Mean Percent Mortality Research Articles

Phytochemical screening and insecticidal activities of some medicinal plants against the maize weevil, Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae)

This study emphasizes the phytochemical study of some locally available botanicals against maize weevils. Nine plant parts were collected from six plant species. The test plant powder (200 g) was suspended sequentially in 600 ml of petroleum ether, chloroform, acetone, methanol, and distilled water for 72 h with frequent agitation. Different concentrations of the crude extracts were applied to maize seeds at rates of 10 ml, 15 ml and 20 ml per 100 g. All treatments with different extracts at different rates of application showed significant differences (p < 0.05) in the cumulative mean percentage mortality of the maize weevil. The seed extract of Maesa lanceolata and Croton macrostachyus and the leaf extract of Clausena anisata showed cumulative percent mortality ranged 95.32–98.02% in 28 days after treatment application. There was no significant difference (p > 0.05) among all treatments for the prevention of F1 progeny emergence. In all extracts, Clausena anisata showed 100% inhibition of F1 progeny emergence. All treatments significantly reduced seed weight loss and damage. The treated maize seeds were germinated with an acceptable germination quality. In conclusion, an increased dosage of the extract resulted in significant mortality in maize weevils. The seed extracts of Maesa lanceolata and Croton macrostachyus and Clausena anisata leaf extract were observed to be the most promising botanical in protecting stored maize against maize weevil.

In vitro Acaricidal Effect of Jatropha curcas Methanol Extract on ‎Rhipicephalus (Boophilus) decoloratus larvae

Tick infestation is considered a major problem because ticks cause widespread nuisance and losses and vectors of disease-causing agents, resulting in economic losses in livestock production. The use of chemical agents is the main stay in tick-control though current research into viable plant extracts as alternatives are on the increase. This study evaluated the larvicidal effect of crude methanolic extract of Jatropha curcas seed oil extract on Rhipicephalus (Boophilus) decoloratusticks. Various concentrations of 6.25, 12.5, 25 and 50 mg/ml were prepared from a stock (100 mg/ml) solution of the sample; control using 1% tween 80 and standard acaricide; Amitraz (positive control) were used. The mortalities were observed at time intervals of 6, 12, 18, 24 and 48 hours. The experiment was performed in triplicate. The extract had an LC50 and LC90 of 2.88mg/ml and 6.76mg/ml respectively after 48h. Carbohydrates, cardiac glycosides, saponins, tannins, steroids, terpenes, alkaloids and flavonoids were detected as phytoconstituents, and the extract exhibited significant mean percentage mortality from the control across all the concentrations after 24h. The result confirms that J. curcas is a good alternative to be used as a larvicidal agent in the control of Rhipicephalus (Boophilus) decoloratus.

Evaluation Of Phytochemical Active Ingredients Present In Organic Solvent Extracts And Larvicidal Properties Of Some Selected Plants From Taraba State Against Anopheles Larvae

The Continuous use of synthetic insecticides and its toxicity problems coupled with the incidence of insect resistance calls for the need for alternative insecticide. Plants extracts a rich source of bioactive compounds can provide an alternative source of insecticide which are ecofriendly. The research evaluated the phytochemical active ingredients present in organic solvent extracts and larvicidal effect of some selected plants from Taraba state against Anopheles larvae. World Health Organisation protocol was adopted for the larvicidal bioassay. Twenty group of fourth instar Anopheles larvae were exposed to various concentrations of 200,400,600 and 800ppm, mortality was observed and recorded after 24 hours. The results of preliminary qualitative phytochemical analyses of tested plants revealed the presence of some secondary metabolite that may be responsible for the bio control potentials. Acetone extract of Hyptis suaveoleons against the fourth instant anopheles larval was observed to have the highest percentage mortality among the entire plants extracts than the aqueous. The lowest mortality was observed at 200ppm with 35.0% while the maximum was at 800ppm with 80.0%. Lc50 and Lc90 values were achieved at 438 and 866ppm with the LCL -UCL 340-540 and 722-1151 respectively. While the biological activity of Hyptis suaveolence aqueous extract had its lowest mortality at 200ppm with 36.67% while the maximum was at 800ppm with 80.0%. Lc50 and Lc90 values were achieved at 582 and 1225ppm with the LCL -UCL 449-806 and 942-2636 respectively. Ancova results showed no significance difference at p&gt;0.05 among the mean percentage mortality of the treated doses.&#x0D;

Toxicity Assessment of Produced Water Using Nitrosomonas sp.

