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Subject: Agricultural Entomology × End date: 2021 × Start date: 2021 × Thesis Type: M.Sc ×
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    ThesisItemOpen Access
    Susceptibility of Tetranychus okinawanus Ehara (Prostigmata: Tetranychidae) infesting ornamental plants to novel acaricides
    (Department of Agricultural Entomology, College of Agriculture, Vellanikkara, 2021) Sreshma, M; KAU; Haseena, Bhaskar
    Spider mites of the family Tetranychidae are well-known agricultural and horticultural pests that feed on a wide variety of plants, including vegetables, fruit trees, and ornamentals. Many traditional insecticides and acaricides have been used to manage mite pests for several decades. The widespread usage of acaricides around the world has facilitated development of resistance in different mite species, making mite management challenging. As a result, many novel acaricides with distinct chemical structures and modes of action have been developed and marketed for mite control. However, after a few years of use, mite populations developed resistance to these newly introduced compounds too. The spider mite species, Tetranychus okinawanus, recently recorded on an ornamental plant Adenium in Thrissur district, for the first time in India, has now emerged as the predominant species of mite infesting ornamental plants in Kerala. Recently, several growers reported inefficacy of the commonly used novel acaricides against mite pests in many ornamental crops, suggesting that the mite populations might have developed resistance to acaricides. Hence a study was carried out to investigate the status of acaricide resistance in Tetranychus okinawanus infesting Adenium in horticultural nurseries and also to elucidate the biochemical mechanism involved in development of resistance. Purposive surveys were conducted in six commercial horticultural nurseries in Thrissur district viz., National Rose Garden, Mangadan Botanical Garden, Ayyappa Nursery, Saranamayyappa Nursery, Pooja Gardens and Nursery, and Manalur Adenium Garden and samples of spider mite infesting Adenium were collected. Mites were maintained as separate isoline cultures assigning unique accession numbers as NrAd1, MgAd2, AyAd3, SyAd4, PjAd5 and MnAd6. Morphological characterisation of the slide mounted mite specimens from the isoline cultures was carried out to confirm the species identity as T. okinawanus. Susceptibility of the six field populations to three acaricides viz., spiromesifen, fenazaquin and dicofol was evaluated in the laboratory, in comparison with the reference susceptible population maintained without exposure to any acaricides in the laboratory, following toxicological bioassay. Susceptibility studies with fenazaquin revealed that the accession NrAd1 recorded the highest LC50 value (27.85 ppm) and has developed moderate level of resistance (14.38-fold) to fenazaquin. This was followed by PjAd5 (9.70-fold), AyAd3 (4.06-fold), MnAd6 (3.78-fold), and SyAd4 (3.23-fold). The lowest resistance ratio was recorded by the accession MgAd2 (1.66). The toxicity studies of spiromesifen also recorded low to moderate levels of resistance in different populations of T. okinawanus. The accession NrAd1 recorded highest resistance ratio of 27.31 followed by PjAd5 (7.18), MnAd6 (3.94), AyAd3 (1.78), MgAd2 (1.42) and SyAd4 (1.06). However, the mite populations showed only low level of resistance to dicofol, recording resistance ratios in the range of 3.65 to 1.22. Biochemical basis of acaricide resistance in different populations of T. okinawanus was investigated by estimating the activity of detoxifying enzymes such as carboxyl-esterase, cytochrome P450 and glutathione S- transferase. Carboxyl-esterase enzyme showed an enhanced activity of 1.03 to 3.52-fold, while cytochrome P450 monooxygenases recorded 1.01 to 2.08-fold higher activity in the field collected populations, compared to the susceptible population. The level of these detoxifying enzymes was found to be higher in the accession NrAd1, which also recorded the highest resistance ratio in the study. However, the activity of glutathione S-transferase (GST) did not differ significantly among the field populations and also with susceptible population, indicating that GST is not a contributing factor in the development of resistance in T. okinawanus against spiromesifen, fenazaquin and dicofol. The study recorded development of resistance in the spider mite, T. okinawanus on Adenium to spiromesifen and fenazaquin, in the horticultural nurseries in Thrissur district, Kerala for the first time in the world. The significant role of the detoxifying enzymes, carboxyl-esterases and cytochrome P450 monooxygenases in imparting resistance in T. okinawanus to the two novel acaricides, fenazaquin and spiromesifen was also confirmed in the study. The study demands formulation of a suitable resistance management strategy in horticultural nurseries in the state for suppressing or delaying resistance development in mite populations.
