How Sugar Quality and Concentration Influence Oviposition Preference in Drosophila Melanogaster

Abstract

Female insects possess a complex chemosensory system that enables them to identify optimal oviposition substrates for their developing offspring. Both calorie-rich and protein-rich substrates are particularly attractive for laying eggs. We hypothesize that females detect concentrations of sweet compounds and preferentially select those concentrations that enhance larval survival. To test this, we investigated how female Drosophila melanogaster evaluate substrates with varying concentrations of sugars and amino acids, and whether these preferences correlate with larval survival. Using choice assays, we found that females preferentially deposited eggs on substrates containing 0.1 mol/L sucrose, while higher concentrations (2 mol/L) were consistently avoided-a response not attributable to differences in substrate hardness or prior feeding experience during mating. In contrast, when presented with monosaccharides, females favored intermediate concentrations: 0.5 mol/L for both glucose and fructose, with a marked overall preference for fructose even when combined with an amino acid mixture. Moreover, substrates aligning with the females' oviposition choices often supported best survival of larvae. These findings indicate that female flies assess not only the concentration but might also consider the chemical nature of sweet compounds when making oviposition decisions and they underscore a critical link between maternal site selection and larval development.

Keywords: Drosophila; Gustatory Cues; Larval Survival; Oviposition Behavior; Sugar Concentration.

Fig. 1

Females prefer to oviposit on 0.1 mol/L sucrose. (A) Schematic of the paradigm used to test oviposition preference of individual D. melanogaster females. (B) Heat map showing the number of eggs each female laid over 24 h on neutral substrate (0 mol/L, 0.3% w/v agar) and on three different sucrose concentrations of sucrose (n = 45). (C) Comparison of the number of eggs laid during the oviposition test on different sucrose concentrations. A Friedman test followed by Dunn`s test for multiple comparison was used to test for significance (α = 0.5, n = 45). Significant differences (P < 0.05) among concentrations are shown with the Compact Letter Display (CLD) system on the top of each violin plot. For the hardness of the substrates used see Figure S1D. (D) Oviposition preference of females that had prior experience on different sucrose concentrations before the test. Symbols depict the pre-treatments on different sucrose concentration, and colored columns depict the test concentration. Not all the data exhibited a Gaussian distribution (Shapiro-Wilk test). Therefore, a mixed-effects model was used to assess the effect of repeated measures of the prior experience on oviposition preference (n = 43 for each treatment, α = 0.5, total number of eggs in the pre-treatments on 0, 0.1, 0.2, and 2 mol/L were 893, 723, 788, and 772, respectively. Fixed effects: substrate concentration, pre-treatment concentration, and substrate concentration x pre-treatment concentration)

Fig. 2

Females D. melanogaster show distinct oviposition preferences based on both chemical identity and concentration. (A) Comparison of the number of eggs laid during the oviposition tests with various glucose concentrations. See Figure S2A for the total number of eggs laid by each female and Figure S3B for substrate hardness. B) Comparison of the number of eggs laid during the oviposition test with various fructose concentrations. See Figure S2B for the total number of eggs laid by each female and Figure S3C for substrate hardness. C) Comparison of the number of eggs laid during the oviposition test on neutral substrate (0 mol/L), 0.1 mol/L sucrose, 0.5 mol/L glucose, and 0.5 mol/L fructose. See Figure S2C for the total number of eggs laid by each female and Figure S3D for substrate hardness (A-C) Friedman test followed by Dunn`s test for multiple comparison test was used (α = 0.5, n = 45). Significant differences (P < 0.05) among concentrations are shown with the Compact Letter Display (CLD) system on the top of each violin plot

Fig. 3

Females prefer to oviposit on substrates with 0.5 mol/L fructose. (A) Comparison of the number of eggs laid during the oviposition test using various amino acid concentrations. See Figure S4A for the total number of eggs laid by each female and Figure S4D for substrate hardness. (B) Comparison of the number of eggs laid during the oviposition test on 5% w/v amino acids mixture, 0.1 mol/L sucrose, 0.5 mol/L glucose, and 0.5 mol/L fructose. See Figure S4B for the total number of eggs laid by each female and Figure S4E for substrate hardness. (C) Comparison of the number of eggs laid during the oviposition test on 5% w/v mixture of amino acids (8-AA), 5% w/v 8-AA + 0.1 mol/L sucrose, 5% w/v 8-AA + 0.5 mol/L glucose, and 5% w/v + 0.5 mol/L fructose. See Figure S4C for the total number of eggs laid by each female and Figure S4F for substrate hardness. (A-C) Friedman test followed by Dunn`s test for multiple comparison test was performed (α = 0.5, n = 45). Significant differences (P < 0.05) among concentrations are shown with the Compact Letter Display (CLD) system on the top of each violin plot

Fig. 4

Larvae survive longer on those substrates were females laid more eggs. (A) Kaplan-Meier survival curve of Drosophila larvae on different sucrose concentrations. (B) Kaplan-Meier survival curve of Drosophila larvae on different glucose concentrations. (C) Kaplan-Meier survival curve of Drosophila larvae on different fructose concentrations. (D) Kaplan-Meier survival curve of Drosophila larvae on 5% w/v mixture of amino acids (8-AA), 5% w/v 8-AA + 0.1 mol/L sucrose, 5% w/v 8-AA + 0.5 mol/L glucose, and 5% w/v + 0.5 mol/L fructose. (A-D) Log-rank (Mantel-cox) test with pairwise comparison and Bonferroni’s’ test for multiple comparison test were performed (α = 0.5, # of larvae per treatment = 100). Significant differences (P < 0.05), are shown with the Compact Letter Display (CLD) system in lower case on the right side of the legends in each graph