Bioassay Trials Research Articles

Salinity stress alters plant-mediated interactions between above- and below-ground herbivores

Below-ground herbivory impacts plant development and often induces systemic responses in plants that affect the performance and feeding behavior of above-ground herbivores. Meanwhile, pest-damaged root tissue can enhance a plant's susceptibility to abiotic stress such as salinity. Yet, the extent to which herbivore-induced plant defenses are modulated by such abiotic stress has rarely been studied. In this study, we examine whether root feeding by larvae of the turnip moth, Agrotis segetum (Lepidoptera: Noctuidae) affects the performance of the above-ground, sap-feeding aphid Aphis gossypii (Hemiptera: Aphididae) on cotton, and assess whether those interactions are modulated by salinity stress. In the absence of salinity stress, A. segetum root feeding does not affect A. gossypii development. On the other hand, under intense salinity stress (i.e., 600 mM NaCl), A. segetum root feeding decreases aphid development time by 16.1 % and enhances fecundity by 72.0 %. Transcriptome, metabolome and bioassay trials showed that root feeding and salinity stress jointly trigger the biosynthesis of amino acids in cotton leaves. Specifically, increased titers of valine in leaf tissue relate to an enhanced performance of A. gossypii. Taken together, salinity stress alters the interaction between above- and below-ground feeders by changing amino acid accumulation. Our findings advance our understanding of how plants cope with concurrent biotic and abiotic stressors, and may help tailor plant protection strategies to varying production contexts.

Epiphytic yeasts as potential antagonists against Fusarium head blight of wheat (Triticum aestivum L.) caused by Fusarium graminearum sensu stricto

Fusarium head blight (FHB), caused by Fusarium graminearum , is a significant disease of wheat in all wheat-growing areas. In this study, we screened a total of 344 yeast epiphytes isolated from cereal and weed plants against F. graminearum in vitro . Twelve potential antagonists were selected and subjected to in planta screening trials. In the in vitro bioassay trials, the highest average percentage inhibition of 64.31% (Isolate MGO2) was observed. The in vivo evaluation of the best 12 isolates showed a reduction in FHB severity and deoxynivalenol (DON) concentration of up to 15.62% (Isolate WL3) and 28.96% (Isolate SCH7), respectively. We observed a positive correlation between Area Under the Disease Progress Curve (AUDPC) and percentage seed infection. The 100-seed weight, however, was negatively correlated to both the AUDPC and the percentage seed infection. The best three yeast antagonists were selected based on AUDPC units, percentage seed infection, and 100-seed weight parameters and were identified as Papiliotrema flavescens (Isolates WL3 and WL6) and Pseudozyma sp. (Isolate MGO1) using 16S rRNA sequence analysis. These three yeast antagonists showed biocontrol efficacy against F . graminearum, and their incorporation in an integrated management programme could provide enhanced FHB control. To the best of our knowledge, this is the first report of yeast epiphytes isolated from Panicum maximum, and Ophiopogon japonicus tested as potential biological control agents against F. graminearum.

Miticidal activity of fenazaquin and fenpyroximate against Varroa destructor, an ectoparasite of Apis mellifera.

BACKGROUNDThe Varroa mite (Varroa destructor) is an ectoparasite that can affect the health of honey bees (Apis mellifera) and contributes to the loss of colony productivity. The limited availability of Varroacides with different modes of action in Canada has resulted in the development of chemical resistance in mite populations. Therefore, an urgent need to evaluate new potential miticides that are safe for bees and exhibit high efficacy against Varroa exists. In this study, the acute contact toxicity of 26 active ingredients (19 chemical classes), already available on the market, was evaluated on V. destructor and A. mellifera under laboratory conditions using an apiarium bioassay. In this assay, groups of Varroa‐infested worker bees were exposed to different dilutions of candidate compounds. In semi‐field trials, Varroa‐infested honey bees were randomly treated with four vetted candidate compounds from the apiarium assay in mini‐colonies.RESULTSAmong tested compounds, fenazaquin (quinazoline class) and fenpyroximate (pyrazole class) had higher mite mortality and lower bee mortality over a 24 h exposure period in apiariums. These two compounds, plus spirotetramat and spirodiclofen, were selected for semi‐field evaluation based on the findings of the apiarium bioassay trials and previous laboratory studies. Consistent with the apiarium bioassay, semi‐field results showed fenazaquin and fenpyroximate had high efficacy (>80%), reducing Varroa abundance by 80% and 68%, respectively.CONCLUSIONThese findings suggest that fenazaquin would be an effective Varroacide, along with fenpyroximate, which was previously registered for in‐hive use as Hivastan. Both compounds have the potential to provide beekeepers with an alternative option for managing Varroa mites in honey bee colonies. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Development of aquaculture protocols and gonadal differentiation of green sunfish (Lepomis cyanellus)