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    ThesisItemOpen Access
    Microbial diversity in hive-stored pollen of indian honey bee, Apis cerana indica (Fabricius)
    (Department of Agricultural Entomology, College of Agriculture, Vellanikkara, 2021) Abhishek, V; KAU; Mani Chellappan
    Honey bees are eusocial flying insects. Among all insects that pollinate, honeybees are considered to be one of the crucial pollinators. Honey bees represent only a small fraction of the roughly 20,000 known species of bees. Honey bees obtain all of their nutritional requirements from a diverse combination of pollen and nectar. Pollen grains referred to as 'bee bread' or 'bee meat' are the natural sources of proteins, vitamins, fats, lipids and minerals, of which proteins are very much essential for building the body tissues of the bees, especially during the early embryonic growth. Worker bees of Apis cerana indica help in the fermentation of pollen which releases additional nutrients that are used in the production of antibiotics and fatty acids which inhibit spoilage. Pollen analysis of samples provides the information regarding the plants preferred by bees for nectar, as the pollen grains dispersed are mostly collected by bees along with nectar. Honey has two sources of contamination, primary one being the hive stored pollen. Thus, it is very essential to study the microbial diversity of pollen, which may lead to spoilage of pollen and nectar. The present investigation on “Microbial diversity in hive-stored pollen of Indian honey bee, Apis cerana indica (Fabricius)” was conducted at Department of Agricultural Entomology, College of Agriculture, Vellanikkara, Kerala Agricultural University during 2020-2021 in order to study the diversity of hive-stored pollen and associated microbes in A. cerana indica (Fabricius) colonies. Purposive surveys were conducted in six locations at Palakkad and Wayanad district viz., Mannarkkad, Nellipuzha, Nottaamala, Kenichira, Kayakunnu and Cheengode. Hive stored pollen collected were maintained in refrigerated conditions after assigning unique accession numbers as PKD-1, PKD-2, PKD-3, WYD-1, WYD2, WYD-3. Microbial diversity, microbial load of hive stored pollen, identification and characterization of pollen with respect to its nature, size, shape, aperture, exine pattern along with physicochemical properties viz., moisture content, water activity, pH, ash content, total acidity and protein content were studied. Palynological identification plays a crucial role in beekeeping industry. Pollen aids as a food supplement to honeybees for their growth and development. It assists in the identification of geographical and botanical origin of pollen. A total of 21 plants were recorded as pollen sources by bees from the study area (six locations) of two districts. Ten pollen types were identified based on its nature, size, shape, aperture, exine pattern using PalDAT software. Identified plant species were Sphagneticola trilobata (Asteraceae), Caesalpinia pulcherrima (Fabaceae), Zinnia elegans (Asteraceae), Ocimum sanctum (Lamiaceae), Clitoria ternatea (Fabaceae), Biophytum sensitivum (Oxalidaceae), Bauhinia acuminata (Fabaceae), Mimosa pudica (Fabaceae), Tecoma stans (Bignoniaceae), Portulaca grandiflora (Portulacaceae). Characterization of pollen revealed that ten plant species belonging to seven families serve as pollen sources in respective survey locations. Physicochemical properties of hive stored pollen of A. cerana indica collected from six locations were investigated by estimating the moisture content, water activity, pH values, ash content, total acidity and protein content. Moisture content varied from 15.29-15.38 (g/100g). Water activity varied from 0.73 to 0.74 (aw) and the pH varied between 3.77 and 3.83. Ash content varied from 1.87-2.01 (g/100g). Total acidity varied from 9.64-10.13 (mmol/g). Protein content varied from 3.46-3.69 (%). Parameters like moisture content, water activity, protein content were more in the Wayanad sample, it may be because of high humidity and temperature variations. Parameters like pH, total acidity and ash content were more in Palakkad sample, which infers that mineral content might be more. Microbial diversity of hive stored pollen of Apis cerana indica collected from six locations was investigated by identifying the microbes through their morphological, cultural, molecular characterization. Other parameters like microbial diversity, microbial