Forest Ecology and Management, 15 (1986) 69--74 69 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

A D E C A D E OF S U C C E S S F U L L C O N T R O L OF PINE C A T E R P I L L A R , D E N D R O L I M U S P U N C T A T U S W A L K E R ( L E P I D O P T E R A : L A S I O C A M P I D A E ) , BY M I C R O B I A L A G E N T S

SZE-LING YING

Taiwan Forestry Bureau, Department of Agriculture and Forestry, Taipei (Taiwan)

(Accepted 19 December 1985)

ABSTRACT

Ying, S.-L., 1986. A decade of successful control of pine caterpillar, Dendrolimus puncta- tus Walker (Lepidoptera: Lasiocampidae), by microbial agents. For. Ecol. Manage., 15: 69--74.

Dendrolimus punctatus Walker has been one of the most serious pests of the pine trees Pinus luchuensis, P. elliottii and P. massoniana in northern Taiwan. It develops three gen- erations each year. A combination of locally isolated species of fungus (Isaria farinosa), Bacillus thuringiensis, and a cytoplasmic polyhedrosis virus (CPV) isolated from D. spec- tabilis Butler in Japan was used to control the pest in different plantations during 1966-- 1971. The I. farinosa in combination with B. thuringiensis was applied for the first gen- eration larvae (October--March) when it was cool and wet, and temperature and humidity were most suitable for the fungus. CPV and B. thuringiensis were applied in the second (May---June) or third generation (July--August) when conditions were favourable for the development of the virus. Since the applications, yearly observations have been made, and there was no occurrence of the pest until 1982, when outbreaks were seen in some of the plantations, and again in 1983. It is believed that the successful control was due to the microbial agents, and that their effectiveness had lasted for some 10--12 years.

INTRODUCTION

Pine caterpil lar ( D e n d r o l i m u s p u n c t a t u s Walker) (Lep idop te ra : Las iocam- pidae) is a serious de fo l i a to r o f pine trees, par t icular ly in the n o r t h e r n par t of Taiwan, wi th a small n u m b e r occur r ing in the central and sou the rn par t o f Taiwan (Yie et al., 1966) . The suitable elevation for this insect is f r o m 0 to 500 m, bu t a few can be f o u n d as high as 1000 m. A heavy defo l ia t ion m a y occu r anywhere in p lan ta t ions ; luchu pine (Pinus luchuensis Mayr,) , slash pine (P. el l iot t i i Engelm.) and Chinese red pine (P. massoniana Lamb. ) are m o s t o f t en a t tacked , bu t black pine (P. thunbergi i Parl.) is rare ly a t tacked. Before 1945, the pine caterpil lar epidemics occur red once a yea r or once every few years and then subsided. However , in 1952 luchu pine was intro- duced f rom R y u k y u Islands; it shows a be t te r g rowth at e levat ions under 1200 m in Taiwan and was widely p lanted on 40 000 ha to m e e t demands by

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the pulp and paper mills. Since then, the pine caterpillar has caused tremend- ous devastation yearly. A catastrophic outbreak in the Wenshun Forest District of Yangmingshan killed 24 659 12-year-old pine trees during 1954. It has been observed that trees of all ages are suceptible to attack by this in- sect, but trees approximately ten years old are particularly easily attacked. Some infestations affect areas of up to several hundreds to thousands of hec- tares per year.

Defoliation by pine caterpillars not only retards tree growth but may also kill trees. Frequently the secondary pests, such as long-horned beetles and bark beetles, will attack pine trees and the damage will be even worse. In the past, persistent insecticides such as dieldrin or carbaryl were used to kill the pine caterpillars. Normally, over 90% of pine caterpillars and parasites are killed by these chemicals. However, since the moth can complete three gen- erations in one year, the activity of pine caterpillars probably resumes after 2 or 3 months (Takahashi, 1930; Wang, 1955; Yie et al., 1966). As a result, even after insecticide was applied every year we still suffered great loss of pine trees because the damage done by pine caterpillars was even worse than before. In order to find an efficient control measure for this pest, we tried several methods and finally adopted the use of microbial agents to control the larvae. The results are that the pest populat ion can be completely and rapidly destroyed by the dissemination of I. farinosa, CPV, and B. thurin- giensis, either singly or combined, depending on the environmental condi- tions.

METHODS

A native fungus, Isaria farinosa (Dicks) Ft., was isolated and cultivated in a glass bott le (500 ml) containing a medium consisting of wheat-bran (1000 g), rice-bran (250 g), dry yeast (30 g), sugar (20 g) and water (1600 ml). After incubation for one month at room temperature, the culture was diluted with 30 1 of water and then applied to plantations by spraying on to the tree with a mist blower. Fourteen days after spraying, dead I. fari- nosa, the infected larvae, and pupae with white mycelium were found every- where on the ground. These dead larvae and pupae were collected and ground to make a suspension to be used to spray other trees (Ying, 1970).

