Efficacy and environmental fate of copper sulphate applied to Australian rice fields for control of the aquatic snail Isidorella newcombi

Copper sulphate pentahydrate (CuSO₄·5H₂O) is widely used for controlling Isidorella newcombi, an aquatic snail that causes substantial damage to rice crops in southeastern Australia. We conducted field trials on a Birganbigil clay loam soil that demonstrate high levels of efficacy against adult I. newcombi (95% mortality at 6.38 kg ha⁻¹ CuSO₄·5H₂O (1.14 mg Cu L⁻¹)). Dissolved copper fell below the detection limit (0.02 mg Cu L⁻¹) between 7 and 20 d after spraying at application rates up to 2.16 mg Cu L⁻¹ (12 kg ha⁻¹ CuSO₄·5H₂O). Total copper concentrations in the water column fell below the detection limit (0.007 mg Cu L⁻¹) 7–12 d after spraying at initially applied concentrations of 0.52–1.12 mg Cu L⁻¹, but remained detectable (0.01–0.02 mg Cu L⁻¹) until 30 days after spraying (the conclusion of monitoring) when applied at higher initial concentrations (1.18–2.16 mg Cu L⁻¹). There was a strong positive correlation (r² = 0.90, P < 0.001) between copper application rate and copper concentrations in surface sediments 30 d after spraying. Bioassays with immature snails using three different test soils beneath irrigation water showed that underlying soil type strongly influenced the response of snails to applied copper, with significant (P < 0.05) differences between LC₉₀ values which ranged from 0.41 to 1.04 mg applied Cu L⁻¹. Laboratory studies showed that dissolved copper concentrations remained significantly higher (P < 0.05) in the water column above the soil that had the most deleterious effect on copper toxicity. Dissolved organic carbon concentrations were significantly (P < 0.05) higher in both this soil and in the overlying water in the corresponding bioassay system, and correlated more closely with LC₉₀ values than other water chemistry parameters such as total hardness. Our results support the ongoing use of a variable copper application rate of 6–12 kg ha⁻¹ CuSO₄·5H₂O to allow for site-specific variations in efficacy, and suggest that variations in the release of dissolved organic carbon compounds from flooded soils may be a key factor moderating copper toxicity to I. newcombi in rice fields.     

Effectiveness of imidacloprid in combination with a root nitrogen fertilizer applied to tomato seedlings against Bemisia tabaci (Hemiptera: Aleyrodidae)

The whitefly Bemisia tabaci (biotype B) is a worldwide pest of vegetables and field crops. We tested the efficacy of imidacloprid (IM) with a root fertilizer ‘Root Feed (RF)’ (9% N, 7% Ca, 1.5% Mg and 0.1% B) sub-irrigated in the growing medium against the whitefly on tomato. Tomato seedlings (3–4 true leaves) were treated with 0, 3, 6 or 12 mg active ingredient (a.i.) seedling⁻¹ of IM and with RF (0, 0.02, 0.04 or 0.08 ml seedling⁻¹). The efficacy of 12 mg IM seedling⁻¹ was further evaluated in the greenhouse for 60 days. The survival of B. tabaci adults, nymphs, and egg production were negatively affected by the treatments in a dosage-dependent manner. Treatment of 12 mg IM seedling⁻¹ caused >60% adult and nymph mortality 50 days after treatment (DAT). The active ingredient of IM in tomato leaves also increased with the increase of IM dosage. The RF exhibited a limited effect on B. tabaci. However, the mortality of whitefly adults and nymphs treated with RF (0.02 or 0.04 ml seedling⁻¹) positively interacted with IM, and was greater than IM alone. In the greenhouse, 12 mg IM seedling⁻¹ greatly reduced the number of whitefly adults and increased the dry weight of the tomato plants at 30 DAT. In conclusion, application of 12 mg IM seedling⁻¹ on tomato seedlings before transplanting effectively controled B. tabaci for up to 50 days, and the efficacy of IM combined with 0.02 ml RF seedling⁻¹ performed even better. This could be a cost-effective method for managing B. tabaci on tomato and other vegetables.     

Effect of neemarin on life table indices of Plutella xylostella (L.)

