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PubMed1977

The properties of a carboxylesterase from the peach-potato aphid, Myzus persicae (Sulz.), and its role in conferring insecticide resistance.

Carboxylesterases from different strains of Myzus persicae were examined to try to understand their contribution to insecticide resistance. Preliminary evidence that they are involved comes from the good correlation between the degree of resistance and the carboxylesterase and paraoxon-degrading activity in aphid homogenates. Furthermore the carboxylesterase associated with resistance could not be separated from the insecticide-degrading enzyme by electrophoresis or ion-exchange chromatography. Homogenates of resistant aphids hydrolysed paraoxon 60 times faster than did those of susceptible aphids, yet the purified enzymes from both sources had identical catalytic-centre activities towards this substrate and also towards naphth-1-yl acetate, the latter being hydrolysed by both 2x10(6) times faster than paraoxon. These observations provide evidence that the enzyme from both sources is identical, and that one enzyme hydrolyses both substrates. This was confirmed by relating the rate of paraoxon hydrolysis to the rate at which paraoxon-inhibited carboxylesterase re-activated. Both had the same first-order rate constant (0.01min(-1)), showing clearly that the hydrolysis of both substrates is brought about by the same enzyme. Its K(m) for naphth-1-yl acetate was 0.131mm, and for paraoxon 75pm. The latter very small value could not be measured directly, but was calculated from substrate-competition studies coupled with measurements of re-activation of the diethyl phosphorylated enzyme. Since the purified enzymes from resistant and susceptible aphids had the same catalytic-centre activity, the 60-fold difference between strains must be caused by different amounts of the same enzyme resulting from mutations of the regulator gene(s) rather than of the structural gene.

Animals↗
PubMed2026

Historical metabolic adaptation potentiates the rapid evolution of flonicamid resistance in Myzus persicae.

Rapid adaptation to novel environments is often shaped not only by newly acquired mutations but also by historical genetic backgrounds established through prior evolutionary events. However, the extent to which such historical contingency contributes to the rapid evolution of insecticide resistance remains poorly understood. Here, we investigated the emergence of resistance to flonicamid, a recently deployed insecticide, in the green peach aphid, Myzus persicae. We show that constitutive overexpression of the P450 enzymes CYP6CY3 and CYP6CY4, already widespread in populations of M. persicae before flonicamid deployment, confers a previously cryptic tolerance phenotype to flonicamid. However, biochemical and transgenic analyses demonstrated that these metabolic adaptations provide only weak protection against flonicamid. Following flonicamid deployment, however, a novel target-site mutation, NaamV251I, in the recently identified molecular target of 4-trifluoromethylnicotinamide (TFNA-AM), emerged in M. persicae on a genetic background of CYP6CY3 or CYP6CY4 overexpression. Structural modeling, enzymatic assays, and CRISPR-Cas9 genome editing demonstrated that this mutation reduces target sensitivity and independently confers moderate resistance. Strikingly, combining the nicotinamidase (Naam) mutation with pre-existing CYP6CY3 or CYP6CY4 overexpression produced substantially elevated resistance phenotypes that far exceeded the effects of either mechanism alone. Our results demonstrate that the pre-existing metabolic background did not itself evolve further following flonicamid deployment but fundamentally altered the phenotypic consequences of a subsequently acquired target-site mutation. These findings provide direct evidence that historical adaptive variation can potentiate rapid resistance evolution to newly introduced insecticides and reveal how interactions between past and contemporary adaptations shape evolutionary responses to novel environmental challenges.

Animals↗
PubMed1978

[Breeding of a biotype of the aphia Myzus persicae on a synthetic medium. IV. Influence of vitamins, especially vitamin C and pyridoxine, on the nutritional value of nutritive fluids].

The nutritive value of synthetic diets for Myzus persicae was evaluated by measuring reproduction of the third generation on each medium: 1. In the presence of a double dose of pyridoxin, the nutritional value of the basic diet was improved. This improvement disappeared when all the vitamins of the B group were also at double dose; 2. In the presence of a double dose of ascorbic acid, the nutritional value of all the diets was improved. This improvement was observed for a single or a double dose of pyridoxin and a single or a double dose of all the vitamins of the B group. The beneficial effect of a double dose of pyridoxin was not adding with the beneficial effect of a double dose of ascorbic acid; 3. A double dose of EDTA was detrimental to the aphid but a double dose of ascorbic acid was sparing this detrimental effect. The results are discussed in relation with the nutritional needs in vitamins and the action of the vitamins in the mineral nutrition of the aphid.

Animals↗
PubMed1977

[Laboratory and field tests about the transmission of Erysimum latent virus by Phyllotreata species (Chrsomelidae) (author's transl)].

Erysimum latent virus (ELV) proved to be transmissible by Phyllotreta atra, P. nemorum, P. nigripes, and P. undulata. From them P. nemorum is a new discovered vector. The acquisition of the virus by the beetles was possible within a feeding time of less than 10 minutes. Because virus transmission could be performed within 30 to 60 minutes immediately after virus uptake there exists apparently no latent period in the vector. The retention or persistence of ELV in the Phyllotreta species amounted up to 3 days. Trials to induce infectivity of Phyllotreta species by injection of the virus were unsuccessful. ELV was transmissible by Aphis frangulae gossypii, Brevicoryne brassicae, and Myzus persicae neither in short nor in long feeding times. Field tests showed that the Phyllotreta species are able to spread ELV under natural conditions.

Animals↗
PubMed1978

[A conbribution to the characterization of asparagus virus 2 (author's transl)].

In host range investigations with 152 plant species of 37 families, 96 species from 28 families proved to be experimentally susceptible to asparagus virus 2 (AsV 2). From these, 82 species of 26 families were systematically infectible and 14 species of 10 families only locally. Most frequently were symptomless systemic infections. Of 86 species, their susceptibility for AsV 2 was unknown before. The number of families that contant experimental hosts of the virus increased from 11 to 33. Transmission of AsV 2 was neither possible with Myzus persicae nor with Cuscuta californica or C. campestris. AsV 2-infected mother plants transmitted the virus by about 40 per cent to their seedings. Open-pollinated plants, not infested by AsV 2, showed 3 to 22 per cent of infected seedings. Mechanical back-transmission of AsV 2 from test plants to asparagus succeeded only in one case. The properties of the virus in vitro were as follows: thermal inactivation point between 64 and 66 degrees C, dilution end point between 10(-3) and 10(-4), stability in sap, stored at room temperature, up to 96 hours. Serological investigations demonstrated no relationship to the virus to numerous other viruses. An antiserum with a titer of 1 to 16 was useful for the detection of AvV 2 in asparagus sap. Electron microscopical investigations proved for the virus isometric particles for the first time. In negatively stained preparations they had a diameter of 27 nm.

Plant Viruses↗