Although I. farinosa leads to 100% mortali ty of pine caterpillars at tempe- ratures of 20--30°C and a relative humidi ty of over 90%, in Taiwan the pine caterpillar completes three generations in a year. The second and third gen- erations occur from May to June and from July to August respectively, when the weather is hot and dry and control by I. farinosa is generally ineffective. During August 1968, 3 ha of the 10-year-old luchu pine plantations at Hein Fong Shian were at tacked severely by pine caterpillars in 4--5 instar. If not control led in time, the outbreak would destroy the whole plantation. To en- sure control, a combinat ion of cytoplasmic polyhedrosis virus (CPV), with an aqueous virus susPension of 1 X 1011 PIB/ml, and Bacillus thuringiensis

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Berliner (Thuricide 90 TS) was used. The CPV was isolated from Dendroli- mus spectabilis Butler in Japan.

In October 1968, three kinds of pathogens -- I. farinosa, B. thuringiensis (Bt) and CPV -- were used either individually or by combining any two of them. Because the materials we had on hand were not sufficient to cover the vast area {more then 30 ha) of the damaged plantat ions, at first only a por- tion of the pine trees were sprayed. After 7--10 days, the dead larvae were collected, ground and mixed with a ten-fold amoun t of natural water. The resulting suspension was then filtered and diluted 200--400 times with water and resprayed to other trees with hand-operated pressure sprayers.

R E S U L T S

Outstanding success in controlling the pest by I. farinosa was achieved in February 1966. About 1 ha of some 11- or 12-year-old luchu pines were attacked severely by pine caterpillars. Approximately 1000 pine caterpillars were present on each tree, most of them instars 5 and 6, all of which were killed. As a result of a mixed suspension of cytoplasmic polyhedrosis virus and B. thuringiensis, the mortali ty rate of pine caterpillars was up to 99% (Table 1). One month after spraying of these three pathogens all pine cater- pillars had been killed (Ying, 1970).

In 1956, the infected area of pine caterpillar reached over 1000 ha (Fig. 1). The dot ted line shows the area (ha) to which control measures were applied. During 1958, we used I. farinosa once, and the effect was very good for

1200

i000

8OO

IO0 f

o l

53 54

Years

~ 6oo v

~o 400

2OO

.A.

I J ~'" J "I I 56 58 60 62 64 66 68 70 72 74 76 78 80 82

Occurrence of pine caterpillars

........... Microbial agents control

Fig. 1. Area of luchu pine damaged by pine ca terpi l lars , and area to which microbia l agents were appl ied as a con t r o l measure f rom 1 9 5 3 - - 1 9 8 3 .

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TABLE 1

The mortality of pine caterpillar in different locations caused by Isaria farinosa alone or in combinations with cytoplasmic polyhedrosis virus (CPV) or with Bacillus thuringiensis (Bt) or with both

Pathogen Date of Location Infected Age of Mortality (%) sprayed spraying stand stand

(ha) (years) 14 days 30 days

I. farinosa 2-23-66 #40 Nan-yun 1 11--12 100±0 Sec. of Wen- shun Forest Distric in Keelung

CPV+Bt 8-9-68 Hsin Fong Shian 3 10 99-+0.78 Leeward pine 5 9 96-+ 1.63 plantation

L farinosa 10-11-68 Hsing Fong 30 10--15 100±0 +CPV+Bt golf field (either invidually or combining any two of them)

I. farinosa 2-4-69 +CPV+Bt (either individually or combining any two of them)

I. farinosa 4-4-69 +CPV+Bt (either individually or combining any two of them)

52 compartment, Lotung working circles

42 compartment, Leelo working circles

20 15 95.5-+1.56

8 11 95-+2.16

2 years . The re was a decrease in infes ted area in 1960 . However , the n u m b e r of p ine caterpi l lars increased again in 1961 , wi th a high peak b e t w e e n 1961 and 1962. A f t e r app l i ca t ion o f the c o m b i n a t i o n o f th ree microb ia l agents in 1966 , the p ine ca terp i l la r was r educed to very low incidence f r o m 1972 unt i l 1981 , bu t a f t e r F e b r u a r y 1982 the n u m b e r o f p ine caterpi l lars increased again. A to t a l o f a b o u t 40 h o f p ine p l an ta t ions were a t t a cked in Taipei , I-lan and Hs inchu a r o u n d the n o r t h e r n pa r t o f Taiwan, and in 1983 , 7 ha o f p ine t rees were d a m a g e d in Liu-kwei , the sou the rn pa r t o f Taiwan.

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DISCUSSION

The combination of three kinds of pathogens to control pine caterpillar has been successful. The method of applying Isaria farinosa combined with Bacillus thuringiensis was used against the first generation {October--March) during the cool and wet season, while the temperature and humidity condi- tions were most suitable for the fungus. CPV + Bacillus thuringiensis were applied against second generation {April--May) or third generation larvae during the hot and dry season (July--August), when the environmental con- ditions were most suitable for development of the virus. We applied these three kinds of pathogens during several years (1966--1971) to control pine caterpillars.

