Insecticidal action of PF2 lectin from Olneya tesota (Palo Fierro) against Zabrotes subfasciatus larvae and midgut glycoconjugate binding.

Zabrotes subfasciatus (Boheman) is the main pest of common beans (Phaselous vulgaris). Some wild legume seeds may contain lectins with insecticidal activities against this insect. The larval developments of Z. subfasciatus on seeds of Olneya tesota (a desert wild legume) and on artificial seeds containing purified PF2 lectin were evaluated. PF2 susceptibility to proteolysis was assessed by incubation with midgut extract at different times. PF2 binding to midgut glycoconjugates was assessed by histochemistry. A reduced level of oviposition and a lack of emergence of adult beetles were observed in O. tesota seeds (compared to common beans), and in artificial seeds containing PF2 at 0.5 and 1%. PF2 was resistant to larval midgut proteolysis for 24 h, while PHA-E (lectin control) was fully digested after 4 h. Histochemistry analysis of midguts incubated with PF2 showed recognition for microvillae and possibly with peritrophic gel. On the other hand, PHA-E exhibited no interaction with larval midgut glycoproteins. Proteolysis resistance and glycan recognition could in part explain why PF2 is toxic to Z. subfasciatus while PHA is not.