Contents - Faperta

Genetic Engineering of Natural Enemies for Integrated Pest Management 297
inherited as extrachromosomal arrays. This technique, along with transposable elements
(P-elements), can be used for stable integration of exogenous DNA.
Paratransgenesis
Foreign genes can also be expressed in endosymbionts in insect gut or other organs rather
than by the insect. This system has been used in the case of tsetse fl ies, Glossina morsitans
Westwood and kissing bugs, Rhodnius prolixus (Stal). Genetic engineering of endosymbionts
in tsetse fl y to express antitrypanosome agents could prevent transmission of sleeping
sickness (Aksoy, 2000). Flies with recombinant Sodalis species expressing antimicrobial
peptide attacin reduced the infection rate to 3,000 (Aksoy, 2003). The symbiont of kissing
bug, R. prolixus, the vector of Chagas disease, has been transformed with a marker gene
and gene for cecropin A, a trypanocidal peptide found in insect hemolymph (Durvasula
et al., 1997). Cecropin was stably expressed and killed Trypanosoma cruzi Chaggas without
affecting the kissing bugs.
Vectors for Genetic Engineering of Arthropods
Transgenic expression requires an appropriate promoter and other regulatory elements.
Four different transposable elements from four separate families of eukaryotic transposable
elements can be used to transform nondrosophilid insects (Atkinson and O’Brochta,
1999). In addition, viral and bacterial endosymbiont gene delivery systems have also been
developed for some insect species. Many genes have been cloned and inserted into
Drosophila by P-element-mediated transformation, but very few cloned genes are of value
for genetic manipulation of benefi cial arthropods.
Transposable Elements
Transposable elements, called P-elements, are mobile pieces of DNA that have the ability
to move from one site on a chromosome to another (Liao, Rehm, and Rubin, 2000). They
move vertically to the progeny, but they can also move horizontally between individuals
of different species (Kidwell, 1992). The P-elements can be used to transform insects by
macroinjecting the embryos with two circular DNA plasmids (a vector and a helper). The
vector plasmid contains the transposable element, exogenous DNA to be incorporated under
the control of promoter, and a marker gene. Since the vector lacks the transposase, the
transposase is provided by the helper plasmid. The helper plasmid catalyzes the excision of
exogenous DNA and the marker gene from the vector plasmid, and helps in their integration/insertion
into the host genome (Rubin and Spradling, 1982). The P-elements are effective
only in the case of Drosophila, but type II transposable elements, unrelated to P-elements,
have been used in other insects. Minos, a member of the Tc1 family, has been used for
transformation of C. capitata (Loukeris et al., 1995) and mosquito, Anopheles stephensi Lister
(Catteruccia et al., 2000). Mariner, consisting of several subfamilies, has been used in the
case of Lucilia cuprina Weid. (Coates et al., 1997). The hAT elements (mariner and hobo) have a
broad host range. Interplasmid transposition assays have shown that hobo is mobile in
Musca domestica (L.) and Helicoverpa armigera (Hubner) (O’Brochta et al., 1994; Pinkerton,
O’Brochta, and Atkinson, 1996). PiggyBack elements isolated from cabbage looper, Trichoplusia
ni (Hubner), have also been used to transform nondrosophilid insects (Kramer, 2004).