The 10--12-year suppression of pine caterpillar indicates the potential for population suppression in the long term by applications of microbial agents. Microbial control of forest insect pests is very effective both for short- and long-term control of the pine caterpillar. It is believed that the viruses can be transmitted from generation to generation (Bird, 1961). The virus intro- duced is capable of drastically reducing population densities in the year of spraying as well as carrying over into subsequent generations of survivors for long term control (Morris, 1980).

Mixtures of CPV or NPV (nuclear polyhedrosis virus) with B. thuringiensis were reported to be more lethal for some forest insect pests than the virus or bacteria alone (Stelzer, 1967; Stelzer et al., 1975; Katagiri and Iwate, 1976). In Japan, Katagiri and Iwata {1976) reported that field applications of CPV + B. thuringiensis mixtures were more effective against D. spectabilis than the application of pathogens separately, and they suggested such combina- tions as a very effective short-term strategy against pine caterpillars.

The greatest impact of the use of entomopathogenic viruses in forest in- sect control will probably be realized in integrated pest management sys- tems. The key factors in implementing such systems include knowledge of the dynamics of the pest population, ability to predict pest occurrence, population densities and potential economic damage, biology of the pest spe- cies including its natural enemies and its major host plants, relationships be- tween the pest and its environment, and the effects of various cultural prac- tices and strategies on the pests. Because of the complexity of agroforest ecosystems, simulation models have been used to coordinate and synthesize the massive amount of information into a decision-making tool for pest managers (Morris, 1980). The rapidity with which control of an insect popu- lation is obtained depends not only on the pathogenicity of the virus but on other factors, such as number of generations each year, flight and oviposition habits of the adults and prevalence of parasites and predators, all of which are concerned with virus transmission {Bird, 1961). Thus, there is more rapid control of D. punctatus in Taiwan, where there are three or even four genera- tions per year than in two- or one-generation areas. Disease spreads more

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rapidly bo th because adu l t p ine ca terp i l la rs depos i t thei r eggs singly, establishing m a n y foci o f i n f e c t i o n , and because o f the m u c h grea ter num- bers o f well es tabl ished paras i t e s and p r e d a t o r s (Yie et al., 1967) which are i m p o r t a n t agents in virus t r ansmis s ion . Otherwise , using Isaria is the key f ac to r in t e rmina t ing the p ine ca te rp i l l a r o u t b r e a k s .

ACKNOWLEDGEMENTS

We gra teful ly a c k n o w l e d g e the gi f t o f c y t o p l a s m i c po lyhedros i s virus by Dr. R y o n o s u k e K o y a m a and t h a n k Dr. Wen-yung Lee fo r reviewing the manusc r ip t .

REFERENCES

Bird, F.T., 1961. Transmission of some insect viruses with particular reference to ovarial transmission and its importance in the development of epizootics. J. Insect Pathol., 3: 352--380.

Katagiri, K. and Iwata, Z., 1976. Control of Dendrolimus spectabilis with a mixture of cytoplasmic polyhedrosis virus and Bacillus thuringiensis. Appl. Entomol. Zool., 11: 363--364.

Morris, O.N., 1980. Entomopathogenic viruses: strategies for use in forest insect pest management. Can. Entomol., 112: 573--584.

Stelzer, M.J., 1967. Control of virus in tent caterpillar, Malacosoma fragile incurva, with an aerial application of a nuclear polyhedrosis virus and Bacillus thuringiensis. J. Econ. Entomol., 60: 38--41.

Stelzer, M.J., Neisess, J. and Thompson, C.G., 1975. Aerial applications of a nuclear poly- hedrosis virus and Bacillus thuringiensis against the Douglas fir tussock moth. J. Econ. Entomol., 68: 269--272.

Takahashi, R., 1930. The investigations on the pine caterpillar, Dendrolimus punctatus Walker, injurious to pine trees. Bull. Cent. Agric. Res. Inst, No. 78 (in Japanese).

Wang, T.T., 1955. Forest protection in Taiwan. Econ. Res. Lab. Suppl. 29, Taiwan Bank, China (in Chinese).

Yie, S.T., Lee, P.P., Tang, M.Y. and Hsu, S.J., 1966. Biological study of the more im- portant insect pests attacking genus Pinus introduced from the U.S.A. Biology of pine caterpillar Dendrolimus punctatus Walker. PIant Prot. Bull., 8: 1--8.

Yie, S.T,, Lee, P.P., Hsu, S.J. and Tang, M.Y., 1967. Biological study of the more im- portant insect pests attacking genus Pinus introduced from the U.S.A.Q.J. Chinese For., 1: 1--24.

Ying, S.L., 1970. Application of Isaria sp., cytoplasmic polyhedrosis virus and Bacillus thuringiensis against the pine caterpillar Dendrolimus punctatus Walker (Lepidoptera: Lasiocampidae). Q. J. Chinese For., 4: 51--68.