We provide detailed rearing methods and describe green sunfish (Lepomis cyanellus) gonadal development and histological differentiation for both sexes. Developing in-depth aquaculture protocols and describing the gonadal differentiation of green sunfish could facilitate strategies to control nuisance populations, enhance stocking programs, and provide information for this species' use in bioassay trials or toxicology studies. Our methods resulted in consistent year-round production of green sunfish and allowed us to identify the timing of their gonadal differentiation through histological assessment. Our spawning methods provided year-round volitional spawns from green sunfish broodstock. Our rearing methods involved weaning larval green sunfish off live nauplii and onto only artificial diets by 37 days post-hatch (dph). Most of the offspring generation reached sexual maturity by 213 dph. Green sunfish are gonochoristic, with testes and ovaries differentiating directly from undifferentiated gonads. Ovaries begin to differentiate by 39 dph and testes begin to differentiate by 69 dph. This information can provide biologists consistent means to produce this Centrachid and understand their gonadal development.

Assessment of probiotic bacteria from marine coasts against Vibrio parahaemolyticus (AHPND strains) in Litopenaeus vannamei

Acute hepatopancreatic necrosis disease (AHPND) outbreaks caused by Vibrio parahaemolyticus (VPAHPND) emerged in Mexico in 2013, causing a 65% drop in shrimp tonnage produced. This work aimed to isolate bacterial strains from Mexican marine ecosystems antagonistic towards VPAHPND. Among 258 bacterial isolates, only 17 showed antagonist activity in vitro, but only (Bacillus pumilus-Y100, B. pumilus-Y119, B. pumilus-43, Vibrio alginolyticus-32a and V. campbellii-H-A) were chosen for bioassay challenge. These probiotic bacteria were sprayed on commercial shrimp pellets, and experimental infection was carried out by immersing the shrimp in VPAHPND inoculum. Bacterial strains 32a, Y100 and H-A significantly reduced the cumulative mortality of shrimp exposed to AHPND (4.76%, 12.54% and 16% respectively). Y119 and 43 did not show any beneficial effect against VPAHPND but were pathogenic in previous assays with post-larval white shrimp and bioassay trials. Concerning the qPCR results, the presence of low numbers of DNA copies of VPAHPND was found only in the H-A trial, suggesting that H-A exerts a bacteriostatic effect; in contrast, the results for 32a, Y100, Y119 and 43 were negative, indicating that these strains exhibited a microbicidal effect against VPAHPND. The histopathological results agreed with the qPCR results and did not show compatible lesions caused by AHPND. In conclusion, 32a and Y100 seem to be the first antagonists to specifically inhibit VPAHPND in vivo.

Inventory of Varroa destructor susceptibility to amitraz and tau-fluvalinate in France.

