Baculovirus changes the dietary choices of Spodoptera exigua

Infection with the baculovirus SeMNPV alters food choice and oviposition in Spodoptera exigua, with a shift in preference towards plants and diets with higher protein content. The effect involves the regulation of the olfactory receptor SexiOR23, according to a study by Chinese researchers.

Scientists used the system formed by Spodoptera exigua multiple nucleopolyhedrovirus, or SeMNPV, and its host Spodoptera exigua. The objective involved evaluating how a baculovirus infection modifies host selection, larval feeding, and oviposition site selection.

In assays with fifth-instar caterpillars, uninfected individuals preferred Brassica oleracea. After infection with SeMNPV, the preference changed. The caterpillars began to select more selectively Glycinemax (soybeans) and Apium graveolens (celery). These plants showed higher soluble protein content and a higher protein-to-carbohydrate ratio in the leaves.

Artificial diets

The team also tested artificial diets. One diet had a higher proportion of carbohydrates, with a protein:carbohydrate ratio of 1:7. The other had a higher proportion of protein, with a ratio of 7:1. Uninfected caterpillars chose the carbohydrate-rich diet. Infected caterpillars chose the protein-rich diet.

The researchers annotated 66 olfactory receptor genes in Spodoptera exigua. Six showed increased expression after infection. SexiOR23 registered the strongest induction in RNA-seq analysis, with a 23,25-fold increase. Validation by qRT-PCR showed a 5,71-fold increase in infected larvae.

The expression of SexiOR23 was concentrated in the head of the caterpillars. After infection, the gene maintained high expression in this tissue and also showed increased expression in the midgut and fat body. The high expression in the head reinforces the link with chemosensory processes associated with host selection.

Testing gene function

To test the gene's function, the authors silenced SexiOR23 using RNA interference. Silencing reduced gene expression and reversed the dietary shift caused by the infection. Caterpillars infected with silenced SexiOR23 reverted to a preference for the carbohydrate-rich diet. In the plant test, silencing reduced the choice for Apium graveolens, host with the highest protein:carbohydrate ratio, and re-established the preference for brassica oleracea.

Consumption and survival

The study also assessed consumption and survival. Infected caterpillars consumed more of the high-protein diet than the normal-protein diet. Individuals maintained on the high-protein diet showed greater tolerance to SeMNPV, with delayed mortality and higher survival compared to caterpillars maintained on a normal diet. Seven days after infection, survival was higher on the high-protein diet.

Silencing SexiOR23 did not consistently alter susceptibility to the virus until pupation. According to the authors, this result indicates a primary role for the receptor in behavioral reprogramming, rather than in the direct activation of antiviral defenses.

Adult stage

The change persisted into the adult stage. Females originating from infected caterpillars showed a 39,40-fold increase in SexiOR23 expression. In the antennae, the increase reached 11,10 times compared to uninfected adults. The higher expression in the antennae suggests involvement in decisions related to host location.

Oviposition also changed. Uninfected females laid more eggs in brassica oleracea, host with the lowest protein:carbohydrate ratio. Females carrying SeMNPV directed egg laying towards Apium graveolens, host with the highest protein-to-carbohydrate ratio.

Further information can be found at DOI 10.1016/j.pestbp.2026.107156