Johnson Stanley

Risk assessment of insecticides used in rice on miridbug, Cyrtorhinus lividipennis Reuter, the important predator of brown planthopper, Nilaparvata lugens (Stal.).

The green miridbug, Cyrtorhinus lividipennis, an important natural enemy of the rice brown planthopper (BPH), Nilaparvata lugens plays a major role as a predator in suppressing the pest population. The study assessed the impact of certain potential insecticides used in the rice ecosystem on the miridbug predator and brown planthopper through contact toxicity. Eleven insecticides, including neonicotinoids, diamides, azomethine pyridines, carbamates, pyrethroids, organophosphates and cyclodienes were selected to test their toxicities against the nymphs of C. lividipennis and N. lugens. Median lethal concentration (LC(50)) was determined for each insecticide using an insecticide-coated vial (scintillation) residue bioassay, which revealed BPMC as the highly toxic chemical with an LC(50) of 0.003mga.iL(-1) followed by ethofenprox and clothianidin with LC(50) of 0.006mga.iL(-1) at 48 HAT against C. lividipennis and ethofenprox as the highly toxic chemical with an LC(50) of 0.009mga.iL(-1) followed by clothianidin with an LC(50) of 0.211mga.iL(-1) at 48h after treatment (HAT) against N. lugens. Among the insecticides tested, the cyclodiene compound, endosulfan had the lowest acute contact toxicity (LC(50)=66.65mga.iL(-1) at 48 HAT) to C. lividipennis. Among the insecticides tested, endosulfan, chlorpyriphos, acephate and methyl parathion are regarded as safer to C. lividipennis based on selectivity ratio, hazard quotient and probit substitution method of risk assessments.

Evaluation of pesticide toxicity at their field recommended doses to honeybees, Apis cerana and A. mellifera through laboratory, semi-field and field studies

A series of experiments were carried out to determine the acute toxicity of pesticides in the laboratory, toxicity through spray on flowering plants of mustard (Tier II evaluation) and field on both Apis cerana and A. mellifera bees. The overall mortality of honey bees through topical (direct contact) were found significantly higher than that of indirect filter paper contamination assays. Insecticides viz., chlorpyriphos, dichlorvos, malathion, profenofos, monocrotophos and deltamethrin when exposed directly or indirectly at their field recommended doses caused very high mortality up to 100% to both the bees at 48 HAT. The insecticides that caused less mortality through filter paper contamination viz., flubendiamide, methyl demeton, imidacloprid and thiamethoxam caused very high morality through direct exposure. Apart from all the fungicides tested, carbendazim, mancozeb, chlorothalonil and propiconazole, insecticides acetamiprid and endosulfan were found safer to both the bees either by direct or indirect exposures. Tier II evaluation by spray of pesticides at their field recommended doses on potted mustard plants showed monocrotophos as the highly toxic insecticide with 100% mortality even with 1h of exposure followed by thiamethoxam, dichlorvos, profenofos and chlorpyriphos which are not to be recommended for use in pollinator attractive flowering plants. Acetamiprid and endosulfan did not cause any repellent effect on honey bees in the field trials endorse the usage of acetamiprid against sucking pest in flowering plants.

Toxicity of diafenthiuron to honey bees in laboratory, semi-field and field conditions.

BACKGROUND Cardamom, an important spice crop often attacked by many insect pests, is controlled mainly using synthetic insecticides. As honey bees play a vital role in pollination in cardamom, the impact of insecticides on honey bees needs to be explored to assess its safety. RESULTS Risk assessment based on contact toxicity revealed diafenthiuron to be a non-selective insecticide to bees with a low selectivity ratio (the ratio between the LD(50) for beneficial and pest species). A dose of diafenthiuron that killed 90% of cardamom borer, Conogethes punctiferalis Guenee, was found to kill 100% of Indian bees. Based on the hazard ratio (the ratio between the field-recommended dose and the LD(50) for the beneficial), diafenthiuron was found to be slightly to moderately toxic to bees. Diafenthiuron, even at low concentrations of LC(1) (the concentration that killed 1% of bees), was found to affect the foraging and homing behaviour of Indian bees. Of bees fed with 30 microg mL(-1) of diafenthiuron, 40% were found missing on the third day after exposure. However, diafenthiuron did not affect bee visits to the cardamom fields. CONCLUSION Diafenthiuron is more highly toxic to Apis cerana indica F. than to C. punctiferalis by contact, using selectivity ratio and probit substitution methods of risk assessment, but the hazard ratio revealed diafenthiuron to be a slightly to moderately toxic chemical. Diafenthiuron was found to affect the foraging and homing behaviour of bees at sublethal concentrations. Thus, sublethal effects are more relevant in risk assessment than lethal and acute effects.

