Virulence of Aerial Conidia of Beauveria bassiana Produced under LED Light to Ctenocephalides felis (Cat Flea)

Ctenocephalides felis is an ectoparasitic flea species commonly found on dogs and cats. The current study verified the in vitro virulence of conidia of the entomopathogenic fungus Beauveria bassiana produced under different color LED light (red, blue, purple, green, yellow, and white) to adults of C. felis. The fungal isolates were cultivated on malt extract agar (MEA). Bioassay treatments used aerial conidia in test tubes. Adult fleas were obtained from a house cat in Chiang Mai province, Thailand. The experiments were composed of one control and eleven treatment groups. All of the treatments with B. bassiana conidia caused adult mortality after an exposure of 12 h. Among the conditions used in this study, B. bassiana cultured under red LED and fluorescent light were the most effective in causing mortality (100 %) in adult fleas after 36 h. The experimental results indicate that these aerial conidia of B. bassiana have promising potential for use in control of C. felis adult stages.


Introduction
The dog and cat fleas (Insecta: Siphonaptera), Ctenocephalides canis (Curtis), and Ctenocephalides felis felis (Bouché) are small, laterally flattened, wingless, and highly specialized insects. They are very important obligate hematophagous ectoparasites and have worldwide distribution [1,2]. The adult flea lives on the host and the female lays eggs which fall from the animal and develop into larvae in the environment [3][4][5]. Both adult males and females are blood feeding and cause the immunoallergic skin affliction which is responsible for flea allergy dermatitis (FAD) of mammals and birds [6,7]. Fleas can also be competent vectors for numerous pathogens, including zoonotic such as Rickettsia typhi (murine typhus), Bartonella henselae ("cat scratch disease" in humans), and Yersinia pestis (plague) and act as the intermediate host of the tapeworm species Dipylidium caninum [5,[8][9][10]. Traditional management of adult flea infestations on animals, during the past 15 y is by topical and oral applications of insecticides such as fipronil, imidacloprid, selamectin, and most recently by insect growth regulators (IGRs) such as lufenuron [2,9,[11][12][13][14][15][16]. Recent studies show that these therapies eliminate the need to treat indoor and outdoor environments, and their use markedly reduces the severity and prevalence of flea infestations [17][18][19][20]. However, control of fleas by synthetic chemicals at present is very deleterious to the environment, pets, and pet owners.
Entomopathogenic fungi are microorganisms in nature that have high potential to infect, kill, control, and prevent subsequent reinfestation of many insect pests [4,10,21]. Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Clavicipitaceae) is one of the most important biological control agents used in insect IPM programs and has been formulated as many commercial products. Moreover, this fungus has a wide insect-host range and has been one of the most widely studied [22,23]. B. bassiana produces conidia for dispersal, transmission, and infection of other insect pests. This approach is safe for the environment pets and pet owners. The objective of this study was to evaluate the virulence of aerial conidia of B. bassiana produced under different colors of LED light to adult cat fleas.  Experiments were kept at 27±1 ∘ C and relative humidity (RH) ≥ 80%.

Results
Previous studies have shown that different color LED light has great potential to stimulate B. bassiana conidial production with a high virulence to pests. In the current study, the mortality of Ctenocephalides sp. observed in treatments 1-11 was time-dependent (  (Table 1). All fleas treated with entomopathogenic fungi were killed within 48 h after exposure. No mortality was observed in the control group. After dead host fungal will formation mycelial outgrowth from insect cadaver and production of new conidia (Figure 1).

Discussion
To the best of our knowledge, the work of seeking efficient entomopathogenic fungi against Ctenocephalides sp. was also only undertaken by De-Melo et al. [1,21,24]. B. bassiana has shown pathogenicity as a biological control agent for different arthropod species and it is commercially available as various mycoinsecticides [1,10,21]. In our study, aerial conidia of B. bassiana produced under LED light start killing fleas within 12 h after treatment administration [21]. Moreover, B. bassiana had a cumulative flea mortality of 100% in 36-48 h as short time similar some synthetic chemicals [2,7,9,14,23]. In general, for flea control in dogs and cats garden or backyard areas are treated with insecticides in an attempt to control flea infestations. However, such applications of insecticides are often poorly targeted. Hence, entomopathogenic agents have benefits in terms of effectiveness against flea infestations. It is difficult for fleas to become resistant to entomopathogenic fungi. But this insect can readily develop resistance to chemical insecticides [17,25]. Similarly, in a study conducted by Coles and Dryden [22] it was reported that control of fleas with entomopathogenic fungi can be conducted safely in terms of positive benefits for the environment, pets, and pet owners [10,19]. Previous research [26] showed that different isolates of M. anisopliae had different effects on insect pests. So, identification, application and screening of different fungal isolates in bioassays may provide promising biopesticides. Our study screened both B. bassiana and M. anisopliae with activity against adult fleas. The current research showed that growth of B. bassiana under LED lights enhanced production of conidia that resulted in 100% overall flea mortality. Future research will examine the ovicidal and larvicidal capacity of this entomopathogenic fungus. In the future such entomopathogenic fungi could be developed as bioinsecticides for practical use in pet care products like Chaingard5 pets powder. The evidence presented here indicates that both B. bassiana and M. anisopliae have a high level of adulticidal activity, and potential for inclusion in flea management systems.

Conclusions
A previous study showed the efficacy of flea control by using aerial conidia of B.

Data Availability
The data used to support the findings of this study are included within the article.

Conflicts of Interest
The authors declare that there are no conflicts of interest.