Science > Research > Effects of Optical Brighteners on Enhancement of CfMNPV Activity

The Effects of Optical Brighteners on Enhancement of CfMNPV Activity Against the Western Spruce Budworm

Li, S.Y. and Otvos, I.S.

[ Introduction | Methods | Results | Summary | Acknowledgements | References ]

Introduction

The western spruce budworm, Choristoneura occidentalis Freeman, is one of the most destructive forest defoliators in western North America. Earlier tests using C. fumiferana multicapsid nuclear polyhedrosis virus (CfMNPV) to control C. occidentalis were not efficacious enough in the field (Otvos et al. 1989, Shepherd et al. 1995). Control efficacy might be improved if the CfMNPV virulence can be enhanced. Previous studies with other insects showed that efficacy of insect viruses was enhanced when optical brighteners were added to the virus (Shapiro and Robertson 1997). Laboratory experiments were conducted to determine the effects of optical brighteners on the viral activity of CfMNPV against C. occidentalis.

Choristoneura occidentalis larva

Defoliation caused by western spruce budworm

Methods

Optical Brighteners. Nine optical brighteners were tested: Blankophor BBH, Blankophor BSU, Blankophor DML, Blankophor HRS, Blankophor LPG, Blankophor P167, Blankophor RKH (Bayer Corp., Pittsburgh, PA), Tinopal LPW (Sigma, St. Louis, MO), and Leucophor BSB [Clariant (Canada), Inc., Lachine, PQ).

Bioassays

Selection of larvae

(< 24 h old fourth instar)

Starvation of larvae

(16-20 h)  

Inoculation of larvae

(fed on small artificial diet plugs that had individually received 1 µL of viral dilution with or without brightener in 24-well tissue culture plates)

Transfer larvae

(only those larvae that had consumed the entire diet plug)

Incubation

(larvae were reared on untreated diet in 20 mL creamer cups until mortality or pupation)

Mortality check

(every other day)

Data analysis

(probit analysis)

Results

The values of LD50 and LD95 were lowered by the addition of five of the nine optical brighteners tested. The enhancement levels of viral activity by brighteners ranged from 1.9- to 3.6-fold in terms of LD50s and from 4.0- to 13.1-fold in terms of LD95s (Li and Otvos 1999a) (Fig. 1).

Fig. 1. Effects of optical brighteners on enhancement of CfMNPV activity againstlarvae of C. occidentalis.

In general, larval mortality increased with an increase of concentrations of optical brighteners. However, further increases in larval mortality were not observed as concentrations of brighteners were increased beyond 1%. For treatments with HRS, LPW or P167, the highest larval mortality was found when 1% brightener was used (Fig. 2).

Fig. 2. Larval mortality of C. occidentalis by 12.6 PIBs/larva of CfMNPV with different concentrations of optical brighteners.

The time to mortality (LT50) of the larvae was significantly reduced by the addition of HRS, LPW, P167 and RKH, but not by BBH (Fig. 3), suggesting that C. occidentalis died more quickly when brighteners were added to the virus. At a 1% concentration, the LT50s were significantly reduced by 23, 42, 45 and 50%, respectively, by the addition of RKH, HRS, P167, and LPW.

Fig. 3. Effects of optical brighteners on the time to mortality of C. occidentalis larvae by CfMNPV.

Without optical brighteners, larval mortality was not significantly different between males and females (Fig. 4). With the addition of 1% brightener, the differences in larval mortality became significant between the two sexes for all treatments except RKH (Li and Otvos, 1999b).

Fig. 4. Mortality of male and female C. occidentalis larvae exposed to CfMNPV with or without 1% optical brighteners.

The time to mortality was not significantly different between males and females when the virus was used alone. With the addition of 1% optical brighteners, female larvae died sooner than males in two of four treatments (Fig. 5).

Fig. 5. Time to mortality of male and female C. occidentalis larvae exposed to CfMNPV with or without 1% optical brighteners.