The effects of neemarin at 5, 10, 15 and 20 mg l⁻¹ on the life table indices of Plutella xylostella (L.) were studied on cauliflower in the laboratory. Survivorship was increased with increasing concentrations. A total of 69% eggs hatched at 20 mg l⁻¹ compared 85% in the control. Mortality (d_x) of 1st instars was higher than the other instars in both exposed and unexposed individuals. Life expectancy (e_x) was high in the untreated control and reduced at 20 mg l⁻¹. Development times of immatures were prolonged to 32 days at 20 mg l⁻¹ as compared to 18.6 days in the untreated control. Neemarin significantly reduced the emergence of adults. Potential fecundity (P_f) was 34 females/female/generation at 20 mg l⁻¹ and 92 in the control. The net reproductive rate (R₀) was significantly reduced with the increase in concentration. The intrinsic rate of increase (r_m) and finite rate of increase (λ) were significantly decreased at 20 mg l⁻¹ as compared to other concentrations tested and in the control. Mean generation time (T_c) and corrected generation time (τ) were prolonged at 20 mg l⁻¹ and significantly differed to those of the untreated control. Doubling time (DT) was significantly extended to 28.4 days at 20 mg l⁻¹ as compared to 6.1 days in the control.     

Demographic changes in Helicoverpa armigera after exposure to neemazal (1% EC azadirachtin)

We estimated the effect of 5, 10, 15 and 20 mg l⁻¹ of neemazal (1% EC azadirachtin) on life table parameters of Helicoverpa armigera (Hübner) developing on chickpea (Cicer arietinum L.). The effects were assessed on the survivals emerged from 6th instar larvae that had ingested neemazal-treated chickpea pods. Survivorship (I) and expectancy of life (e_x) were highest with the commencement of age (egg) and decreased gradually with the advancement of age with all the concentrations of neemazal including unexposed cohort. All the eggs hatched in the unexposed group while highest numbers of unhatched eggs (10%) were recorded with 20 mg l⁻¹. Mortality of 1st instars was higher at 20 and 15 mg l⁻¹ than that of other concentration tested. Potential fecundity (pf) was reduced in concentration dependent manner and was lowest with 20 mg l⁻¹ (418 eggs/female/generation) and highest in control (898 eggs/female/generation). Net reproductive rate (R₀) was significantly reduced with the increase in concentration of neemazal. The intrinsic (r_m) and finite rate of increase (λ) were significantly decreased at 20 mg l⁻¹ than that of unexposed population. The mean generation time (T_c) was prolonged at 20 mg l⁻¹ and significantly differed with non-treated individuals. Development of immature stages was prolonged to 38 days with 20 mg l⁻¹ while reduced to 32 days with 15 mg l⁻¹ of neemazal as compared to 37 days in untreated individuals. Doubling time (DT) was significantly extended to 5.02 days with 20 mg l⁻¹ as compared to 3.84 days in the non exposed ones.     

Are traditional neem extract preparations as efficient as a commercial formulation of azadirachtin A?

Neem seeds contain many substances with insecticidal properties, the main insecticidal ingredient being azadirachtin A. In developing countries such as Mali, a neem seed water extract is prepared by soaking ground seeds in water for three or seven days. The aim of this study was to check the effectiveness of this extract in terms of azadirachtin A extraction yield and insecticidal activity. The yield of extraction was 0.19 g azadirachtin A/100 g seeds. The concentration of azadirachtin A in the seed extract was approximately 200 mg l⁻¹, eight times higher than the recommended concentration of commercial products (25 mg l⁻¹). A comparison of the extractive capacity of different solvents indicated that the best solvents were water and methanol. The azadirachtin A concentration declined in extracts stored for more than 3 days at a temperatures higher than 30 °C. Bioassays were performed on target insects (the leafhopper Macrosteles quadripunctulatus, the moth Spodoptera littoralis and the tobacco whitefly Bemisia tabaci) in order to compare the insecticidal activity of the neem extract with that of the commercial product Neemazal T/S and of a solution of pure azadirachtin A. The bioassays conducted on the leafhopper and the moth demonstrated that the neem extract at the recommended concentration (25 mg l⁻¹ active ingredient) was as effective as the azadirachtin-based commercial product at the same concentration, while for the control of the whitefly B. tabaci a higher concentration of the water extract was needed.     

