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 13

is partially inside of the cotyledon (Figure 4E) , the seed coat is completely perforated (Figure
4F) as it is also perforated the cotyledon (Figure 4G) .
The neonate larvae development on natural soybean seed coats was similar in all studied
seeds. The eggs showed anomalies already visible after the first day of oviposition, consisting
of bubbles in the egg surface (Figure 5A) and alteration in the content appearance (Figure
5B). Other eggs were completely withered at the fourth day after oviposition (Figure 5C).
Some neonate surviving larvae were apparently formed inside the egg at the sixth day (Figure
5D) and at the eighth day (Figure 5E). At the tenth day after oviposition, flour was seen inside
some eggs (Figure 5F) indicating that the larva began to dig the seed cotyledon. Only at the
twelfth day after oviposition, the complete perforation of the seed coat and the initial
perforation of the cotyledon were observed (Figure 5G). In this stage the larva was partially
inside the cotyledon (Figure 5H). Although the normal behavior of the larvae is to open holes
in the inferior surface of the egg in order to penetrate the seed cotyledon, an inverse behavior
was observed for some larvae laid on the soybean seed coats. Some eggs showed a hole in the
superior surface after the twelfth day after oviposition (Figure 5I), through which some larvae
came out (Figure 5J). Up to the fortieth day after oviposition, no emergency of adult insects
was observed; all larvae were dead inside the eggs (Figure 5K) or in the surface of the
cotyledons (Figure 5L).
Influence of the Seed Coats on Larval Mass
Artificial seeds covered with natural seed coat (Figure 6) confirmed the negative
interference of the soybean seed coats in the C. maculatus larval development. In these
experiments, a total of 9 eggs was considered as 100 % of oviposition. All artificial seeds
covered with soybean seed coats reduced the number of oviposited eggs, ecloded larvae and
larvae that perforated completely the seed coat (Figure 6A). The percentage of larvae that
died inside the eggs varied from 25 % for the larvae oviposited onto commercial and UFV 20
Florestal soybean seed coats to 100 % for those onto Elite, Conquista, Tucunaré and UFUS
2003 cultivars. About 93 % of the larvae which survived in experiments with commercial
soybean seed coat succeed in perforating completely the seed coat; however, after 20 days of
development, these larvae had only about 23.8 % (3.34 mg) of the mass of a control larva
which developed in artificial seeds covered with V. unguiculata natural seed coat (14 mg)
(Figure 6B).
Toxicity of the Seed Coat Flour to Larvae
The toxicity experiments showed that flour from all seed coats interfered with the normal
development of the C. maculatus larvae, reducing considerably the weight and survival of the
20 days-old larvae. The toxicity levels varied from cultivar to cultivar and were dose-
dependent.
The results corresponding to the incorporation of the seed coat flour are shown in figure
7. The seed coat of UFV 20 Florestal cultivar was highly toxic and no larva survived in
artificial seeds containing 2% of this flour. In artificial seeds containing 16.0 % of UFUS
2003 and UFUS 2005 seed coat flours no surviving larva was found after 20 days. In respect