The field strain ofC. occidentalis was 2.7 times more tolerant to the virus than the laboratory strain. When a 1% concentration of brightener was added to the virus, lethal doses for the field strain were reduced by 7-11 times, compared with 3-4 times for the laboratory strain (Li and Otvos, 1999c). Although larval susceptibility to CfMNPV was different between the two strains, LD50 values for both strains were reduced to the same level with the addition of 1% optical brighteners (Fig. 6).

Fig. 6. Effects of optical brighteners on enhancement of CfMNPV activity against larvae of the laboratory and field strains of C. occidentalis.

Mortality occurred sooner in the laboratory strain of C. occidentalis than in the field strain. With the addition of 1% optical brighteners, the time to mortality was significantly reduced for both strains, and differences in the time to mortality increased between the two strains (Fig. 7).

Fig. 7. Time to mortality of larvae of the laboratory and field strains of C. occidentalis exposed to CfMNPV with or without 1% optical brighteners.

Summary

1. Five of the nine optical brighteners tested significantly enhanced viral activity, while four did not.
2. The effective optical brighteners enhanced viral activity by 1.9 to 13.1 times.
3. The highest larval mortality was found when 1% of the five most effective brighteners were added to the virus.
4. Female larvae were more susceptible than male larvae to the virus, and became even more susceptible with the addition of 1% optical brightener.
5. Female larvae died sooner than male larvae with the addition of 1% optical brightener.
6. The field strain of C. occidentalis was more tolerant than the laboratory strain to the virus, and both strains were equally susceptible when 1% brightener was added to the virus.
7. The laboratory strain of C. occidentalis died sooner than the field strain with or without optical brighteners.

Acknowledgements

Financial support was provided in part by Forest Renewal British Columbia (FRBC) and Natural Resources Canada (A-base). The original poster was prepared by Dion Manastyrski and modified by Nicholas Conder.

References

Argauer, R. and M. Shapiro. 1997. Fluorescence and relative activities of stilbene optical brighteners as enhancers for the gypsy moth (Lepidoptera: Lymantriidae) baculovirus. Journal of Economic Entomology. 90: 416-420.

Li, S.Y. and I.S. Otvos. 1999a. Optical brighteners enhance activity of a nuclear polyhedrosis virus against western spruce budworm (Lepidoptera: Tortricidae). Journal of Economic Entomology. 92: 335-339.

Li, S.Y. and I.S. Otvos. 1999b. Differential mortality between male and female Choristoneura occidentalis (Lepidoptera: Tortricidae) larvae exposed to a baculovirus with or without optical brighteners. The Canadian Entomologist. 131: 65-70.

Li, S.Y. and I.S. Otvos. 1999c. Comparison of the activity enhancement of a baculovirus by optical brighteners against laboratory and field strains of Choristoneura occidentalis (Lepidoptera: Tortricidae). Journal of Economic Entomology. 92: 534-538.

Otvos, I.S., J.C. Cunningham, and W.J. Kaup. 1989. Aerial application of two baculoviruses against the western spruce budworm, Choristoneura occidentalis Freeman (Lepidoptera: Tortricidae), in British Columbia. The Canadian Entomologist. 121:209-217.

Shapiro, M. and J.L. Robertson. 1992. Enhancement of gypsy moth (Lepidoptera: Lymantriidae) baculovirus activity by optical brighteners. Journal of Economic Entomology. 85: 1120-1124.

Shepherd, R.F. J.C. Cunningham, and I.S. Otvos. 1995. Western spruce budworm, Choristoneura occidentalis. pp. 119-122 In: J.A. Armstrong and W.G.H. Ives (eds.). Forest Insect Pests in Canada. Natural Resources Canada, Canadian Forest Service, Ottawa, ON.

Other publications by Imre S. Otvos

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[ Introduction | Methods | Results | Summary | Acknowledgements | References ]