## 1 Introduction  
Controlling aphids is a challenge for growers because, not only do aphids cause damage to crops by direct feeding, but also by transmission of economically costly plant viruses [1]. Aphids also have extremely high recundities and short developmental times, allowing populations to grow very rapidly [2]. For these reasons, control commonly relies on intensive use of systemic chemical insecticides which, coupled with their reproductive rate, has led to the emergence of widespread resistance to currently-available modes of action [3]. Entomopathogenic fungi are the most important microbial control agents naturally regulating aphid populations and, therefore, have great potential as biological control agents of these pests [4].  
Most fungal species naturally infecting aphids are from the Entomophthornycota and Ascomycota (order Hyporecales). Species in the Ascomycota have been commercialized for aphid control because they can be readily mass-produced in vitro and easily formulated for spray application [5]. Indeed, several mycoinsecticides for aphid control are available on the market and sold as environmentally-safe products that fit perfectly into current legislation requirements [6]. They can be applied by spraying, drenching or seed dressing [7; 8], or can be established as transient endophytes in targeted crops where they protect the plants from pests [9; 10; 11].  
Whilst the efficacy of transient endophytic colonization has been proven against some sucking insects, such as whiteflies [10], it should be noted that the immature developmental stages of these species are attached to the plant and do not move within and between plants. In contrast, all stages of aphids (except eggs) are mobile and probe the phloem to feed [12; 13]. Hence, they could avoid contact with fungal propagules. For this reason, it is important to determine whether endophytic colonization of plants by entomopathogenic fungi can cause aphid mortality. It also remains unclear whether the conidia that remain coating the leaves and stems combined with endophytic colonization can affect aphid survival.  
Furthermore, pre-mortality effects are known to occur following direct exposure to entomopathogenic fungi [14; 15; 16; 17; 18]; possible pre-mortality effects on reproductive capacity (i.e., per capita aphid fecundity) following exposure to endophytic entomopathogenic fungi have yet to be investigated.  
Many behavioral responses in insects (foraging, finding mates and oviposition sites, and avoiding natural enemies) are mediated by olfactory chemical cues emitted by both the plants and the insects [19]. Plant volatile emissions can also change when the plant is colonized by microorganisms, which can influence the responses of herbivorous insects and their natural enemies to those plants [20; 21; 22; 23; 24; 25]; whether endophytic colonization induces analogous effects remains unknown, even though it has been reported that entomopathogenic fungi do emit volatiles and that microbial volatiles may modify insect interactions [26; 27]. In this study, we determined the lethal and pre-mortality effects of several isolates of entomopathogenic fungi against the cotton aphid _Aphis gossypii_ [PERSON] when the aphids were either exposed to leaves that were both sprayed with the fungal suspension and endophytically colonized or only endophytically colonized by the fungi. Aphid preference for uncolonized or endophytically-colonized melon plants was evaluated, as well as the volatile emissions from endophytically-colonized and uncolonized plants.