Susceptibility of three biocontrol agents of brinjal insect pests to seven selected insecticides

Susceptibility of three biological control agents of Brinjal insect pests to seven selected insecticides were evaluated. Lowest mortality (6.67 %) of Camponotus compressus was found in Bactoil and Nimbicidene 0.03 EC treated brinjal and the highest mortality (100%) was recorded from Necstar-50 EC and Booster-10 EC treatments. The lowest mortality of Micraspis crocera Muls was recorded from Bactoil (3.67%) treatment while the highest mortality of Micraspis crocera Muls was found in Necstar-50 EC (100.00%) and Booster-10 EC (100.00%) treated brinjal. In case of Trathala emergence from infested shoot, the highest percentage (22.22%) was observed in the untreated control plots and lowest emergence was in Necstar-50 EC (2.22%) and Proclaim-5 SG (3.33%) treated brinjal shoots. In case of the infested fruit specimen, the highest (22.22%). Trathala emergence was found in the untreated control plots followed by the plots treated with Bactoil (18.89 %) and Nimbicidene 0.03 EC (17.78 %) while the lowest was in Necstar-50 EC (1.11%) and Booster-10 EC (2.22 %) treated brinjal fruits. Compatibility factor was highest for Bactoil (13.94, 25.33 and 27.92 with C. compressus , M. crocera and Trathala, respectively) and was lowest for Booster-10 EC (0.86, 0.86 and 4.30 with C. compressus , M. crocera and Trathala, respectively). Therefore Bactoil, Nimbicidene 0.03 EC and Tracer-45 SC were found to be the most compatible insecticides for controlling the Brinjal shoot and fruit boruss.


INTRODUCTION
Predators of five different orders such as Coleoptera, Neuroptera, Diptera, Hymenoptera and Mantoidea were reported to be found in brinjal ecosystem (El-shafie 2001). Eight different taxonomic groups of soil dwelling natural enemies were also recorded, among them Formicidae, Forficulidae, Araneae, Gryllidae, Carabidae and Staphylinidae were common. Major parasitoids recorded in the brinjal field were Trathala sp., Trichogramma sp., Erioborus sp., Ceranisus sp. (FAO, 2003).
In brinjal cultivating field different kinds of natural enemies viz., ladybird beetles, carabid beetles (ground beetle), lacewings, preying mantids, spiders, earwigs, predatory bugs, syrphid flies, Trathala, true bugs, predatory flies, predatory mites etc. are frequently active and play important role against insect pests of brinjal. Among them spiders, ladybird beetles, black ants are the most frequently occurring predators (FAO, 2003 For controlling insect pests of brinjal, farmers usually spray different kinds of chemical insecticides during the crop season, which kill natural enemies and lead to the resurgence of target pest and outbreak of secondary pests, resistance biotype development, environmental pollution and health hazards (Pedigo, 2002). It also leads to the development of the pesticides resistance of the target pests. However some pesticides are less toxic, more selective and less harmful to natural enemies (Schuster & Stansly, 2000). The botanical and microbial insecticides are more selective and less harmful for natural enemies as well as to the environment. Considering the above facts, the present study was undertaken to know the mortality rates of biological control agents of brinjal insect pest by exposing them to insecticides under laboratory condition and to identify the safer ecofriendly or more compatible insecticide (s) with the biological control agents.

