Vector-borne plant pathogens often change host traits to manipulate vector behavior in a way that favors their spread. By contrast, infection by opportunistic fungi does not depend on vectors, although damage caused by an herbivore may facilitate infection. Manipulation of hosts and vectors, such as insect herbivores, has not been demonstrated in interactions with fungal pathogens. Herein, we establish a new paradigm for the plant-insect-fungus association in sugarcane. It has long been assumed that Fusarium verticillioides is an opportunistic fungus, where it takes advantage of the openings left by Diatraea saccharalis caterpillar attack to infect the plant. In this work, we show that volatile emissions from F. verticillioides attract D. saccharalis caterpillars. Once they become adults, the fungus is transmitted vertically to their offspring, which continues the cycle by inoculating the fungus into healthy plants. Females not carrying the fungus prefer to lay their eggs on fungus-infected plants than mock plants, while females carrying the fungus prefer to lay their eggs on mock plants than fungus-infected plants. Even though the fungus impacts D. saccharalis sex behavior, larval weight and reproduction rate, most individuals complete their development. Our data demonstrate that the fungus manipulates both the host plant and insect herbivore across life cycle to promote its infection and dissemination.

Background: In tropical sugarcane crops, the fungus Fusarium verticillioides, the agent responsible for the occurrence of the red rot complex, occurs in association with the sugarcane borer Diatraea saccharalis. This fungus, in addition to being transmitted vertically, can manipulate both the insect and the plant for its own dissemination in the field. Due to the complex interaction between F. verticillioides and D. saccharalis, and the high incidence of the fungus in the intestinal region, our objective was to investigate whether F. verticillioides could alter the intestinal structure of the insect. Methods: We combined analysis of scanning electron microscopy and light microscopy to identify whether the presence of the fungus F. verticillioides, in artificial diets or in sugarcane, could lead to any alteration or regional preference in the insect’s intestinal ultrastructure over the course of its development, or its offspring development, analyzing the wall and microvillous structures of the mid-digestive system. Results: Here, we show that the fungus F. verticillioides alters the intestinal morphology of D. saccharalis, promoting an increase of up to 3.3 times in the thickness of the midgut compared to the control. We also observed that the phytopathogen colonizes the intestinal microvilli for reproduction, suggesting that this region can be considered the gateway of the fungus to the insect’s reproductive organs. In addition, the colonization of this region promoted the elongation of microvillous structures by up to 180% compared to the control, leading to an increase in the area used for colonization. We also used the fungus Colletotrichum falcatum in the tests, and it did not differ from the control in any test, showing that this interaction is specific between D. saccharalis and F. verticillioides. Conclusions: The phytopathogenic host F. verticillioides alters the intestinal morphology of the vector insect in favor of its colonization.

Some pathogens can manipulate their host plants and insects to optimize their fitness, increasing the attraction of insects to the infected plant in ways that facilitate pathogen acquisition. In tropical American sugarcane crops, the fungus Colletotrichum falcatum, the red rot causal agent, usually occurs in association with the sugarcane borer Diatraea saccharalis, resulting in large losses of this crop. Considering this association, we aimed to identify the effects of C. falcatum on D. saccharalis host preference and performance as well as the effect of this insect on C. falcatum sugarcane infection. Here, we show that the fungus C. falcatum modulates D. saccharalis behavior to its own benefit. More specifically, C. falcatum-infected sugarcane plants showed a dramatic increase in VOCs, luring D. saccharalis females to lay eggs on these plants. Therefore, sugarcane infection by the fungus C. falcatum increased in cooccurrence with insect herbivory, benefiting the pathogen when associated with D. saccharalis.

Sugarcane is a crop of major importance used mainly for sugar and biofuel production, and many additional applications of its byproducts are being developed. Sugarcane cultivation is plagued by many insect pests and pathogens that reduce sugarcane yields overall. Recently emerging studies have shown complex multitrophic interactions in cultivated areas, such as the induction of sugarcane defense-related proteins by insect herbivory that function against fungal pathogens that commonly appear after mechanical damage. Fungi and viruses infecting sugarcane also modulate insect behavior, for example, by causing changes in volatile compounds responsible for insect attraction or repelling natural vector enemies via a mechanism that increases pathogen dissemination from infected plants to healthy ones. Interestingly, the fungus Fusarium verticillioides is capable of being vertically transmitted to insect offspring, ensuring its persistence in the field. Understanding multitrophic complexes is important to develop better strategies for controlling pathosystems affecting sugarcane and other important crops and highlights the importance of not only studying binary interactions but also adding as many variables as possible to effectively translate laboratory research to real-life conditions.

Colletotrichum falcatum is a major fungal pathogen responsible for severe disease in sugarcane. Here, we report the complete genomic characterization of a novel mycovirus infecting C. falcatum , designated Colletotrichum falcatum victorivirus 1 (CfVV1). The CfVV1 genome is 4,906 base pairs (bp) long and comprises two open reading frames encoding a capsid protein (CP) and an RNA-dependent RNA polymerase (RdRP), overlapping at an AUGA motif. The predicted proteins share ca. 70% and 68% identity with those of Colletotrichum cliviicola victorivirus 1 and Colletotrichum nativitas totivirus 1, respectively. Phylogenetic analysis based on concatenated RdRP and CP amino acid sequences places CfVV1 within the genus Victorivirus of the recently established family Pseudototiviridae . Transmission electron microscopy confirmed the presence of isometric virus-like particles ca. 40 nm in diameter, consistent with the typical morphology of victoriviruses. To our knowledge, this is the first report of a complete victorivirus genome infecting C. falcatum .