Integration of indigenous plant extracts and a fungus, beauveria bassiana (Bals). For the management of Tribolium castaneum (Herbst) and Trogoderma granarium (Everts)

Abstract

The present study was conducted to check the toxic, growth inhibitory and combined effects of Azadirachta indica, Nicotiana tabacum, Eucalyptus globolus and an entomopathogenic fungus (EP), Beauveria bassiana against Tribolium castaneum and Trogoderma granarium. Plant extracts were applied on filter papers at a rate of 5, 10 and 15 % with the help of pipette, placed in petri-dishes, containg 50 g of wheat grains. One petri dish was kept as a control for each treatment containing untreated diet (wheat grains). Thirty 3rd instar larvae of Tribolium castaneum and Trogoderma granarium were released in each petri-dish and data regarding mortality was recorded after 24, 48 and 72 hrs. B. bassiana formulation (Racer TM) was applied at a rate of 0.3 x 108, 0.6 x 108 and 0.9 x 108 conidia/kg-1 of wheat grains. Three treated samples, each of 50 g were taken in separate small plastic jars and thirty 3rd instar larvae were used in mortality bioassay. The data regarding mortality was observed after 7, 14 and 21 days of treatment application. In the case of plant extracts, highest larval mortality 38.27 % was found against T. castaneum population of Bahawalpur (BWP) ethanol based A. indica extract, followed by 33.90 % in FSD with acetone extract at 15 % concentration after 72 hrs. The lowest mortality (11.33 %) was calculated in Bhakkar (BHAK) strain of T. castaneum with acetone extract of N. tabacum at 15 % concentration after 72 hrs. Highest mortality (35.02 %) was observed in BWP strain of T. granarium by ethanolic extract of A. indica while lowest (10.21 %) was recorded in acetone based extract. In the case of fungal toxicity bioassay, highest mortality (57.35 %) was found in the BWP population of T. castaneum, followed by Faisalabad (FSD) (50.61 %) after 21 days at concentrations of 0.9 x 108 conidia/kg-1 of wheat grains whilst lowest larval mortality (47.37 %) was observed in BHAK strain. In the case of T. granarium, highest larval mortality (54.41 %) was observed in BWP strain, followed by (46.25 %) of FSD strain. While lowest (44.43 %) was observed in FSD strain. Results of growth inhibition bioassays by extracts revealed highest pupal inhibition (66.65 %) was recorded in case of BWP strain of T. castaneum at 15 % of ethanol extract of A. indica followed by (62.06 %) as in FSD strain while comparatively low (48.27 %) was recorded in case of BHAK strain. Comparatively low pupal inhibition values were observed for T. granarium. Highest adult inhibition (48.18 %) was noticed in case of T. castaneum strain of BWP (with ethanolic extract of A. indica) while lowest (18.87 %) was observed in BHAK strain with ether extract of N. tabacum. In case of T. granarium, comparatively low adult inhibition inhibition values were observed. In case of fungus, highest pupal inhibition (56.76 %) was recorded for BWP strain of T. castaneum whilst comparatively low inhibition (43.97 %) for BHAK strains of T. granarium. In combined toxicity assays, mortality reached 77.32 % of at 15 % concentration of A. indica after longest exposure interval (21 hrs.) for T. castaneum (BWP strain) while comparatively low 71.05 % was noticed in case of T. granarium strain of Faisalabad. Pupal inhibition showed that 67.81 and 58.62 % values were recorded in case of T. castaneum and T. granarium respectively, at highest treatment combination (15 % of A. indica + 0.9 x 108 of Racer TM) while the lowest inhibitions 30.62 and 19.70 %, respectively, were achieved at lower concentrations (5 % of A. indica + 0.3 x 108 of Racer TM) of the treatment combination. Highest adult inhibitions (55.54 and 51.38 % of T. castaneum and T. granarium respectively) were recorded at highest treatment combination than 28.08 and 21.64 % noticed at lowest concentration combination of both treatments (extract + Racer TM). The overall results revealed that both bio-pesticides have proved very effective against both tested insect pests of stored commodities; especially their combined application can play a key role in IPM of stored grain insect pests. Bio-based insecticides can be used in integrated manner with other insect pest management tactics, save our expenses on traditionally used insecticides leading to potential and economical management the stored grain insect pests.