Strength of enemy release from parasitoids is context-dependent in the invasive African Fig Fly, Zaprionus indianus

Understanding the mechanisms underlying the success of biological invasions is essential to employ effective prediction and management strategies. The escape from natural enemies in invaded regions (enemy release hypothesis) and increased competitive ability are hallmarks of invasive species; however, these two processes are rarely studied within the same context. Here, we examined the effect of enemy release on the competition outcomes of a successful invasive insect pest in North America, the African fig fly (Zaprionus indianus). Parasitoid wasps such as Leptopilina heterotoma that parasitize drosophilid larvae may seek out established species with known host suitability over a novel species, so we hypothesized Z. indianus may have low susceptibility to parasitoids, giving them a competitive advantage over co-occurring drosophilids. We tested this hypothesis by comparing the adult emergence rates from Z. indianus larvae reared alone or in competition with Drosophila hydei or D. simula..., Drosophilid larva (Zaprionus indianus, Drosophila simulans, and D. hydei) were reared in the presence or absence of the parasitoid wasp Leptopilina heterotoma under high or low larval densities. We counted the number of adults of each species that emerged from each vial to calculate an emergence rate to estimate rates of parasitization under different treatments. We conducted five main experiments to examine the effects of parasitoids in different contexts:
1) Z. indianus alone
2) Lines of Z. indianus collected from different locations 
3) Z. indianus competing with D. hydei
4) Z. indianus competing with D. simulans
5) Z. indianus competing with D. simulans with different exposure times to the parasitoid
The data were analyzed with generalized linear models in R and specific comparisons between experimental groups were made using linear contrasts. , , # Strength of enemy release from parasitoids is context-dependent in the invasive African Fig Fly, *Zaprionus indianus*

Invasive species are thought to succeed in new environments in part because they are less susceptible to diseases and parasites that have co-evolved with local hosts, giving them a competitive advantage. We tested this hypothesis by competing an invasive fruit fly against established species in the presence of parasitoid wasps that lay eggs in fruit fly larvae. We found that the invasive species generally experiences less harm from parasitoids, but the extent of its advantage depended on the species it was competing against and the number of larvae present.

# Data file list

1. ZHcomp.csv
2. ZScomp_2024.csv
3. FL_CT_Y.csv
4. ZSduration.csv

# Code file list

1. competition_analysis.R
2. FL_CT.R
3. ZS_duration.R

# Interspecific / intraspecific competition assays

These experiments examine adult emergence rates of fly larva exposed to parasitoid wasps. Vials contained...