Dynamics of canopy-dwelling arthropods under different weed management options, including glyphosate, in conventional and genetically modified insect-resistant maize

The use of genetically modified varieties tolerant to herbicides (HT varieties) and resistant to insects (Bt varieties) in combination with application of a broad-spectrum herbicide such as glyphosate could be an effective option for the simultaneous control of weeds and pests in maize. Nevertheless, the possible impact of these tools on nontarget arthropods still needs to be evaluated. In a field study in central Spain, potential changes in populations of canopy-dwelling arthropods in Bt maize under different weed management options, including glyphosate application, were investigated. Canopy-dwelling arthropods were sampled by visual inspection and yellow sticky traps. The Bt variety had no effect on any group of studied arthropods, except for the expected case of corn borers-the target pests of Bt maize. Regarding the effects of herbicide regimes, the only observed difference was a lower abundance of Cicadellidae and Mymaridae on yellow sticky traps in plots not treated with pre-emergence herbicides. This effect was especially pronounced in a treatment involving two glyphosate applications. The decrease in Cicadellidae and Mymaridae populations was associated with a higher density of weeds in plots, which may have hindered colonization of the crop by leafhoppers. These differences, however, were only significant in the last year of the study. The low likelihood of the use of glyphosate- and herbicide-tolerant varieties for weed control triggering important effects on the nontarget arthropod fauna of the maize canopy is discussed.

Impact of Feeding on Contaminated Prey on the Life Parameters of Nesidiocoris Tenuis (Hemiptera: Miridae) Adults

Insecticide selectivity to natural enemies is an important concern in integrated pest management programs. Although there is a wide range of information concerning pesticide lethal and sublethal effects on contaminated surfaces, little is known when the route of exposure occurs at a trophic level. This study evaluates this route of pesticide intake on the omnivorous predator Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) for the first time. Under laboratory conditions, prey treated with six insecticides (flubendiamide, spirotetramat, deltamethrin, flonicamid, metaflumizone, and sulfoxaflor) were offered to N. tenuis adults for 3 days. Mortality (24, 48, and 72 h after treatment), offspring production (third until eighth day) and longevity were documented. Metaflumizone and sulfoxaflor were classified as moderately harmful products because although the percentage of mortality was only 28 and 36%, respectively, both products caused a severe decrease in offspring production and longevity. Flonicamid and flubendiamide were classified as slightly harmful products; although they did not have a lethal effect, sublethal impact was important on the parameters studied. Spirotetramat and deltamethrin were insecticides categorized as harmless. This information could be useful for selecting the most appropriate insecticides to control pests in tomato crops in which N. tenuis is a relevant biological control agent.

Laboratory evaluation of alternative control methods against the false tiger, Monosteira unicostata (Hemiptera: Tingidae)

BACKGROUND

Monosteira unicostata is an important pest of almond tree in the Mediterranean region requiring control methods alternative to synthetic pesticides. The efficacy of kaolin, azadirachtin and potassium salts of fatty acids combined with thyme essential oil against adults and fourth instar nymphs of this tingid was evaluated in laboratory assays.

RESULTS

In no choice assays with adults, kaolin significantly increased mortality compared to control (42.7% versus 23.8%) and reduced the oviposition of females (11.8 versus 35.3 eggs), the feeding activity (169.6 versus 471.2 excrements) and the damage caused (1.1 versus 2.3 damage index). In choice assays with adults, the repellence index calculated for kaolin (48.2%) was significantly higher compared to control (-15.3%), resulting in oviposition, feeding and damage deterrence indices also significantly higher than the control. In no choice assays with nymphs, all products increased mortality and reduced the feeding activity and the damage caused on leaves. Potassium soap with thyme essential oil and azadirachtin were the most effective compounds (98.0% and 97.6% mortality versus 13.3% control mortality, respectively).

