Ismael Sánchez-Ramos

Acaricidal activity of natural monoterpenes on Tyrophagus putrescentiae (Schrank), a mite of stored food.

Seven natural monoterpenes (pulegone, eucalyptol, linalool, fenchone, menthone, alpha-terpinene and gamma-terpinene), out of 13 tested, were shown to possess a high acaricidal activity by vapour action against mobile stages of Tyrophagus putrescentiae. Of these seven, pulegone, menthone, linalool, and fenchone yielded LC(90) values of 14 µl/l or below. However, no effect was recorded on egg hatching. Interestingly, the larvae and males of T. putrescentiae presented a mortality rate significantly higher than females (about 2-fold) when exposed to the same vapour concentration of the active monoterpenes. The high acaricidal activity recorded on immature and adult stages might be primarily related to desiccation, since dead mites presented symptoms usually considered to be associated with this phenomenon. Moreover, since larvae and males are significantly smaller than females and their surface/volume ratios are higher, they tend to lose relatively more water, thus supporting the notion that the greater acaricidal activity recorded on larvae and males might be primarily related to desiccation. Nevertheless, action by interference with respiratory processes cannot be discarded. The potential of these natural monoterpenes for practical use against mobile stages of T. putrescentiae in warehouses of traditional Spanish dry-cured ham is discussed.

Development and Survival of Tyrophagus putrescentiae (Acari: Acaridae) at Constant Temperatures

Abstract The developmental rate and survival of immature stages of mold mite, Tyrophagus putrescentiae (Schrank), were examined at seven constant temperatures, ranging from 10 to 34°C, and a relative humidity of 90 ± 5%. The larval stage was particularly susceptible to low and high temperatures with 93.6 and 54% mortality at 10 and 34°C, respectively. The optimal temperature for development and survival appeared to be 30°C. Three nonlinear (Logan type III, Lactin, and Briere) models provided a reliable fit of the relationship between developmental rates and temperature (Ra2 > 0.93) for all immature stages. The upper threshold predicted by the three models were similar for all developmental stages, ranging from 35.5°C (larvae) to 37.4°C (eggs). In contrast, the lower threshold was greater using the Briere (8.8–10.5°C) model compared with the Logan type III and Lactin model for all stages. Both Lactin and Logan III predicted similar lower threshold, though it was lower for Logan III (4.4–7.3°C) for all stages, except for the larvae, where both models predicted the same temperature threshold (6.1°C). The low thermal variations of the environments where T. putrescentiae live have probably favored similar thermal threshold variations in the different immature stages. The potential of these models to predict the development of this mite is discussed.

Frequency of resistance to Bacillus thuringiensis toxin Cry1Ab in greek and spanish population of Sesamia nonagrioides (Lepidoptera: Noctuidae)

Abstract The high-dose/refuge strategy is considered as the main strategy for delaying resistance in target pests to genetically modified crops that produce insecticidal proteins derived from Bacillus thuringiensis Berliner. This strategy is based on a key assumption that resistance alleles are initially rare (<10−3). To test this assumption, we used an F2 screen on natural populations of Sesamia nonagrioides Lefebvre (Lepidoptera: Noctuidae) from Greece and Spain. In total, 75 lines from Greece and 85 lines from Spain were screened for survival of F2 larvae on Cry1Ab corn, Zea mays L., leaves. No major resistance alleles were found. The frequency of resistance alleles in the Greek population was <9.7 × 10−3 with 95% probability, which was very similar to that of the Spanish population (<8.6 × 10−3 with 95% probability), and the expected frequencies were 3.2 × 10−3 (0–0.0097) and 2.9 × 10−3 (0–0.0086) in Greece and Spain (pooled 1.5 × 10−3). The experiment-wise detection probability of resistance was 94.0 and 97.5% for the Greek and the Spanish population, respectively. Evidence of alleles conferring partial resistance to Cry1Ab was found only for the Greek population. The frequency of alleles for partial resistance was estimated as 6.5 × 10−3 with a 95% credibility interval between 8 × 10−4 and 17.8 × 10−3 and a detection probability of 94%. Our results suggest that the frequency of alleles conferring resistance to Cry1Ab, regarding the population of S. nonagrioides, may be rare enough so that the high-dose/refuge strategy could be applied with success for resistance management.

Laboratory Evaluation of Selective Pesticides Against the Storage Mite Tyrophagus putrescentiae (Acari: Acaridae)

Abstract The storage mite, Tyrophagus putrescentiae (Schrank), is an important source of airborne allergens, especially on farms. Three insect growth regulators (halofenozide, pyriproxyfen, hexaflumuron), one botanical insecticide (azadirachtin) and one naturalyte (spinosad) were tested to assess their efficacy against this mite. The organophosphate chlorpyrifos was used as a standard. Immature stages and adults were treated with different concentrations of the chemicals in diet-incorporation bioassays. All chemicals significantly increased the developmental time of immature stages at doses higher than 1,000 ppm. Pyriproxyfen and halofenozide yielded mortality rates of immature stages similar to that obtained with chlorpyrifos, with values near 100% at 10,000 ppm. At 1,000 ppm, only halofenozide significantly increased the mortality of immature stages. Similarly, adult survival and fecundity were significantly reduced with halofenozide at 1,000 ppm, whereas it required 10,000 ppm of chlorpyrifos to obtain a significant reduction in survival and fecundity, with no effect observed with pyriproxyfen. This data suggests that halofenozide could be a good alternative for the control of T. putrescentiae in farming environments.

Proteolytic activities in body and faecal extracts of the storage mite, Acarus farris

Abstract.  Trypsin, chymotrypsin, cathepsins B and D, aminopeptidase and carboxypeptidases A and B were detected in body extracts of the storage mite Acarus farris (Oudemans) (Astigmata: Acaridae). Faeces‐enriched medium exhibited higher (10–50‐fold) specific protease activity rates than those measured with mite body extracts for trypsin, chymotrypsin and carboxypeptidases A and B, suggesting that they are involved in mite digestion. However, the activity of cathepsin B was only three‐fold higher in faecal than in body extracts, indicating that its presence in the lumen of the digestive tract is low compared to that of serine proteases. The activity of aminopeptidases was higher in mite bodies, indicating that they might be membrane bound. Cathepsin D activity was only detected in body extracts, indicating that this enzyme is not a digestive protease in this species. Zymograms resolved three major bands of gelatinolytic activity, but at least one protease form was only present in body extracts. Protease inhibitors of different specificity were tested in vivo to establish their potential as control agents. The development of A. farris was significantly retarded when the immature stages were fed on artificial diet containing inhibitors of serine and cysteine proteases and aminopeptidases, whereas no such effect was found with inhibitors of aspartyl proteases and carboxypeptidases. Interestingly, the most significant effects on A. farris occurred when a combination of inhibitors targeting different enzyme classes was supplied mixed in the diet, suggesting a synergistic toxicity. Several plant lectins were also tested, but only wheat germ agglutinin and concanavalin‐A affected development.