Abstract
The sterile insect technique (SIT) is widely used in integrated pest management programs for the control of the Mediterranean fruit fly (medfly), Ceratitis capitata. The genetic interactions between the released individuals from the genetic sexing strains (GSS), used for SIT applications worldwide, and wild individuals have not been studied. Under the hypothesis that a number of Vienna GSS individuals released to the field might not be completely sterile and may produce viable offspring, we have analyzed medfly Spanish field populations to evaluate the presence of Vienna strain genetic markers. To this goal, we have used contrasted nuclear and mitochondrial genetic markers, and two novel sets of nuclear polymorphisms with the potential to be markers to discriminate between Vienna and wild individuals. Nuclear Vienna markers located on the 5th chromosome of Vienna males have been found in 2.2% (19 from 875) of the Spanish wild medfly females captured at the area where SIT is applied. In addition, a female-inherited mitochondrial Vienna marker has been found in two from the 19 females showing nuclear Vienna markers. The detection of several of these markers in single individuals represents evidence of the introgression of Vienna strain into natural populations. However, alternative explanations as their presence at low frequency in wild populations in the studied areas cannot be fully discarded. The undesired release of non-fully sterile irradiated GSS individuals into the field and their interactions with wild flies, and the potential environmental implications should be taken into account in the application of the SIT.
Highlights
The Mediterranean fruit fly Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) is a polyphagous and worldwide distributed insect with a high adaptive capacity
In silico analyses comparing RNA-Seq from Vienna strain to a wild Hawaiian population (Calla et al 2014) and the C strain originated from Spanish populations allowed us to recover up to 313 positions that showed characteristic mutations in Vienna strain (108 single-nucleotide polymorphism (SNP)/indels for the homozygous genotype of alternative alleles and 205 SNPs/indels for the heterozygous genotype)
The summary of all different genotypes obtained for V0, V2 and V7 markers in Vienna, C strain and Wild-noSIT populations is shown in Table 2
Summary
The Mediterranean fruit fly (medfly) Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) is a polyphagous and worldwide distributed insect with a high adaptive capacity. Multiple approaches and techniques have been developed and applied for medfly control, but current control practices rely mainly on the use of insecticides. Organophosphates, such as malathion, were used during the 1990s and 2000s in Spain (Primo-Millo et al 2003). Spinosad and two pyrethroids (lambda-cyhalothrin and deltamethrin) are currently widely used in citrus crops (Ministerio de Agricultura Pesca y Alimentación 2020). The development of field resistance to malathion (Magaña et al 2007) and lambda-cyhalothrin (Arouri et al 2015) and the recent detection of spinosad resistance alleles in field populations (Guillem-Amat et al 2020) are raising new challenges in medfly control. In the current situation, combining different pest control approaches and boosting biologically based methods in the context of an integrated pest management (IPM) is highly recommended
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