Ecological engineering for pest management in rice Oryza Sativa L

Abstract

Ecological engineering (EE) for pest management is a strategy to enhance the abundance, diversity, and effectiveness of natural enemies in an agricultural ecosystem. Although EE has gained acceptance as a pest management tactic, there still exist knowledge gaps in the identification of the best floral resources for the population build up and biocontrol potential of natural enemies. Hence, the present study entitled Ecological engineering for pest management in rice Oryza sativa L was carried out during 2022-23 to identify suitable flowering plants for habitat management in rice and evaluate their efficacy for ecological pest management. The olfactory response of predators viz.,lady bird beetle (Micraspis discolor), ground beetle (Ophionea nigrofasciata), green mirid bug (Cyrtorhinus lividipennis) and parasitoids Trichogramma chilonis and T. japonicum to different the flowers was assessed in a six arm olfactometer. In each arm of the olfactometer, ten flowers each of sesame, cowpea and cosmos were individually inserted and for marigold and okra, only one flower was used. The arm without flower served as the control. Ten adults of each predator and twenty adults of each parasitoid were released at the center of the olfactometer. The number of predators and parasitoids settled per arm at 5, 10, 15 and 20 min. after release (MAR) as well as the distance covered per min. was assessed. Micraspis discolor showed the highest attraction towards flowers of cowpea and okra (2.33 each arm-1) at 20 MAR followed by marigold (1.00 arm-1) and sesame and cosmos (0.67 each arm-1). The distance covered towards cowpea was 10.61 cm min-1. and whereas for okra it was 7.37 cm min-1. Similarly, for O. nigrofasciata, the highest response was recorded towards cowpea (2.00 arm-1) followed by marigold (1.67 arm-1) and sesame (1.00 arm-1). The distance covered was also higher in cowpea (3.50 cm min 1 ). Cyrtorhinus lividipennis recorded the highest attraction towards sesame (2.67 arm-1) followed by cowpea (1.33 arm-1) and marigold (1.00 arm-1), which showed significant difference with the control. The distance covered was also high in sesame (4.82 cm min 1 ) followed by cowpea (3.42 cm min-1). As for parasitoids, highest attraction of T. chilonis was found towards cowpea (4.33 arm-1), while that of T. japonicum was towards sesame (2.67 arm-1). Thus, the behavioural response studies of predators and parasitoids revealed a significantly higher preference towards the flowers of cowpea, sesame and marigold. To identify the attractive compounds in the volatiles of flowers, through GCMS analysis, their extraction was conducted through head space method and solvent extraction. The headspace analysis of marigold flowers identified seven major compounds, with insect attractant properties. The compounds were alpha ocimene, myrcene, limonene, cis ocimene, trans ocimene and beta caryophyllene. The attractant compounds of marigold flowers through solvent extraction were caryophyllene, heneicosane, squalene, eicosane, tetrapentacontane, tetracontane, hexatriacontane, heptadecane, octadecane 1-chloro- and dotriacontane and that of cowpea flowers were eicosane, heneicosane, hexadecane, dotriacontane, tetracosane, heptadecane, octadecane 1-chloro- and diisoctyl phthalate. Similarily, the attractant compounds from sesame flowers were eicosane, octacosane, nonacosane, beta-bisabolene, heptadecane, dotriacontane, tetracontane, octadecane 1-chloro- and hexatriacontane. A field experiment was laid out to study the effect of flowering plants in ecological pest management in rice with four treatments: T1- PoP of KAU, T2- PoP in combination with flowering plants, T3- farmers practice and T4- untreated control. The seedlings of best three flowers selected from the olfactometer studies viz., marigold, cowpea and sesame were planted around the rice bunds on the day of transplanting to evaluate their effect on natural enemies and insect pests in rice. The population of major insect pests and natural enemies was recorded at 15,30,45,60,75 and 90 days after transplanting. The extent of damage of stem borers (Scirpophaga incertulus and S. fusciflua) was significantly lower in ecological engineering plot (T2) (2.52 %) followed by the PoP (2.86 %), farmers practice (3.26 %) compared to untreated control (5.39 %). Similarly, the mean damage of leaf folder (Cnaphalocrosis medinalis) was lowest in T2 (1.24 %) which was on par with T1 (1.28 %). The mean population of leafhoppers (Nephotettix nigropictus, N. virescens and Cofana spectra) was lowest in PoP (0.37 m 2 ), while for hispa, Dicladispa armigera, the population in all the treatments was non significant. The population of rice bugs (Leptocorisa spp.) was lowest in PoP (4.43 m 2 ) followed by farmers practice (4.86 m-2), and PoP with flowering plants (7.06 m-2) at 90 DAT. Ecological engineering plot recorded a significantly higher population of all natural enemies as against the control, PoP and farmers practice. Five species of coccinellids were recorded from the ecological engineering plot, viz., M. discolor, Coccinella transversalis, Harmonia octomaculata, Cheilomenes sexmaculatus, and Brumoides suturalis, The highest population of ground beetles (O. nigrofasciata) was recorded in ecological engineering plot (1.60 m-2) followed by control (0.90 m-2). Similarly, significantly higher population of rove beetles and damselflies (2.94 and 1.41 m-2 respectively) were recorded in EE plot. Seven species of spiders viz., Tetragnatha javana, T. mandibulata, Pardosa pseudoannulata, Neoscona theisi, N. elliptica, Argiope catenulate and Oxyopes javanus were documented wherein the population was highest in ecological engineering plot (1.97 m-2). The hymenopteran parasitoids were recorded through sweep netting and significantly higher population was recorded in ecological engineering plot (2.20 /5 sweeps), followed by control (1.06 /5 sweeps). The major parasitoids recorded under Ichneumonidae were Xanthopimpla sp., Trathala flavoorbitalis, Amyosoma sp., Isotima sp., Metopius rufus, Goryphus sp. and Stenobracon nicevelli, whereas Tropobracon sp., and Cardiochiles sp. were documented under Braconidae.The parasitization on stem borer egg mass by Tetrastichus sp. and Telenomus sp. was observed, in which the extent of total parasitism was 92.5 per cent in ecological engineering plot, followed by 72.5 percent in the control. The yield recorded in PoP and ecological engineering plot was 529.73 g m-2 and 513.80 g m-2 respectively and was on par with each other, while the control plot recorded the lowest yield of 263.46 g m-2. The benefit-cost ratio in the ecological engineering plot is 2.16 while the control recorded a ratio of 0.95. The present study identified three flowering plants viz., cowpea, marigold and sesame having the potential to enhance the population of predators and parasitoids in the rice ecosystem. Hence the study will pave the way to develop a habitat management module for pest management in rice. Further studies to identify additional plant species for habitat management are to be carried out. Detailed investigations on the impacts of floral resources on the growth and development of entomophagous insects have to be undertaken to fortify conservation biological control strategies