Contents - Faperta

408 Biotechnological Approaches for Pest Management and Ecological Sustainability
Role of Pollinators in Gene Flow
There is a need for risk assessment of the likely spread of transgenes via pollen through
insect pollinators, largely bees (honeybees and bumblebees) to other crops, or to sexually
compatible wild relatives. Insect-mediated pollen and gene fl ow is a function of the deposition
of viable and compatible pollen from donor to recipient plants along insect foraging
routes, and of the spatial dynamics of those foraging routes within the foraging areas.
Knowledge of bee foraging behavior will be useful to design appropriate confi nement strategies
for experimental releases, monitoring protocols, and mitigation procedures for risk
management. Crucial data are lacking for the development of a credible scientifi c basis to
confi rm or deny environmental risks associated with ecological roles of lepidopterans
exploiting specifi c wild relatives of Bt transgenic crops and escape of Bt transgene
constructs to wild relatives (Letourneau, Robinson, and Hagen, 2003).
Insects do not discriminate between conventional and transgenic oilseed rape resistant
to glufosinate (Pierre et al., 2003) and chitinase (Picard Nizou et al., 1995), although some
differences have been observed in the nectar between the transgenic and nontransgenic
lines. Bees (Apidae), hoverfl ies (Syrphidae), and sawfl ies (Symphyta) visited glufosinateresistant
oilseed rape, of which bees were most abundant (Saure, Kuhne, and Hommel,
2001). They were involved in pollination of oilseed rape and the transgene was found in
Brassica juncea (L.) Czern. Oilseed rape pollen was spread through pollen loads of different
types (Ramsay et al., 1999). Presence of pollen from transgenic plant in largely nontransgenic
Brassica pollen loads, and generation of mixed transgenic and nontransgenic progeny
following pollination of male-sterile plants with pollen from single bees indicated that
bees can readily spread pollen around the foraging area. In rape, a total of 94 bee species
and 48 hoverfl y species have been recorded. Mark-recapture experiments with bumblebees
and solitary bees showed that the same individuals visited the fl owers of transgenic rape
and later fl owers of other cruciferous plants (Saure et al., 2003).
The foraging distances of Bombus muscorum (L.) are more restricted to the neighborhood
of the nesting habitat than those of B. terrestris (L.) and B. lapidarius (L.) (Hellwig and
Frankl, 2000). High percentages of B. terrestris workers were recaptured while foraging on
super-abundant resources at distances up to 1750 m from the nest. Isolated patches of
highly rewarding forage crops in agricultural landscapes are probably accessed by bumblebee
species with large mean foraging distances, such as the short-tongued B. terrestris. The
long-tongued B. muscorum, which is relatively rare, depends on a close connection between
nesting and foraging habitat. Long-distance fl ights of bumblebee pollinators need to be considered
for gene fl ow from transgenic plants on a landscape scale. Consistent and signifi cant
reduction in pollen dissemination by insects has been observed in cotton as the distance from
the test plot increased (Umbeck et al., 1991). Outcrossing decreased from 5% to 1% at 7 m
away from the test plot. The leafcutter bees, Megachile spp. used in commercial seed production,
show a directional nonrandom bias when pollinating within fi elds, primarily resulting
in the movement of pollen directly towards and away from the bee domicile (Amand,
Skinner, and Peaden, 2000). Within-fi eld pollen movement was detected only over distances
of 4 m or less. In pigeonpea, the most important insect pollinators are Megachile spp. (Saxena,
Singh, and Gupta, 1990). The fl ower type, the abundance of insect pollinators, and weather
conditions at fl owering infl uence the degree of cross-pollination. Dispersal of pollen from
alfalfa hay and seed production plots occurred up to 1000 m. Random amplifi ed polymorphic
DNA (RAPD) markers detected gene movement up to 230 m. The outcrossing frequency
for large fi elds was nearly 10 times greater than that of small-sized plots.