MATERIALS AND METHODS
Experiment was conducted at Insecticide Toxicology Laboratory of Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU), Gazipur during June to September 2009. Seven insecticides used for the experiment were Bactoil @ 2 ml/l of water, Nimbicidene 0.03 EC @ 4 ml/l of water, Tracer-45 SC @ 0.4 ml/l of water, Helicide @ 0.50 ml/l of water, Proclaim-5 SG @ 1 g/l of water, Necstar-50 EC @ 1 ml/l of water and Booster-10 EC @ 1 ml/l of water. The tested biocontrol agents were two predators viz., black ant (Camponotus compressus) and lady bird beetle (Micraspis crocera Muls) and one parasitoid Trathala sp. Test dose were prepared by diluting a definite amount of each of the insecticides separately in water in a 200 ml volumetric flask. The predators were exposed to the insecticide doses mentioned above by spraying in a 12 cm Petri desh and were covered with a netted cloth. They were supplied with water soaked cotton ball and necessary number of aphids as food. Three replicates and a control were maintained at 30±1 0 C and 70±3% R.H. Mortality counts were made after 24 and 48 hours of exposure. Insects showed abnormal body symptoms such as body contraction, cessation of feeding and paralysis were counted as dead. Abbott's corrections were done wherever necessary (Abbott, 1925). In case of the parasitoid (Trathala sp.) percentage parasitism was assessed by collecting data from infested shoots and fruits of treated and untreated brinjal plants and simulating the difference in emergence of the parasitoids.
From the infested fruit samples, the percentage of Trathala emergence were (22.22%) order control> (18.89%) Bactoil> (17.78%) Nimbicidene 0.03EC> (12.22%) Helicide≥ (12.22%) Tracer-45 SC> SG (5.56%) Proclaim-5> EC (2.22 %) Boster-10> EC (1.11%) Necstar-50. In terms of percentage of Trathala emergence reduction over control from infested brinjal fruit specimen, all insecticides showed negative effect on emergence of Trathala from infected larvae of BSFB.   (Table 3). The findings of present study are more or less in conformity with several studies. Filho et al. (2004) reported that spraying of chlorpyriphos decreased the activity of Solenopsis saevissima up to 2 weeks after spraying but recovered afterwards. Frampton (1999) observed that collembolan abundance decreased after chloropyriphos application but increased after cypermethrin application. Effects of chlorpyriphos varied spatially as a result of faunal heterogeneity among the fields. Latif (2007) found that Nimbicidene 0.03 EC and Flubebdiamite were comparatively safer for natural enemies and would be fit well to the integrated pest management (IPM) programs for brinjal. Azadirachtin had little or no negative effect on beneficial insects and found to be relatively harmless to bees, spiders, ladybeetles, parasitoid wasps and adult butterflies. Neem products are generally thought to be suitable for inclusion into integrated pest management programs (Banken & Stark, 1997).
The specific activity of Bt is considered highly beneficial. Unlike most insecticides, Bt insecticides do not have a broad spectrum of activity, so they do not kill beneficial insects like predators, parasites as well as beneficial pollinators such as honeybees. Therefore, Bt integrates well with other natural controls (Dutton et al., 2003). Nuclear Polyhedrosis Virus (NPV) a viral pesticide is slow acting and very species specific, making it effective under certain circumstances and safer to nontarget insects (Anon, 2011).
Several field studies have confirmed the low activity of Spinosad for many beneficial insect species. Against the sensitive indicator species, Typhlodromus pyri, Spinosad was harmful in the laboratory but safe under field conditions at rate up to 48 g ai/ha approximately one week after application. Against another sensitive indicator species, Aphidius rhopalosiphi, Spinosad was toxic to the adult wasps, but a level of safety was confirmed to wasps developing within mummified aphids. Spinosad was harmless to Poecilus cupreus (ground dwelling predator) and had limited adverse effects on Episyrphus balteatus and Coccinella septempunctata (foliage dwelling predators). Against another foliage dwelling predator, Chrysoperla carnea, Spinosad was harmless at 36 g ai/hL in an extended laboratory study involving realistic application methods (Anon, 2012). Field studies with Spinosad in which bees have been introduced the day following applications to orchards have also demonstrated the lack of Spinosad impacts.
Applications of Spinosad to alfalfa fields, in which honeybee hives were covered for the first 3 hours of post-application, also demonstrated no adverse effects to honeybees or leafcutter bees (Saunders & Bret, 2012).
It was reported that T. flavo-orbitalis was the only parasitoid species recorded from Gannoruwa area of Sri Lanka with the parasitism ranging from 15.9 to 48.9 % in an organically managed brinjal crop (AVRDC, 2003;Wahundeniya, 2003). This result supports the findings of present study. T. flavoorbitalis is larval-pupal parasitoid of brinjal shoot and fruit borer (BSFB), L. orbonalis Guenee, parasitizes many Lepidopterous species throughout the world. It is widely distributed in the orient and has been released in Hawaii (Swezey, 1926) and into several other states of USA. In Sri Lanka T. flavoorbitalis has been recorded from 17 different hosts (Beesan & Chatterjee, 1935). One of which is L. orbonalis (Guen.), the brinjal shoot and fruit borer. T. flavoorbitalis can attack all larval stages of L. orbonalis, but successful development of parasitoid was observed when later instar L. orbonalis larva was parasitized (Sandanayake & Edirisinghe, 1992).
From this experiment it can be concluded that Bactoil, Nimbicidene 0.03 EC and Tracer-45 SC (Spinosad) are less toxic to biological control agents such as, C. compressus, M. crocera and Trathala. Thus on overall basis Bactoil, Nimbicidene 0.03 EC and Tracer-45 SC could be used as the most compatible pesticides for controlling BSFB.