Lethal and sublethal effects of buprofezin and imidacloprid on Bemisia tabaci (Hemiptera: Aleyrodidae)

The sweetpotato whitefly, Bemisia tabaci (Gennadius), has become a major threat to agriculture worldwide. The development of insecticide resistance in B. tabaci has necessitated the exploration of new management tactics. The toxicity of imidacloprid and buprofezin to various life stages of B. tabaci was determined in the laboratory. Also, the sublethal effects of both insecticides were studied on demographic and biological parameters of B. tabaci. Both insecticides were very toxic against first stage larvae of the pest with LC₅₀ values of 1.0 and 19.3 ppm for buprofezin and imidacloprid, respectively. Toxicities decreased between successive stages (LC₅₀ values ranging from 1.0 to 2854.0 ppm). The LC₅₀ values of imidacloprid for adult males, females and eggs were 11.8, 71.6 and 151.0 ppm, respectively. Buprofezin had no significant effect on adults and eggs. The sublethal concentration of imidacloprid had no significant effect on demographic and biological parameters of B. tabaci but the maximal value for the mean generation time (T) (18.8 day) was observed in imidacloprid treatment. Buprofezin significantly decreased stable population and biological parameters of B. tabaci except it did not decrease the rate of population increase or the sex ratio of offspring.     

Efficacy of ketoenols on insecticide resistant field populations of two-spotted spider mite Tetranychus urticae and sweet potato whitefly Bemisia tabaci from Greece

Tetranychus urticae (two-spotted spider mite) and Bemisia tabaci (sweet potato whitefly), two of the most important agricultural pests worldwide, have developed resistance to almost all chemical classes of insecticides. Here we investigated the efficacy of the ketoenols spirodiclofen and spiromesifen against, respectively, T. urticae and B. tabaci populations from Greece with variable levels of resistance to other pesticides in order to evaluate their potential role in insecticide resistance management strategies for sustainable control of both pests. No resistance of T. urticae populations against spirodiclofen was observed. Nine out of ten T. urticae populations exhibited moderate levels of resistance to pirimiphos-methyl (up to 23-fold), pyridaben (up to 39-fold) and fenazaquin (up to 42-fold). Two of them exhibited high resistance ratios (RR) to bifenthrin (RR = 81, 351) and one to fenbutatin oxide (RR = 146). Moreover these nine populations were not cross resistant to spirodiclofen (RR < 5). A single population from greenhouse roses exhibited high resistance levels to most of the pesticides tested (RR = 8413, 1494, 434, and 74 to bifenthrin, fenbutatin oxide, abamectin and pirimiphos-methyl, respectively) showed decreased susceptibility to spirodiclofen (RR = 12). In B. tabaci the variation in response to spiromesifen treatments was very low among the eleven field populations. Most of them exhibited high levels of resistance to imidacloprid, and alpha-cypermethrin. The LC₅₀ of spiromesifen ranged from 4.5 to 14 mg/l and the corresponding LC₉₅ values were in general well below the recommended field doses. Ketoenol resistance risk potential was also investigated by applying constant selection pressure under laboratory conditions against populations from both species, but no increase in LC₅₀s was detected. Ketoenols can be used for resistance management purposes for both pests in Greece as an effective chemical tool in rotation with other pesticides.     

Effect of pre-emergence herbicides and timing of soil saturation on the control of six major rice weeds and their phytotoxic effects on rice seedlings