load, microbial load to pollen grain ratio, microbial population were also observed. In total, four bacteria and three fungal species were identified. However, colonies of actinomycetes and yeast were not obtained. Out of four bacteria, B2, B3, B4 – gram positive while B1- gram negative. The shape of all bacterial isolates was rod with change in their colony colour.16s rRNA sequencing of bacterial isolates revealed that B1 as Pseudomonas aeruginosa, B2 as Bacillus megaterium, B3 as Bacillus aryabhattai and B4 as Bacillus megaterium respectively. Out of the three fungi, colony colour of T1 colony colour was green, W1 colony colour was white and A1 colony colour was orange. All isolates have flat elevation with an entire margin. ITS sequencing of fungal isolates revealed that T1 as Trichoderma reesei, W1 as Westerdykella multispora and A1 as Neurospora crassa. Microbial diversity was more in sample collected Wayanad with two fungal and two bacterial colonies whereas, one fungal and two bacterial colonies in sample collected from Palakkad. Microbial load was more in samples from Wayanad (6.6x104 cfu/g) when compared with Palakkad sample (3.3x104 cfu/g). Comparison of microbial load to pollen grain ratio revealed that Wayanad sample recorded highest with 6.6x104 cfu/g to Palakkad sample with 3.3x104 cfu/g. Bacterial and fungal populations were observed more in Wayanad sample when compared to Palakkad sample. The study recorded the pollen sources of different localities in and around the Palakkad and Wayanad districts of Kerala. Moisture content plays a significant role which might be the reason for high microbial diversity and microbial load in Wayanad. The present study demands the investigations of other physicochemical properties like EC, starch content, amino acid composition, microbial spores present in pollen which could be useful for the food preservation industry or potentially hazardous in due course of time.
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    ThesisItemOpen Access
    Insecticide resistance management in Rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae)
    (Department of Agricultural Entomology, College of Agriculture, Vellayani, 2021) Neethu, P; KAU; Thania Sara Varghese
    The research work entitled "Insecticide resistance management in rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae)" was done at College of Agriculture, Vellayani during 2019 to 2021.The objectives of the study were to assess the resistance levels in rice weevil, biochemical basis of resistance and screening of new molecules for the management of S. oryzae. Different sample populations of S. oryzae were collected from the three godowns of Food Corporation of India (FCI) viz., Kollam, Valiyathura, and Thikkodi, as well as a susceptible lab culture of S. oryzae maintained without pesticide exposure, was obtained from the Division of Entomology, Indian Agricultural Research Institute (IARI). Resistance levels of the commonly used insecticides in FCI viz., malathion and deltamethrin were evaluated in the three populations collected from Kollam, Valiyathura and Thikkodi by film method of bioassay and compared it with the susceptible lab population from IARI. Kollam population showed highest resistance to both malathion and deltamethrin with resistance ratios of 14.94 and 9.03 followed by Valiyathura with resistance ratios of 11.39 and 7.79, respectively. Thikkodi population showed the least resistance to malathion and deltamethrin, with resistance ratios of 8.74 and 5.48, respectively. Malathion resistance was higher in all the three populations than the deltamethrin resistance. The most resistant population selected from the previous experiment i.e., the Kollam population was further assayed for its biochemical basis along with the susceptible IARI lab culture. The Kollam population was found significantly higher in total protein (6 mg ml-1 ) and activity of detoxifying enzymes viz., carboxylesterases (0.65 µmol min-1 mg protein-1 ), glutathioneS-transferases (0.41 µmol min-1 mg protein-1 ) and cytochrome P450 (0.74 p mol min-1mg protein-1 ) than the lab sample. The sample population collected from Kollam was again screened for their susceptibility to new generation insecticides like fipronil, indoxacarb and chlorantraniliprole by film method of bioassay. Fipronil was found to be more toxic with LC50 value of 5.86 ppm followed by indoxacarb (90.57 ppm) and chlorantraniliprole (4041.43 ppm). Fipronil