Aim: Most studies on the effect of produced water are centred on the effects on the physicochemical parameters of the recipient environment, but not much has been conducted on biogeochemical processes such as the nitrogen cycle. This study aims to determine the median lethal concentration (LC50) of the produced water that would cause mortality of 50% of the exposed population of Nitrosomonas sp. (test organism) which is involved in the ammonification step of the Nitrogen cycle.&#x0D; Study Design: For the purpose of this study, acute toxicity testing was done for 48 hours to determine the effect of the untreated and treated produced wastewater on the test organism. The LC50 is the median lethal concentration that would cause mortality of 50% of the exposed population of the test organisms.&#x0D; Methodology: Toxicity effects of treated and untreated produced wastewater were determined following standard procedures against the test organism (Nitrosomonas sp). The resultant output of the probit analysis was generated from the SPSS statistical programme.&#x0D; Results: Results showed that the mean LC50 for the untreated produced wastewater at the 48-hour test period of bioassay was 3.27mg/L, while the mean LC50 for the treated wastewater was found to be 6.69mg/L. The mean percentage mortality of Nitrosomonas sp. for the untreated produced waster water ranged from 37%(0.01mg/l) to 90%(100mg/l), while for the treated, percentage mortality ranged from 27%(0.01mg/l) to 84%(100mg/l) at the end of the 48 hour test duration.&#x0D; Conclusion: Toxicity of treated and untreated wastewater against Nitrosomonas sp increased with time and decreased considerably with treatment, corresponding to positive correlation as observed statistically between toxicants with respect to concentration and time of exposure for untreated and treated wastewater against Nitrosomonas sp. These results indicate a likey inteference of the nitrogen cycle by contamination of untreated produced water in the environment and by extension impairment of the productivity of the environment.

Efficacy of powder formulations of some tropical flora and clay against Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae) on maize in storage

A study was carried out to determine the efficacy of three plant materials; pawpaw (Carica papaya) seed powder, kapok tree (Ceiba pentandra) leaf powder, soursop (Annona muricata) leaf powder as well as clay and Permethrin dust against Sitophilus zeamais (Mots.) under laboratory conditions. The experiment was laid out in 5×4 factorial with 5 replicates in Completely Randomized Design in the laboratory. Maize grains weighing 50 g were treated with the plant powders, clay and the synthetic Permethrin at the rate of 0.00 g, 1.5 g, 3.5 g and 5.0 g by weight and then infested with 10 adult weevils in each vial for assessments of adult mortality, F1 emergence and damage. The comparative effectiveness of each of the treatments were assessed by counting weevils’ mortality at 14 days, 28 days, 42 days and 56 days post treatment and progeny emergence at 28 days, 42 days and 56 days post-treatment. The results were subjected to statistical analysis after transforming the data using mean percentage method and the ANOVA, the significant means were separated using the least significant differences test at 5% level. The Permethrin, a synthetic insecticide proved to be very effective followed by clay among all the treatments. Among the botanicals, C. papaya was the most effective followed by A. muricata, but were concentration dependent while C. pentandra was the least or not effective. In all trials, percentage mortality among adult S. zeamais reared on maize treated with Permethrin powders was observed to be the highest (100%) followed by those treated with C. papaya seed powder (56.6%), clay (55.5%) and A. muricata seed powder (38.8%). However, grains treated with powdered leaves of C. pentandra exhibited a low mean percentage mortality of 0.00, 0.20, 0.57 and 0.63, respectively, at different intervals post treatment which was not significantly different when compared with the untreated (control). These percentage mortality among adults were significantly (P&lt;0.05) different from the untreated (control). Thus, all the treatments were found to significantly affect the survival of the S. zeamais at different concentration except in C. pentandra. Effect of plant powder on the emergence of adult S. zeamais was significantly (P&lt; 0.05) different and reduced the F1 progeny emergence. The result indicated that C. pentandra had no significant effect on mortality and F1 emergence of adult S. zeamais (P&lt; 0.05) resulting in severe damage of the grains and weight loss.

