Insect Control: Biological and Synthetic Agents - Index of

A12 Addendum: Insect Transformation for
Use in Control
P W Atkinson, University of California, CA, USA
ß 2010 Elsevier B.V. All Rights Reserved
A12.1. Introduction 447
A12.2. Progress in strategies Dependent on the Release of Sterile Insects 447
A12.3. Progress in Strategies of Population Replacement 448
A12.4. Challenges that Remain 449
A12.1. Introduction
The past 5 years witnessed some extremely promising
developments in the laboratory studies of
the genetic manipulation of pest insects, yet demonstration
of any of these in a field environment
remains elusive, partly because of both the underlying
complexity of generating the necessary insect strains
and public misgivings concerning the release of genetically
engineered pest insects. Most promisingly, these
developments have occurred in alternative strategies
in genetic control with the logical expectation that at
least one of these should emerge as a true candidate
for large field cage studies followed by, pending success
and regulatory approval, limited field trials. This
addendum briefly summarizes these developments
and also outlines areas in which technological progress
still needs to be made.
A12.2. Progress in strategies
Dependent on the Release of
Sterile Insects
The sterile insect technique (SIT) has proved to be a
cost-effective method of pest insect control. Genetic
innovations in improving strains available for SIT
have been hampered by a lack of genetic tools available
for use in these species; however, some recent
outcomes illustrate that use of site-specific recombination
systems can lead to rather elegant genetic
manipulations in transgenic strains. The ability of
serine site-specific FC31 integrase from a broad
host range bacteriophage of Streptomyces to function
correctly in a wide range of organisms has
now been successfully extended to insect pests such
as the Mediterranean fruit fly, Ceratitis capitata,
and the mosquito Aedes aegypti (Nimmo et al.,
2006; Schetelig et al., 2009b). An advantage of this
integration system is that it enables site-specific
insertion of a transgene, provided that the target
site is present in the genome. This integration system
is introduced into the genome of pest species by
transposon-mediated transformation, which can remain
a rate-limiting step, especially in Ae. aegypti,
for implementation of these strategies. The FC31
site-specific recombination system is mechanistically
different from tyrosine site-specific recombinases
such as the Flp recombinase from yeast and the Cre
recombinase from bacteriophage P1, which enjoy
use in the construction of novel genetic strains in
D. melanogaster but are yet ineffectively employed
in other insects (Horn and Handler, 2005). A particularly
useful feature of the FC31 system is that it
relies on two different integration sites, attP and
attB, which, once combined, form two different
sites, attR and attL, that are not recognized by the
integrase (Thorpe and Smith, 1998). As a consequence,
integrants are stable, even in the presence
of integrase. A particularly elegant use of this system
is demonstrated by its use to remove one of the
terminal inverted repeats (TIRs) of a piggyBac
transposon following its integration into the C. capitata
genome rendering the remainder of the piggy-
Bac transposon, together with the transgene it
contains, stable in the genome (Schetelig et al.,
2009b). This system relied on the prior introduction
of the genetically tagged piggyBac transposon containing
an attB integration site; however, transformation
efficiencies in this pest species using the
piggyBac, Minos, or Hermes transposons can be
reasonably high.
Use of an efficient transposon-mediated transformation
technology with multiple fluorescent protein
genes when combined with subsequent deployment
of site-specific recombination does therefore permit
sophisticated genetic manipulations common in
D. melanogaster genetics to be deployed in C. capitata
and in principle, any insect in which an efficient