Physical and biological compatibility of diafenthiuron with micro/macro nutrients fungicides and biocontrol agents used in cardamom

In the context of complex field problems, compatibility of an efficacious insecticide with other agrochemicals normally used in the field is essential. In this view diafenthiuron, a novel insecticide which inhibits ATP synthesis, used widely for pest management in cardamom, was tested for its compatibility with agrochemicals viz., fungicides and nutrients normally used in the crop. The results revealed that all the chemicals tested were physically and biologically compatible with diafenthiuron by means of physical stability and phytotoxicity ratings in the field. But the bioefficacy study on Conogethes punctiferalis in the laboratory and bioefficacy studies in the field against Sciothrips cardamomi reveal that diafenthiuron is incompatible and should not be sprayed along with fungicides like mancozeb and copper oxychloride. Another study on the compatibility of diafenthiuron with antagonistic microorganisms of plant pathogens viz., Trichoderma viride and Pseudomonas fluorescens revealed that diafenthiuron had some inhibitory effect on the mycelial growth of T. viride. Diafenthiuron did not affect the growth of P. fluorescens and thus can be used simultaneously for the control of insect pests and seed- and soil-borne diseases.

Brevibacterium frigoritolerans a novel entomopathogen of Anomala dimidiata and Holotrichia longipennis (Scarabaeidae: Coleoptera)

We describe the isolation, biochemical characterization, phylogenetic analysis, and pathogenecity of a novel entomopathogenic bacterium Brevibacterium frigoritolerans to first instar larvae of Anomala dimidiata and Holotrichia longipennis. The almost full length 16S rRNA sequence of the bacterium has 99% identity with the type strain of B. frigoritolerans, while phylogenetic analysis revealed that the isolate formed a tightly linked branch with the type strain of B. frigoritolerans. Under in vitro bioassay conditions, the isolate infected and caused 89±5.4 and 74±7.7% mortality, in first instar larvae of A. dimidiata and H. longipennis, respectively. The infected larvae exhibited bacteremia like symptoms and mortality occurred between the second and fifth weeks after inoculation. This is an early report on the entomopathogenic potential of the hitherto lesser-known bacterium Brevibacterium frigoritolerans.

Honey bees of the cardamom ecosystem and the selective toxicity of diafenthiuron to four different bee species in the laboratory

Summary Bees are important pollinators necessary for fruit set in cardamom (Elettaria cardamomum). Apis cerana indica, Apis dorsata, Trigona iridipennis and Amegilla spp. were observed in cardamom plantations of south India. Since cardamom is attacked by an array of insect pests, synthetic insecticides were used in crop management. Diafenthiuron is one such insecticide found to be very effective against the cardamom borer, Conogethes punctiferalis and thrips, Sciothrips cardamomi. Most insecticides used in crop protection are reported to be hazardous to bees, so diafenthiuron was also tested for its toxicity to bees. Diafenthiuron was found to be slightly harmful to A. dorsata, A. cerana indica, A. foreaand moderately harmful to T. iridipennis. In particular, it was slightly to moderately toxic to bees on contact with treated surfaces in the laboratory. T. iridipennis and A. dorsata are found abundantly in the cardamom ecosystem and unfortunately highly susceptible to the insecticide. It was found that diafenthiuron is highly toxic when applied to the thorax of bees but it is less toxic on ingestion, i.e, contact toxicity is higher than oral toxicity. The labellum, the attractive part of the cardamom flower, where the bees land is not heavily exposed to pesticide sprays in the field because of its position and other reasons, so bees have a reduced chance of exposure to the pesticide in the field. Under critical situations, however, spraying of the chemical during peak bee activity should be avoided.