Varroa destructor is one of the greatest threats for the European honeybee, Apis mellifera. Acaricides are required to control mite infestation. Three conventional chemical acaricide substances are used in France: tau-fluvalinate, flumethrin and amitraz. Tau-fluvalinate was used for over 10years before experiencing a loss of effectiveness. In 1995, bioassay trials showed the first mite resistance to tau-fluvalinate. In some countries, amitraz was widely used, also leading to resistance of V. destructor to amitraz. In France, some efficiency field tests showed a loss of treatment effectiveness with amitraz. We adapted the bioassay from Maggi and collaborators to determine mite susceptibility to tau-fluvalinate and amitraz in France in 2018 and 2019. The lethal concentration (LC) which kills 90% of susceptible mite strains (LC90) is 0.4 and 12µg/mL for amitraz and tau-fluvalinate, respectively. These concentrations were chosen as the determining factors to evaluate mite susceptibility. Some mites, collected from different apiaries, present resistance to amitraz and tau-fluvalinate (71% of the mite samples show resistance to amitraz and 57% to tau-fluvalinate). As there are few active substances available in France, and if mite resistance to acaricides continues to increase, the effectiveness of the treatments will decrease and therefore more treatments per year will be necessary. To prevent this situation, a new strategy needs to be put in place to include mite resistance management. We suggest that a bioassay would be a good tool with which to advise the policymakers.

Biochar enriched with organic fertilizer improves the survival and growth rate of Anthocepalus cadamba seedlings planted on degraded spodosols

Abstract. Syahrinudin, Hartati W, Sudarmadji T, Krisdianto N, Ibrahim. 2019. Biochar enriched with organic fertilizer improves the survival and growth rate of Anthocepalus cadamba seedlings planted on degraded spodosols. Biodiversitas 20: 3741-3750. The application of biochar for the improvement of soil properties and fertility has drawn enormous interest worldwide nowadays and numerous application options are now available. This research was aimed to evaluate the effects of the application of biochar and organic fertilizers on the survival and growth of Anthocepalus cadamba seedlings planted on degraded spodosols soil on bioassay trial in the nursery. Bioassay trial was carried out in the nursery of Faculty of Forestry, Mulawarman University, Samarinda, Indonesia, employing a 2-factors Completely Randomized Design (CRD) with factor 1 was the rate of biochar application (i.e. six levels of treatment: 0 (control), 2, 5, 10, 25 and 100%v of biochar), and factor 2 (enrichment of organic fertilizers, i.e. with enrichment and without enrichment), and each treatment combination had 3 replications. The results showed that biochar application alone improved height and diameter growth rate of A. cadamba seedlings by 253% and 116% of control treatment (without biochar), respectively. Enrichment of organic fertilizers gave further improvement in height and diameter growth rate of A. cadamba seedlings to 386% and 150% of control treatment (without biochar), respectively. Furthermore, biochar application improved survival and biomass growth rate of the seedlings. Enrichment of organic fertilizers into biochar improved not only seedling growth rate but also more interestingly the carrying capacity of spodosols to biochar application rate. We concluded that biochar application complemented with enrichment of organic fertilizers on spodosols is highly promising for the improvement of both soil carbon sequestration and plant growth performance.

Ecotoxicological risk assessment of revegetated bauxite residue: Implications for future rehabilitation programmes

Around 3 billion tonnes of bauxite residue (BR), the by-product of alumina extraction, have been produced and stockpiled worldwide, representing a potential risk for the environment due to the high alkalinity and the presence of relatively high concentrations of trace elements. Phytoremediation (or simply revegetation) is regarded as the most promising in situ remediation option to mitigate the environmental risk that might arise from the land-disposal of BR. Rehabilitation strategies (including the incorporation of amendments such as gypsum and organic matter) have been employed to address the main limitations to plant establishment and growth on BR, typically the high alkalinity, salinity and sodicity. However, the potential for trace element uptake and phytotoxicity have been largely unreported in revegetated BRs.In order to assess the ecotoxicological risk, samples of previously revegetated BR were collected from the field, characterized in the laboratory, and used to conduct ex-situ plant bioassays (Phytotoxkit™ and the RHIZOtest). Without rehabilitation, fresh BR severely inhibits seed germinationand root/shoot development in test species Lepidium sativum, Sinapis alba and Sorghum saccharatum. Plant uptake for Al, As, Cr, V was assessed with RHIZOtest bioassay trials with Lolium perenne and demonstrated that plants exposed to fresh BR take up and translocated trace elements to their shoots at concentrations (As = 4.13 mg/kg dm; Cr = 3.29 mg/kg dm; V = 85.66 mg/kg dm) exceeding phytotoxic levels (vanadium) or maximum levels specified for animal feed (arsenic), showing visible stress symptoms in the seedlings.Conversely, revegetated BR show improved chemical properties, allow seed germination, and permits seedling growth with no evidence of trace element phytotoxicity. However, Na can be taken up at concentrations that could elicit phytotoxicity and impair the success of revegetation. For future rehabilitation programmes, direct revegetation on BR after the incorporation of amendments such as gypsum and organic matter is recommended.

