Abstract: In the present study, in order to find a more effective and safe biological control agent against common pests of Coryllus sp, Balaninus nucum (Hazelnut beetle, Coleoptera) and Euproctis chrysorrhoea (Browntail moth, Lepidoptera), we tested the insecticidal effects of various biological agents. The highest insecticidal effects that we determined for each pest within 10 days are 90 percent using Lymantria dispar nuclear polyhidrosis virus (LdNPV, as gypchek) and toxin (BTS-1) isolated from tenebrionis strains of B. thuringiensis against B. nucum and 73.6 percent using LdNPV and 57.8 percent using toxin (HD-1) isolated from Harry Dumagae strain of B. thuringiensis against E. chrysorrhoea. We think that the insecticidal effects of all agents are the results of cytotoxicity.
Introduction
The main purpose of the agricultural studies is to increase the yield of product per hectare. Even though Turkey places on the top of the list among all the countries producing hazelnut in hazelnut production and export, it is way back of many of them in terms of product harvested per unit field. One of the main causes of this situation is that hazelnut has a lot of damagers and they can not be controlled effectively.
Balaninus mucum (Hazelnut beetle, Coleoptera) and Euproctis chrysorrhoea (Browntail moth, Lepidoptera) are common pest of Caryllus sp in Turkey while B. mucum damages on hazelnut fruit by feeding and laying (Martin, 1949; Ural et al., 1973), Euproctis chrysorrhoea has a characteristics of population increases almost in 3 or 4 years, causes important damages on hazelnut leaves by feeding. Surprisingly, despite their mass occurrence and wide distribution, very little is known about the agents limiting their populations. For this reason, these insects are very attractive objects of biological control studies, as well as a target for control by introduction of biological agents. Up to now, chemical substances have been utilized to control these pest. The rapid widespread adoption of organic insecticides have been brought the new problems which are the destruction of the biotic agent pressure on pests, wile fife, human health and to others. For this reason, scientists consider finding more effective and sate control agents. However, a few authors have studied natural enemies of these insects (Demirbag and Yaman, 1999; Sezen and Demirbag, 1999).
In this study, in order to find a more effective and safe pesticide against B. mucum and E. chrysorrhoea, we tested the insecticidal effects of various biological agents on the larvae of these pests. The tested agents are Autographa califomica nuclear polyhidrosis virus (AcNPV), Lymantria dispar nuclear polyhidrosis virus (LdNPV, as gypchek) and toxins isolated from Harry Dumagae (HD-1) and tenebrionis strains (BTS-1) of B. thuringiensis.
Materials and Methods
Virus samples: Two types of virus samples were used in bioassays: (a) Lymantria dispar nuclear polyhidrosis virus (LdNPV) was obtained from Edward M. Daugherty (USDA, Beltsville, Maryland, 20705 USA) as ready used pesticide, gypchek. Two g of this sample was suspended in 5 ml of phosphate buffer solution (PBS) and used; (b) Autographa californica nuclear polyhidrosis virus (AcNPV, m.o.i. = 1) was produced in Spocloptera frugiperda (Sf IPLB-21) cells (Martens et al., 1990). At 3 days post infection (occurrence of polyhedral inclusion bodies), the cells (3 x 107 cell/ml) were centrifuged at 3.000 rpm for 10 min. The pellet was re-suspended in 5 ml of sterilized PBS and used.
Bacillus thuringiensis toxins: Two types of toxins, isolated from Harry Dumage (HD-1) and Tenebrionis (BTS-1) strains of B. thuringiensis were (obtained from Stefan Jansens, Plant Genetic Systems J. Plateaustraat 22, 9000 Gent, Belgium) used in bioassays. 0.5 mg of these toxins was suspended in 5 ml PBS (100 μg/ml) (Moar et al., 1995).
Bioassays: For this study, the larvae of B. nucum and E. chrysorrhoea were collected in the vicinity of Trabzon. The caught insects were taken from the gardens to the laboratory with appropriate boxes, larvae were reared in groups of 20 larvae in containers. Containers were punched to permit air flow. Each group was fed for 48 hr with fresh leaves, exiles or fruits of hazelnut using equal amount from each one.. For this purpose, diets were placed into glass containers of 80 mm in diameter for each type of different biological agents. The surface of diet in each container was contaminated individually with the agent prepared in phosphate buffer solution (PBS) using sterilized syringe (Dulmage, 1981). Twenty larvae were placed on diet in each containers for each assay. After 48 hr, the larvae received fresh diet every 24 hr (Lipa and Wiland, 1972). Twenty control larvae received diet contaminated with PBS for the first 48 hr and then fresh diet every 24 hr. finally dead larvae were removed (Thiery and Frachon, 1997). Hundred larvae of each insect were tested for each agent. All larvae tested were kept at 26 2 C and 60 per cent RH on a 12:12 hr photoperiod (Lipa and Wiland, 1972; Ben-Dov et al., 1995). Dead larvae were removed immediately and bioassay checked daily till 10th day. Data were evaluated by using Abbot’s formula.
Results and Discussion
In this study, in order to find a more effective and safe pesticide, we tested the insecticidal effects of four different biological agents on the larvae of B. nucum and E. chrysorrhoea. The insecticidal effects determined on larvae of B. nucum and E. chrysorrhoea respectively, are 90 and 73.6 percent with gypchek, 60 and 36.8 percent with AcNPV, 90 and 26.3 per cent with BTS-1 and 77.7 and 57.8 percent with HD-1 (Fig. 1).
| Fig. 1: | The insecticidal effects of biological agents on Balaninus nucum and Euproctis CJrrysvrrhoea. LdNPV: Lymantria dispar nuclear polyhidrosis virus, as gypchek; AcNPV: Autographa californica nuclear polyhidrosis virus; BTS-1: toxin isolated from tenebrionis strain of B. thuringiensis and HD-1: toxin isolated from Harry Durnagae strain of B. thuringiensis |
We determined that the larvae which followed during ten days, showed different signs before death. Generally, the larvae of B. nucum displayed sluggish and appetite less. The only major symptom of infection is decreased larval life of both B. nucum and E. chrysorrhoea. In all of the assays, the highest insecticidal effect determined on larvae of both B. nucurn and E. chrysorrhoea respectively are 90 and 73.6 percent with gypchek. The insecticidal effect of AcNPV is 36.8 percent on E. chrysorrhoea and 60 percent on B. nucurn. While the effect of BTS-1 is 90 per cent on B. nucum, it is only 26.3 percent on E. chrysorrhoea. The effect of HD-1 toxin is 77.7 percent on B. nucum and 57.8 percent on E. chrysorrhoea. Moar et al. (1995) determined that HD-1 toxin (4.83 pgig of diet) causes 50 percent mortality against lesser cornstalk borer, while the control mortality was <20 percent determined. It is thought that various species has different resistance against this toxin because some insects ave a sufficiently high pH in the mid-gut to solubilize the protein and release the toxin of B. thuringiensis (Deacon, 1983). According to previous studies, effect of each Bacillus strains are different on various insect species (Esters, 1996). There is some evidence that the enzymes of different insects release different polypeptide from the proteins, so further specificity may arise I this way (Deacon, 1983).
As a result, it was determined that especially BTS-1 and gypchek can be used as biological control agents on B. nucum larvae and that HD-1 gypchek can be used as biological control agents on E. chrysorrhoea larvae. The high speed of action and the higher rate of mortality are always desired. Therefore, further researches will he directed to start biological control against B. micum and L. chrysorrhoea using these pesticides or other newly developed pesticides.