84 L. Pathak et al.
trol strategies on a wider basis. Several biological
insecticides have been developed ranging from
bacterial, fungal, viral, etc., for the efficient pest
control in formulations suitable for agroclimatic
conditions. Among these agents, Bt is the most
widely studied and exploited worldwide (Estada
and Ferre 1994 ).
Bt occurs over a wide range of habitats such
as soil, insect hosts, treated habitats, phylloplane,
stored products, etc. (Uribe et al. 2003 ). The abil-
ity of Bt to produce many insecticidal crystal-
line toxins during sporulation has been exploited
and δ-endotoxin, the main principle of insect
toxicity is successfully utilized in pest-control
programmes. Despite many efforts over the suc-
cessful exploitation of Bt, insects have developed
resistance to Bt-toxins. The first report on insect
resistance to Bt was published by McGaughey
1985 in Indian-meal moth. Plutella xylostella
was the first insect to develop resistance in field
(Tabashnik et al. 1994 ) while other species have
the genetic potential to develop resistance in the
near future. First, Bt commercial formulation
was made available for field in 1958. Whiteley
and Schnepf cloned a Bt-toxin gene in 1981.
Monsanto developed first transgenic cotton plant
in 1990. According to ISAAA Executive Report,
the global area of biotech crops continued to in-
crease for the 16th year at a sustained growth rate
of 8 % or 12 million ha (30 million acres), reach-
ing 160 million ha or 395 million acres (Fig. 1 ).
Biotech crops have set a precedent in that the
biotech area has grown impressively every single
year for the past 16 years, with almost a remark-
able 94-fold increase since commercialization
began in 1996. Thus, biotech crops are consid-
ered as the fastest adopted crop technology in the
history of modern agriculture (James 2011a).
Action of Bt is very specific. Different strains
of Bt are specific to different receptors in insect
gut wall. Bt toxicity depends on recognizing re-
ceptors, damage to the gut by the toxin occurs
upon binding to a receptor. Each insect species
possesses different types of receptors that will
match only certain toxin proteins, like a lock to
a key. However, the history of insecticide resis-
tance informs us that adaptation by insects could
diminish the long-term efficacy of Bt crops and
the associated economic, health, and environ-
mental benefits. To date, field-evolved resistance
to Bt crops has been documented in only three
insect species: Helicoverpa zea, Spodoptera fru-
giperda, and Busseola fusca to Bt cotton and Bt
corn producing Cry1Ac, Cry1F, and Cry1Ab, re-
spectively (Tabashnik 2008). This chapter sum-
marizes the current status of resistances in Bt
crops, the principles of IRM for Bt crops and
what they mean for the design of IRM programs.Fig. 1 Global area of biotech crops, 1996–2011 (mha)