Pesticide Toxicity to Non-target Organisms

Arthropod predators perform ecosystem service by natural pest suppression. Since they are mostly seen along with the pests, they are affected by the pesticidal sprays or by ingesting intoxicated preys. So pesticides are to be tested for their non-target toxic effects. Acute toxicity of pesticides to arthropod predators is being done by calculating the median lethal concentrations. Apart from acute toxicity, testing of chronic, persistent and sublethal toxicities are to be done because sublethal effects especially if affects the reproduction of predators are dangerous. Tier II toxicity evaluation through semi-field experiments are needed to find the toxic effects in a realistic manner than that of laboratory experiments. Finally field experiments are being done to find the real effect of pesticides on these natural enemies. Pesticide risk assessment for predators are being done by categorizing the pesticides based on the mortality in the laboratory and semi-field trials and reduction in field studies. Apart from this, hazard ratio/risk quotient, comparison of LC50 with field recommended concentrations are explained. Toxicity of pesticides to predators in comparison with their associated pests are being done by calculating selectivity ratio and probit substitution to find which one of them is more vulnerable. A tiered approach or sequential testing scheme starting from laboratory, proceeding with semi-field and field studies seems to be useful in risk assessment. To find the sublethal toxicity especially on the reproduction of the predators, calculation of total effect of the pesticide, coefficient of toxicity and population growth rate are found promising for assessing the risk of pesticides to predators in agro-ecosystem. 1 Importance of Arthropod Predators in Pest Management In an ecosystem, predation is a biological interaction where a predator (hunter) feeds on its prey (Begon et al. 1996). Predators are mostly free-living and consume a large number of preys during their lifetime. In general, carnivores are termed as predators but have to prey on other organism. Predators are of different hierarchy in food chains (primary, secondary and tertiary) and many predators eat from multiple levels of the food chain. Arthropod predators on crop pests include beetles, bugs, flies, wasps, spiders and predatory mites. Some predators are so effective in managing the pest problems by themselves naturally. But in some cases, natural pest suppression alone cannot be sufficient to bring pests below economic threshold levels,

Efficacy of Neem Oil on Cardamom Thrips, Sciothrips cardamomi Ramk., and Organoleptic Studies

The neem tree contains promising pest control substances which are effective against many pests. Oil extracted from neem seeds was used against cardamom thrips, Sciothrips cardamomi, a severe and economic pest of cardamom. Neem oil formulations, namely, Tamil Nadu Agricultural univeristy neem oil (TNAU NO) (acetic acid & citric acid), were found effective against the pest with a overall damage reduction of 30% after 14 days of treatment. The percent damage reduction in capsules over control after three consecutive sprays of TNAU NO(C) 2% and TNAU NO(A) 2% was 78.3 and 75.2 percent, respectively. The newly extracted and unformulated neem oil, though found inferior to the formulated one, still found to cause 50% and 70% reduction in damage caused by thrips at two and three rounds of sprays, making it useful in pest management. Organoleptic tests conducted on cardamom capsules sprayed with neem oil revealed no significant difference in taste, aroma, and overall acceptability of cow milk boiled with cardamom. Thus, TNAU NO (A and C) 2% was found effective against cardamom thrips with no adverse organoleptic properties and can be recommended.

INFLUENCE OF NEONICOTINOID INSECTICIDES ON THE PLANT GROWTH ATTRIBUTES OF COTTON AND OKRA

Neonicotinoids are crop protection agents used against sucking pests acting on receptor proteins of insect nervous system. Although many reports detail their insecticidal properties, reports on the effect on plant growth are minimal. We investigated the effect of neonicotinoids viz. imidacloprid, thiamethoxam, acetamiprid and thiacloprid on plant height, chlorophyll, and soluble protein of cotton and okra. Thiamethoxam was found to exert an influence on the plant height of cotton and okra. There was no marked influences of neonicotinoids on the total chlorophyll content of cotton leaves, whereas acetamiprid recorded a gradual increase in the total chlorophyll content of okra leaves at 7, 14 and 21 days after treatment. All the neonicotinoid insecticides under study showed an increase in the soluble protein content of cotton and okra. An increase in soluble protein content is reported to increase the ability of plants to fix carbon dioxide (CO2) effectively and thus increase photosynthesis.

Baseline toxicity of emamectin and spinosad to Helicoverpa armigera (Lepidoptera: Noctuidae) for resistance monitoring

Acute toxicity studies of emamectin and spinosad against Helicoverpa armigera revealed that the pest is highly susceptible to both the insecticides. The median lethal dose (LD50) of emamectin is 3.86 × 10−3 µg per larva. The median lethal concentrations (LC50) of emamectin and spinosad were found to be 0.09 and 2.94 ppm, respectively. The discriminating doses were fixed based on the LC95 of the susceptible population of H. armigera as 0.80 ppm for emamectin and 10 ppm for spinosad. Resistance was not observed when the discriminating doses of emamectin and spinosad were applied on field‐collected populations of H. armigera from two intensive cotton growing areas, Coimbatore and Madurai, India.