Endophytic Potential and Larvicidal Efficacy of Entomopathogenic Fungi against the Spotted Stem Borer, Chilo partellus

Entomopathogenic fungi (EPF) of different genera are known to have the potential to engage in fungus-plant interactions as fungal endophytes. This hidden endophytic interaction offers several advantages to host plants, such as insect pest management. Hence, this study aimed to explore the endophytic potential and virulence of EPF collections after artificial inoculation. A total of 27 EPF isolates from the genera Beauveria and Metarhizium were screened for virulence. Two inoculation methods (leaf and seed dressing) were used to study the endophytic colonisation potential of the selected isolates. There was a significant variation among the tested isolates in their ability to kill C. partellus larvae. Lower mean percentage mortality was recorded for isolates B4, DS-51-21, and B1,9 which scored 28.01%, 32.29%, and 34.58%, respectively. All the screened EPF isolates were able to colonise maize tissues after artificial inoculation, except for APPRC-34GM. The percent colonisation of maize tissues varied with strains, and delivery methods ranged from a minimum of 0% to a maximum of 53%, where the maximum was recorded by S#10H. Larval mortality after feeding maize leaves inoculated with EPF ranged from 18% to 60%. The findings of this study indicated that Beauveria spp. and Metarhizium spp. have the potential to colonise maize after artificially inoculating and translocating from the site of infection. Hence, the potential to move from the site of infection and larvicidal activity after colonisation may give the advantage to manage insect pests acting on the different parts of maize.

The parasitic impact of Romanomermis iyengari Welch (Nematoda: Mermithidae) on the survival and biology of the common mosquito, Culex pipiens L. (Diptera: Culicidae)

The extensive use of chemical insecticides to control mosquitoes led to the development of insecticide resistance and environmental health hazards. This caused a surge in interest in eco-friendly biocontrol agents. The present study aimed to explore the susceptibility of different instar larvae of the common mosquito, Culex pipiens Linnaeus, 1758, to the mermithid nematode, Romanomermis iyengari Welch, 1964. Moreover, the effects of R. iyengari on the mosquito pupal developmental time, adult emergence, longevity, female fecundity, as well as egg-hatching rate were determined after larval treatment with an LC50 quantity of the nematode pre-parasites. Different instars of Cx. pipiens (1st–4th) were exposed separately to R. iyengari at concentrations of 1–6 pre-parasites/mosquito larva. Mortality rates of mosquito larvae were observed and the LC50 values were calculated. The estimated LC50 values for the 1st–4th larval instars were 3.18, 2.73, 3.79 and 4 pre-parasites/larva, respectively. Mean percent mortality of the 1st–4th larval instars ranged from 10–94%, 16–100%, 4–100% and 0–52%, respectively. The results indicated that exposure of 4th larval instar to the LC50 of R. iyengari pre-parasites significantly prolonged the duration of pupal development, reduced the percentage of emerged adults and reduced mosquito female fecundity compared with the control. In contrast, adult longevity and the egg-hatching rate did not differ between the control and the exposed group. In conclusion, this isolate of R. iyengari could be a promising biocontrol agent for Egyptian Cx. pipiens. Other trials are required to assess the biocontrol potential of this parasite in field conditions.

Larvicidal Efficacy of Ozone and Ultrasound on Angiostrongylus cantonensis (Rat Lungworm) Third-Stage Larvae.

The parasitic nematode Angiostrongylus cantonensis (rat lungworm) is the leading cause of human eosinophilic meningitis worldwide. Most human infections occur through the accidental consumption of A. cantonensis hidden within produce as infectious third-stage larvae (L3), yet little research has been published addressing possible methods to mitigate this means of transmission. Here, we describe our tests of ozone gas—an oxidizing agent—and ultrasound, both used for disinfection of food and municipal water supplies and in industrial cleaning. We found that exposure to ozone, produced using two different commercially available ozone generators over varying durations of time and concentrations, was capable of achieving 100% larval mortality. In addition, we evaluated the impact of different sound frequencies on A. cantonensis L3 survival using two different commercially available ultrasonic cleaners, and found that 60 s of 40 kHz produced 46% mortality within 2 h. The combined use of ultrasound and ozone gas simultaneously resulted in a minimum of 89% normalized mean percent mortality within 2 h of treatment. Our study suggests that both ozone and ultrasound show high larvicidal efficacy, both independently and together, and thus show promise as methods for reducing the risk of rat lungworm infection via accidental consumption.

