Evaluation of Relative Host Preference of Batocera rufomaculata De Geer on Different Age Stages of Jackfruit Trees

MATERIALS AND METHODS

The study was conducted in three jackfruit growing districts Gazipur, Gaibandha and Khagrachhari of Bangladesh in farmers’ orchard in terms of trunk infestation during 2009-2011. The districts were selected in consideration of collecting the information regarding jackfruit based agroforestry and intensive jackfruit growing area of Bangladesh.

Data collection: For the present study, different age groups were considered as treatments and the three districts were considered as replications while the three villages under each district were considered as replications. Observations were made on the jackfruit trees on 2.5 m height of trunk from ground level. In order to determine host preference of jackfruit trees of different age groups jackfruit trees of each orchard were classified into five age groups (<10, 10-20, 21-30, 31-40 and >40 years).

Data processing and analysis: All the collected data were analyzed by using descriptive statistical methods including the computer-based statistical package SPSS 13 version, Microsoft Excel and MSTAT-C. The data obtained for different characters were statistically analyzed to find out the significance of effects/impacts of different age group of trees on trunk borer infestation including severity of infestation, percent infestation, duration of infestation, yield and yield contributing characters. The mean values of all the parameters were evaluated and analysis of variance (ANOVA) was performed by the “F” (variance ratio) test MSTAT-C program. The significance of the difference among the different combinations for different characters was estimated by Dancan’s Multiple Range Test (DMRT) at 1% level of probability (Gomez and Gomez, 1984). Percent of trunk infestation were calculated as bellow:

RESULTS AND DISCUSSION

Among the different age groups, the Batocera rufomaculata De Geer showed preference significantly (p<0.01) in Gazipur and Gaibandha districts as presented in Table 1. The trunk infestation was maximum (45.87%) in Gazipur in age group of 10-20 years which was statistically similar with age group of 21-30 years (45.06%) followed by 33.85 and 34.73% in 31-40 years and below 10 years age group, respectively. But the trunk infestation was minimum (21.38%) in the age group of above 40 years. However, between other two districts infestation was maximum (27.97%) in Gaibandha in 10-20 years age group which is statistically identical with 21-30 years age group (26.65%) which was followed by 31-40 years, age group (8.33%).

Table 1:	Infestation by Batocera rufomaculata according to the age groups of jackfruit trees in three districts during 2009-2011
Means followed by common letter(s) in a column are not significantly different at 1% level by DMRT. Values are the averages of three replications. Figures in parentheses indicate data based on square root transformation

In this district, there was no infestation in above 40 years age group and the lowest infestation was in below 10 years age group (3.81%). In Khagrachhari the infestation was the highest (27.16%) in 21-30 years age group and the lowest was in age group below 10 years (17.06%). In case of trunk infestation, the order of age groups of jackfruit trees was 10-20>21-30>31-40>below 10 and >above 40 years old. The susceptibility to borer infestation may be the tender age tree which does not develop woody tissue in the trunk that may be difficult for feeding by grub stage. Infested trees were larger in trunk diameters of the trunks than non-infested trees (Ezaki, 1995). Kannan and Rao (2006) found Batocera rufomaculata De Geer were more predominant on the old age trees (>15 years) than young age trees (0-5 years). Similar higher rate of infestation or susceptibility of trunk infestation was reported by Sing and Sing (1986) and Rasel (2004). They explained the probable reason of higher rate of trunk infestation of middle age group was that with the increase of age the tree loose their vigor and the initial infestation become predominant through a longer duration. Tissues of woody plants vary in the following ways in their nutritional quality for wood-boring insects: (a) Bark is generally very low in nutrients (carbohydrates, nitrogen), (b) Subcortical zone tissues (inner bark, cambium, immature xylem) have many times higher concentrations of nutrients, (c) The much thicker sapwood is low in nutritional quality and (d) High nitrogen was found in pith than heartwood (Cowling and Merrill, 1966; Graham, 1925; Haack and Slansky, 1987; Hosking and Hutcheson, 1979; Savely, 1939). The cellulase is a major factor influencing the infestation by insects. Larvae that feed in nutrient-deficient tissues, however, may depend on cellulose-digesting enzymes to assist in nutrient assimilation (Mishra and Singh, 1978).

Many insects can produce cellulases (Bhat, 2000; Marsden and Gray, 1986; Watanabe and Tokuda, 2001). The cellulase of some cerambycid contains higher percentages of sulfur containing amino acid residues (Cys) (Lee et al., 2004, 2005). Reflecting relative nutritional quality of woody tissues according to their age, the preference is detected for feeding of trunk borer.

In case of Gazipur district, a strong second order polynomial regression was also found between percent infestation (Y) and tree age (X) as presented in Fig. 1. Relationship between percent infestation and tree age reflected an increasing infestation with increasing tree age up to a certain point (45.06% infestation at 15 years) beyond which a decreasing trend was recorded.

Fig. 1:	Relationship between age of jackfruit trees and trunk infestation by trunk borer during 2009-11 at Gazipur region

Fig. 2:	Relationship between age of jackfruit trees and trunk infestion by trunk borer during 2009-11 at Gaibandha region

The maximum percent infestation was recorded at age range 10-30 years (34.93-45.06% trunk infestation). This polynomial regression was fitted between trunk borer infestation and tree age. The regression equation:

Y = a+b₁X+b₂X²

where, Y is trunk infestation (%), a is 23.871, b₁ is 1.7907, b₂ is -0.0418 and X is tree age, was obtained. The contribution of the regression (R² = 0.9144) was 91%.

In Gaibandha district, a strong second order polynomial regression was also found between percent infestation (Y) and tree age (X) as presented in Fig. 2. Relationship between percent infestation and tree age reflected an increasing infestation with increasing of tree age up to a certain point (33.33% infestation at 15 years) beyond which a decreasing trend was recorded. The maximum percent infestation was recorded at age range 15-30 years (30.57-33.33% trunk infestation). This polynomial regression was fitted between trunk borer infestation and tree age. The regression equation:

Y = a+b₁X+b₂X²

where, Y is trunk infestation (%), a is -17.251, b₁ = 3.8121, b₂ is -0.078 and X is tree age, was obtained. The contribution of the regression (R² = 0.7077) was 70%.

Fig. 3:	Relationship between age of jackfruit trees and trunk infestation by trunk borer during 2009-11 at Khagracharri

In Khagrachhari district, a strong second order polynomial regression was also found between percent infestation (Y) and tree age (X) as presented in Fig. 3.

Relationship between percent infestation and tree age reflected an increasing infestation with increasing of tree age up to a certain point (26.85% infestation at 25 years) beyond which a decreasing trend was recorded. The maximum percent infestation was recorded at age range of 15-30 years (11.38-26.85% trunk infestation).

This polynomial regression was fitted between trunk infestation and tree age. The regression equation:

Y = a+b₁X+b₂X²

where, Y is trunk infestation (%), a is -8.3068, b₁ is 2.5917, b₂ is -0.0505 and X is tree age, was obtained. The contribution of the regression (R² = 0.930) was 93%.

CONCLUSION

From the results of the study it is concluded that the trees of middle age group suffered more severe infestation than tender age trees or very old trees in three selected regions. The preference of age of trees as attractive host as observed in this study complies with jackfruit trunk borer Batocera rufomaculata De Geer preferred a particular age of host plant or group of plants. Relationship between percent infestation and tree age reflected an increasing infestation with increasing of tree age up to a certain point beyond which a decreasing trend was recorded.