## 8 Insect Frass Against Agricultural Pests and Pathogens
### Against Plant Pathogens  
To help crops fight diseases caused by pathogens, different insect frass-mediated mechanisms of action have been described. Both frass itself and extracts derived from it have been described as products with antimicrobial properties, due to the presence of antibacterial, antifungal, and nematicidal compounds. The frass obtained from the common earwig (_Forficula auricularia_) is capable of inhibiting the in vitro growth of the plant pathogenic bacterium _Staphylococcus aureus_ and the pathogenic fungus _Aspergillus niger_, due to the possible presence of antimicrobial compounds that have not yet been identified [113]. On the other hand, extracts obtained from the frass of _H. illucens_ also inhibited the in vitro growth of different phytopathogenic fungi and oomycetes, such as _Alternaria solani_, _Botrytis cinerea_, _F. oxysporum_, _Rhizoctonia solani_, _S. sclerotorium_, and _Phtyophthora capsaicin_[129]. Furthermore, these frass extracts also exhibited nematicidal activity when applied to spinach plants, causing the suppression of nematode egg hatchability (by 42%), the paralysis and death of J2s (100% and 95%, respectively), and the suppression of gall development (by 85%) in the root-knot nematode (_Meloidogyne incognita_) [123]. This antimicrobial activity reported in insect frass may result from the synthesis of antimicrobial compounds via the microorganisms present in this product, as has been previously described in several works with beetle and lepidopteran frass. Different bacteria with antifungal properties have been isolated from the insect frass obtained from the beetle _Protaeta brevitarsis_ through in vitro confrontation assays. For example, _Bacillus subtilis_ was capable of inhibiting the growth of the pathogenic fungi _S. sclerotorium_, _S. rofsii_, and _F. oxysporum_[134]; or _Streptomyces albidid flavus_ and _Nocardiopsis flavescens_, which acted against _F. oxysporum_, _Pyricularia grisea_, _R. solani_, and _Stagonsporopsis cucurbitacarum_[122]. These antimicrobial effects have also been confirmed in in planta assays. From the frass of the Japanese rhinoceros beetle (_Allomyrina dichotoma_), the KB3 strain of the bacterium _Bacillus amyloliquefaciens_ was obtained, which produces the antifungal and oomyceticidal lipopeptides iturin A and surfactin. The cell-free filtrates obtained from this bacterium inhibited the in vitro growth of the pathogenic fungi _R. solani_, _F. oxysporum_, and _Colletotrichum cocodes_, as well as the oomycete _P. capsici_; their biocidal effects were confirmed in planta after infecting rice, tomato, wheat, barley, and pepper plants [141]. Furthermore, fungi with a potential antimicrobial capacity have been isolated from insect frass. The fungus _Accmonium zeae_ was isolated from the frass of the maize stalk borer (_Busseola fusca_), a fungus capable of producing the antifungal compounds pyrrolidines A and B, which have been described as effective in the control of the maize pathogen _Fusarium verticillioides_. However, the real antifungal activity of this isolate from insect frass has not yet been described [107]. Another frass-mediated mechanism of action for plant pathogen control is the induction of plant defenses. To date, only two studies have addressed this topic; however, it is an interesting area of research with many future possibilities. Using frass from _T. molitor_, different strategies for activating plant defenses in the model plant _Arabidopsis thaliana_ were studied. Firstly, callose deposition in the roots was analyzed as a marker of local plant defense activation after exposure to mealworm frass. Results indicated that this frass did not activate local plant defenses. Conversely, systemic plant defense induction was studied by applying this frass to the soil and using the fungus _B. cinerea_ as a foliar pathogen. It was found that the plant activated systemic defense responses upon recognizing _T.