Dendrolimus punctatus
(Masson pine caterpillar)

Dendrolimus punctatus occurs in eastern China and south to Vietnam. The northern limit of D. punctatus lies between 32° and 33°N latitude. The western limit is Daxiangling in Sichuan province. The south-west limit in China is Bose region in Guangxi autonomous region. In addition to the distribution records listed in this datasheet for China, D. punctatus is present, native and not invasive in Chongqing (Cai and Liu, 1962).

Based on the topography and climate conditions, the areas of occurrence in China are classified into three types: the hilly coastal region with a hot and dry climate where three to four generations occur each year; the hilly and mountainous region with a warm humid climate where two to three generations occur each year; and the plains and hilly region with a temperate and moderately humid climate where two or more generations occur each year (Xue, 1983).

Although D. punctatus can feed on over 12 pine species, it generally could not develop well on hosts other than its preferred host, Pinus massoniana. Therefore the potential risk in areas without its preferred host is considered low.

Typical vegetation in the D. punctatus distribution areas consists of deciduous and evergreen broad-leaved trees and coniferous trees. Pinus massoniana is very common in areas with < 500 m altitude. Less common pine species are Pinus thunbergii, Pinus elliottii, Pinus taeda, and Pinus latteri. In high mountains, the following pine trees also exist: Pinus taiwanensis and Pinus armandii. Outbreaks of D. punctatus frequently occur south of the Yangtze River and in the south-east coastal region of China. In regions above 500 m altitude, the following pine caterpillars may also be found: Dendrolimus marmoratus, Dendrolimus sericus, Dendrolimus atrilineis, Dendrolimus kikuchii, Dendrolimus kikuchii hainanensis and Dendrolimus houi. Among these species, only D. kikuchii occasionally occurs in high numbers (Chen, 1990).

Dendrolimus punctatus is a serious pest on Masson pine (Pinus massoniana), a very common tree species found in southern China. As a result, a huge number of studies on the biology, ecology and management of D. punctatus have been conducted by Chinese researchers. Summaries about D. punctatus can be found in Chen (1990) and Hou (1987).
Physiology and Phenology

There are two to five generations of D. punctatus per year, depending on the distribution area, altitude, climate and condition of the host plant. More generations occur as the latitude decreases. In Henan province and north of Anhui province, only two generations occur each year. In provinces near the Yangtze River, two to three generations occur each year. In Guangdong, Guangxi, and southern Fujian provinces, three to four generations occur each year. In Hainan province, four to five generations occur each year. In Vietnam, three to five generations occur each year (Bassus, 1974). In regions where two to three generations occur per year (around 30°N latitude), close correlations were found between the differentiation rates of the third generation, high temperature in July and population levels (Zhang et al., 2002). The differentiation rate is also correlated with high density and the peak of the hatching date of the second generation (Wang et al., 1995). The first-instar was sensitive to photoperiod. A shorter photoperiod and lower temperature will cause diapause and lower ratios of the third generation (Li et al., 1994). In Anhui province, the average temperature in August and the photoperiod when mean temperature was >10°C were correlated with high ratios of the third generation (Chen et al., 1988).

Dendrolimus punctatus prefers old needles to young needles. Old needles have more cellulose, carbohydrates, and protein, and lower acid materials and water content. Trees over 6 years old begin to suffer damage by D. punctatus (Hou, 1987).

Reproductive Biology

The life cycle of D. punctatus includes eggs, larvae, pupae (in cocoons) and adults. The development period for each generation varies according to climate, the number of generations and occurring area. For example, in Hunan (Dong-an region), the first (summer) generation only needs 53 days to develop. However, the second generation needs 74 days. The over-wintering generation needs 260-310 days (Hou, 1987).

The females lay their eggs on needles or small branches of the middle and lower layers of the tree crown. They are either in clumps or in a thread (similar in appearance to a string of beads). Each group of eggs includes tens to hundreds of eggs. Average numbers of eggs per clump are between 300 and 400. In stands with extensive defoliation, emerging female moths tend to migrate to nearby stands where defoliation is less severe. The duration of the egg stage varies with the area and generation. In Hunan, the first generation requires 11 days, the second and third generations require 7 days; in Guangxi, the first generation needs 8 days, the second and third generations require 6 days. Newly hatched larvae may feed on the eggshells. Hatching mostly occurs in the early morning (Hou, 1987).

Newly hatched larvae stay in a group on needles near the eggshells. When the first- and second-instar larvae are disturbed, they suspend in the air through a silk thread extended from the mouth. They may also roll off the needles. Wind, storm and natural enemies kill a large percentage of the young larvae before entering into the fourth-instar.

The larvae moult five to eight times. In areas where two generations occur each year, the first generation moults five to six times. The second generation (over-wintering generation) moults seven to eight times. The female larvae moult one more time than the male larvae. Consumption of the last instar larva accounts for >70% of the total feeding of the larval stage. At high densities, the larvae may completely consume all the needles of a tree. Large numbers of mature migrating larvae may be seen on the forest floor when heavy defoliation occurs. If all needles are consumed before the fifth-instar, the larvae will starve to death. The male larvae are more likely to survive from food shortages than the female larvae.

