In pursuance to the information received from Dr. P.K. Shukla, IFS, Additional Principal Chief Conservator of Forests, Government of Madhya Pradesh, Department of Forest, Bhopal dated 10th April 2008, periodical visits in the sal forests of Umaria Forest Division and Bandhavgarh National Park were made to study the leaf defoliators of sal. The first and second visits were undertaken by a joint team of scientists from State Forest Research Institute, Jabalpur and Tropical Forest Research Institute, Jabalpur in the month of April 2008 under the leadership of Mr. Vijay Bahadur, IFS, Director, State Forest Research Institute, Jabalpur. The team surveyed 6 affected compartment no. 108, 116, 117, 118, 119, 120 of Dhamokhar range and adjoining sal forests of Bandhavgarh Tiger Reserve and reported the presence of 3 species of insects responsible for defoliation. These species were identified as Paectes subapicalis Walk., Ascotis selenaria and an unidentified semilooper, feeding voraciously on young leaves of sal in all the affected compartments.
Subsequently, 3rd, 4th,
5th, and 6th visits to the affected compartments and
areas adjoining to them were made periodically at 15 days interval from May to
June 2008 by Dr. K.C. Joshi, Head of Forest Entomology Division, Tropical
Forest Research Institute,
Effect of Defoliation
Insect defoliation affects the trees by reducing photosynthesis, interfering with transpiration and translocation of food within a tree. Light defoliation normally has very little effect on trees but moderate to severe defoliation not only reduces the growth but also increases their susceptibility to the attack of secondary insects and diseases. Destroying of buds and young shoots lead to forking of leading shoots or epicormic branching resulting bushy appearance of affected trees.
In the present case, large number of larvae of more than 5 species of insects was observed defoliating sal trees of different age group together in some compartments (no. 107, 108 and 144) and the trees remained leaf less for nearly 3 months i.e. April to June. It is definitely reducing the annual growth besides making them more susceptible to the attack of various diseases and insect pests. In other compartments, however, the sprouting of new leaves appeared just after the April and thereafter the defoliation was moderate and sporadic in some trees.
History of defoliation in sal forest
The earliest known epidemic in sal is
reported from Goalpara sal forest of lower Assam in 1879, when localized
epidemic defoliation occurred due to lymantrid hairy caterpillar Dasychira
grotei Moore accompanied with Dasychira thwaitesi, Lymantria
spp. and others. Later, another
similar severe outbreak occurred in 1884 in over 200 square miles of sal forest
towards north of the Brahmaputra river.
The area was again infected by same lymantrid species of defoliators in
1897. Similar outbreaks by same species
of defoliators were recorded in Bengal during the year 1899 and in Madhya
Pradesh in 1909. Localised population eruption of same lymantrid defoliators
were again reported in Assam in the years 1907, 1914, 1922 and 1936. The attack was severe from August to October
in sal trees irrespective to their age.
Thereafter, these lymantrids recorded to cause light defoliation in
different sal forests of the country and there was very little effect on sal
trees. In the year 1964, localized
population outbreak of a defoliator recorded in sal forests of
Latest status of defoliation
Status to the affected compartments on 2nd July 2008 was very severe. At the same time, some caterpillars of Ascotis selenaria and Ophiusa janata defoliating sal were found to be infected by some disease probably caused by a bacterium Bacillus. Next visit made on 24th July 2008 showed that the natural bacterium is not effective to minimize the population of defoliators.