and indoxacarb were 619.8- and 40.13-fold toxic to resistant population of S. oryzae with respect to malathion. The newer insecticides in the previous experiment along with malathion and deltamethrin were further screened simulating the conditions of FCI godown. The insecticides were sprayed on jute bags containing 1 kg of rice grains and 50 adult beetles of Kollam population of S. oryzae. The dosages of newer insecticides were taken 10 times more the LC50 value obtained in the laboratory bioassay and FCI recommended dosage was taken for malathion and deltamethrin. Fipronil 5% SC @ 0.006% recorded significantly higher mortality of 86.5 and 89.5 per cent at 24 and 48 h of treatment followed by indoxacarb 14.5% SC @ 0.09% and chlorantraniliprole 18.5% SC @ 4.04%. The persistence of the most effective insecticide fipronil along with malathion and deltamethrin on rice grains were further studied by recording the residue levels at different time intervals after spraying. Dosages were same as the previous experiment. Insecticides were sprayed on jute bags containing rice grains and residues were analysed at 0 (2 h after spray), 1, 3, 5, 7,10, 15, 20 and 30days intervals using the methods validated prior to residue estimation. Fipronil residues were below the limit of quantification at 2 h after spraying. The residues of deltamethrin and malathion persisted up to 3 and 5 days after spraying with a half-life of 2.48 and 2.71 days, respectively. From the present study it is revealed that S. oryzae collected from Kollam, Valiyathura and Thikkodi were resistant to the commonly used insecticides viz., malathion and deltamethrin and it is confirmed here by the presence of higher levels of detoxifying enzymes in the resistant population. Further screening of newer insecticide molecules against the resistant population of S. oryzae suggested that fipronil 5% SC @ 0.006% is highly effective and less persistent on grains when compared to malathion and deltamethrin.
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    ThesisItemOpen Access
    Antifeedant and growth regulatory activity of Sphagneticola trilobata(L) Pruski on tobacco caterpiller, Spodoptera litura (Fab)(Lepidoptera: noctuidae)
    (Department of Agricultural Entomology, College of Agriculture, Vellanikkara, 2021) Rahul, Raj M; KAU; Mani, Chellappan
    One of the most important aspects of agriculture is pest management. Pesticides used in the past produced a variety of environmental problems, including ecological imbalances, soil fertility loss, and marine life degradation. Conventional pesticides have also been linked to a number of significant and detrimental effects on human and animal health, including severe malignancies, neurological diseases, hormone disruptions, and reproductive troubles. Botanical pesticides are found to be an effective alternative to conventional pesticides for pest management. Sphagneticola trilobata (L.) Pruski, is an herb included in the Asteraceae and is well known for its medicinal properties, information about its bioactivity against insects is very less. Hence, in this study we evaluated the antifeedant and growth regulatory activity of various extract of Sphagneticola trilobata against Spodoptera litura. Dried and powdered S. trilobata plant materials were sequentially extracted with hexane and methanol followed by concentrated in vacuo in a rotary evaporator at a lower temperature to obtain crude extracts of S. trilobata. Hexane extracts of aerial parts and roots were named as SP1 and SP3 and methanol extract of aerial parts and roots were named as SP2 and SP4. The yield of methanol extract of aerial parts (5.67% w/w) was higher followed by methanol extract of roots (2.32% w/w), hexane extract of aerial parts (1.96% w/w) and hexane extract of roots (1.23% w/w) The antifeedant activity of various extracts of Sphagneticola trilobata tested in nochoice leaf disc bioassay revealed that methanol extract of aerial parts of S. trilobata had the maximum antifeedant activity of 52.10 per cent at 0.1 per cent of the extract against S. litura after 24h of feeding. Compared to aerial extracts, root extracts were less active against S. litura. At lower concentrations, the antifeedant activity of all the extract were not much prominent and are not statistically significant. The antifeedant activity of all the extract increased in 48h experiment except for 0.1 per cent concentration. The decreasing order of antifeedancy of four