Chapter-1 INTRODUCTION

Transcription

1 Chapter-1 INTRODUCTION Termites belong to insect order Isoptera which have been identified by their social behavioral characteristics. The name of this insect order Isoptera is derived from two Greek words isos means equal and pteron means a wing, so the termites have two identical wings in adult stage (Thorne and Carpenter, 1992). A colony of the termites usually consists of reproductives (a queen and a king) as well as the workers and soldiers. These colonies are present within wood above-ground and/or are subterranean. A total of 2650 species all over the world, include 300 termites species as pests have been recognized (Kambhampati and Eggleton, 2000). Termites mostly occur in timber, decaying wood, plant refuse or in those soil which have high organic/humus contents. Some species of termites play a beneficial role for the regulation of soil processes like nutrient and water cycling as well as maintenance and formation of the soil structure. They also help to promote biodiversity and creating suitable conditions for plants and other biota (Korb, 2008). Most of the termite species are known for their economic importance and cause damage to the agricultural crops (Ahmed et al, 2006). The most troublesome termites in the agriculture (Pakistan) are the fungus-growing termites (Termitidae). These termites are the major menace of semi-arid and sub-humid tropics, causing economic losses to the field crops, forests trees, rangelands and buildings (Anonymous, 2000). Termites fauna of the Pakistan consists of 50 species. Out of which, nine termites species i.e., Odontotermes obesus, Odontotermes assmuthi, Odontotermes guptai, Odontotermes gurdaspurensis, Odontotermes horai, Microtermes mycophagus, Microtermes obesi, Microtermes unicolor and Microtermes paradoxalis were recorded in Punjab, Pakistan (Shahid and Akhtar, 1992; Akhtar and Shahid, 1993). In the past, the control of termites was totally based on the synthetic insecticides especially the persistent organochlorine (OC) (Khan and Singh, 1985; Anonymous, 2000, Ahmed et al., 2006). The maximum residual effect as well as the development of insecticides resistance in target pests is considered their drawbacks. Similarly, adverse effects on human health and environmental deterioration concerns (Potter and Hillery, 1

2 2001; Verkerk and Bravery, 2001) resulted in the replacement of synthetic insecticides with bio-rational ones and is now a universal acceptable and practical approach worldwide. In this regard, bioactive compounds of plant origin are considered as ecologically safe alternatives, consequently the plant extracts with complex mixtures of bioactive compounds have been investigated for their insecticide, repellent, and antifeedant properties (Zhu et al., 2001; Isman et al., 2006). Botanicals / natural insecticides should be from local plants, easily available with little or no processing and these plants should not develop into weeds or act as hosts for the crop pests. In addition, they should have low toxicity to non-target organisms, especially humans and beneficial insects (Zue et al., 2001). Active substances extracted from plants may not only act as toxicants, but also as insect growth regulators (Bowers et al., 1972) as repellents and synergists (Su and Harvort, 1981; Burfield and Reekie, 2005). Most of the plant oils are also effective as control agents against a number of insect pests (Lee et al., 2004; Al-Dosary, 2007). The pool of plants possessing insecticidal substances is enormous, as more than 1000 species of the plants stem, leaves, seeds, flowers as well as roots contain chemicals which have been used for the insect s control. Plant chemicals are mostly alkaloids which are nitrogenous in nature and these alkaloids when applied to insect bring about disturbance in the nervous system causing death (Shahid, 2003). The deleterious effects of these plant extracts on insects have been observed in several ways including suppression of calling behaviour (Khan and Saxena,1986), growth retardation (Breuer and Schmidt, 1995), toxicity (Hiremath et al.,1997), oviposition deterrence (Zhao et al., 1998), feeding inhibition (Wheeler and Islam, 2001) and reduction of fecundity and fertility (Muthukrishnan and Pushpalatha, 2001). Like alkaloids, plant flavonoids are naturally occurring substances and play an important role in insect control. These compounds function as performed or inducible anti-insect compounds (Dixon, 1999), so they may serve as natural pesticides. Many of them are being tested for repellent and deterrent effect against the insects (Simmonds, 2003). Flavonoids can modulate the feeding behaviour of the insects (Nawrot et al., 1986). The use of plant and plant derived products to control pests is very common and several plant-based products are used to control a wide variety of insects e.g., Azadirachtin from neem oil, Nicotine from Nicotiana tobacum, and rotenoids from the 2

