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, Jabalpur.  The observations showed that the epidemic, though localized, but spread to 2 neighbouring compartment no. 107 and 144.  The species contributing in this defoliation were identified as larvae of Altha nivea Walk, Anua triphaenoides Walk.,  Ophiusa (Achaea) janata Linn., O. tirhaca Cramer, Paectes subapicalis and Ascotis selenaria.  The other species observed to feed on sal leaves, though, had very low population, were identified as Arhopala (Amblypodea) amantes Hewiston,  A. hewitsoni B.B. and Cryptothelea (Clania) crameri Westw.


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 Dehra Dun Division, which was later identified as a looper, Ascotis selenaria imparata Walk.  This species was naked i.e. without hairs on the body and again observed in the same sal forest compartment during the years 1967, 1971 and 1974.  Later, Singh and Thapa (1988) reported the epidemic of this species in 3 sal compartments of Mohammadpur block of Asarori range of West Dehra Dun Division in the spring of 1975, which continued till the end of September.  In Madhya Pradesh existence of hairy caterpillar of lymantrid, Lymantria mathura feeding on sal leaves recorded from East Mandla Division in the year 1998 to 2000 and by naked caterpillars of Paectes subapicalis in Karanjia range of Dindori Forest Division 2000-2001.  Both of them remained below the economic threshold.  But, this year in 2008, the localized sudden outbreak of Ascotis selenaria accompanied with naked caterpillars of Anua triphaenoides Walk., Ophiusa (Achaea) janata Linn., Paectes subapicalis, were recorded from April 2008 onwards.


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.