extracts was SP2>SP1>SP4>SP3. ii Similar results were recorded in the choice method of bioassay of extracts against S. litura. Maximum antifeedant activity of 46.65 per cent was obtained for methanol extract of aerial parts (SP2) after 24h of feeding. At lowest concentrations of 0.005, 0.01 and 0.03 per cent none of the extracts exhibited significant difference in activity. Increasing concentration beyond 0.03 per cent had a significant effect on antifeedancy in the choice method. As similar to the no-choice method, reduced activity was recorded after 48h of feeding. Maximum antifeedant activity of 38.81 per cent was recorded for SP2 after 48h of feeding. Similar to the no-choice method, root extracts exhibited a low level of activity against S. litura. Insect growth regulatory activity of various extracts was evaluated by diet incorporation method against five-day old larvae of S. litura. A maximum larval weight reduction of 31.4 per cent was recorded for SP4 at 0.1 per cent of the extract. A significant increase in larval duration compared to control was recorded for SP2 extracts at higher concentrations. Similar to larval weight reduction, a dose-dependent pupal weight reduction was recorded for SP1 (29.57 per cent at 0.1 per cent of the extract). Compared to the other three extracts, pupal weight reduction was very less for SP3. Pupal duration increased to a maximum period of 13.54 days at 0.1 per cent of SP4. Observations on abnormal pupae were not significant for any of the extracts. No larval mortality could be obtained with any of the treatments. A maximum of 16.7 per cent larval pupal intermediates was recorded for SP4 at the highest dose, but it was not significantly different from other treatments. Similar to larval mortality, no pupal adult intermediates were recorded for any of the extracts. Maximum pupal mortality of 41.00 per cent was recorded at 0.1 per cent of SP1, and it was significantly different from other treatments. For all the extracts, pupal mortality was dose-dependent. Minimum adult emergence was noticed for SP1 at 0.1 per cent of the extract. GC-MS/MS and LC-MS/MS analysis of active fractions revealed that more phytochemicals are present in aerial parts than roots. The higher activity of aerial parts might be due to the presence bioactive compounds like andrographolide, artemisin, iii genistein and taxifolin. Most of the chemicals identified were derivatives of steroids, terpenoids and flavonoids. The study results indicate that methanol extract of aerial parts of S. trilobata has strong antifeedant activity against S. litura. All other extracts were relatively less active against S. litura. Insect growth regulatory activity was maximum for hexane extract of aerial parts. All the extracts adversely affected the growth and devolvement of S. litura. The absence of larval mortality indicates that all the extracts have less contact toxicity.
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    ThesisItemOpen Access
    Antifeedant and growth regulatory activity of Sphagneticola trilobata(L) Pruski on tobacco caterpiller, Spodoptera litura (Fab)(Lepidoptera: noctuidae)
    (Department of Agricultural Entomology, College of Agriculture, Vellanikkara, 2021) Rahul Raj, M; KAU; Mani, Chellappan
    me Browse Help Sign on to: Search DSpace DSpace logo Kerala Agricultural University Digital Library 1. KAUTIR (Kerala Agricultural University Theses Information and Retrieval) PG Thesis a Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/12249 Title: Antifeedant and growth regulatory activity of Sphagneticola trilobata(L) Pruski on tobacco caterpiller, Spodoptera litura (Fab)(Lepidoptera: noctuidae) Authors: Mani, Chellappan Rahul, Raj M Keywords: Agricultural Entomology Tobacco Spodoptera litura Lepidoptera Noctuidae Pruski Issue Date: 2021 Publisher: Department of Agricultural Entomology, College of Agriculture, Vellanikkara Abstract: One of the most important aspects of agriculture is pest management. Pesticides used in the past produced a variety of environmental problems, including ecological imbalances, soil fertility loss, and marine life degradation. Conventional pesticides have also been linked to a number of significant and detrimental effects on human and animal health, including severe malignancies, neurological diseases, hormone disruptions, and reproductive troubles. Botanical pesticides are found to be an effective alternative to conventional pesticides for pest management. Sphagneticola