3 roots of leguminous plants, Lonchocarpus spp. All these compounds are pest management agents acting as insect growth regulators and feeding deterrents (Ismann, 2006). Regionally and locally, different plant chemicals have been used against various insects i.e., Datura alba (Shah and Ahmed, 1983), Solanum xanthocurpum (Husain, 1995), Thevetia neriifolia, Arachis hypogaea, Carissa carandas, Ricinus communis (Talukder et al., 1998); Chenopodium ambrosioides to reduce the population and infestation of stored products beetles (Tapondijou et al., 2002). In recent years, the use of local botanicals has gained much importance mainly among the researchers because of their high bio-efficacy against the termites. Many plants have been recognized to have anti-termitic and repellent activities against the termites, such as lemon grass (Cymbopogon citratus), Cassia leaf (Cinnamomum cassia), vetiver oil (Vetiveria zizaniodes), Eucalyptus (Eucalyptus citrodora, Eucalyptus globules), cedar wood (Cedrus atlantica), clove bud (Syzgium aromaticum) (Zhu et al., 2001), Calotropis procera (Singh et al., 2002), isoborneol (Blaske et al., 2003) and Coleus amboinicus (Singh et al., 2004). Isolation of novel classes of termiticides and their active analogs from the plants having termiticidal activity, including thiophenes from several species of Echinops and others were found to be highly active against the invasive Formosan subterranean termite, Coptotermes formosanus (Fokialakis et al., 2006; Meepagala et al., 2006). Many of the medicinal plant extracts have also anti-termite properties and termite resistant formulations prepared from such extracts have been reported by Singh et al. (2001). Phyto-extracts of Adhatoda vasica, Cynodon dactylon, Pongamia pinnata, Rauvolfia serpentina, Cleistanthus collinus, Tamarindus indica and Eichhornia crassipes controlled the termites, Microcerotermes mycophagus (Das and Chattopadhyay, 2003). Adhatoda vasica leaves and Nerium oleander stem extracts have indicated significant insecticidal activities against Nilaparvata lugens (Homoptera: Delphacidae) (Hiremath et al., 1997). Dodonaea viscosa (Purple hop bush) is a termite resistant shrub (Anonymous, 2001) and the biopesticidal activity of Dodonaea angustifolia against Helicoverpa armigera (Hub.) showed significant reduction in adult longevity and also adversely effected their reproductive potential (Subashini et al., 2004). The crude extracts of Dodonaea angustifolia against Earias vittella drastically reduced the number of larvae as 3

4 compared with neem product (Malarvannan et al., 2007). Shoots (leaves, flowers and branches) of Ocimum basilicum have been reported to control the termites (Matovu, 2010). Essential oils of O. basilicum,, Cymbopogon winterianus Jowitt, Cinnamomum camphora, Rosmarinus officinalis were toxic and repellent against the dry-wood termite Cryptotermes brevis (Sbeghen et al., 2002). The plant component from O. basilicum may be feasible alternatives for the control of Macrotermes spp. (Owusu et al., 2008). Jatropha curcas L. leaf and seed extracts had toxic and repellent action against the Philippine milk termite Coptotermes vastator (Acda, 2009). Singh (2008) reported that the oil of Jatropha curcas and its toxic fraction were effective for the control of Microcerotermes beesoni. Many plant extracts have been found to alter the behaviour and gut enzyme of the termites. Seed and leaf extracts of Withania somnifera, Croton tiglium and Hygrophila auriculata have been investigated in order to determine toxicity of these extracts through change in tunnel behaviour and termite s gut fauna (Microtermes obesi) in the laboratory (Ahmed et al., 2006). Oil of Jatropha curcas L. induced reduction in tunneling activity in Coptotermes vastator (Acda, 2009) as well as leaf extracts of Azadirachta excelsa had inhibitory effect and hindrance to the tunneling activity of the termites (Sajap and Aloysius, 2000). Blaske et al. (2003) assessed the repellency of the plant-derived bicyclic monoterpenoid isoborneol on the subterranean termites in the laboratory bioassays by putting the isoborneol treated soil, untreated soil with food source of oven dried pine wood (Pinus sylvestris L. Pinaceae) in plastic zip-lock bag and releasing a group of 100 termite workers. Out of 0, 500, 1000 ppm isoborneol, latter prevented the tunneling of Reticulitermes santonensis. Isoborneol was efficient in creating repellent soil barriers. Many of the plant leaf and seeds extracts were considered very effective that they inhibit the enzymatic activities of the termites (Ahmed et al., 2006). Midgut of termite s species (Macrotermes annandalei, Odontotermes formosanus, pericaproitermes nitobei, Termes comis and Nasutitermes takasagoensis) has high amino acid concentration and proteases activities (Fujita and Abe, 2002). Zhou et al. (2007) investigated the efficacy of three prototype termite cellulase inhibitors, cellobiose imidazole (CBI), fluoromethylcellobiose (FMCB) and fluoromethylglucose (FMG) using biochemical and feeding assays. Validative bioassays with the sugars glucose, maltose and cellobiose 4

5 showed no feeding stimulation or mortality as occurred in feeding inhibitor bioassays. These results indicated the efficacy for two cellobiose-based inhibitors, FMCB and CBI, suggesting potential for these inhibitors as novel termite control agents. Davis et al. (1995) characterized the esterases of workers of the eastern subterranean termite, Reticulitermes flavipes (Kollar) and detected seven zones of esterase activity. However, effect of crude / pure extracts of the plants on enzymes of midgut have not been categorized that can be important for antitermite activity. The present project was carried out with an objective, to explore bio-efficacy of some of local plant extracts against Odontotermes obesus (Ramb.) (Isoptera: Termitidae). The current study evaluated the leaf and seed extracts of Dodonaea viscosa, Adhatoda vasica, Jatropha curcas, Moringa oleifera and Ocimum basilicum in various and their effects on the mortality, tunneling and gut enzymes activities of the O. obesus. Finally, active agent of the most efficacious extract was seaparated to validateve mentioned parameters under the laboratory conditions. 5