The study evaluated the effects of pre-emergence herbicides and their rates [oxadiazon (0.5 and 1 kg ai ha⁻¹), pendimethalin (1 and 2 kg ai ha⁻¹), and pretilachlor with safener (0.6 kg ai ha⁻¹)], and time of soil saturation establishment after herbicide application [1, 3, 5, and 7 days after spray (DAS)] in controlling the six major rice weeds, and their phytotoxic effects on rice seedling growth. All herbicides provided 100% control of Echinochloa colona, Echinochloa crus-galli, Leptochloa chinensis, Cyperus iria, and Amaranthus spinosus. Murdannia nudiflora was 100% controlled by oxadiazon and pretilachlor with safener, but poorly controlled (22–75%) by pendimethalin. Pendimethalin at 2 kg ai ha⁻¹ was more effective than at 1 kg ai ha⁻¹ in reducing the biomass of the stem, leaf, and root of M. nudiflora irrespective of timing of soil saturation. Rice plant height was reduced to a maximum (77–96%) by pendimethalin at 2.0 kg ai ha⁻¹ followed by oxadiazon at 1.0 kg ai ha⁻¹ (38–70%) compared to the non-treated control. In contrast, the tallest rice plants were observed in the non-treated control and those treated with pretilachlor with safener which had 80–100% rice plant survival. The lowest rice plant survival of 0, 6, 7, and 16% was found in the soil applied with pendimethalin at 2 kg ai ha⁻¹ and saturated at 1, 3, 5, and 7 DAS, respectively, which was followed by oxadiazon at 1 kg ai ha⁻¹. All herbicides except pretilachlor with safener reduced SPAD values with early soil saturation, which improved with delay in soil saturation timing. Pendimethalin at 2 kg ai ha⁻¹ reduced the SPAD values of rice plants by 100–164% relative to the non-treated control and produced the highest phytotoxicity symptoms. Pendimethalin also reduced rice shoot biomass more than oxadiazon, which was compounded by early soil saturation after herbicide application. Pretilachlor with safener was the only herbicide that exhibited low phytotoxic symptoms on rice plants and did not reduce leaf, stem, root, and shoot biomass of rice. Percent reduction in rice leaf, stem, root, and shoot biomass by the different herbicides was in the order of pendimethalin 2 > oxadiazon 1 > pendimethalin 1 > oxadiazon 0.5 > pretilachlor with safener 0.6 kg ai ha⁻¹. Each herbicide treatment reduced rice growth parameters as soil saturation was delayed in the order of 1 DAS > 3 DAS > 5 DAS > 7 DAS. The study suggests that soil water content and herbicide rates are important factors in influencing herbicide phytotoxicity in rice. The application of herbicides should be avoided when the soil is too wet, and irrigation should be delayed at least one week after herbicide application.     

Evaluation of systemic acquired resistance inducers for control of downy mildew on basil

Basil downy mildew, caused by Peronospora belbahrii Thines sp. nov., is a devastating foliar disease of fresh-cut basil first discovered in the U.S. in South Florida in 2007. Since then the pathogen has been found in over 20 U.S. states and has become a major threat to sweet basil production. In this study, acibenzolar-S-methyl (ASM, Actigard 50WG), DL-3-aminobutyric acid (BABA), isonicotinic acid (INA), salicylic acid (SA) and sodium salicylate (SS) were evaluated for their potential to control basil downy mildew in the greenhouse. Efficacy of these systemic acquired resistance (SAR) inducers varied in control of basil downy mildew depending on the rate, method and timing of application. Foliar sprays of ASM applied pre-, post- or pre- + post-inoculation at rates ranging from 25 to 400 mg l⁻¹ significantly (P = 0.05) reduced disease severity compared to the non-treated control in all experiments. ASM sprayed at 50 mg l⁻¹ three times on a weekly basis starting 3 and 7 days post- inoculation resulted in a 93.8 and 47.1% reduction in disease severity, respectively. Six weekly foliar sprays of BABA as pre- + post-inoculation at rates equal or higher than 125 mg l⁻¹ significantly suppressed downy mildew compared to the non-treated control. Foliar treatments of ASM or BABA followed by one or two post-inoculation sprays of a mixture of potassium phosphite (Prophyt) and azoxystrobin (Quadris) significantly improved efficacy for disease control. Sporangia counted on ASM treated leaves were significantly lower than leaves sampled from the non-treated control. ASM and BABA at concentrations lower than 1.0 mM did not inhibit sporangial germination in vitro. The effect of INA, SA and SS on disease reduction was generally inconsistent and not significant compared to the non-treated control.     

