No abstract

Tribolium castaneum is one of the major pests of stored grains which causes extensive damages. To control this insect pest many synthetic chemical pesticides are used. However, continuous usage of synthetic fumigants causes pest resurgence, toxic residues, genetic resistance in pests, environmental contamination and health hazards etc., To avert these problems, essential oils are used as bio-fumigants to control the stored pests. They could act as best alternatives to synthetic fumigant in closed environment. Hence, the present study aimed to evaluate the pesticidal activity of Callistemon citrinus oil against Tribolium castaneum. GC-MS analysis of C. citrinus essential oil (EO) showed 10 compounds; among them, the major constituent was eucalyptol (1, 8-cineole) at 40.44%. The lethal concentration (LC50) values were 37.05 μL/L (adults) and 144.31 μL/L (larvae) at 24 and 48 hrs respectively. Exposure to C. citrinus EO significantly reduced the beetle fecundity, ovicidal activity, egg hatchability, larvae survival and emergence of adult. The effect of EO on enzymatic activity of T. castaneum adults was examined using Acetylcholinesterase, α-Carboxylesterase, β-Carboxylesterase, Glutathione-S-Transferase, Acid and Alkaline phosphatase assays. The results indicated that the activity of detoxification enzymes drastically varied when compared with control. This EO had toxicant effects on all stages of the life of T. castaneum.

Essential oil (EO) was extracted from Callistemon citrinus leaves by hydro-distillation. The extracted oil was analysed by GC and Mass Spectroscopy. Analysis report showed that the major constituent of the essential oil was eucalyptol (40.44%). The EO of C. citrinus exhibited 100% fumigation toxicity (adult mortality) against adult and 95.8% larvicidal activity against Tribolium castaneum at 160 μL/L (12 hrs) and 320 μL/L (48 hrs), respectively. The effective concentration of 37.05 μL/L (adult) and 144.31 μL/L (larva) at 24 and 48 hrs respectively. A 100% repellent activity was observed at 20 μl for adult beetles and 93.3% for larvae of T. castaneum at 20 μl after 24 h. Exposure to C. citrinus EO significantly reduced beetle fecundity, ovicidal activity, egg hatching, larvae survival, and emergence of adult. The effect of EO on detoxification enzymes of T. castaneum adults was examined. Results indicated that the activity of detoxification enzymes drastically varied when compared with control. This EO had toxicant effects on all stages of the life of T. castaneum. Hence it may be used as fumigant instead of the use of using synthetic chemical fumigants.

Mosquitoes are a key threat to millions of people worldwide. They spread the pathogens that cause deadly diseases among humans and animals. Synthetic pesticides are the best agents to control mosquitoes, but they cause several problems for the environment as well as public health. Continuous usage of commonly available insecticides develops multiple resistances among pests. In search of alternatives to synthetic pesticides, botanicals could be one of the best alternatives to control mosquitoes. The present study explores the insecticidal activity of Ocimum americanum against Aedes aegypti larvae and their effect on detoxification enzymes. Leaves of O. americanum were sequentially extracted using hexane, chloroform, and methanol. Among these, hexane extract showed 100% larvicidal activity at 1 g/L concentration for 24 h and the LC50 value was 0.3 g/L. The phytochemical screening of hexane extract was performed through gas chromatography‐mass spectrometry analysis, which showed 27 compounds. The major compounds are squalene (13.03%), camphor (9.77%), and 1‐Iodohexadecane (8.02%). The toxicity of active hexane extract was tested against third instar larvae of Chironomus costatus (nontarget organism). Results revealed less toxicity (12.2%) at 1 g/L concentration on the nontarget organism. The enzyme activity of acetylcholinesterase and β‐carboxylesterase was significantly inhibited by the hexane extract. The present study reveals the insecticidal potential of O. americanum with minimum effects on nontarget organisms. The O. americanum extract inhibited the activity of A. aegypti's major insecticide‐resistant enzymes. O. americanum could be one of the best alternatives to controlling mosquitoes.

Pests in stored grains pose a global threat to food security. Tribolium castaneum (Coleoptera: Tenebrionidae) is one of the most serious stored-grain pests in the world, capable of surviving harsh environments and developing resistance to certain classes of insecticides. Fumigation toxicity and the impact of Melaleuca alternifolia Cheel (Myrtaceae) essential oil on T. castaneum were investigated in this study. The 50% lethal concentration (LC50) fumigation toxicity of M. alternifolia essential oil for T. castaneum adults and larvae was 122.7 µL/L at 24 hours and 280 µL/L at 48 hours, respectively. Gas chromatography–mass spectrometry showed that the oil’s major volatile compounds included terpinen-4-ol (31.78%), α-terpineol (20.24%), and terpinolene (17.94%). The treatment disrupted the normal enzymatic activity of acetylcholinesterase, carboxylesterase, and glutathione-S-transferase in T. castaneum adults and caused DNA damage. Melaleuca alternifolia essential oil is a strong fumigant and may be a good substitute for synthetic fumigants used to control pests of stored grain.