CONCLUSION

The products tested have shown high and different efficacy on nymphs and adults of Monosteira unicostata. This activity might be suitable for the practical application of these compounds to control its populations under real field conditions.

Characterization of a Trichoplusia ni hexamerin-derived promoter in the AcMNPV baculovirus vector

The promoter sequences of the encoding genes for the three most abundant hexamerins of the Lepidoptera Trichoplusia ni were isolated and cloned into the Autographa californica multiple nucleopolyhedrovirus (AcMNPV)-derived baculovirus expression vector. From the sequences analyzed, the DNA region driving the expression of the Basic juvenile hormone-suppressible protein 2 (BJHSP-2), denominated pB2, presented the highest promoter strength in the context of the baculovirus vector in Sf21 insect cells. This promoter activity occurred earlier in baculovirus-infected cells than that achieved by a conventional polyhedrin promoter (polh), but surprisingly stopped at 48h post-infection. A mapping of pB2 essential promoter elements determined that a region of about 400bp, denominated pB29, retained and even increased the transcriptional activity with respect to the parental full-length sequence. Finally, several chimeric combinations of the insect-derived pB2 with the virus-derived conventional polh or p10 promoters were constructed and incorporated into an AcMNPV baculovirus vector. The pB2-p10 combination showed increased recombinant protein expression at early times post-infection and similar expression levels at very late times post-infection in Sf21 cells with respect to conventional late promoters. To the best of our knowledge, pB2 is the first promoter isolated from the Lepidoptera T. ni, the natural host of AcMNPV, to be assayed in a baculovirus expression vector.

Laboratory tests of insect growth regulators as bait sprays for the control of the olive fruit fly, Bactrocera oleae (Diptera: Tephritidae)

BACKGROUND

Insect growth regulators (IGRs) act specifically on arthropods. This selectivity makes them an interesting alternative to traditional insecticides for pest control. The aim of this work was to test the IGRs azadirachtin, cyromazine, flufenoxuron, lufenuron and pyriproxyfen as useful pesticides for the control of the olive fruit fly, Bactrocera oleae (Rossi), a key pest of olive crops.

RESULTS

Of the products tested, the chitin-synthesis inhibitor lufenuron showed the highest efficacy. The life parameter showing the strongest effect was the egg hatch, because lufenuron caused nearly 100% egg mortality 7 days after treatment. However, sterility was not transmitted from the treated males to the untreated females. The LC50 and LC90 values for a 7 day evaluation period were 19.3 and 86.2 µg AI mL(-1) respectively. Azadirachtin, cyromazine and flufenoxuron also caused significant increases in egg mortality. However, these increases were less than those produced by lufenuron. Pyriproxyfen had a stimulatory effect on B. oleae fecundity.

CONCLUSION

Applied as a bait treatment, a procedure used frequently in the field for the control of B. oleae, lufenuron is potentially useful against this important pest.

Comparative gene expression of gonadotropins (FSH and LH) and peptide levels of gonadotropin-releasing hormones (GnRHs) in the pituitary of wild and cultured Senegalese sole (Solea senegalensis) broodstocks

The Senegalese sole (Solea senegalensis) is a valuable flatfish for aquaculture, but it presents important reproductive problems in captivity. Spawning is achieved by wild-caught breeders but cultured broodstocks fail to spawn spontaneously and, when they do, eggs are unfertilized. To gain knowledge on the physiological basis underlying this reproductive dysfunction, this study aimed at analyzing comparative hormone levels between wild and cultured broodstocks at the spawning season. The Senegalese sole gonadotropin (GTH) subunits, FSHbeta, LHbeta and GPalpha, were cloned and qualitative (in situ hybridization) and quantitative (real-time PCR) assays developed to analyze pituitary GTH gene expression. In females, FSHbeta and GPalpha mRNA levels were higher in wild than in cultured broodstocks, whereas in males all three subunits were highest in cultured. By ELISA, three GnRH forms were detected in the pituitary, displaying a relative abundance of GnRH2>GnRH1>GnRH3. All GnRHs were slightly more abundant in wild than cultured females, whereas no differences were observed in males. Plasma levels of vitellogenin and sex steroids were also analyzed. Results showed endocrine differences between wild and cultured broodstocks at the spawning period, which could be related to the endocrine failure of the reproductive axis in cultured breeders.

