Depression of the minimum concentration of methyl bromide effective against diapausing warehouse moth larvae at 15°c by prior exposure at a moderate concentration

Warehouse moth (Ephestia elutella) larvae in diapause were exposed at 15°C to methyl bromide at 8 mg litre^?1 for 14.5 h and then immediately exposed at a lower concentration. The exposure at 8 mg litre^?1 killed 44–69% of the larvae treated. Subsequent concentrations down to 1.1 mg litre^?1 obeyed Haber's rule (concentration × time= k, a constant for mortality), but a higher concentration-time product (ct) was required for over 90% kill at 0.8 mg litre^?1. Only concentrations down to 1.9 mg litre^?1 obey Haber's rule if there is no prior exposure at a higher concentration. Although minimum effective concentrations are lower at 15°C than at 25°C, exposure at a higher concentration depresses the subsequent level to a similar extent at each temperature. The contribution to the efficacy of a treatment, of low concentrations persisting at the end of fumigation, is thus likely to be even greater at moderate to low temperatures than at 25°C. The implications for the development of resistance to methyl bromide are discussed.     

Modelling the effects of sub-lethal doses of herbicide and nitrogen fertilizer on crop–weed competition

The effects of sub‐lethal dose of herbicide and nitrogen fertilizer on crop–weed competition were investigated. Biomass increases of winter wheat and a model weed, Brassica napus, at no‐herbicide treatment with increasing nitrogen were successfully described by the inverse quadratic model and the linear model respectively. Increases in weed competitivity (β₀) of the rectangular hyperbola and parameter B in the dose–response curve for weed biomass, with increasing nitrogen were also successfully described by the exponential model. New models were developed by incorporating inverse quadratic and exponential models into the combined rectangular hyperbola with the standard dose–response curve for winter wheat biomass yield and the combined standard dose—response model with the rectangular hyperbola for weed biomass, to describe the complex effects of herbicide and nitrogen on crop–weed competition. The models developed were used to predict crop yield and weed biomass and to estimate the herbicide doses required to restrict crop yield loss caused by weeds and weed biomass production to an acceptable level at a range of nitrogen levels. The model for crop yield was further modified to estimate the herbicide dose and nitrogen level to achieve a target crop biomass yield. For the target crop biomass yield of 1200 g m^?2 with an infestation of 100 B. napus plants m^?2, the model recommended various options for nitrogen and herbicide combinations: 140 and 2.9, 180 and 0.9 and 360 kg ha^?1 and 1.7 g a.i. ha^?1 of nitrogen and metsulfuron‐methyl respectively.     

Effects of the springtail Folsomia fimetaria and the nematode Aphelenchus avenae on Rhizoctonia solani stem infection of potato at temperatures of 10 and 15°C

Effects of mycophagous soil mesofauna on Rhizoctonia solani infection of potato stems were investigated in two experiments carried out in growth chambers at 10 and 15°C. The springtail Folsomia fimetaria and the nematode Aphelenchus avenae were selected as organisms suppressive to R. solani . Reduction in Rhizoctonia stem infection by mycophagous soil mesofauna was equally effective at 10 and 15°C. F. fimetaria tended to be more effective than A. avenae , but the best control was obtained when both organisms were present in the soil at high densities.     

Competition between annual weeds and vining peas grown at a range of population densities: effects on the crop

Competition between annual weeds and vining peas (Pisum sativum L.) at five target population densities between 11 and 194 plants/m² was examined by means of periodic destructive sampling of weedy and weed-free plots. A further area of each plot was cut and vined to assess yields. Weeds impaired vegetative development, particularly by reducing tillering in low density crops. This resulted in weedy plots having fewer pods per plant at harvest but a lower proportion of flat pods than weed-free plots. Weeds had no effect on numbers or weights of peas in full pods nor on tenderometer values of samples of vined peas. Adverse effects of weeds on the growth of individual crop plants decreased with increasing crop density. However, at lower crop densities many of the additional pods on weed-free plots contributed little to vined yield, while at higher densities, direct or indirect effects of weeds increased the problem of maintaining sufficient photosynthetic area during pod swelling to prevent pod abscission and poor ovule development. Regression analysis of yield on crop density and of yield on numbers of pods per plant showed that vined yield per hectare was reduced by weeds by a constant amount across the range of densities and numbers of pods examined. Vining throughput was also reduced in weedy as compared with weed-free crops, even on high density plots where little or no weed vegetation remained at harvest. In general, weed presence had effects similar to those caused by increasing crop density, but without the additional contribution to yield made by extra plants. Higher density crops suppressed weeds very effectively but were no less vulnerable to yield loss than those of lower density; they therefore merit just as much attention to effective weed control as crops suffering more visibly from competition by weeds.     