trilobata (L.) Pruski, is an herb included in the Asteraceae and is well known for its medicinal properties, information about its bioactivity against insects is very less. Hence, in this study we evaluated the antifeedant and growth regulatory activity of various extract of Sphagneticola trilobata against Spodoptera litura. Dried and powdered S. trilobata plant materials were sequentially extracted with hexane and methanol followed by concentrated in vacuo in a rotary evaporator at a lower temperature to obtain crude extracts of S. trilobata. Hexane extracts of aerial parts and roots were named as SP1 and SP3 and methanol extract of aerial parts and roots were named as SP2 and SP4. The yield of methanol extract of aerial parts (5.67% w/w) was higher followed by methanol extract of roots (2.32% w/w), hexane extract of aerial parts (1.96% w/w) and hexane extract of roots (1.23% w/w) The antifeedant activity of various extracts of Sphagneticola trilobata tested in nochoice leaf disc bioassay revealed that methanol extract of aerial parts of S. trilobata had the maximum antifeedant activity of 52.10 per cent at 0.1 per cent of the extract against S. litura after 24h of feeding. Compared to aerial extracts, root extracts were less active against S. litura. At lower concentrations, the antifeedant activity of all the extract were not much prominent and are not statistically significant. The antifeedant activity of all the extract increased in 48h experiment except for 0.1 per cent concentration. The decreasing order of antifeedancy of four extracts was SP2>SP1>SP4>SP3. ii Similar results were recorded in the choice method of bioassay of extracts against S. litura. Maximum antifeedant activity of 46.65 per cent was obtained for methanol extract of aerial parts (SP2) after 24h of feeding. At lowest concentrations of 0.005, 0.01 and 0.03 per cent none of the extracts exhibited significant difference in activity. Increasing concentration beyond 0.03 per cent had a significant effect on antifeedancy in the choice method. As similar to the no-choice method, reduced activity was recorded after 48h of feeding. Maximum antifeedant activity of 38.81 per cent was recorded for SP2 after 48h of feeding. Similar to the no-choice method, root extracts exhibited a low level of activity against S. litura. Insect growth regulatory activity of various extracts was evaluated by diet incorporation method against five-day old larvae of S. litura. A maximum larval weight reduction of 31.4 per cent was recorded for SP4 at 0.1 per cent of the extract. A significant increase in larval duration compared to control was recorded for SP2 extracts at higher concentrations. Similar to larval weight reduction, a dose-dependent pupal weight reduction was recorded for SP1 (29.57 per cent at 0.1 per cent of the extract). Compared to the other three extracts, pupal weight reduction was very less for SP3. Pupal duration increased to a maximum period of 13.54 days at 0.1 per cent of SP4. Observations on abnormal pupae were not significant for any of the extracts. No larval mortality could be obtained with any of the treatments. A maximum of 16.7 per cent larval pupal intermediates was recorded for SP4 at the highest dose, but it was not significantly different from other treatments. Similar to larval mortality, no pupal adult intermediates were recorded for any of the extracts. Maximum pupal mortality of 41.00 per cent was recorded at 0.1 per cent of SP1, and it was significantly different from other treatments. For all the extracts, pupal mortality was dose-dependent. Minimum adult emergence was noticed for SP1 at 0.1 per cent of the extract. GC-MS/MS and LC-MS/MS analysis of active fractions revealed that more phytochemicals are present in aerial parts than roots. The higher activity of aerial parts might be due to the presence bioactive compounds like andrographolide, artemisin, iii genistein and taxifolin. Most of the chemicals identified were derivatives of steroids, terpenoids and flavonoids. The study results indicate that methanol extract of aerial parts of S. trilobata has strong antifeedant activity against S. litura. All other extracts were relatively less active against S. litura. Insect growth regulatory activity was maximum for hexane extract of aerial parts. All the extracts adversely affected the growth and devolvement of S. litura. The absence of larval mortality indicates that all the extracts have less contact toxicity.