BIOCHAR YANG DIPRODUKSI DENGAN TUNGKU DRUM TERTUTUP RETORT MEMBERIKAN PERTUMBUHAN TANAMAN YANG LEBIH TINGGI (BIOCHAR PRODUCED BY RETORT CLOSED DRUM KILN PROMOTES HIGHER PLANT GROWTH RATE)

ABSTRACTInterests on biochar application for the improvement of soil properties and fertily are increasing worldwide nowadays and numerous of production techniques are now available. This research was aimed at the investigation (a) on the characteristics biochar produced by 3 (three) different techniques, i.e: (1) traditional soil pit, (2) retort closed drum and (3) open drum kilns, as well as (b) on growth (height, leaf number and survival) response of Shorea leprosula seedling to 20%v biochar application on bioassay trial in the nursery. Bioassay trial was carried out in nursery of Forestry Faculty of Mulawarman University, Samarinda, Indonesia and was in accordance with Completely Randomized Design (CRD) applying 4 treatments and 3 replications.Of those 3 production techniques, retort closed drum kiln production technique was the most promising for further development and adoption providing not only that the biochar produced gave better properties and soil improvement capacity but also higher production recovery and less time and labour involvement. Furthermore, eventhough it was not statistically significant, biochar produced by retort closed drum gave better growth (height and leaf number) rate to S. leprosula seedlings in bioassay trial compared to those given by biochar produced by other techniques and without biochar treatments.

BIOCHAR YANG DIPRODUKSI DENGAN TUNGKU DRUM TERTUTUP RETORT MEMBERIKAN PERTUMBUHAN TANAMAN YANG LEBIH TINGGI (BIOCHAR PRODUCED BY RETORT CLOSED DRUM KILN PROMOTES HIGHER PLANT GROWTH RATE)

ABSTRACTInterests on biochar application for the improvement of soil properties and fertily are increasing worldwide nowadays and numerous of production techniques are now available. This research was aimed at the investigation (a) on the characteristics biochar produced by 3 (three) different techniques, i.e: (1) traditional soil pit, (2) retort closed drum and (3) open drum kilns, as well as (b) on growth (height, leaf number and survival) response of Shorea leprosula seedling to 20%v biochar application on bioassay trial in the nursery. Bioassay trial was carried out in nursery of Forestry Faculty of Mulawarman University, Samarinda, Indonesia and was in accordance with Completely Randomized Design (CRD) applying 4 treatments and 3 replications.Of those 3 production techniques, retort closed drum kiln production technique was the most promising for further development and adoption providing not only that the biochar produced gave better properties and soil improvement capacity but also higher production recovery and less time and labour involvement. Furthermore, eventhough it was not statistically significant, biochar produced by retort closed drum gave better growth (height and leaf number) rate to S. leprosula seedlings in bioassay trial compared to those given by biochar produced by other techniques and without biochar treatments.

