BRUCHIDS INFESTATION ON SEEDS OF SOME FOREST TREES

Ajay Singh, Shiwani Bhatnagar, Sangeeta Singh and Parveen Goran. 1. Lachoo Memorial College of Science and Technology Shastri Nagar, Jodhpur. 2. Forest Protection Division, Arid Forest Research Institute, New Pali Raod, Jodhpur. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

In the present study infestation by bruchids on the pods/seeds of some forest tree species was recorded. The findings revealed a 60.36 percent infestation of Bruchidius albizziae on Albizia lebbak and 11.13 percent infestation of Bruchidius andrewesi on Acacia senegal. Whereas Pongamia pinnata, Colophospermum mopane, Leucaena leucocephala and Tectona grandis were found free from bruchid infestation.

Introduction:-
Many tree species are subject to infestation by bruchid beetles of the family Bruchidae (Coleoptera). About 30 species of pulse beetles or seed beetles are found to be serious pests in the world (Kingsolver, 2004). Predation by bruchid beetles, which lay their eggs on ripening pod, has been shown to cause negative effect on seed viability (El-Atta, 1993; Mucungazi, 1995;Miller, 1996;Walter andMilton, 2003 andSchelin et al., 2004). The larva of bruchid beetles enter the seeds by drilling and feeds on the embryo and endosperm leaving most of the infested seeds nonviable, which may threaten their population (El-Atta, 1993). Many species show substantial reduction in seed germination under bruchid beetles infestation (Rohner and Ward, 1999).
In an investigation from Pakistan it was found that 86% of the seed-infesting insects belonged to the order Coleoptera and the rest under order Lepidoptera and Hymenoptera (Wali ur Rehman, 1995). Coleopteran insect have most pronounced host specificity, whereas Hymenoptera and Lepidoptera are more general feeders (Auld 1991). Females of coleopteran insect generally lay eggs on or inside fruits, or they glue their eggs directly to seeds that are exposed in dehiscent pods or are found on the soil surface (Southgate, 1979). Larval stage is the destructive life stage of this order which feed entirely within seed, making their detection and control difficult, while adults live free and feed on pollen and nectar (Gupta et al., 2009).
In some cases, seed-beetle larvae may attack a majority of seeds in the local plant population, but infestation rates of some hosts can be chronically low (Miller, 1994a;Takakura, 2002). In some cases, the insect clearly acts as a seed predator; larval feeding effectively kills the embryo or removes so much endosperm that the seed cannot germinate The present study was conducted to identify and record seed infestation by bruchids on the pods/seeds of Albizia lebbak, Pongamia pinnata, Acacia senegal, Colophospermum mopane, Leucaena leucocephala and Tectona grandis in field.

Material and methods:-
To assess percentage seed infestation due to bruchids (Coleoptera), pods/ fruits of Albizia lebbak, Pongamia pinnata, Acacia senegal, Colophospermum mopane, Leucaena leucocephala and Tectona grandis were collected and the damage done by insect pests was examined. Observations on different parameters viz., length of pod, no. of seeds per pod, no. of infested seeds per pod were recorded to calculate the percent insect infestation.

Result and Discussion:-
The data on the above parameters revealed a 60.36 percent infestation of Bruchidius albizziae on the seeds of Albizia lebbak and 11.13 percent infestation of Bruchidius andrewesi (Pic) on the seeds of Acacia senegal. Seeds of other trees under study were found to free from bruchids infestation (Table 1).

Table 1:-Pod characteristics and seed infestation.
Percentage seed infestation on different tree species Scale Y axis = Percent infestation, Average No. of seeds per pod, Average No. of infested seeds X axis= Name of species Bruchid beetles larvae can exploit a considerable proportion of the cotyledons and thus infestations can have an enormous negative effect on seeds viability and seedling vigour. Vir (1996) reported that no seeds of the leguminous trees Prosopis cineraria, Prosopis juliflora, Acacia tortilis, Acacia senegal and Albizia lebbeck (the major component of afforestation programmes and sand dune stabilization works) damaged by bruchids, germinated. Ponnuswamy (1990) found infestation of a bruchid, Bruchus sparsimaculatus on the pods of Albizia lebbeck. In a field studies in Jodhpur, Rajasthan, Ahmed et al., (1995) (2010), seed infestation of 21.6% due to bruchids (Coleoptera) in the seeds of Acacia senegal was recorded. Bhasin and Roonwal (1954) accounted that larva of Bruchidius andrewesi damage seeds of Acacia leucophloea. It has also been recorded as a serious pest of pods and seeds of Acacia tortilis by Vir and Jindal (1994).