and off at 20:30 pm.

A previous study on Dacus tryoni found that the rhythm of egg hatching played a certain role in total egg development (Bateman 1955). Meanwhile, our study found that neither Drosophila species displayed a photoperiodic rhythm for egg hatch, nor while both species' eggs may contain a timing mechanism, it is not related to the circadian system.

Fig. 7.

The feeding rhythms of Drosophila suzukii and Drosophila melanogaster. Data represent the mean values ± SEM (n = 4) in 4 h observation periods. Both species fed more extensively during the photophase than during the scotophase. Error bars topped with different letters are significantly different. Lights were turned on at 4:30 am and off at 20:30 pm.

While the behavior of Sarcophagidae larvae before pupation and adult eclosion were found to be rhythmic (Saunders 1986), pupation itself was not rhythmic (Richard et al. 1986), possibly because pupation occurred underground. The two Drosophila species in this study, however, both showed different pupation rhythms and the process occurred aboveground. As peak pupation of D. suzukii was in the morning, it seems likely that light promotes the formation of the puparium. The two peaks of D. melanogaster occurred in the morning and afternoon, and such a rhythm may serve to protect the newly emerged adults from the effects of intense sunlight.

Emergence rhythms of a variety of insects have been studied, but those of Drosophila spp. have been reported on in the most detail. The circadian rhythm period of Drosophila emergence is about 24 h, and the eclosion rhythms are endogenous. The emergence of Drosophila pseudoobscura, for instance, is usually concentrated at dawn, and the peak shifts with changing photoperiod (Pittendrigh 1965). For example, the emergence peak occurred before dawn under short illumination conditions (light periods shorter than 6–7 h), after dawn under long photoperiod conditions, and from 2∼3 h after the start of the photoperiod under 12:12 h L:D conditions (Bünning 1935). This study found that both D. suzukii and D. melanogaster had a single peak, generally concentrated from 0:00∼8:00 and 0:00∼12:00, respectively. One of the possible explanations is that relative humidity and cool air favor the expansion of wings in newly emerged adults, and high temperatures disturb the process of wing expansion significantly (Tanaka & Watari 2009; Shereen & Shakunthala 2012). In addition, among the newly emerged adults of the two species, females were found to outnumber males, and this may be related to the carbon/nitrogen ratio in the diet.

While a mating rhythm controlled by an endogenous biological clock has been confirmed in some insects (Smith 1979), the mating behavior of insects is affected to some extent by photoperiod. The mating rhythms of Anastrepha ludens (Flitters 1964) and Dacus tryoni (Tychsen & Fletcher 1971) both showed a certain light-based cycle. Our study found that D. suzukii mating had a bimodal pattern, with the peak concentrating in 20:00 ∼ 12:00 (the next day), indicating that individuals' mating ability might be affected by light duration in one photoperiod. The mating of D. melanogaster was unimodal, with more than 50% concentrated in the 4 h immediately after the dark period and more than 80% in the 8 h following the dark period, showing an extremely significant effect of photoperiod.

No research on the feeding rhythm of fruit flies has been found, but other studies found that cockroaches are the most active at night and usually feed in the dark. The American cockroach, Periplaneta americana feeds in the early to middark period, exhibiting an endogenous circadian rhythm (Lipton & Sutherland 1970). Nymphs and adults of the cricket Acheta domesticus also showed a feeding rhythm (Nowosielski & Patton 1963). In laboratory experiments, bumble bee foragers showed free-running circadian rhythms in both LL and DD, with mean free-running periods significantly shorter in LL than DD (Stelzer et al. 2010). In addition, Xiao et al. (2009) found that a wild variety of D. melanogaster exhibited an obvious bimodal feeding pattern with peaks in the morning and evening. In our study, both D. suzukii and D. melanogaster individuals preferred to feed in the light, with the percentage of feeding individuals in the morning being slightly larger than that in the afternoon.

The damage caused by Drosophila larvae feeding inside fruit is imperceptible at first, and as the systemic use of insecticides increases the risk of residues in fruit, adult trapping techniques are an important tool in the prevention and control of fruit flies (Sun et al. 2005). Behavioral rhythms factor into the control of D. suzukii and D. melanogaster, and an understanding of these patterns should be helpful in the forecasting populations and further improving the control of these pest species.