Retrospective mortality assessment of Glossina palpalis palpalis collections from Ijah-Gwari field station, Niger state Nigeria

Handling and transportation of tsetse flies are fundamental for mortality assessment during fly collections. Previous works have indicated that tsetse fly mortalities increase with the rise in ambient temperatures. A seasonal mortality assessment of Glossina palpalis palpalis population collected from Ijah-Gwari field station was carried out based on the record as kept in the insectary of the Nigerian Institute for Trypanosomiasis Research, during the period between 2011- 2018; in order to determined fly mortality rates associated with handling and transportation of flies. Results indicated that whereas high percentage mortalities were recorded between 2016 (44%) and 2017 (57%); moderate mortalities were recorded in 2011 (36%), 2014 (29%), 2015 (19%) and 2018 (30%); while low mortalities of 10% were recorded in 2012 and 2013. Hot months of May (51%) and July (25%) gross mortalities contributed significantly to the increase in mortalities recorded in these years. The findings of this study show that extreme temperatures and relative humidity might be contributing factor of fly mortality. The handling and transport conditions might have sustained the high temperatures and humidity during transportation. Mean percentage mortality was observed to be higher in male (44%) than the female (33%) flies from Ijah-Gwari. The implication of this study as pertains salivary gland hypertrophy virus transmission is discussed.

Survey and identification of entomopathogenic nematodes in the province of Cotabato, Philippines, for biocontrol potential against the tobacco cutworm, Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae)

BackgroundThe tobacco cutworm, Spodoptera litura [Fab.] (Lepidoptera: Noctuidae), is a devastating insect pest of several crops. Entomopathogenic nematodes (EPNs) of the families Heterorhabditidae and Steinernematidae are used as an alternative control measure in lieu of the hazardous synthetic chemical applications.ResultsA survey of naturally occurring EPNs was conducted across the province of Cotabato, Philippines, covering a total of 5 municipalities with 25 villages. Galleria-baiting technique was employed to recover nematodes from peanut and grassland soils. Out of 50 soil samples collected, only 5 samples harbored nematodes, indicating a recovery of 10%. Preliminary morphological data identified only one EPN under the genera Heterorhabditis (1 isolate), whereas 4 were facultative necromenic nematodes from the genera Metarhabditis (2 isolates) and Oscheius (2 isolates). Analysis of D2D3 segments of the 28S rDNA confirmed high sequence similarity to Heterorhabditis indica, Metarhabditis rainai, Oscheius insectivora, and Oscheius sp. This is the first record of H. indica and M. rainai in the entire region, whereas the first record for Oscheius spp. in the Philippines. Furthermore, the biocontrol potential of the local H. indica infective juvenile (IJ) populations (PIGCD1) isolated from peanut was assessed against the tobacco cutworm, S. litura, under laboratory conditions. The mean percentage mortality caused by H. indica on S. litura at 7 different concentrations ranged from 0-100% at 24 h post inoculation. The lethal concentration (LC50) required to kill 50% of the S. litura larvae population with H. indica was 7.13±1 (IJs/larva).ConclusionsThe use of Galleria-baiting method is a convenient approach to detect EPNs including other facultative necromenic nematodes from the soils. Obtained data indicated that the local H. indica isolate can be a promising alternative measure to suppress the economically important insect pest, S. litura, and this may provide significant outlook to establish the biocontrol program in the country.

