The invasive pest Drosophila suzukii has evolved morphological and behavioural adaptations to lay eggs under the skin of fresh fruits. This results in severe damage to a wide range of small fruits. Drosophila suzukii females typically lay few eggs per fruit, preferring healthy fruits. Hence, larvae are exposed to a reduced amount of nitrogenous waste. Differently, the innocuous Drosophila melanogaster lays eggs on fermented fruits already infested by conspecifics, with larvae developing in a crowded environment with the accumulation of nitrogenous waste such as ammonia and urea. These compounds derive from nitrogen metabolism, protein degradation, and amino acids catabolism and are relatively toxic at high concentrations in an organism. The observed differences in oviposition site and larval ecological niche suggest that these species might differ in behavioural and physiological mechanisms used to cope with nitrogenous waste. We investigated how different concentrations of ammonia and urea affect oviposition and larval development in both species. Females and larvae of D. suzukii showed greater susceptibility to high concentrations of both compounds, with a dramatic decrease in the number of eggs laid and egg viability. Moreover, we tested the chemotactic response of third instar larvae to high concentrations of the compounds. Interestingly, ammonia resulted in a repulsive behaviour in respect of the control and urea groups. To better understand the pathways underlying these differences, we evaluated the effect on ornithine aminotransferase and glutathione-S-transferase, two enzymes involved in nitrogen metabolism and stress response that are expressed during larval development. Both ammonia and urea significantly reduced the expression of these enzymes in D. suzukii compared to D. melanogaster. This shows how the ecological shift of D. suzukii to fresh fruit is accompanied by less efficient detoxifying and excretory mechanisms, with important implications for evolutionary biology and applied research. Our data suggest that the ecological shift of D. suzukii to fresh fruit as oviposition substrate is accompanied by a reduced tolerance to metabolic toxins during larval development.

Genome instability is a condition characterized by the accumulation of genetic alterations and is a hallmark of cancer cells. To uncover new genes and cellular pathways affecting endogenous DNA damage and genome integrity, we exploited a Synthetic Genetic Array (SGA)-based screen in yeast. Among the positive genes, we identified VID22, reported to be involved in DNA double-strand break repair. vid22Δ cells exhibit increased levels of endogenous DNA damage, chronic DNA damage response activation and accumulate DNA aberrations in sequences displaying high probabilities of forming G-quadruplexes (G4-DNA). If not resolved, these DNA secondary structures can block the progression of both DNA and RNA polymerases and correlate with chromosome fragile sites. Vid22 binds to and protects DNA at G4-containing regions both in vitro and in vivo. Loss of VID22 causes an increase in gross chromosomal rearrangement (GCR) events dependent on G-quadruplex forming sequences. Moreover, the absence of Vid22 causes defects in the correct maintenance of G4-DNA rich elements, such as telomeres and mtDNA, and hypersensitivity to the G4-stabilizing ligand TMPyP4. We thus propose that Vid22 is directly involved in genome integrity maintenance as a novel regulator of G4 metabolism.

Summary 25 26The invasive species Drosophila suzukii has evolved morphological and behavioral adaptations to lay 27 eggs under the skin of fresh fruits. This results in severe damage of a wide range of small and stone 28 fruits, thus making this species a serious agricultural and economical threat. 29Drosophila suzukii females typically lay few eggs per fruit, preferring not infested fruits. Hence 30 larvae are exposed to a reduced amount of nitrogenous waste products. On the contrary, the innocuous 31 Drosophila melanogaster lays eggs on fermented fruits already infested by conspecifics, with larvae 32 developing in a crowded environment characterized by accumulation of nitrogenous waste such as 33 ammonia and urea. Given these differences in oviposition and larval ecological niche, we expected 34 different behavioral and physiological mechanisms in the two species to cope with nitrogenous waste. 35We investigated the impact of different concentrations of ammonia and urea on fecundity and larval 36 development in both species. Females and larvae of D. suzukii showed a greater sensitivity to high 37 concentration of both compounds, with a dramatic decrease in fecundity and egg viability. 38To better understand the pathways underlying these differences, we evaluated the effect on ornithine 39 aminotransferase and glutathione-S-transferase, two enzymes involved in nitrogen metabolism and 40 stress response that are expressed during larval development. Under ammonia and urea exposure, the 41 expression of these enzymes was significantly reduced in D. suzukii. 42The fact that D. suzukii's shift from rotten to fresh fruit as oviposition and larval substrate resulted in 43 less efficient detoxifying and excretory mechanisms represents a potential approach for its control. 44Fecundity and larval development are in fact dramatically impaired by nitrogen waste products. These 45 findings can help in planning effective strategies of sustainable pest management that targets both 46 females and larvae. 47All rights reserved. No reuse allowed without permission.was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.

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