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    ThesisItemOpen Access
    Toxicity of insecticides to cheilomenes sexmaculata fabricius (coleoptera:coccinellidae)
    (Department of Agricultural Entomology, College of Agriculture, Vellanikkara, 2021) Pavithrakumar, K; KAU; Smitha, M S
    Biocontrol represents a sustainable and economically feasible way of pest management. However, under high herbivore pressure, bioagents alone are often unable to provide quick reduction of pest population, calling for insecticide based interventions. Chemical control, though designed to cause rapid mortality of target pests also adversely impact the natural enemies, leading to reduction in their growth, survival and reproduction. Hence it becomes imperative to evaluate the effects of insecticides on efficient natural biocontrol agents, to select safe insecticides and use them harmoniously. The six spotted zigzag lady beetle, Cheilomenes sexmaculata (Coleoptera: Coccinellidae), is an efficient natural enemy of aphid species in various crops due to its voracious feeding habit and density responsiveness. It is very common in cowpea and plays a major regulatory role against the cowpea aphid, Aphis craccivora. However, biocontrol by C. sexmaculata is often destabilized by the indiscriminate use of insecticides. Selection of insecticides safe to C. sexmaculata requires knowledge on direct and indirect effects of insecticides on the growth and development of the predator. Hence five insecticides and a botanical that are recommended in cowpea for pest management were evaluated for their toxicity to C. sexmaculata in the laboratory as well as their impact on field efficacy of the predator. Assessment of direct lethal impact, by exposing the life stages of the predator to field doses of insecticides, revealed the highly toxic nature of dimethoate and thiamethoxam to grub, pupa and adult stages of C. sexmaculata, leading to 100.00 per cent mortality. Exposure to dimethoate caused complete mortality of eggs while thiamethoxam was harmless to eggs with only 22.50 per cent mortality. Neem oil emulsion (3%) was found harmful to the non-feeding egg and pupal stages by completely inhibiting hatching and adult eclosion. In grub and adult stage, neem oil caused a mortality of 32.5 and 50 per cent respectively. Flubendiamide and spinosad were relatively harmless to all stages, inducing 22.50 and 15.00 per cent mortality in eggs, less than 10 per cent mortality to grubs and pupae, and 12.5 per cent mortality to adults of C. sexmaculata. Exposure of first instar grubs to sub lethal doses of insecticides also revealed adverse effects on development and reproduction of the predator. While exposure todimethoate led to complete mortality of grubs, exposure to thiamethoxam and neem oil prolonged the development period by two days and reduced the oviposition period by eight and five days, respectively. Adult longevity also was reduced by 4-8 days, after exposure to these insecticides. The fecundity was also reduced to 1637.13±92.10 and 1727.13±51.75 eggs/female respectively in thiamethoxam and neem oil as compared to 2151.88±27.31 in control. In both thiamethoxam and neem oil treatments, fertility was reduced by 15.00 per cent of 1868±26.50 offsprings/female recorded in control. Flubendiamide had no influence on the development period but reduced the oviposition period by seven days and male and female longevity by four and eight days respectively. There was a reduction in fecundity and fertility by 27.00 and 14.00 per cent respectively as well. Spinosad had no significant influence on developmental period of immatures but reduced the fecundity to 1917.00±89.43 eggs/female. Evaluation of insecticides in cowpea field demonstrated the effectiveness of dimethoate and thiamethoxam in managing aphids with drastic reduction in population till 15 th day with 3.20 and 1.80 aphids/10cm twig compared to 33.88 aphids in control 15 days after spray. The plots treated with flubendiamide, neem oil emulsion and spinosad recorded 17.90, 17.35 and 17.00 aphids/10cm twig respectively at 15 DAS and were inferior to dimethoate and thiamethoxam in aphid management. However, there was a gradual increase in the predator population after third day of spray from 1.05, 1.25 and 1.20 numbers/plant to 1.90, 2.00 and 1.90 numbers/plant at 15 DAS in flubendiamide, neem oil emulsion and spinosad treatments respectively compared to control (1.55 and 2.15 numbers/plant). This indicates the safety of these insecticides to predator in field. Whereas, no predator population was observed in dimethoate and thiamethoxam treatments till 15 DAS. The study provides a measure of safety of insecticides in an IPM programme with C. sexmaculata, a promising bioagent against the key pest, A. craccivora in cowpea. The results point out the deleterious effect of dimethoate and thiamethoxam to C. sexmaculata. Botanical, neem oil is harmless to grubs but harmful to other life stages of the predator and also adversely affects growth and reproduction at sublethal doses. Flubendiamide, though harmless at field doses, alters the reproductive parameters at sublethal level. Spinosad, with only minimal reduction in fecundity, is harmless to C. sexmaculata.