LABORATORY EVALUATION OF BORIC ACID SUGAR BAITS AGAINST IRRADIATED AEDES AEGYPTI

The use of attractive toxic sugar baits (ATSBs) is a new paradigm in mosquito control. ATSBs kill both female and male mosquitoes attracted to sugar feed on a sugary solution containing a toxic substance such as boric acid. The impact of boric acid sugar baits on irradiated and non-irradiated Aedes aegypti was evaluated in the laboratory to determine any difference in mortality between the two groups. The mortality rates from the toxic sugar baits in both irradiated with 50 Gy and non-irradiated groups were highly significantly different, compared to those of corresponding control groups (t=6.916, p &lt;0.0001 and t=6.451, p&lt;0.01, respectively). Irradiated Ae. aegypti were not significantly different in mortality rates from non-irradiated counter parts after 24 and 48 h exposure to toxic sugar bait (t=0.576, p=0.578 and t=0.642, p=0.535 respectively). There was no significant difference in mortality caused by toxic sugar baits between the two sexes (t=0.595, p=0.869 and t=0.169, p=0.869 for irradiated and non-irradiated groups, respectively). The mean percent mortality after 48 h of exposure to toxic sugar baits was 43.3% for irradiated mosquitoes and 38.6% for non-irradiated mosquitoes. Mortality rates were significantly higher during second 24 h period in both irradiated and non-irradiated groups (t=-6.612, p&lt;0.01 and t=-5.278, p&lt;0.01 respectively). The study suggests that the toxic sugar bait approach could not be used within a sterile insect technique program to reduce the wild male population to increase the chances of wild females mating with irradiated males.

Evaluation of Long-Lasting Insecticidal Nets (DuraNet®) Under laboratory and Semi-Field Conditions Using Experimental Huts Against Anopheles Mosquitoes in Jimma Zone, Southwestern Ethiopia

Background:Long-Lasting Insecticidal Nets (LLINs) efficacy could be compromised due to a lot of influences together with user compliance and vector population insecticide resistance status. Thus, this study was to assess the biological efficacy of DuraNet® with the help of the World Health Organization cone bioassay and field experimental hut.Methods:A laboratory and a semi-field conditions experimental huts against Anopheles Mosquitoes were conducted in southwestern Ethiopia from September 2015 to January 2016. The bio efficacy of DuraNet® was evaluated using the WHO cone bioassay test and then its field efficacy was evaluated using experimental huts against the malaria vector population.Results:World Health Organization cone bioassay tests against pyrethroid-resistant An. arabiensis led to mean percent mortality and knockdown of 78% and 93%, respectively. Washing of DuraNet® successively reduced its efficacy from 93% knockdown (0 wash) to 45% knockdown (20 washes). Similarly, mean mortality decreased from 84% (0 wash) to 47% (20 washes). A total of 1575 female mosquitoes were collected over 40 nights out of which 1373(87.8%) were An. gambiae s.l., 116 (7.4%) were Anopheles coustani and 107 (6.8%) were An. pharoensis. The mean blood-feeding rate was significantly lower (P < .001) in hut containing unwashed DuraNet® when compared to hut containing untreated DuraNet®. The mean mortality rate was significantly higher (P < .001) in hut containing DuraNet® when compared to hut containing untreated DuraNet®. Unwashed DuraNet® showed the highest personal protection 88.7% and 100% against An. Arabiensis and An. pharoensis, respectively.Conclusion:Both DuraNet® and PermaNet 2.0 moderate efficacy against a pyrethroid-resistant population of An. arabiensis from Ethiopia. The bio efficacy of DuraNet® was found below the WHO recommendation. Therefore, the real impact of the observed insecticide resistance against DuraNet® to be further studied under phase-III trials, the need for new alternative vector control tools remains critical.

Effects of Spray Volume and Application Frequency on Insecticide Efficacy Against Adult Western Flower Thrips (Frankliniella Occidentalis) under Greenhouse Conditions

The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is a major insect pest of greenhouse-grown horticultural crops. Western flower thrips causes direct and indirect damage by feeding on plant leaves, flowers, and fruits, and by transmitting viruses that can result in greenhouse producers experiencing substantial economic losses. Consequently, insecticides are used to suppress western flower thrips populations. However, issues associated with applying insecticides may affect the suppression of western flower thrips populations. Therefore, experiments were conducted under greenhouse conditions to determine the effects of the spray volume applied and application frequency on insecticide efficacy against western flower thrips adults located in transvaal daisy, Gerbera jamesonii, cut flowers. Four spray volumes (5.0, 10.0, 12.5, and 25.0 mL), two application frequencies (one or two spray applications), and three insecticides [spinosad (Conserve), chlorfenapyr (Pylon), and flonicamid (Aria)], each with a different mode of action, were tested. The insecticide treatments had the greatest effects on the mean percent mortality of western flower thrips adults regardless of spray volume or application frequency. However, in Expt. 3, the 5.0- and 10.0-mL spray volumes resulted in a higher mean percent mortality of western flower thrips adults than the 2.5-mL spray volume. Spinosad and chlorfenapyr resulted in a mean percent mortality of more than 72% for western flower thrips adults, whereas flonicamid resulted in mean percent mortality between 40% and 91%. Our study demonstrates that certain insecticides are more effective against western flower thrips adults located in transvaal daisy flowers than others, which will help greenhouse producers effectively manage western flower thrips populations.

