Estudio de la herencia y mapeo de la resistencia de Ceratitis capitata (Wiedemann, 1824) (Diptera, Tephritidae) al insecticida λ-cihalotrina

La mosca mediterránea de la fruta, Ceratitis capitata (Wiedemann, 1824), es una de las principales plagas de cítricos y otros frutales en España. Las actuales estrategias de control, basadas mayoritariamente en el uso de insecticidas, están viendo amenazada su eficacia debido a la aparición de resistencia en poblaciones de campo. Recientemente se ha descrito resistencia metabólica a lambda-cihalotrina mediada por P450s. Con el fin de estudiar el tipo de herencia de la resistencia a lambda-cihalotrina, se realizaron cruzamientos recíprocos entre una línea de laboratorio resistente a este insecticida y una línea susceptible, se obtuvieron la generación F1 y la F2 y se realizó el retrocruce de la F1 con el parental susceptible. Los resultados muestran que la herencia de la resistencia es completamente dominante y autosómica, y que no se ajusta a un modelo mendeliano monogénico. Asimismo, se está realizando un mapeo genético de la resistencia a lambda-cihalotrina a partir de los individuos ensayados en el estudio de la herencia, con el propósito de identificar marcadores moleculares que nos permitan la detección precoz y el seguimiento de la resistencia en campo, facilitando así el control de la plaga. Por último, mediante el simulacro en laboratorio de distintos escenarios de tratamiento se ha podido determinar que la rotación de lambda-cihalotrina con spinosad resulta eficaz para el manejo de la resistencia a lambda-cihalotrina

Multiple mutations in the nicotinic acetylcholine receptor Ccα6 gene associated with resistance to spinosad in medfly

Spinosad is an insecticide widely used for the control of insect pest species, including Mediterranean fruit fly, Ceratitis capitata. Its target site is the α6 subunit of the nicotinic acetylcholine receptors, and different mutations in this subunit confer resistance to spinosad in diverse insect species. The insect α6 gene contains 12 exons, with mutually exclusive versions of exons 3 (3a, 3b) and 8 (8a, 8b, 8c). We report here the selection of a medfly strain highly resistant to spinosad, JW-100 s, and we identify three recessive Ccα6 mutant alleles in the JW-100 s population: (i) Ccα63aQ68* containing a point mutation that generates a premature stop codon on exon 3a (3aQ68*); (ii) Ccα63aAG>AT containing a point mutation in the 5' splicing site of exon 3a (3aAG > AT); and (iii) Ccα63aQ68*-K352* that contains the mutation 3aQ68* and another point mutation on exon 10 (K352*). Though our analysis of the susceptibility to spinosad in field populations indicates that resistance has not yet evolved, a better understanding of the mechanism of action of spinosad is essential to implement sustainable management practices to avoid the development of resistance in field populations

Field detection and predicted evolution of spinosad resistance in Ceratitis capitata

BACKGROUND: The sustainable control of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), is compromised by the development of resistance to malathion and lambda‐cyhalothrin in Spanish field populations. At present, field populations remain susceptible to spinosad. However, the resistant strain JW‐100s has been obtained under laboratory selection with spinosad, and resistance has been associated with the presence of different mutations causing truncated transcripts of the α6 subunit of the nicotinic acetylcholine receptor (nAChRα6). RESULTS: An F1 screen assay followed by the molecular characterization of surviving flies has been used to search for spinosad‐resistant alleles in field populations. Two different resistant alleles giving rise to truncated isoforms of Ccα6 have been identified, which corresponds to an estimated allelic frequency of at least 0.0023–0.0046. The fitness values of the resistant nAChRα6 alleles found in the laboratory strain JW‐100s were estimated to be 0.4 for RR and 0.2 for SR. Mathematical modelling predicted that spinosad‐resistant alleles will rapidly decline over time in field populations if their fitness cost was the same as estimated for laboratory‐resistant alleles. However, they are predicted to increase in the field if their fitness cost is lower and resistance management strategies are not implemented. CONCLUSION: Spinosad‐resistant alleles have been detected in field populations for the first time. Our modelling simulations indicate that the best option to delay the appearance of spinosad resistance would be its rotation with other insecticides without cross‐resistance. The integrated F1 screen/molecular genetic analysis presented here can be used for future monitoring studies

Effects of temperature and water activity on FUM2 and FUM21 genes expression and fumonisins B production in Fusarium verticillioides

The fungus Fusarium verticillioides is a pathogen of maize and can produce the mycotoxins fumonisins. The present work examined the effect of abiotic factors on the expression of two fumonisin biosynthetic genes (FUM2 and FUM21) and fumonisin production in the fungus. Specifically, the effects of water activity (0.901-0.990), temperature (20-30\ub0C) and incubation time (7-21 days) were analysed in cultures of F. verticillioides strains ITEM 10027 and ITEM 1744. Fumonisin B were measured through liquid chromatography tandem mass spectrometry and gene expression was quantified with relative real-time PCR, using the Livak method. Fumonisin production increased with incubation time up to 21 days and the transcription of both genes was highest at 14 days; however intraspecific variability was observed. FUM2 and FUM21 expression was positively correlated to fumonisin synthesis (p 640.01 and 0.05) at different water activity and temperature regimes. . A sensibly higher transcription of FUM2 in comparison with FUM21 was observed for all the conditions considered. Incubation time played a significant role on fumonisin production and gene expression, with the highest contamination and the highest gene expression respectively after 21 and 14 days of incubation. Temperature significantly affected only FUM21 expression, with optimum at 25\ub0C; while water activity did not have a significant effect