Contents - LAC Biosafety

300 Insect pests in plantations: case studies
Others are in between and their management may be decided based on the
severity of the outbreak situation.
Knowledge gaps The causes of sal borer outbreak largely remain unknown
although it is generally believed that dense stands with overmature trees
precipitate the outbreaks. It is most likely that events like lightning strikes,
storm damage or heavy defoliation by caterpillar outbreaks that weaken a large
number of trees, making them susceptible to attack, may provide an epicentre
for build-up of the outbreak populations. Most research on the sal borer problem
has been conducted during the periods of outbreak. Obviously, systematic
population ecological studies covering the non-outbreak periods in the outbreak
prone areas, and covering areas where outbreaks are not known to occur, can be
expected to throw further light on the factors regulating population build-up
and the causes of outbreak.
‘Trap-tree operation’ is an effective method for attracting and collecting
beetles but is cumbersome. Isolation, synthesis and formulation of the attractive
components in the sal tree sap should help to develop a more convenient, and
perhaps more effective, trapping method. In a recent study, Kaur et al. (2003)
reported 28 volatile compounds from the bast (cambium and secondary phloem)
of sal, of which nine - T-cadinol, alpha-cadinol, globulol, alpha-copaene,
gamma-cadinene, viridiflorene, beta-elemene, alpha-terpineol and gammamuurolene
- made up nearly 49%. If a more convenient and effective adult
trapping system were developed, it should be possible to use it as a continuous
population monitoring tool to warn of impending outbreaks so that suitable
preventive measures can be taken in time.
10.16 Swietenia species (Meliaceae) (common name: mahogany)
Tree profile
Swietenia species, commonly known as ‘mahogany’, are native to tropical
America, occurring between latitudes 20°N and 18°S (CABI, 2005). Three species
are recognized. The most well-known and widely planted is Swietenia macrophylla
King, commonly called ‘big-leaved’ or ‘broad-leaved’ mahogany, to distinguish it
from the small-leaved S. mahagony (L.) Jacq. The natural distribution of
S. macrophylla covers south-east Mexico in North America; Belize, Costa Rica, El
Salvador, Guatemala, Honduras, Nicaragua and Panama in Central America; and
Bolivia, Brazil, Colombia, Ecuador, Peru and Venezuela in South America.
S. mahogany is common in the Caribbean countries. These evergreen trees grow
up to 30–45 m tall. The third species, S. humilis Zucc., is a smaller tree, 8–10 m in
height, and commonly distributed in Central America. The biological boundaries