Characterization of Pseudomonas aeruginosa ghost and evaluation of its immune proficiency in Nile tilapia (Oreochromis niloticus)

Pseudomonas aeruginosa is known to be multidrug-resistant organisms so its infection is challenging. This study aimed to use the sponge-like reduced protocol in preparation of P. aeruginosa ghosts (PAGs) as a vaccine alternative and evaluate its competency in stimulating the immune response in Nile tilapia. Characterization of PAGs was done using the light, fluorescent and transmission electron microscope. 240 fish have been divided into four groups (60 fish each; three groups were injected with a high, medium, or low dose of PAGs, and a control group. Total and differential leukocyte count, phagocytic activity, lysozyme activity, and gene expression of some immune-related genes were done after the first and booster ghost dose injection. All fish groups were challenged intraperitoneally with P. aeruginosa (1 × 107 CFU ml−1); the mean percent mortality was calculated. Significant immunization potency of the large dose of PAGs was prominent. It is associated with a significant increased number of WBCs, heterophile, lymphocytes, and monocytes. Also the phagocytic activity and indexes were significantly increased by the high and moderate dose of PAGs. Additionally, significant upregulation of immune-related gene (MHC-II) and inflammatory-related gene (IL8) and maintained expression level of TLR7 were recorded. We conclude that chemically prepared P. aeruginosa ghosts maintained both the 3D structure and surface molecules of live bacteria and also are capable of inducing specific immune responses in Nile Tilapia, and reduced mortalities in challenged fish. Our results indicate the advantage of this procedure for production of bacterial ghost, which can be used in wide a range of hosts.

Model prediction of a Kunitz-type trypsin inhibitor protein from seeds of Acacia nilotica L. with strong antimicrobial and insecticidal activity.

A Kunitz-type trypsin inhibitor protein has been purified and characterized from seeds of Acacia nilotica L. LC-MS/MS analysis of Acacia nilotica trypsin inhibitor (AnTI) provided the N-terminal fragment of 11 amino acids which yielded 100% identity with already reported Kunitz-type trypsin inhibitor protein of Acacia confusa (AcTI) in UniProtKB database search. SDS-PAGE showed a single band of ~21 kDa under nonreduced condition and appearance of a daughter band (17 kDa) in the presence of β-mercaptoethanol indicating the presence of interchain disulfide linkage typical for Kunitz-type trypsin inhibitors. AnTI was purified from seed extract by using a combination of anion exchange and gel filtration chromatography. Since AnTI showed maximum homology with AcTI, a molecular structure of AcTI was predicted which showed highly β-sheeted molecular conformation similar to crystallographic structure of Enterolobium contortisiliquum trypsin inhibitor (EcTI). AnTI (20 µg) produces significant population inhibition against different human pathogenic bacteria along strong antifungal activity (50 µg). Entomotoxin potential of AnTI was evaluated against two stored grain insect pests Tribolium castaneum (Herbst) (Tenebrionidae: Coleoptera) and Sitophilus oryzae (Linnaeus) (Curculionidae: Coleoptera). Statistically significant mortality of T. castaneum adults was observed at 1.5 mg after 15 days in comparison to control. Additionally, number of total eggs, larvae, pupae, adults, and their male/female ratio were also severely reduced in comparison to control. Similarly, two generation progeny of S. oryzae was studied after mixing AnTI with rice kernels. Mean percent mortality of adult population was significantly higher after 9 days of exposure in comparison to control group. AnTI significantly reduced the F1 generation while little mortality was observed for F2 generation. Exploration of such potent molecules is the prerequisite of our time regarding the anticipation of postantibiotic era and the development of insect resistance against chemical pesticides.