Effectiveness of Natural Herbal Oil Formulation against White Spot Syndrome Virus in Penaeus vannamei

The Natural Herbal Oil Formulation (NHOF) have been designed to work against White Spot Syndrome Virus (WSSV) in Shrimp. The essential oil blend extracted from the following plants, Lavandula latifolia, Pinus sylvestris, Jasminum officinale, Citrus limon, Prunus avium, Viola odorata, Gardenia jasminoides, Cocos nucifera, Rosa damascene and Eucalyptus globulus, mixed together to develop as anti-WSSV product. The product were added in the feed, as feed additive. Another product developed which was applied in tank water as water supplement named as “Pondguard” (Reg no. KKP RI no. D16060285-HBC). The Pondguard is composed of three essential oils i.e., Eucalyptus globulus, Pinus sylvestris and Lavandula latifolia. A bioassay trial was conducted to determine the efficacy of developed formulation as an anti-WSSV candidate. The experimental shrimp was fed on NHOF-mixed feed and “Pondguard” applied in the tank water whereas control shrimp were fed on the regular feed. The shrimp of both experimental and control were challenged by WSSV on 15th day of feeding. Two methods of WSSV challenge were applied, per-os challenge and immersion challenge. The cumulative mortality in positive control reached up to 100% on DPI 10 whereas no mortality appeared in the experimental group and in negative control. The trial results show that the developed natural herbal formulation has significant effect against WSSV in a controlled condition.

Can insecticide-treated netting provide protection for Equids from Culicoides biting midges in the United Kingdom?

BackgroundBiting midges of the genus Culicoides Latreille, 1809 (Diptera: Ceratopogonidae) cause a significant biting nuisance to equines and are responsible for the biological transmission of African horse sickness virus (AHSV). While currently restricted in distribution to sub-Saharan Africa, AHSV has a history of emergence into southern Europe and causes one of the most lethal diseases of horses and other species of Equidae. In the event of an outbreak of AHSV, the use of insecticide treated nets (ITNs) to screen equine accomodation is recommended by competent authorities including the Office International des Épizooties (OIE) in order to reduce vector-host contact.MethodsSeven commercially avaliable pyrethroid insecticides and three repellent compounds, all of which are licensed for amateur use, were assessed in modified World Health Organization (WHO) cone bioassay trials in the laboratory using a colony line of Culicoides nubeculosus (Meigen), 1830. Two field trials were subsequently conducted to test the efficiency of treated net screens in preventing entry of Culicoides.ResultsA formulation of cypermethrin (0.15 % w/w) and pyrethrins (0.2 % w/w) (Tri-Tec 14®, LS Sales (Farnham) Ltd, Bloxham, UK) applied to black polyvinyl-coated polyester insect screen (1.6 mm aperture; 1.6 mm thickness) inflicted 100 % mortality on batches of C. nubeculosus following a three minute exposure in the WHO cone bioassays at 1, 7 and 14 days post-treatment. Tri-Tec 14® outperformed all other treatments tested and was subsequently selected for use in field trials. The first trial demonstrated that treated screens placed around an ultraviolet light-suction trap entirely prevented Culicoides being collected, despite their collection in identical traps with untreated screening or no screening. The second field trial examined entry of Culicoides into stables containing horses and found that while the insecticide treated screens reduced entry substantially, there was still a small risk of exposure to biting.ConclusionsScreened stables can be utilised as part of an integrated control program in the event of an AHSV outbreak in order to reduce vector-host contact and may also be applicable to protection of horses from Culicoides during transport.

Biochar increases soil pH, but is as ineffective as liming at controlling clubroot.

The use of pyrolysed carbon, in the form of biochar, as an agricultural soil amendment has recently gained considerable scientific interest. However, its adoption in practice has been slow due to a need to satisfy concerns about the safety of biochar and the need for more evidence of system improvements in temperate soils. Clubroot, caused by Plasmodiophora brassicae, is a disease of economic importance in Brassicaceae production systems. There is only limited plant resistance and disease limitation is currently managed via rotation breaks and liming. Biochar can alter the pH of soils so a series of glasshouse bioassay trials were established to determine if biochar could provide a similar level of clubroot control as traditional liming. Soil pH was raised from an initial pH of 5.4 to pH of 7.2 upon the addition of lime and to between 5.9 to 7.3 by the addition of biochar, without or with lime. However, the incidence of clubroot was either comparable to the lime treatment, which was similar to the unamended negative control, or exacerbated following the addition of biochar. The results support the existing knowledge of clubroot epidemiology, in that solely altering soil pH is not sufficient to manage this disease infection due to a complex interaction of nutrients, pH, moisture, and inoculum load in contaminated soil. The results highlight that further work is needed within temperate soils, as the addition of biochar to Brassicaceae production systems could potentially exacerbate both the incidence and soil load of the pathogen P. brassicae.

