Gnanadhas Preetha

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.

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.

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.

Estimation of Diafenthiuron Residues in Cardamom (Elettaria cardamomum (L.) Maton) Using Normal Phase HPLC: Dissipation Pattern and Safe Waiting Period in Green and Cured Cardamom Capsules

Diafenthiuron is an effective insecticide used for pest management in cardamom. Residues of diafenthiuron and its degradation/dissipation pattern in cardamom were determined to work out safe waiting period. Samples were collected after three sprays of diafenthiuron @ 400 and 800 g a.i ha−1 and the residues extracted in acetonitrile and quantified in normal phase HPLC in UV detector. Diafenthiuron was detected in min. The limits of detection (LOD) and limits of quantification (LOQ) were determined to be 0.01 and 0.05 μgmL−1. The initial deposits were found to be 3.82 and 4.10 μg g−1 after sprays of diafenthiuron @ 400 g a.i ha−1 in the first and second experiments, respectively. Nearly cent percent of residues dissipated at 10 days after treatment in the recommended dose of diafenthiuron 400 g a.i ha−1 and the half life varied from 2.0 to 2.8 days with a waiting period of 5.5 to 6.7 days in green capsules of cardamom. The waiting period was 5.4 to 7.0 days in cured capsules of cardamom. With harvest being the focal point for enforcement of residue tolerances, the suggested waiting period of seven days is safe without the problem of pesticide residues in harvestable produce.

How Efficient Is Apis cerana (Hymenoptera: Apidae) in Pollinating Cabbage, Brassica oleracea var. capitata? Pollination Behavior, Pollinator Effectiveness, Pollinator Requirement, and Impact of Pollination

Cabbage is a cross-pollinated crop because of sporophytic self-incompatibility, and honey bees play an important role in its pollination. Though Asian honey bees, Apis cerana F., are used in pollination of cabbage, the rate of visitation, behavior, pollinator efficacy, and impact on seed-set are to be determined. Apis cerana occupy a share of 19.18% of all the flower visitors of cabbage in natural habitat of North Western Indian Himalayas. Pollination behavior in terms of peak activity, flowers processed per unit time, time spent per flower, and time spent in search of flowers are studied separately for both pollen and nectar foragers. Pollinator effectiveness as measured by seed set in flowers excluded from bee visitation, single bee visit, and unrestricted pollinator visits was 0.11. Studies on the impact of A. cerana bee pollination in cabbage seed production revealed an increase of 17.28% in siliqua per panicle, with 26.11% increase in seed yield. For assessing the requirement of A. cerana to pollinate one hectare of cabbage, flower availability and the speed with which the pollen and nectar foragers process the flowers are taken into consideration. A forager is estimated to pollinate 4,780 flowers a day, but cabbage flower requires 9.09 visits of A. cerana for optimum seed set. Thus, a maximum of 4,999 bee foragers or 8.33 colonies are needed to effectively pollinate 1 ha of cabbage. Though A. cerana is a good pollinator, our findings suggest that it is not an ideal pollinator of cabbage.

Pesticide Toxicity to Arthropod Predators: Exposure, Toxicity and Risk Assessment Methodologies

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.