Competition between annual weeds and vining peas grown at a range of population densities: effects on the weeds

Linear regression of dry weight of weeds against crop density, together with the use of diversity indices and principal component analysis were used to derive information about changes in the behaviour of annual weeds over the growing season and in response to a wide range of crop densities in vining peas Pisum sativum L. Using linear regression it was possible to quantify reductions in weed dry weights per unit increase in crop plant density The ‘weed losse’ factor was acceptably consistent between experiments. Indices examining richness and evenness showed that numbers of weed species declined with increasing crop density and as the season progressed, but although species evenness became less at successive sampling dates the presence of a pea crop, whatever its density, did not radically alter the composition of the weed flora. Principal component analysis demonstrated that although there was competition within the weed flora, the crop did not replace the dominant weed species on high density plots, but reduced growth of all weed species alike.     

Investigation on the storage possibilities of <Emphasis Type="Italic">Rhyzobius lophantae</Emphasis> Blaisdell (Coleoptera: Coccinellidae) at different temperatures and periods

Storage of natural enemies at low temperatures has an important role in biological control programs. It is an very critical factor that the stored individuals is used without losing their characters such as longevity, survival, fecundity, etc. In this study, the storage possibilities of Rhyzobius lophantae Blaisdell (Coleoptera: Coccinellidae) adults under low temperatures (4 °C and 12 °C) for four different periods (10, 20, 30 and 40 days) were investigated. The survival rates and life span of adults (male and female), daily and total egg numbers laid by females stored at 4 °C and 12 °C for 10, 20, 30 and 40 days were determined. The survival rates of adults stored at 4 °C for 10 and 20 days were found to be 94.54% and 58.02% respectively. However, no adults stored at 4 °C for 30 and 40 days were observed to survive. The highest survival rate was 88% for the adults stored at 12 °C for 10 days. The average daily laid egg numbers were 12.51 and 9.37, and total egg numbers were 850.30 and 738.30 of adults stored at 4 °C for 10 and 20 days, respectively. The decrease in daily and total egg numbers of females stored at 12 °C was observed with increasing storage period. There was no significant difference in longevities of male and female stored at 4 °C and 12 °C. These results show that short-term storage at low temperatures does not affect certain properties of the predator when compared to 12 °C and storage periods.     

Lethal and sublethal effects of three insecticides on the aphid parasitoid, <Emphasis Type="Italic">Lysiphlebus fabarum</Emphasis> Marshall (Hymenoptera: Aphidiidae)

Lysiphlebus fabarum Marshall is the main parasitoid of the black bean aphid, Aphis fabae Scopoli. Lethal and sublethal effects of insecticides, thiacloprid+deltamethrin, pirimicarb and pymetrozine were evaluated on the parasitoid under laboratory conditions. One-day-old mummies were exposed to the recommended field concentration of either insecticides via dipping method. Adult emergences were reduced by 82.67, 19.98 and 10.67 % for thiacloprid+deltamethrin, pirimicarb and pymetrozine treatments, respectively. Thiacloprid+deltamethrin had the most adverse effect on the fecundity of the emerged females, while pirimicarb and pymetrozine did not have such effects. According to International organization for biological control (IOBC) insecticide toxicity classification, thiacloprid+deltamethrin resulted to be moderately harmful (E = 97.39%), whereas pirimicarb (E = 15.78%) and pymetrozine (E = 5.15%) were harmless. Thiacloprid+deltamethrin negatively affected five of the estimated demographic parameters (GRR, R ₀ , r _m , λ and T ). Pirimicarb negatively affected GRR, R ₀ and T, while it had no adverse effects on r _m and λ. None of the studied demographic parameters were affected by pymetrozine. Our results suggest that pirimicarb and pymetrozine can be considered as safe for L. fabarum, but that thiacloprid+deltamethrin can have serious detrimental of this parasitoid in the field.     

