The molecular biology of the olive fly comes of age

Abstract

BackgroundOlive cultivation blends with the history of the Mediterranean countries since ancient times. Even today, activities around the olive tree constitute major engagements of several people in the countryside of both sides of the Mediterranean basin. The olive fly is, beyond doubt, the most destructive pest of cultivated olives. The female fly leaves its eggs in the olive fruit. Upon emergence, the larvae feed on the olive sap, thus destroying the fruit. If untreated, practically all olives get infected. The use of chemical insecticides constitutes the principal olive fly control approach. The Sterile Insect Technique (SIT), an environmentally friendly alternative control method, had been tried in pilot field applications in the 1970's, albeit with no practical success. This was mainly attributed to the low, non-antagonistic quality of the mixed-sex released insects. Many years of experience from successful SIT applications in related species, primarily the Mediterranean fruit fly, Ceratitis capitata, demonstrated that efficient SIT protocols require the availability of fundamental genetic and molecular information.ResultsAmong the primary systems whose understanding can contribute towards novel SIT approaches (or its recently developed alternative RIDL: Release of Insects carrying a Dominant Lethal) is the reproductive, since the ability to manipulate the reproductive system would directly affect the insect's fertility. In addition, the analysis of early embryonic promoters and apoptotic genes would provide tools that confer dominant early-embryonic lethality during mass-rearing. Here we report the identification of several genes involved in these systems through whole transcriptome analysis of female accessory glands (FAGs) and spermathecae, as well as male testes. Indeed, analysis of differentially expressed genes in these tissues revealed higher metabolic activity in testes than in FAGs/spermathecae. Furthermore, at least five olfactory-related genes were shown to be differentially expressed in the female and male reproductive systems analyzed. Finally, the expression profile of the embryonic serendipity-α locus and the pre-apoptotic head involution defective gene were analyzed during embryonic developmental stages.ConclusionsSeveral years of molecular studies on the olive fly can now be combined with new information from whole transcriptome analyses and lead to a deep understanding of the biology of this notorious insect pest. This is a prerequisite for the development of novel embryonic lethality female sexing strains for successful SIT efforts which, combined with improved mass-reared conditions, give new hope for efficient SIT applications for the olive fly.

De novo assembly of the olive fruit fly (Bactrocera oleae) genome with linked-reads and long-read technologies minimizes gaps and provides exceptional Y chromosome assembly

“…Despite its economic importance in olive producing countries, several peculiarities of the olive fruit fly's biology (e.g., difficulty in rearing, high natural homozygosity, lack of phenotypic mutations) made the development of classical genetics tools an impossible task. More recently, however, the olive fruit fly has been the subject of several molecular and transcriptomics studies [26][27][28] (Reviewed in Sagri et al [29]).…”

Housekeeping in Tephritid insects: the best gene choice for expression analyses in the medfly and the olive fly

“…The olive fly, on the other hand, is a strictly monophagous cousin of the medfly, of particular interest in the olive producing areas of the world4. Recent development of molecular and genomics tools have made it focus of active research, with renewed interest in its control5556. The tissues selected for the analysis were mostly tissues from either the reproductive (testes, ovaries, male and female accessory glands, ovipositors) or the olfactory (maxillary palps and antennae) systems of the flies.…”

“…For the medfly, primers were based on sequences retrieved in the NCBI database. For the olive fly, primers were based on the sequences obtained during the transcriptome analysis of B. oleae 5567. Specific primers for the amplification of these HKGs were designed by Primer-BLAST44 (Supplementary Table S7).…”

Decoding the reproductive system of the olive fruit fly,Bactrocera oleae

“…For the olive fruit fly, Bactrocera oleae , the major pest of olive cultivation, the morphology and ultrastructure of the male accessory glands with ejaculatory bulb tissues have been analyzed by Marchini et al 36 . The first molecular analysis of the reproductive system was presented in 2014 by Sagri et al 37 . That study focused on the identification of sex differentiation genes, i.e.…”

“…That study focused on the identification of sex differentiation genes, i.e. differentially expressed genes either in male testes or female accessory glands and spermathecae 37 . In order to go a step further and understand the molecular processes that underlie reproduction of the olive fly, one needs to identify genes that are over- or under-expressed during mating of the flies.…”