Herbicide Application in Precision Farming Based on Soil Organic Matter

In the present study, the influence of soil properties on pre-emergence herbicide effectiveness was estimated in bioassays. Dose-response experiments were carried out to estimate the relationship between soil organic matter content and herbicide efficacy. Two weed species (Alopecurus myosuroides and Stellaria media) and two herbicides (pendimethalin, chlorotoluron) were included in the experiments. In bioassay trials on soil with varying organic matter content, dose-response curves were estimated for pendimethalin and chlorotoluron. Effective dose (ED50) values were calculated. The experiments were conducted in a climate chamber under defined conditions. The results demonstrate that the efficacy of soil-applied herbicides is related to the soil organic matter content within agricultural fields. Therefore precise usage with variable herbicide application rates can be part of a precision farming concept. A reduction in herbicide is possible.

Pyrazine analogs are active components of wolf urine that induce avoidance and fear-related behaviors in deer.

Our previous studies indicated that a cocktail of pyrazine analogs, identified in wolf urine, induced avoidance and fear behaviors in mice. The effects of the pyrazine cocktail on Hokkaido deer (Cervus nippon yesoensis) were investigated in field bioassays at a deer park in Hokkaido, Japan. A set of feeding bioassay trials tested the effects of the pyrazine cocktail odor on the behavior of the deer located around a feeding area in August and September 2013. This odor effectively suppressed the approach of the deer to the feeding area. In addition, the pyrazine cocktail odor provoked fear-related behaviors, such as “tail-flag”, “flight” and “jump” actions, of the deer around the feeding area. This study is the first experimental demonstration that the pyrazine analogs in wolf urine have robust and continual fearful aversive effects on ungulates as well as mice. The pyrazine cocktail might be suitable for a chemical repellent that could limit damage to forests and agricultural crops by wild ungulates.

English

Fusarium oxysporum is an abundant plant pathogen in the soil and is found in the rhizosphere of many plant species. The fungus has numerous formae speciales (f.sp.) that infect and cause wilt diseases of a variety of host plants. F. oxysporum f.sp lycopersici (Fol) and F. oxysporum f.sp lini (Foln) are known to infect tomato and flax, respectively. Fluorescent pseudomonads can suppress various soilborne diseases, and their efficacy has been related both to their antagonistic activities and to their rhizosphere competitiveness. In this study, the biocontrol capacity of plant growth-promoting rhizobacteria (PGPR) strains of Pseudomonas fluorescens against fusarium wilt of tomato and flax was evaluated both in vitro and in planta. The P. fluorescens strains exhibited substantial antagonistic activities against the two fungal isolates on three culture media tested: King B (KB), potato dextrose agar (PDA) and a mixture of both (KB + PDA). As compared to the untreated control, the mycelial growth decreased by 8.33 to 49.33%. Conidial germination and germ tube elongation were significantly inhibited and reduced, respectively, by 6.15 to 47.33% and by 1.63 to 45.45%. In bioassay trials, P. fluorescens strains significantly reduced the disease incidence and severity by 4.86 to 74.49% on tomato plants and 3.93 to 79.19% on flax plants. The different efficacy of the biocontrol agents could be due to the influence of several factors, including the efficiency of the strain, the type of pathogen and the host. Key words: Plant growth-promoting rhizobacteria (PGPR), Pseudomonas fluorescens, fusarium wilt, tomato, flax, biocontrol.