The development period of the larval stage varies with the number of generations and regions. The overwintering period lasts approximately 20 days in Guangdong, 90 days in Hunan, and 120 days in Henan province. In Hunan, the average larval development period is 49 days in the first generation and 63 days in the second generation. In Guangxi, the average larval development period is 54 days in the first generation, 46 days in the second generation, and 54 days in the third generation.

In Hunan, the pupal stage lasts 21 days in the overwintering generation, 16 days in the first generation, and 13 days in the second generation. In Guangxi, the pupal stage lasts 16 days in the overwintering generation, 12 days in the first generation, 13 days in the second generation, and 17 days in the third generation.

The adults mate one to three times and the females lay eggs one to four times. In Hunan, the average moth life span is 7.5 days in the overwintering generation, 7 days in the first generation, and 8 days in the second generation. In Guangxi, the average life span is 8 days in the overwintering generation and 7 days in other generations.

Spatial Distribution and Population Dynamics

The larval distribution of D. punctatus in a pine tree is aggregated. Larval density varies greatly among branches of different heights (Xie et al., 1993). The occurrence areas can be classified into three types based on infestation frequencies: frequent infestation areas usually experience outbreaks every 3 years; occasional infestation areas usually have outbreaks every 7-10 years; and rare infestation areas usually do not have outbreaks. Each type has characteristic features in the climate, vegetation, and topography (Hou, 1987).

Environmental Requirements

The distribution areas of D. punctatus are located south of an imaginary line where the mean January temperature is 0°C. Annual precipitation ranges from 1000-2000 mm. The climate type is subtropical or tropical. Soil types are yellow-brown, yellow, red, or brick-red (Hou, 1987).

There are numerous studies on natural enemies of the genus Dendrolimus in China. Organisms belonging to six phyla, 11 classes, 33 orders, and more than 500 species were reported to cause the mortality of Dendrolimus spp. (Chen, 1990; Chai et al., 2000). The biology, behaviour, ecology, conservation and propagation of important natural enemies were studied to suppress the outbreaks of D. punctatus.

The majority of parasitoids of D. punctatus are in the order Hymenoptera. Ichneumonid wasps are important parasitoids of the larvae and pupae of D. punctatus. Casinaria nigripes was reported to cause 66.6% parasitism of D. punctatus larvae in Hunan province (Ma et al., 1989). It caused a parasitic rate as high as 23.6% to the third generation of D. punctatus in Jiangsu province (Qian, 1987). Braconid wasps are also important natural enemies of D. punctatus. However, the existence of several hyperparasitoids may lower their effect on D. punctatus. Trichogramma dendrolimi is a major egg parasitoid of D. punctatus.

Among the parasitic flies, Blepharipa zebina is commonly found in D. punctatus larvae and pupae. Wong and Zhou (1995) reported parasitic rates by Carcelia matsukarehae, Blepharipa zebina and Sacrophaga beesoni on the second generation of D. punctatus as 14, 16, and 34%, respectively, in Guangdong province.

Ants are important natural enemies of young D. punctatus larvae. When the first-, second- and third-instar larvae on the forest floor were encountered by Camponotus japonicus, 70, 23.3, and 10% were predated, respectively (Wang et al., 1991). Once the foraging workers found the first- and second-instar larvae on trees, they killed 48% and 10% of the larvae, respectively. When the first- to third-instar D. punctatus on the forest floor were encountered by Formica japonica, 46.7, 26.7 and 10% were predated, respectively (Wang and Wu, 1991). In Guangxi, Polyrhachis dives and Crematogaster artifex build nests in trees or on the ground. In stands where these ants are common, D. punctatus seldom reach large numbers (Chen, 1990).

Other important predatory enemies include praying mantis, wasps, katydids, predatory true bugs (Pentatomidae, Reduviidae), spiders and birds. Among the microbes, the fungus, Beauveria bassiana, and several viruses are common pathogens found in natural D. punctatus populations. Detailed studies of their effects against D. punctatus were summarised in Chen (1990).

The diversity and abundance of the natural enemies were closely related to the forest conditions. Human activities such as removing grass, shrubs, and dead leaves for fuel or agricultural use may significantly lower the insect diversity and natural enemy population levels. Higher parasitic rates and mortalities of D. punctatus due to the natural enemies were found in better protected forests (Hou, 1987).

This species is very similar to Dendrolimus punctatus tabulaeformis [Dendrolimus punctata ssp. hebes Walker, 1855], but can be distinguished by the markings of the wings. There are no stable differences in their genitalia. Hybridization studies by Zhao et al. (1992) indicated that they could mate and produce fertile progenies. D. punctatus tabulaeformis mainly feeds on Pinus tabuliformis and occurs in the far north and west of China.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Physical Control

Black light traps were effective in reducing the number of eggs (Yan et al., 1980).