Lethal and sublethal effects of a novel cis-nitromethylene neonicotinoid insecticide,cycloxaprid, on Bemisia tabaci

The tobacco whitefly, Bemisia tabaci (Gennadius), is an important pest because of its potential to threaten agricultural crops worldwide. Currently, this pest is controlled by the application of chemical insecticides. In our pursuit to identify better insecticides for an effective control of this insect pest, we investigated the lethal effects of five neonicotinoid insecticides including four commercial neonicotinoids and a novel neonicotinoid (cycloxaprid) on B. tabaci MED and MEAM1 cryptic species. In addition, we assessed the sublethal effects of cycloxaprid on B. tabaci MED. Lethal effects of the insecticides were determined using the leaf-dip bioassay, and the results showed that among the tested insecticides cycloxaprid was more toxic to B. tabaci MED and MEAM1 than others, with LC₅₀ values of 0.70 mg/L and 0.59 mg/L, respectively. Cycloxaprid at LC₂₅ (0.16 mg/L) induced sublethal effects in adult MED by prolonging the developmental periods and decreasing the survival rates of all larval instars, pseudopupal and adult stages. Moreover, it significantly shortened the oviposition period of females and decreased their fecundity. Hatching rate of eggs laid by females exposed to LC₂₅ was also markedly reduced. These results indicate that cycloxaprid is a novel alternate insecticide that may effectively control B. tabaci populations.     

Effects of 1,3-dichloropropene plus chloropicrin on weed seed germination

Telone C-35, a commercial formulation of 1,3-dichloropropene (1,3-D) and chloropicrin (CP), is one of the potential replacements to methyl bromide (MB) for soil fumigation. A laboratory dose–response study and two field trials in tomato were conducted to evaluate their weed control efficacy and their effect on tomato yield. Laboratory studies found that the seeds of Digitaria chinensis were the most sensitive to soil fumigation with Telone C-35, followed by Eleusina indica, Portulaca oleracea and Stellaria media with the LC₅₀ values between 3.35 and 11.68 mg kg⁻¹ soil. Field trials revealed that Telone C-35 applied to the field at 327, 243 and 164 L ha⁻¹ could suppress the percentage of germination weed seeds while maintaining high tomato marketable yields, with no significant differences between MB + CP and the higher two Telone C-35 rates. The yield data from both seasons indicated that all Telone C-35 treatments had a positive effect on tomato yield; there was a 32%–62% increase the mean marketable tomato yield. Our results indicated that Telone C-35 was an excellent MB alternative and could provide acceptable weed control efficacy. Based on our results, Telone C-35, in combination with other alternatives to MB, is recommended to achieve integrated pest management.     

Weed control and yield response to mesotrione in maize (Zea mays)

Mesotrione has recently been registered for weed control in maize in Ontario, Canada; however, there is still little information on the doses required to provide 90% control for the complete spectrum of broadleaved weeds that the product controls. Our objective was to determine mesotrione doses that would provide at least 90% control of four economically important weeds, without impacting final maize yield by more than 5% in comparison to a weed-free control. Sixteen field trials were conducted at six Ontario locations in 1999–2001 to evaluate the effectiveness of mesotrione at doses ranging from 9 to 280 g ai ha⁻¹. The doses required to reduce weed biomass by at least 90% (I₉₀) varied with location and year, and for common lambsquarters and velvetleaf differed by application timing. For lambsquarters, the estimated doses required ranged from 10 to 1984 g ai ha⁻¹ for preemergence applications and 15–38 g ai ha⁻¹ for postemergence applications. Doses of 45 and 19–243 g ai ha⁻¹ were required to effectively reduce the biomass of redroot pigweed. Velvetleaf was effectively controlled preemergence with 288 g ai ha⁻¹ and postemergence with 31 g ai ha⁻¹ of mesotrione. Final maize yield was only reduced by more than 5% of a weed-free control when a dose of less than 35 g ai ha⁻¹ of mesotrione was applied. These results show that biologically effective weed control with reduced doses of mesotrione is possible depending on the spectrum of broadleaved weed species present in the field.     