Susceptibility ofLatrodectus geometricus(Araneae: Theridiidae) to aMucorStrain Discovered in North Central Florida, USA

A population of adult reproductive female brown widow spiders, Latrodectus geometricus Koch (Araneae: Theridiidae) was collected in North Central Florida. Within weeks, the spiders displayed reduced foraging behavior and began to die. A white fungal growth was observed on deceased individuals and others who showed signs of decline. Fungal samples were collected from living spiders as well as from recently deceased specimens. Samples were excised from the spiders and isolated on acidified potato dextrose agar. Morphological characterization was cross referenced with the most recent phenotypic variability studies to confirm probable matches. Molecular identification was rendered using ITS1/5.8S/ITS2 and Mucor fragilis Bainier (Mucorales: Mucoraceae) was indicated with 99% match. Little is documented regarding M. fragilis, and no prior records of pathogenic occurrence are known by the authors. Subsequent bioassay trials supported with 83% mortality that this novel strain of M. fragilis does infect and kill L. geometricus.

Impact of Insecticides on the Reproductive Potential of False Codling Moth,Thaumatotibia leucotreta(Meyrick, 1913) (Lepidoptera: Tortricidae)

False codling moth, Thaumatotibia leucotreta (Meyrick, 1913) (Lepidoptera: Tortricidae), is an important pest on citrus in South Africa. Several new insecticides were screened for their potential negative impacts on T. leucotreta's reproduction through topical insecticide applications and detached fruit bioassays. Detached fruit bioassays showed that the registered standard concentration of Delegate® 20 g/1001 and DPX-HGW86 35 ml/1001 caused females to oviposit significantly fewer eggs (P = 0.0016) than the controls. The same was found for the registered concentration of Coragen®(P < 0.0001). Topical insecticide trials showed that only concentrations of Coragen®, at the registered field rate and above had an effect on the moths’ reproductive output (P <0.0001). Alsystin® and Meothrin™, which were used as industry standards, did not negatively affect the reproductive output of the moths during topical or detached fruit bioassay trials. This study helps to better understand the importance of the application...

Efficient Analysis of Dose—Time—Response Assays

Two approaches to the estimation of relative potency for dose—time—response assays are compared: the application of a generalized linear model to the dichotomized responses and survival analysis of the time to response. Survival analysis is widely used in other fields; however, its application to bioassays has been uncommon. A description of the application of survival analysis to bioassays is provided. A worked example follows, using mouse challenge assay data. This demonstrates that estimates of relative potency based on the time to response can have considerably lower variance than those based on dichotomized responses. A simulation study further supports this conclusion. Routine use of survival analysis techniques has the potential to reduce the number of animals used in bioassay trials by ensuring that the maximum value is recovered from each animal, in line with the new European Union directive on the protection of animals used for scientific purposes.

Evaluation on the efficacy of spinosad dust against major storage insect pests

Laboratory bioassay trials were conducted at the National Agricultural Research Laboratories and Kiboko sub-centre in Kenya to determine the efficacy of spinosad dust 0.125% admixed with shelled grains, compared to a “cocktail” of pirimiphos-methyl 1.6% and permethrin 0.3% (Actellic super dust) against four important storage-insect pests: Sitophilus zeamais (Motsch), Tribolium castaneum (Herbst), Rhyzopertha dominica (F.) and the larger grain borer, Prostephanus truncatus (Horn). Spinosad dust was applied at 0.35, 0.7 and 1.44 parts per million (ppm), and Actellic super dust at 10.5 ppm. All treatments were significantly (P=0.05) better than the control except when applied against T. castaneum. Spinosad at 0.7 and 1.44 ppm was able to controlS. zeamais over the 24-week trial period. Similarly, all treatments gave good control over P. truncatus and R. dominica, with not apparent significant differences (P=0.05) between treatments on the latter. On P. truncatus, Spinosad showed better performance than Actellic super dust (P= 0.05). All levels of spinosad dust appeared to perform better on P. truncatuscompared to Actellic super dust, but spinosad dust, unlike Actellic super dust, was unable to control T. castaneum. The evidence from this trial suggests that spinosad dust may have potential in controlling major storage-insect pests, with special applicability against the destructive larger grain borer, P. truncatus. Key words: Spinosad, Actellic, dust formulations, storage pests, pest control.