Thermal effects on the development of <Emphasis Type="Italic">Bactrocera dorsalis</Emphasis> (Hendel) (Diptera: Tephritidae) and model validation in Taiwan

The oriental fruit fly, Bactrocera dorsalis (Hendel), is a major polyphagous insect pest with a worldwide distribution. The effects of temperature on stage-specific development in B. dorsalis were investigated at eight constant temperatures (13.0 °C, 14.4 °C, 16.2 °C, 19.5 °C, 23.8 °C, 27.7 °C, 31.8 °C and 34.8 °C). B. dorsalis developed successfully from the egg stage to the adult stage at all the tested temperatures, except at the lowest temperatures (13.0 °C and 14.4 °C). Stage-specific lower developmental thresholds and thermal constants were determined using linear regression. The lower and higher temperature threshold (TL and TH, respectively) were estimated using the Sharpe-Schoolfield-Ikemoto model. The lower developmental threshold and thermal constant from egg to adult emergence were 9.8 °C and 325.5 degree-days, respectively. The intrinsic optimum temperatures of the egg, larval, pupal and egg to pupal stage were 20.7 °C, 21.8 °C, 21.1 °C, and 22.4 °C, respectively. The temperature range of the B. dorsalis total immature stage from TL to TH was 20.4 °C (13.8 °C - 34.2 °C). The stage-specific developmental completion of B. dorsalis was determined using a two-parameter Weibull function. The daily adult emergence frequency of B. dorsalis was estimated in relation to adult age and temperature using non-linear developmental rate functions and the Weibull function. The date of cumulative 50% adult emergence estimated using non-linear functions was approximately one day earlier than the experimentally observed date. Thermal performance was compared among B. dorsalis populations from different locations.     

Artificial diet based investigation on the impact of purified Cry1Ac,Cry1Fa and Cry2Ab on the survival and reproductive performance of adult green lacewing, <Emphasis Type="Italic">Chrysopa pallens</Emphasis> (Rambur) (Neuroptera: Chrysopidae)

The green lacewing Chrysopa pallens (Rambur) (Neuroptera: Chrysopidae) is a common and abundant predator in many cropping systems in palearctic realm and it’s conservation is helpful in sustainable pest management in agro-ecosystem. Prior to commercialization of Bt crops in any agro- ecosystem, it is necessary to evaluate the impact of Cry proteins upon non-target organisms especially biological control agents (BCA). In present study an artificial diet consisting of shrimp, beef, beef liver and egg yolk was developed to mass-rear C. pallens for its use as biological control agents in sustainable pest management. Moreover, an artificial diet based risk assessment protocol was developed to investigate the impact of Cry1Ac, Cry1Fa and Cry2Ab on the survival and reproductive performance of C. pallens adults. C. pallens was fed on diets incorporated with Cry proteins and without addition of Cry proteins (control). The same diet containing boric acid was served as a positive control. Temporal stability, bioactivity and intake of Cry proteins by C. pallens were confirmed using double-antibody sandwich, enzyme-linked immunosorbent assay and bioactivity verification bioassays. Survival and reproductive performance of C. pallens, e.g., pre-oviposition period, daily fecundity, total fecundity and 30-day old adults dry weights, exhibited non-significant differences (p?>?0.05) for the diets containing Cry1Ac, Cry1Fa and Cry2Ab (50 μg/g) against Control. However, significant reduction in survival and reproductive performance (p?<?0.05) was observed in positive control. Our findings reveal that artificial diet is a good source of nutritional requirement with enhanced survival and reproductive performance of C. pallens and can be used for mass rearing of predator in case of natural diet scarcity and Cry proteins are safe for adult C. pallens and Bt crops cultivation help in predators conservation in sustainable agriculture.     

An insight on the ethylene biosynthetic pathway of two major fruit postharvest pathogens with different host specificity: <Emphasis Type="Italic">Penicillium digitatum</Emphasis> and <Emphasis Type="Italic">Penicillium expansum</Emphasis>

Although several studies have reported the stress-induced ethylene burst occurring in fruit in response to pathogen attack, relatively little is known about the role of this hormone in the fungal metabolism of many postharvest pathogens. To gain further knowledge, we investigated the ethylene production capacity and which ethylene biosynthetic pathways (including the 1-aminocyclopropane-1-carboxylic acid (ACC), the 2-oxoglutarate (OXO) and the 2-keto-4-methylthiobutyric acid (KMBA) pathways) were used under different in vitro conditions by Penicillium digitatum and Penicillium expansum. Both pathogens were capable of producing ethylene in vitro using different pathways but were dependant on the growing conditions. For instance, both the KMBA and the OXO pathways seemed to be responsible for ethylene biosynthesis in P. digitatum when grown in more stressful conditions (limited surface and nutrient availability as in PDA tubes), while only the KMBA pathway seemed to be activated under other culture conditions (i.e. on PDA plates) or when the fungal mycelium was placed within aqueous solutions containing ethylene precursors. In contrast, the KMBA appeared to be the exclusive pathway responsible for ethylene production by P. expansum yet only when the fungal mycelium was in contact with aqueous solutions containing ethylene precursors. In both pathogens, ethylene production seemed to be synchronized with certain stages of fungal growth rather than conidiation, suggesting a putative role of this hormone in fungal metabolism.