Cultural Control

The most effective strategy for D. punctatus management has been protecting forests from disturbances by human activities (Peng et al., 1993). The trimming of lower branches of pine trees, cutting of shrubs, and removal of grass and dead leaves for fuel and agricultural purposes occur in many areas where there is a shortage of fuel. These practices can significantly lower the natural enemy populations and change the microclimates. Studies indicate that protected stands are less likely to have D. punctatus infestations (Chen, 1990). The hand removal of egg masses, larvae and pupae can immediately reduce the populations. However, this can be time-consuming and potentially dangerous due to the poisonous setae on the larvae and pupae.

Biological Control

The large scale propagation and release of Trichogramma dendrolimi is widely used in China. It caused 80-85% parasitism and effectively suppressed D. punctatus populations (Wu et al., 1988). Anastatus albitarsis released at 45,000 wasps/ha caused 52.3-68.7% parasitism of the first generation of D. punctatus (Tong and Ni, 1989). A supplement with Antheraea pernyi eggs in forests increased the T. dendrolimi populations, and therefore, the parasitic rate (Tong et al., 1988).

Microbial pesticide made from Beauveria bassiana is commonly used to suppress high D. punctatus larval populations in China (Pan et al., 1983). A recent study indicates that Metarhizium anisopliae has similar toxicity against D. punctatus and is superior to B. bassiana in terms of requirement for environmental conditions to control D. punctatus (Jiang, 2000).

Extensive studies were carried out on the control of D. punctatus with Bacillus thuringiensis and a cytoplasmic polyhedrosis virus (Cai et al., 1964; Guangdong Forestry Research Institute, 1977; Hou, 1986; Chen et al., 1997; Zhao et al., 2000). Aerial sprays of B. t. subsp. galleriae caused > 90% population reduction in Hubei province (Anonymous, 1987). Trials in Zhejiang province using B. t. var. dendrolimus caused > 90% population reduction (Li et al., 1984). Cytoplasmic polyhedrosis virus (CPV) powder applied at 3×10¹¹ polyhedra/ha provided a 63% population reduction of third- to fifth-instar larvae (Fan and Jiang, 1983).

In Taiwan, the application of the pathogen Paecilomyces farinosus, B.t. and CPV isolated from Dendrolimus spectabilis successfully controlled the outbreaks of D. punctatus (Ying, 1986).

Peng et al. (1998) reported that Trichogramma dendrolimi carrying D. punctatus CPV can significantly increase the control efficacy against D. punctatus.

Host-Plant Resistance

D. punctatus could not develop well on other pine species besides Pinus massoniana. In areas where frequent outbreaks occur, alternative pine species may be selected in forestry programmes (Chen, 1990). Damaged needles and young needles can negatively affect the survival and fitness of D. punctatus (Wen et al., 1993).

Chemical Control

A variety of pyrethroids, such as deltamethrin and fenvalerate are used for D. punctatus control (Li et al., 1987). They were applied as ultra-low volume aerial sprays for large-area population suppression or oil fogging in ground operations (Li et al., 1990). The insect growth regulator, diflubenzuron, is also widely used for D. punctatus management (Chen, 1990; Liang, 1991).

Early Warning Systems

Various prediction models were proposed to forecast D. punctatus population levels (Zhao, 1981; Wu et al., 1983; Sun and Hu, 1998). Five main factors were important in forecasting the population dynamics: forest type, vegetation, food, natural enemies and climate (Xiao et al., 1964; Shen, 1983). In Jiangxi, the dominant factors influencing outbreaks were precipitation in May and average temperature in February (Zhao, 1981). In Guangxi autonomous region, initial population level, control measures and sunshine hours were found to be important factors in predicting outbreaks (Li et al., 1985).

Field Monitoring/Economic Threshold Levels

Pheromone traps and black light traps are useful tools to estimate the population density and infestation range (Chen, 1990; Zhang et al., 2001). Mark-release experiments showed that moths were recaptured 643 m away in black light traps (Li et al., 1988). Satellite images (Thematic Map) are useful in detecting large areas of infestations (Wu et al., 1995). Airborne videos were tested to locate the infestation areas and determine the infestation levels (Wang et al., 1997). Economic thresholds were developed based on a number of egg masses, larvae, percentage of trees with D. punctatus and defoliation level (Chen, 1985; Ge et al., 1988).

IPM Programmes

An IPM programme for D. punctatus may include frequent monitoring (five to seven times/year in high risk areas), establishment of economic thresholds, protecting forests from human destruction, use of light traps to reduce moth populations, and applying biological pesticides to reduce larval population levels (Chen, 1990). When possible, different pine species or mixed tree species are recommended in forestry programmes. In Vietnam, short-term approaches were to focus on biological control, including mass production and the application of microbial agents and parasitic insects. Long-term solutions recommended were to establish mixed stands of different pine species or pines and broad-leaved trees, replace pines with non-host species in high-hazard areas, increase fire prevention, and further the professional training of protection personnel in all phases of integrated pest management (Billings, 1991).