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    ThesisItemOpen Access
    Biological control of the tobacco cutworm Spodoptera litura (Fabricius) (Lepidoptera:Noctuidae) using Sycanus collaris (Fabricius) (Hemiptera: Reduviidae)
    (Department of Agricultural Entomology, College of Agriculture, Vellanikkara, 2021) Gadikota, Sravanthi; KAU; Madhu, Subramanian
    Salad cucumber (Cucumis sativus L.) is among the most popular vegetables grown in polyhouses across Kerala, which has been gaining significance in recent years. However, the warm, humid conditions, abundance of food and the relatively low presence of natural enemies encourage build up of arthropod pests in polyhouse cultivation. Among these, the tobacco cutworm Spodoptera litura (Fab.) (Lepidoptera: Noctuidae) is one of the destructive pest. Management of the tobacco cutworm using insecticide based management strategies is not advisable as cucumber fruit is consumed in raw form. Biocontrol could be a more ecologically sound and economically feasible alternative. The reduviid bug, Sycanus collaris (Fab.) (Hemiptera: Reduviidae) is one such potential candidate for biocontrol of S. litura in polyhouses. However, S. collaris remains to be evaluated as a biocontrol agent under Kerala conditions. Hence a study was conducted to investigate the biology, functional response and prey stage preference of the reduviid predator S. collaris as well as to evaluate its potential for the management of S. litura on cucumber under polyhouse cultivation. Biology of S. collaris was studied on larvae of Galleria mellonella. Eggs were hatched after a mean incubation period of 13.21 days. Development of nymphs, normally with five instars, with a mean duration of 12.55, 9.12, 8.88, 10.95 and 15.93 days respectively. After the pre oviposition period of 12.60 days, egg laying continued for 51.86 days. Females died in 13.43 days after laying last batch of eggs. Average fecundity of the bug was 451.56 eggs. Mean longevity of 78.95 days was longer for females than 66.29 days for adult males. Functional response of fifth instar nymphs of S. collaris on third instar larvae of S. litura at different prey densities of 1, 2, 4, 8 and 16 larvae/bug was assessed in laboratory. Nymphs of S. collaris killed up to 5.50 larvae in 24 h at a prey density of 16 larvae per bug. Logistic regression analysis revealed a type II curvilinear functional response with an attack rate of 0.0198 h -1 while the handling time was between 0 to 0.460 h.The prey stage preference of the fifth instar nymphs of S. collaris on S. litura was studied by offering all the five different larval instars larval instars in equal proportions of 2:2:2:2:2 ratio. The predator showed marked preference towards first, second and third instar larvae of S. litura larvae over fifth instar larvae. The predator also showed significantly higher preference to third instar S. litura larvae as compared to fourth instar larvae. Biocontrol potential of S. collaris against tobacco caterpillar, S. litura on salad cucumber in polyhouse conditions was evaluated on KPCH 1 variety of cucumber. The plot in which predator was released recorded significantly lower number of S. litura compared to untreated control. The population of S. litura declined by 63.4 and 89.4 per cent, respectively on the first and third day after release of the predator and no larvae were observed on the five days after bug release. However, the larval population of five per plant showed no reduction after five days, in control plots. The mean yield per plant in which predator was released @ 100 nymphs/50 m 2 recorded significantly higher yield than control plot. The study demonstrated that the reduviid predator S. collaris can be used for inoculative release for the management of S. litura in protected cultivation.