Use of fluorescence to determine reduction in Bemisia tabaci (Hemiptera: Aleyrodidae) nymph feeding when exposed to cyantraniliprole and imidacloprid through systemic applications

The Bemisia tabaci whitefly is an important pest of many agricultural crops. Direct feeding by this pest can cause physiological plant symptoms including irregular ripening in tomatoes and silverleaf disorder in squash. In addition, B. tabaci can transmit more than 100 plant viruses that cause severe diseases that affect crop yield and quality. Insecticides are often applied to control this pest and they may be applied to the foliage and/or to the soil. Insecticides that kill quickly or cause feeding cessation reduce the damage caused by B. tabaci on the host plant most effectively. In this study fluorescence was used to assess B. tabaci feeding and to determine the effect of systemically applied insecticides on feeding by the pest. Cyantraniliprole (Verimark™) and imidacloprid (AdmirePro^®) produced a rapid reduction in B. tabaci feeding. At 24 h after a systemic application, the percentage of whitefly nymphs still feeding in plants treated with cyantraniliprole (anthranilic diamide) and imidacloprid (neonicotinoid) were 19% and 33%, respectively. Both products showed a good reduction in insect feeding and since they have different modes of action they should be considered as rotational partners for B. tabaci control in areas where there is no resistance to neonicotinoid insecticides. While the fluorescein sodium salt cannot be used to trace the uptake of insecticides, it has been shown to reliably demonstrate feeding cessation of whitefly nymphs after foliar and systemic applications of insecticides.     

Insecticide resistance in Brazilian populations of the cotton leaf worm, Alabama argillacea

The cotton leaf worm, Alabama argillacea, is a key cotton pest in Brazil and is managed with repeated insecticide applications. Reports of insecticide control failures have recently increased, particularly with pyrethroids. The present work assessed the resistance status of A. argillacea to a number of different insecticides currently used in cotton crops. Bioassays were conducted to estimate the response of 2nd-instar A. argillacea populations to deltamethrin, chlorpyrifos, endosulfan, abamectin and spinosad. A leaf dip bioassay with diluted insecticide formulations was performed in the laboratory with five to nine populations depending on the insecticide. LC₅₀ values were estimated by probit analysis after correction for control mortality data and used to calculate the resistance ratios (RR). All assessed populations exhibited varied and significant levels of resistance to all insecticides tested, but only moderate levels of resistance to deltamethrin were observed (RR = 52.3). The LC₅₀ values for deltamethrin were higher than 30 mg/l for most populations, and above the field rate (12.5 mg/l). This suggests that the frequency of resistant individuals in these populations was likely above the critical frequency. There was low to moderate resistance to abamectin, chlorpyrifos, endosulfan and spinosad formulations (the highest RRs observed were 4.2, 8.4, 11.1 and 23.5, respectively). Despite the moderate levels of resistance to pyrethroids in A. argillacea, overall results indicate the presence of low to moderate resistance of A. argillacea to insecticides currently used against cotton pests in Brazil.     

Effects of nitrogen rate on nitrate–nitrogen accumulation in forage kale and rape crops

Nitrogen fertilizer is applied to supplement soil nitrogen supply to maximize forage brassica crop dry-matter production. However, nitrogen fertilizer applications in excess of that required to maximize growth result in potentially toxic nitrate–nitrogen (NO₃–N) concentrations in grazeable plant tissues. Three experiments, two for forage kale at Lincoln (Canterbury) and one for forage rape at Hastings (Hawke's Bay) in New Zealand were grown under different rates of nitrogen (0–500 kg N ha⁻¹) to determine the effect of different rates of nitrogen on NO₃–N content of different plant parts of the crops. One of the kale experiments was grown with either full irrigation or no rain and no irrigation over summer, hereafter referred to as summer drought. The NO₃–N concentration on a whole plant (weighted average) basis increased from 0·1 mg g⁻¹ dry matter for the control plots to 2·30 mg g⁻¹ for the 500 kg N ha⁻¹ plots for forage kale. It increased from 0·99 for the control plots to 3·37 mg g⁻¹ for the 200 kg N ha⁻¹ plots for forage rape crops. However, NO₃–N concentration increased with N supply under the summer-drought plots from an average of 0·33 mg g⁻¹ when ≤120 kg N ha⁻¹ was applied to 2·30 mg g⁻¹ for the 240 kg N ha⁻¹ treatments but was unaffected by N supply under irrigation. The NO₃–N concentrations were higher in the stems and the petiole (which included the midrib of the leaf) than leaves in all three experiments. The NO₃–N concentration was highest at the bottom of the kale stem and decreased towards the top. We recommend N application rates based on soil tests results, and for conditions similar to the current studies up to 300 kg N ha⁻¹ under irrigation and adjusted lower N rates for regions prone to dry summers.     

