## 8 Insect Frass Against Agricultural Pests and Pathogens
### Against Insect Pests  
The most developed field of study on the use of insect frass against biotic stresses is aimed at reducing the negative effects of insect pests on crops. Several works have reported the effectiveness of insect frass in reducing the damage caused by insect pests on crops, but without identifying the mechanism of action involved. By using insect frass from two species of springtail (_Heteromurus nitiidus_ and _Onychiurus scotarius_), in contact with the roots of annual meadow grass (_Poa annua_) and white clover (_Trifolium repens_), it was possible to reduce the reproduction of the aphid _Myzus persicae_ in the aerial part of the plant by 45%, only in the grass [137]. Other subsequent work has focused on the species widely exploited in insect farming, _H. illucens_ and _T. molitor_. The application of frass from the black soldier fly to the soil caused a reduction in the survival and pupal biomass of the cabbage fly (_Delia radicum_) in Brussels sprouts [87; 126] and mustard [119] crops. Similar results have been reported with the use of mealworm frass mixed with soil for mustard cultivation, both in relation to the cabbage fly and the diamondback moth (_Plutella xylostella_) [119]. Although none of these studies identify the mechanism of action involved in these results, the presence of entomogens in the frass, such as the bacterium _Bacillus thuringiensis_, is suggested as a possibility [126]. In this sense, several works have been carried out describing how insect frass can be used as a vehicle for entomopathogenic microorganisms that effectively contribute to the biological control of agricultural insect pests. In the case of viruses, several insect pests of plants transmit viruses that are capable of killing them through their own frans. This insect frass could be used to control these same pests. For example, the frass from the caculo beetle (_Phylophaga vandinei_) contains the invertebrate iridescent virus 6, capable of killing this beetle [130], or the frass from the _Hyblaea purea_ moth horizontally transmits its nucleopolyhedrovirus [115]. Furthermore, viruses present in insect frass from one species can be effective biocontrol agents against other insect pests. This is the case of frass from the lepidopteran predator beetle _Calosoma suyi_, which, by feeding on the insect pest fall armyworm larvae (_S. frugiperda_), represents an important source of nuclear polyhedrosis virus inoculum that kills the lepidopteran [128]. In addition to in vitro and in vivo studies with insect pests, this use of insect frass as a vehicle for entomopathogenic viruses has been confirmed in planta. Velvetbean moth (_Anticarsia gemmatalis_) larvae are able to actively transmit their multiple nucleopolyhedrovirus to soybean plants via frass, causing the death of the insect pest [100]. In addition to viruses, insect frass has been described as an effective vehicle for entomopathogens of the protozoan and nematode groups. Several microglial protozoa have been actively transmitted through insect frass, such as _Endoreticulatus schubergi_, _Nosema lymantriae_, and _Vairomorpha disparis_, which are present in the frass of the gypys moth (_Lymantria dispar_) and capable of killing the insect pest [99]. Furthermore, microsporidian protozoa can be actively transmitted through the frass of insects that prey on pest insects. This happens with the protozoan _Vairinorpha_ sp., which is capable of killing the lepidopteran _S. frugiperda_ and is actively transmitted through the frass of the lepidopteran-predating beetle _C. suyi_[128]. In the case of nematodes, they can also be transmitted through the frass of insect pests as biological control agents against themselves. This happens with the rosaceae longhorned beetle (_Oshrunteria coerulescens_), a pest insect of woody crops whose frass actively transmits the entomopathogenic nematodes _Heterorhabditis bacterioplora_ and _Steinerema arapcapsae_, both of which can kill the beetle on apricot tree branches [135].