Reproduction, longevity and life table parameters of Tyrophagus neiswanderi (Acari: Acaridae) at constant temperatures

The astigmatid mite Tyrophagus neiswanderi Johnston and Bruce is mainly considered a pest of ornamental and horticultural crops. However, this mite has been found infesting Cabrales cheese in Spain, though its population density is low compared to Acarus farris, the prevalent species of astigmatid mite encountered in Cabrales cheese maturing caves. One of the factors that might be influencing this differential abundance is temperature. In the present study the effect of temperature on reproductive parameters and longevity of T. neiswanderi was examined at six constant temperatures, ranging from 10 to 31 degrees C, and a relative humidity of 90 +/- 5%. Preoviposition period, fecundity and daily fecundity were adversely affected by extreme temperatures while the oviposition period increased as temperature was reduced. Male and female longevity increased as temperature decreased, but males showed significantly greater longevity than females. Additionally, this difference was greater as temperature decreased. The effect of temperature on the intrinsic rate of natural increase of T. neiswanderi populations was described by the non-linear Lactin model. The optimum temperature for development was predicted at 26.6 degrees C. At this temperature, the population doubling time is 2.8 days. The lower and upper thresholds for T. neiswanderi populations were calculated at 7.4 and 31.7 degrees C, respectively. According to these results, the influence of temperature on the low population density of this mite found in Cabrales maturing caves compared with A. farris is discussed.

Frequency of resistance to Bacillus thuringiensis toxin CrylAb in Greek and Spanish population of Sesamia nonagrioides (Lepidoptera: Noctuidae)

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 x 10(-3) with 95% probability, which was very similar to that of the Spanish population (<8.6 x 10(-3) with 95% probability), and the expected frequencies were 3.2 x 10(-3) (0-0.0097) and 2.9 x 10(-3) (0-0.0086) in Greece and Spain (pooled 1.5 x 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 x 10(-3) with a 95% credibility interval between 8 x 10(-4) and 17.8 x 10(-3) and a detection probability of 94%. Our results suggest that the frequency of alleles conferring resistance to CrylAb, 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.

Effects of relative humidity on development, fecundity and survival of three storage mites

The developmental rate of immature stages and the reproduction of adults of Tyrophagus putrescentiae (Schrank), T. neiswanderi Johnston and Bruce and Acarus farris (Oudemans) were examined at 70, 80 and 90% r.h. and a constant temperature of 25 degrees C. At 70% r.h., T. putrescentiae and A. farris immature stages failed to reach the protonymph stage as 100% of the larvae died, whereas T. neiswanderi was able to complete development. The developmental time of all immature stages for the three species was significantly increased as relative humidity was reduced. The mobile stages were particularly susceptible, as the time needed to complete their development at lower relative humidities suffered greater increases than the egg stage. At 70% r.h., T. putrescentiae and A. farris were not able to lay eggs and only 24% of T. neiswanderi pairs were fertile. The reproductive parameters of the three species at the relative humidities at which they were able to lay eggs showed significant differences, except for the percentage of fertile mating at 80 and 90% r.h. As relative humidity increased, preoviposition period was reduced and fecundity and daily fecundity was increased, whereas the oviposition period showed different patterns for the three species. The intrinsic rate of increase (r ( m )) of T. neiswanderi at 70% r.h. was negative indicating that, at these conditions, mite populations of this species will diminish until they disappear. As relative humidity increased from 80 to 90% r.h. this parameter was almost twofold for both Tyrophagus species. The r ( m ) obtained for A. farris at 90% r.h. was similar to that of T. neiswanderi at the same humidity while at 80% r.h. it was very small so that the population doubling time was more than 84 days. The influence of relative humidity on biology of these mites and its practical application as control measure are discussed.