The Toxicity and Detoxifying Mechanism of Cycloxaprid and Buprofezin in Controlling Sogatella furcifera (Homoptera: Delphacidae)

The effects of cycloxaprid (a modified neonicotinoid insecticide) and buprofezin (a thiadiazine insecticide) on mortality of the white-backed planthopper (WBPH), Sogatella furcifera, were determined in laboratory assays. Cycloxaprid killed WBPH nymphs and adults but buprofezin killed only nymphs, and cycloxaprid acted faster than buprofezin. One day after infestation, mortality of third-instar nymphs was >65% with cycloxaprid at 125 mg liter⁻¹ but was <38% with buprofezin at 148 mg liter⁻¹. By the 4th day after infestation, however, control of nymphs by the two insecticides was similar, and cycloxaprid at 125 mg liter⁻¹ caused ≥80% mortality of adults but buprofezin at 148 mg liter⁻¹ (the highest rate tested) caused almost no adult mortality. LC₅₀ values for cycloxaprid were lowest with nymphs, intermediate with adult males, and highest with adult females. Although buprofezin was slower acting than cycloxaprid, its LC₅₀ for nymphs 5 d after infestation was 3.79-fold lower than that of cycloxaprid. Mean carboxylesterase (CarE) specific activity of nymphal WBPH treated with cycloxaprid and buprofezin was higher than that of control, but there was no significant difference between cycloxaprid and control (no insecticide), and it was significantly higher for buprofezin than those of cycloxaprid and control. For glutathione S-transferase and mixed function oxygenase, the specific activity of nymphal WBPH treated with buprofezin was significantly higher than those of cycloxaprid and control, too.     

Quinoa (Chenopodium quinoa Willd.) protein hydrolysates with in vitro dipeptidyl peptidase IV (DPP-IV) inhibitory and antioxidant properties

The potential of quinoa to act as a source of dipeptidyl peptidase IV (DPP-IV) inhibitory and antioxidant peptides was studied. A quinoa protein isolate (QPI) with a purity of 40.73 ± 0.90% was prepared. The QPI was hydrolysed at 50 °C for 3 h with two enzyme preparations: papain (P) and a microbial papain-like enzyme (PL) to yield quinoa protein hydrolysates (QPHs). The hydrolysates were evaluated for their DPP-IV inhibitory and oxygen radical absorbance capacity (ORAC) activities. Protein hydrolysis was observed in the QPI control, possibly due to the activity of quinoa endogenous proteinases. The QPI control had significantly higher DPP-IV half maximal inhibitory concentrations (IC₅₀) and lower ORAC values than QPH-P and QPH-PL (P < 0.05). Both QPH-P and QPH-PL had similar DPP-IV IC₅₀ and ORAC values. QPH-P had a DPP-IV IC₅₀ value of 0.88 ± 0.05 mg mL⁻¹ and an ORAC activity of 501.60 ± 77.34 μmol Trolox equivalent (T.E.) g⁻¹. To our understanding, this is the first study demonstrating the in vitro DPP-IV inhibitory properties of quinoa protein hydrolysates. QPHs may have potential as functional ingredients with serum glucose lowering properties.     

Effects of 1,3-dichloropropene on nematode,weed seed viability and soil-borne pathogen