Evaluation of Some Botanical Extracts Against Major Insect Pests (Leafminer, Armored scale and Woolly Whitefly) of Citrus Plants in Central Zone of Tigray, North Ethiopia

Citrus fruit production is suffering from various yield-limiting factors particularly the sucking pests viz, citrus leafminer Phyllocnistis citrella, woolly whitefly, Aleurothrixus floccosus and scale insects especially armored scales Aonidiella auriantii. The present paper tries to identify the effective botanical insecticides against these insect pests on citrus orange. An experiment was conducted in the established citrus orange farm in Kolla Temben at two farmer’s fields, Adiha and Agibe during the off-season of 2018 under irrigation growing condition in a randomized complete block design with six treatments and replicated thrice. The findings in both experimental sites showed that the neem seed extract had a significantly (P=0.001) lower leafminer infestation levels compared to the untreated control which is on par to the insecticide treatment of dimethoate. On the other hand, in both areas, whitefly mortality of more than 81% on average was recorded from neem seed extract followed by Tree tobacco (70%) (P=0.001). For scale insects however, in both experimental sites, the highest mean percent mortality was recorded from the insecticide dimethoate 40% EC (86.9%, 87.2 &amp; 86.0%on average) followed by neem seed and tree tobacco extracts,70.1 and 65.4% respectively. The botanicals particularly the neem seed extracts followed by tree tobacco are as effective as the chemical insecticide, dimethoate 40% EC, even superior in some cases, in controlling the target pests. Therefore, these botanicals could be used as an IPM component for against the target pests.

Effects of low-pressure storage of food commodities on the mortality of adult stored product insects

The food industry faces serious problems regarding pest infestation leading to high storage loss of food commodities. Due to adverse impacts of chemical preservation methods, a promising physical method of food protection could be considered as an urgent need. This study investigated the effect of low-pressure (vacuum) on the mortality of adults of three stored product pests of drug store beetle (Stegobium paniceum L.), southern cowpea weevil (Callosobruchus chinensis L.) and red flour beetle (Tribolium castaneum Herbst). The pests were exposed to 20 kPa and 10 kPa vacuum at 37 ºC and 75% relative humidity. Mortality of the insects was recorded at 8 h and 32 h after vacuum treatments. There were significant differences (p&lt;0.05) in the susceptibility to the vacuum treatment among the tested pests. Adults of C. chinensis showed comparatively less susceptibility to the vacuum treatment compared to S. paniceum and T. castaneum. Mortality of insects exposed to two low-pressure treatments did not show 100% mortality at the two exposure periods, irrespective of the type of food materials and species. The mean percentage mortality increased by about 66.0±5.7% when vacuum pressure increases from 20 kPa to 10 kP irrespective of the species, exposure time and the products. The oxygen concentration decreased to &gt;70% inside the vacuum chamber during treatments.

Characterization of Growth and Virulence of Five Nigerian Isolates of Entomopathogenic Fungi Using Galleria mellonella Larvae for Pathogenicity Testing

Entomopathogenic fungi (EF) are naturally occurring insect population regulators, with several species that are exploited as biocontrol agents against insect pests. Five EF consisting of two strains of Isaria farinosa, (IF-I and IF-II) and one strain each of Metarhizium anisopliae, Beauveria bassiana and Entomophaga sp. (Sensu lato) were isolated from soil using Tribolium castaneum (Coleoptera: Tenebrionidae) (Herbst) larvae as bait. The isolates were cultured on standard Potato Dextrose Agar (PDA) (Sigma-Aldrich, UK) and identified based on phenotypic appearance and micro-morphology. Growth rates (mm day-1), number of conidia per cm2 colony area after incubation for 14 days at ambient temperature (25±2°C), viability of conidia (% germination), based on 24-hours incubation period and virulence of the infective conidia against Galleria mellonella were evaluated. The data on growth was subjected to analysis of Variance (ANOVA) procedure and means were separated using Tukeys Honestly Significant Difference (P=0.05). The number of conidia produced by Entomophaga sp was (7.0×105 conidia cm 2 per colony area), while the isolate of M. anisopliae produced (5.2×104 conidia cm2 per colony area). The number of conidia produced by the two isolates of I. farinosa, IF-I and IF-II and B. bassiana were 9.4×104, 7.2×104 and 2.1×105 conidia cm2 per colony area respectively. Eighty percent of Entomophaga sp conidia germinated after incubating for 24 hours at 25°C while 100% germination occurred in the other fungal isolates. There were statistically significant variabilities in the rates of growth of the EF isolates F(4,2.064) =12.97, P=0.001. The B. bassiana isolate had the fastest growth rate, with statistically significant value of 3.3 mm day-1. The rates of growth of the two I. farinosa isolates: IF-I, IF-II and M. anisopliae were comparable, being 1.53, 1.4 and 1.28 mm day-1 respectively, without statistically significant difference. The growth rate of Entomophaga sp was 2.0 mm day-1, which was significantly higher than the growth rates of I. farinosa and M. anisopliae. The mean percentage mortality values of, G. mellonella larvae treated with 1×108 conidia ml-1 of the infective conidia of I. farinosa, IF-I, IF-II, M. anisopliae, after five days were 70, 60, 60% respectively while Entomophaga sp and B. bassiana caused 50% mortality. The results suggest that the five isolates examined can potentially be developed into experimental formulations and tested against important horticultural pests in future studies.

