INFLUENCE OF THE SOYBEAN SEED COAT UPON SEED INFESTATION AND DEVELOPMENT OF THE INSECT CALLOSOBRUCHUS MACULATUS - Soybean and Wheat Crops: Growth, Fertilization, and Yield - page 10

Figure 3. Seed coat surfaces observed under a stereoscopic microscope coupled to a digital CCD video
camera. A - Vigna unguiculata (cv. Fradinho); B - cv. Elite; C - cv. Conquista; D - Commercial
soybeans; E - cv. UFV 20 Florestal; F - cv. UFUS 2003; G - cv. UFUS 2005 and H - cv. Tucunaré. Bar
= 0.5 mm.
Influence of the Seed Coat on the Larval Ability to Perforate the Seed Coat
The time necessary for the surviving larvae to perforate completely the seed coat was
evaluated. We observed that in the host V. unguiculata seeds (positive control), at the sixth
day after the oviposition the larvae already crossed completely the seed coat and reached the
cotyledons, while for soybean seeds this time varied from 12 to 13 days (Figure 2A). This
result shows an increase of up to 116 % in the necessary time for the larva to perforate the
seed coat.
When the thickness of the seed coat was evaluated, we noticed that was no significant
variation in the thickness of the studied seed coats. The result indicates that there is no
relationship between the thickness and the ability of the larva for crossing this tissue (Figure
2B).
The textures and pigmentation of the seed coat surfaces were also analyzed and we
observed that the seed coat of Conquista (Figure 3C), commercial soybean (Figure 3D),
UFUS 2005 (Figure 3G) and Tucunaré (Figure 3H) soybean cultivars are slightly more rough.
However there was no direct correlation between this characteristic and the performance of
the eggs or ecloded larvae on the seed coats. The pigmentation of the seed coats did not differ
in the studied seeds (Figure 3).
Influence of the Seed Coat on the Development of Neonate Larvae
Observations of the development of C. maculatus neonate larvae on natural seeds of V.
unguiculata showed that, at the first day after oviposition, the egg content is clear, transparent
(Figure 4A); at the fifth day, the larva is apparently formed (Figure 4B); in the inferior
surface of the egg of the fifth day it becomes visible the perforation through which the larva