Title: A genomic perspective towards assessing quality of mass-reared SIT flies used in Mediterranean fruit fly eradication in California Authors
Submitted to: Biomed Central (BMC) Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 31, 2014
Publication Date: February 5, 2014
Citation: Calla Zalles, B., Hall, B., Hou, S., Geib, S.M. 2014. A genomic perspective towards assessing quality of mass-reared SIT flies used in Mediterranean fruit fly eradication in California. Biomed Central (BMC) Genomics. 15:98. Interpretive Summary: The Mediterranean fruit fly C. capitata (Medfly) is considered to be the most economically important insect pathogen attacking fruits and vegetables around the world. The sterile insect technique (SIT), is the main control method used against this fly in the state of California to prevent establishment and thus potentially disastrous economic losses to agriculture. This method makes use of artificially reared gamma ray sterilized males released into potential areas of fly introduction to compete with wild males. We have built and compared the transcriptomes of flies from the artificially reared colonies with a flies form a wild population of Medfly found in Hawaii. Our results showed artificially reared flies having marked differences from the wild population in transcript levels in about one thousand identified unigenes. These differences are significant in several transcripts, more remarkably in those related to light stimuli response and neuronal development, which were less abundant in the reared flies. Additional differences were found when comparing sterilized males and reared males previous to sterilization. Together, these results suggest that the efficiency of the SIT programmes may not be reaching its potential efficiency due to reduced fly quality with possible competitive disadvantage to the wild population.
Technical Abstract: Temperature sensitive lethal (tsl) mutants of the tephritid C. capitata, are extensively used in control programmes involving sterile insect technique. These flies are artificially reared and treated with ionizing radiation to render males sterile for further release into the field to compete with wild males. Several lines of evidence indicate that the efficiency of these programmes is compromised, as artificial environment added to the irradiation process is detrimental to the quality of the released flies. The transcriptome of C. capitata was assembled using paired-end RNA sequencing. A set of 18 libraries were sequenced to compare the Vienna-7 tsl mutants used in SIT programmes in California at both pupal and adult stages as well as irradiated and non-irradiated flies. Additionally, flies from a wild colony found in Hawaii were sequenced. Comparisons were made between absolute and relative transcript levels between the repeated samples. Our results provide a general map of the mRNA populations in C. capitata, we compared these mRNA abundances between the Vienna-7 and the wild type populations and between stages and treatments tested. While our results clearly showed differential expression between adult and pupa stages, we focused our analyses on the differences between colonies and the irradiation treatment. Flies from the Vienna-7 colony showed a marked reduced abundance of transcripts related to light stimuli, neural development and signalling pathways when compared to wild flies. Additionally the possible presence of a virus was detected in the artificially reared flies. Irradiated flies showed several transcripts related to nucleic acid and DNA-repair mechanisms to be up-regulated when compared with non-irradiated flies form the same colony. We propose that these differences affect the competitiveness of reared flies and that alternative methods to irradiation and to the whole SIT approach should be evaluated to increase the efficiency of control and eradication programmes.