Effect of the entomopathogenic fungus, Beauveria bassiana, combined with diatomaceous earth on the red flour beetle, Tribolium castaneum (Herbst) (Tenebrionidae: Coleoptera)

An assay was designed to evaluate the efficacy of each entomopathogenic fungus, Beauveria bassiana, and diatomaceous (DE) and their combinations at concentrations of 1 × 106 and 1 × 108 conidia kg−1 of wheat and 200 and 400 ppm, respectively, on the red flour beetle, Tribolium castaneum (Herbst) (Tenebrionidae: Coleoptera), infesting wheat. Percent mortality of T. castaneum was recorded after 7, 14, and 21 days. Percent mycosis on dead cadavers was assessed after 21 days. Alive adults were removed from plastic jars after 21 days and kept for the next 60 days to assess the progeny production. The results indicated that the highest concentrations of B. bassiana and DE in their combinations were more effective for the virulence and progeny suppression of T. castaneum. Maximum mean percent mortality (88.13%) was recorded by B. bassiana (1 × 108 conidia kg−1 of wheat) and DE (400 ppm) in their combination after a 21-day exposure interval, while a minimum percent mean mortality (10.00%) was recorded by B. bassiana (1 × 106 conidia kg−1 of wheat) alone. The maximum percent mycosis (78.89%) on dead cadavers was recorded at a low concentration rate (1 × 106 conidia/kg) of B. bassiana. Mean progeny adult emergence was the highest (62.67 adults) at the low concentration of B. bassiana alone. Present studies showed that B. bassiana and DE are more effective in combination against T. castaneum on wheat as both substances are advantageous.

Larvicidal activity of Ocimum campechianum, Ocotea quixos and Piper aduncum essential oils against Aedes aegypti.

Aedes aegypti, the main arbovirus vector of the Yellow fever, Dengue, Chikungunya and Zika viruses, is widely distributed in tropical and subtropical areas throughout the world. Preventive control efforts have been implemented worldwide aimed at reducing its impact on human health. The recent reduction of chemicals available for vector control due to their negative impact on the environment and human health and the increase in mosquito resistance to insecticides have driven the research community to identify and evaluate sustainable alternatives to synthetic insecticides. In this study, the potential larvicidal effect of essential oils extracted from Ocimum campechianum, Ocotea quixos and Piper aduncum were tested in vitro. GC and GC–MS analyses showed that the main compounds were eugenol (18%), 1,8-cineole (39%) and dillapiole (48%), respectively. Susceptibility to essential oils was measured according to the WHO protocol. After 24 h, the mean percentage mortality ranged from 2.7 to 100% for P. aduncum, from 2.2 to 100% for O. campechianum, and from 2.9 to 100% for O. quixos. The highest potential was displayed by P. aduncum, followed by O. campechianum and O. quixos, with LC50 values of 25.7, 69.3 and 75.5 ppm, respectively. The rapid and effective larvicidal activity of these three oils led us to consider these results to be promising, also considering the possibility of local cultivation of these plants in tropical and subtropical areas and the simple technology for their large-scale preparation and production. Further studies are needed to evaluate the individual components and their activity as larvicides.