Effects of co-occurrence and intra- and interspecific interactions between Drosophila suzukii and Zaprionus indianus

Abstract

In drosophilids, competition and coexistence can impact survivorship, growth, and reproductive output. Here, we evaluated direct competition between two co-occurring fruit flies, the spotted-wing drosophila Drosophila suzukii and the African fig fly Zaprionus indianus, comparing results from field collections with laboratory experiments. Field collections were conducted to evaluate co-occurrence between species. In the laboratory, different densities of eggs of each species were provided an artificial diet, and intra- and interspecific densities were evaluated regarding biological traits such as development and fecundity. Field collections showed a prevalence of Z. indianus, followed by other drosophilid species, including D. suzukii. Pupal survival and adult emergence were higher in D. suzukii than in Z. indianus at both intra- and interspecific densities, with decreasing values in response to increased densities. Fecundity did not differ significantly for either species at different intraspecific densities, but when reared together at different densities, Z. indianus was significantly more fecund than D. suzukii. Development time showed no significant difference at intraspecific densities, but when reared together, Z. indianus had longer development times than D. suzukii. Leslie Matrix projections indicated that D. suzukii showed practically the same dynamics at intraspecific and interspecific densities, with increasing oscillations at low and intermediate densities and decreasing oscillations at high densities. Zaprionus indianus showed a similar oscillation to D. suzukii, except at intermediate intraspecific densities, when the pattern was cyclic. Low interspecific densities resulted in decreasing oscillations. In the two-choice oviposition bioassays, D. suzukii females showed no significant preference for diets previously infested or not with either conspecific or heterospecific eggs at different densities. Understanding competitive interactions between co-occurring heterospecific species should be considered when establishing management tactics for spotted-wing drosophila.

Fig 1. Fruit sample collections and drosophilid diversity assessment.

Number of insects emerged from strawberry fruits collected from the field in Atibaia municipality, São Paulo, Brazil (23°04’16”S, 46°40’52”W) in October (A) and December (B) 2020.

Fig 2. Development bioassay.

Percentages of egg-pupa and pupa-adult viability of Drosophila suzukii (D) and Zaprionus indianus (Z) fitted to regression functions at eight intra- and interspecific egg densities, ranging from 8 to 400. (A) Egg-pupa intraspecific survival. (B) Egg-pupa interspecific survival. (C) Intraspecific emergence percentage of adults. (D) Interspecific emergence of adults.

Fig 3. Fecundity bioassay.

Fecundity response of Drosophila suzukii (D) and Zaprionus indianus (Z) fitted to regression functions to eight intra- and interspecific egg densities, i.e., 8 to 400 eggs. (A) Intraspecific mean fecundity per female. (B) Interspecific mean fecundity per female. Black points and curves represent D. suzukii; green points and curves represent Z. indianus.

Fig 4. Development time.

Mean emergence times of Drosophila suzukii (D) and Zaprionus indianus (Z) fitted to regression functions in the 8 different densities. The black line and points represent intraspecific competition; the blue line and points represent interspecific competition.

Fig 5. Leslie matrix simulations showing population sizes for life stages of Drosophila suzukii (A) and Zaprionus indianus (B) from intra and interspecific combinations in scenarios of low (D8), moderate (D60), and high (D400) densities.

Fig 6. Choice behavior of Drosophila suzukii with eggs of Zaprionus indianus or with eggs of D. suzukii.

Experiments indicating the total eggs laid by D. suzukii on a diet previously infested with different egg densities (1, 3, 7, 10, or 15 eggs) versus a blank diet. (A) Intraspecific: oviposition behavior of D. suzukii in one diet with eggs of D. suzukii versus a blank diet (no eggs). (B) Interspecific: oviposition behavior of D. suzukii in one diet with eggs of Zaprionus indianus versus a blank diet (no eggs).