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 16

these were highly toxic to the bruchid when compared to control host seed coats (Figure 8).
Lowest LD 50 values were found for the seed coats of UFV 20 Florestal, UFUS 2005 and
UFUS 2003 (1.0, 1.0 and 1.3 %, respectively) (Figure 9B). Although it has been observed a
great variation in the values of WD 50 and LD 50 , all soybean seed coats may be considered as
highly toxic to C. maculatus , since during the insect development in natural seeds the larvae
firstly enter in contact with this tissue, being exposed and relying on a diet 100% based on
this tissue compounds.
Figure 8. Picture of developing Callosobruchus maculatus control larvae and larvae grown on artificial
seeds containing different concentrations (2, 8 and 16%) of soybean seed coats from Elite, Conquista
and UFUS 2003 cultivars.
C ONCLUSION
The soybean seed coat prevented the penetration of up to 82.5% of the Callosobruchus
maculatus larvae. There was not direct relationship between thickness, color and/or texture of
the seed coat from several soybean cultivars with the ability of the larva to cross or not the
seed coats of these seeds. A high retard in the larval perforation of the soybean seed coat and
abnormalities in neonate larvae were observed during perforation attempts. Other larvae
began to perforate the seed coat and died while trying to penetrate the cotyledons. The
reasons for this are probably of non-physical nature, since the seed coat flours were very toxic
to insect larvae reducing the mass and the number of surviving larvae reared on artificial
seeds. We believe that the expression of the C. maculatus detrimental compounds in the seed
coats of the non-host soybean seeds reinforces the idea that the seed coat plays an important
role for the evolutionary discrimination of legume seeds by this bruchid.