Evaluation of low humidity treatments to control Acarus farris (Acari: Acaridae) in Cabrales cheese

Laboratory experiments were conducted to establish the best combination of relative humidity (r.h.) and time of exposure to be applied on Cabrales cheeses infested with Acarus farris. Laboratory assays revealed that less than 30 h were required to obtain 90% mortality of mites at 50% and 60% r.h. Males were more susceptible than females to low relative humidity, since their lethal period values (LP) were lower than those obtained for females at the same relative humidity. Moreover, the response within sexes to low moisture treatments changed as exposure time increased, since the LP50 obtained for each sex at 50 and 60% r.h. were statistically different whereas the LP90 showed no significant differences within sexes. Accordingly, two modifications of the traditional maturing process were established to assess the efficacy of low moisture treatments to control A. farris on infested cheeses. The first modification consisted of one single exposure of 48 h at 50% r.h. and the second one consisted of two exposures of 48 h at 50% r.h. separated by a time interval of 15 days. No significant differences in final population density were observed for both low moisture treatments compared to control cheeses. Therefore, low humidity treatments are not effective to control A. farris in Cabrales cheese, despite the good results obtained in laboratory assays.

Effect of temperature on reproductive parameters and longevity of Tyrophagus putrescentiae (Acari: Acaridae)

The effect of temperature on reproductive parameters and longevity of the mold mite, Tyrophagus putrescentiae (Schrank) was examined at seven constant temperatures, ranging from 10 to 34 degrees C, and a relative humidity of 90 +/- 5%. Preoviposition period and fecundity were adversely affected by extreme temperatures and the oviposition period increased as temperature was reduced. Different patterns were observed for longevity data for males and females, with greater longevities for males at intermediate temperatures and more similar values for both sexes at extreme temperatures. Polynomial and non-linear models provided a good fit of the relationship of reproductive and longevity parameters with temperature. The effect of temperature on the intrinsic rate of increase of T. putrescentiae populations was established by the non-linear Lactin model. The optimum temperature for development was obtained at 30 degrees C. At this temperature, the population doubling time is 1.75 days. The lower and upper thresholds for T. putrescentiae populations were established at 10.4 and 34.8 degrees C, respectively. Altogether, these data provide basic information to develop sound physical control strategies of the mold mite.

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

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.

Laboratory evaluation of selective pesticides against the storage mite Tyrophagus putrescentiae (Acari: Acaridae)

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.

Characterization of proteases from a stored product mite, Tyrophagus putrescentiae

Extracts of Tyrophagus putrescentiae feces exhibited higher (>50-fold) specific protease activity rates than those measured using mite body extracts for the substrates azocasein, BApNa, SA(2)PPpNa, HA, and HPA. This suggests that trypsin, chymotrypsin, and carboxypeptidases A and B are involved in mite digestion. Hydrolysis of the substrates ZAA(2)MNA and LpNa was only 3 times higher in fecal extracts, suggesting that levels of cathepsin B and aminopeptidases in the lumen of the digestive tract are low compared to the other enzymes. The hydrolysis of hemoglobin was only detected in body extracts indicating that cathepsin D is not a digestive protease in this species. Protease inhibitors of different specificity were tested invivo to establish their potential as control agents. We found that development from larvae to adult was significantly retarded in larvae fed on brewers' yeast containing inhibitors of serine proteases, whereas no such effect was found with inhibitors of cysteine and aspartyl proteases. Interestingly, when dietary mixtures of serine protease, aminopeptidase and carboxypeptidase inhibitors were fed to T.putrescentiae, a synergistic effect was observed that retarded development. Several plant lectins were also tested, but none affected development.

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.