1,3-dichloropropene (1,3-D, C₃H₄Cl₂) is one of the potential candidates as soil disinfectant since the restriction of methyl bromide (MeBr) in soil fumigation due to its ecological risk. Its nematode, soil-borne pathogen and weed control efficacies were evaluated in a laboratory dose-response study and in two commercial tomato fields. Laboratory studies found that the seeds of Digitaria chinensis Hornem. were the most sensitive to soil fumigation with 1,3-D, followed by Eleusina indica (Linn.) Gaertn., Echinochloa crusgalli (L.) Beauv. and Amaranthus retroflexus L. with the LC₉₀ values between 14.23 and 73.59 mg kg⁻¹ soil. Among the pathogens, Phytophthora capsici Leonian was the most sensitive and Fusarium oxysporum f. sp. fragariae was the least sensitive to 1,3-D fumigation with the LC₅₀ values were 0.24 and 1.55 g m⁻². Rhizoctonia solani Kühn., Phytophthora nicotianae var. nicotianae and Botrytis cinerea Persoon exhibited intermediate susceptibility. Field trials revealed that 1,3-D applied to the field at 180, 120 and 80 L ha⁻¹ could suppress Meloidogyne incognita root galling while maintaining high tomato marketable yields, better than Dazomet at the concentration of 400 kg ha⁻¹. Our results indicated that 1,3-D was an excellent nematicide and could provide good to moderate weed and pathogen control. Based on our results, 1,3-D, in combination with other alternatives to MeBr is recommended to reach an integrated pest management.     

The effects of nitrogen rate and the ratio of NO3:NH4 on Bemisia tabaci populations in hydroponic tomato crops

Nitrogen fertilization is one of the factors that influences Bemisia tabaci (Gennadius) population density. The aim of this study was to determine the effects of three N application rates (75, 205 and 335 mg/l) and three ratios of NO₃⁻:NH₄⁺ ions (92:8, 75:25 and 55:45) in standard nutrient solution (205 mg/l N) on the population density of B. tabaci. The experiments were conducted on spring-summer hydroponic crops of tomato. The effect of plant stratum on the whitefly population was also determined. The aggregation of B. tabaci adults as well as their oviposition rate was higher at 205 and 335 mg/l N than on plants grown at 75 mg/l N. By the end of the experiment (60 d after infestation), the number of nymphs on plants at 205 mg/l N was higher than on plants at 75 mg/l N. The number of pupae was lowest on plants supplied with 75 mg/l N. An increase in NH₄⁺ percentage in standard nutrient solution (from 25% to 45% of the total N) reduced adult population density and oviposition rate. The density of nymphs and pupae, at 60 d after infestation, was lower on the tomato plants grown at 75:25 and 55:45 NO₃⁻:NH₄⁺ ratios compared to the 92:8 ratio. The 75:25 and 55:45 NO₃⁻:NH₄⁺ ratios resulted in a higher incidence of blossom-end rot of tomato fruit, with a lower incidence of disorder at 75:25 than at the 55:45 ratio. Plant stratum influenced adult whitefly distribution in two years of the study. Middle stratum leaves were more attractive to adults in both years. The results demonstrate the effects of N fertilization (N rate and the ratio of NO₃⁻:NH₄⁺) and plant stratum on B. tabaci population density.     

Acute toxicity and sublethal effects of methoxyfenozide and thiodicarb on survival,development and reproduction of Helicoverpa armigera (Lepidoptera: Noctuidae)

The cotton bollworm Helicoverpa armigera (Hubner) is one of the most destructive pest insects in Iran and many other countries. In this study, lethal and sublethal effects of methoxyfenozide, and thiodicarb were evaluated against H. armigera larvae that fed on insecticide-treated artificial diet. The effects of methoxyfenozide and thiodicarb were assessed in 3rd instars. Methoxyfenozide and thiodicarb showed LC₅₀ values of 4 and 639 mg a.i./ml, respectively, in H. armigera larvae. Sublethal effects on development, adult longevity, and reproduction were observed in H. armigera larvae that survived exposure to an LC₃₀ of the insecticides. Larvae that were exposed to an LC₃₀ concentration of methoxyfenozide exhibited lower pupal weight and increased larval and pupal developmental times compared with thiodicarb treated larvae or control larvae. Adults that were exposed as larvae to an LC₃₀ concentration of methoxyfenozide or thiodicarb showed reduced fecundity (35% and 30%, respectively) compared to control adults. The tested insecticides significantly reduced adult longevity. The longevity of adult females that as larvae were treated with an LC₃₀ concentration of methoxyfenozide or thiodicarb was reduced by 28% and 23%, respectively, in comparison to control females. We predict that the combination of lethal and sublethal effects of the insecticides, especially methoxyfenozide, will induce significant effects on field population dynamics of H. armigera.