Synergistic effect of the Bacillus thuringiensis toxins CryIAa and CryIAc on the gypsy moth, Lymantria dispar

Abstract

The insecticidal activity of toxins CryIAa, CryIAb, and CryIAc against Lymantria dispar (gypsy moth) and Bombyx mori (silkworm) was examined by force-feeding bioassays. Toxin CryIAa exhibited higher toxicity than toxins CryIAb and CryIAc for L. dispar and B. mori. To evaluate possible synergism among these toxins, bioassays were performed with mixtures of CryIAa and CryIAb, CryIAb and CryIAc, and CryIAa and CryIAc. Expected toxicity was calculated from the activity of each individual toxin and its proportion in the mixture by using the equation described by Tabashnik (B. E. Tabashnik, Appl. Environ. Microbiol. 58:3343-3346, 1992). Observed 50% growth-inhibitory doses were calculated from mixing experiments by probit analysis. In L. dispar bioassays, synergism was observed with a mixture of CryIAa and CryIAc while a mixture of CryIAa and CryIAb exhibited an antagonistic effect. No synergistic effect on B. mori was observed with any toxin combination. Voltage clamping assays of isolated L. dispar midguts also demonstrated that the mixture of CryIAa and CryIAc induced a greater slope of inhibition of short circuit current than did other toxin combinations.

Host range and gene contents of Bacillus thuringiensis strains toxic towards Spodoptera exigua

“…Anyway, crystal proteins reach up to 30% of the dry weigh of B. thuringiensis sporulated cultures (Schnepf et al, 1998). Thus, the content in Cry proteins as well as the interactions between individual toxins recently reported (Lee et al, 1996;Del Rincón-Castro et al, 1999) should be taken as the main causes for the biological activity of spore and crystal mixtures. The distribution of the cry genes was very wide, but their frequency among serovars discards a random distribution in some cases: cry1B was limited to thuringiensis strains and the frequency of the subclass of cry1C, cry1D and cry1E genes varied with serovar.…”

PCR-based identification of Bacillus thuringiensis pesticidal crystal genes

“…Another case of Cry protein interaction was described when three Cry1A proteins were tested against Lymantria dispar [45]. In this species, synergism was found between proteins Cry1Aa and Cry1Ac, whereas Cry1Aa and Cry1Ab interacted antagonistically.…”

Insecticidal potential of Bacillus thuringiensis for the biological control of neotropical brown stink bug

“…Numerous synergistic effects between Cry toxins have been observed in other insect orders. Synergistic effects of Cry1Aa and Cry1Ac proteins against Lymantria dispar (L.) were observed by Lee et al (1996), and an additive effect between Xentari and Dipel formulations to Heliothis virescens (Fabricius) was observed by Ameen et al (1998). Cry1Aa and Cry1Ca toxins expressed in GM-plants showed synergism against H. virescens, Diatraea saccharalis (Fabricius), and Spodoptera frugiperda (JE Smith) (Pinto et al, 2014).…”

“…The presence of two or more genes for specific protein toxins in the same isolate of B. thuringiensis is very common. In this way, the pathogenicity and virulence conferred by the isolates are directly related to the mode of action of the proteins and how they will interact in the intestine of the target insect (Lee et al, 1996;Fiuza et al, 2013). Mortality calculations were corrected according to Abbott (1925).…”