Endophytic Bt expands caterpillar control in tomatoes

The use ofBacillus thuringiensis (Bt) how endophytes in tomatoes enhance control of Spodoptera littoralis. A recent study demonstrated systemic colonization of the plant, reduced larval survival, and increased effectiveness of foliar applications of the bioinsecticide.

Researchers inoculated tomato plants with a Bt isolate from a commercial formulation. The drench method in seedlings ensured colonization in roots, stems, and leaves. Spores showed greater efficiency. Colonization reached 100% of the tissues with this type of inoculum.

Evaluation with insects

In the insect evaluation, neonate larvae fed with colonized leaves showed a sharp reduction in survival. Only 45% reached the third instar. Surviving larvae completed the cycle, but showed shorter adult lifespan and lower fecundity. There was also a reduction in pupal survival.

Histological analyses showed damage to the midgut. There was epithelial rupture, loss of microvilli, and mitochondrial disorganization. The pattern coincides with the action of Cry and Vip toxins.

Consumption of colonized tissue led to the active presence of Bt in the larvae's intestines. This effect altered cellular immunity. There was a reduction in nodulation and phagocytosis. The number of hemocytes did not vary.

Susceptibility to bioinsecticide

The altered immune response increased susceptibility to the bioinsecticide. Foliar applications at sublethal doses caused near 100% mortality in young caterpillars fed on colonized plants. There was a sharp drop in survival after five days.

The effect also occurred in more advanced instars. These stages usually show low sensitivity to Bt in isolated sprays.

Integrated strategy

The researchers propose an integrated strategy. The management combines soil inoculation in seedlings with subsequent foliar applications. The system promotes dual action: Bt acts inside the plant and on the leaf surface.

The results indicate a new avenue for integrated management programs. Field studies are still needed to validate colonization stability and agronomic efficiency under different environmental conditions.

Further information at doi.org/10.1002/ps.70771