Selection of a Bacillus pumilus Strain Highly Active against Ceratitis capitata (Wiedemann) Larvae

Abstract

Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), the Mediterranean fruit fly (medfly), is one of the most important fruit pests worldwide. The medfly is a polyphagous species that causes losses in many crops, which leads to huge economic losses. Entomopathogenic bacteria belonging to the genus Bacillus have been proven to be safe, environmentally friendly, and cost-effective tools to control pest populations. As no control method for C. capitata based on these bacteria has been developed, isolation of novel strains is needed. Here, we report the isolation of 115 bacterial strains and the results of toxicity screening with adults and larvae of C. capitata. As a result of this analysis, we obtained a novel Bacillus pumilus strain, strain 15.1, that is highly toxic to C. capitata larvae. The toxicity of this strain for C. capitata was related to the sporulation process and was observed only when cultures were incubated at low temperatures before they were used in a bioassay. The mortality rate for C. capitata larvae ranged from 68 to 94% depending on the conditions under which the culture was kept before the bioassay. Toxicity was proven to be a special characteristic of the newly isolated strain, since other B. pumilus strains did not have a toxic effect on C. capitata larvae. The results of the present study suggest that B. pumilus 15.1 could be considered a strong candidate for developing strategies for biological control of C. capitata.

The internal bacterial diversity of stored product pests

“…Bacillus pumilus is a naturally occurring bacterium that is especially common in soil and on dead plant tissue (Priest 1993). Molina et al (2010) also showed that this bacterium is toxic to Ceratitis capitata larvae (Weidemann) (Diptera: Tephritidae). With this study, we also showed that the genus of Bacillus might be associated with stored product pests in different ways, pathogenic or symbiotic.…”

Cooperation and bacterial pathogenicity: an approach to social evolution

“…The first study that demonstrated the entomopathogenicity of B. pumilus is detailed in a patent that describes a strain active against the corn rootworm (e.g., Diabrotica undecimpunctata (Mannerheim, 1843), Diabotrica longicornis (Say, 1824)), the armyworm (Spodoptera exigua (Hubner, 1808)), and some species of nematodes (Heins et al 1999). The entomopathogenic activity of B. pumilus was confirmed in a study that described the isolation of the strain 15.1, a highly toxic strain against Mediterranean fruit fly larvae, Ceratitis capitata (Wiedemann, 1824) (Molina et al 2010). Since B. pumilus has never been considered as a classic entomopathogenic bacteria, the origin and the possible evolutionary route of the insecticidal activity of the B. pumilus 15.1 strain is a fairly interesting topic that would help to explain the process of pathogenicity.…”

“…In addition, the presence of crystals has been described in sporulating cultures of B. pumilus 15.1 that are similar to the Cry proteins of B. thuringiensis (Molina et al 2009). The role of these structures has not yet been elucidated.…”

“…The role of these structures has not yet been elucidated. However, it could be suggested that they are involved in the entomopathogenicity of B. pumilus 15.1 due to their structural similarity with the insecticidal toxins of B. thuringiensis (Molina et al 2009). The molecules synthesized and excreted by B. pumilus 15.1 would be considered as the bacteria public goods; therefore, it is possible that they would have the same social behavior as that which has been widely reported.…”

“…The B. pumilus 15.1 strain was isolated from a partially decomposed reed plant (Molina et al 2010), suggesting that plants can also form part of the natural habitat of this bacterium. Besides, as it has been mentioned above, other B. pumilus strains have been reported playing many other roles: first, as a growth-promoting rhizobacteria; second, providing protection to the plants as a result of its antifungal properties against phytopathogenic fungi; and finally playing a role in the plant defense reactions (Benhamou et al 1996).…”