Bacillus insecticides are not acutely harmful to corals and sponges

Abstract

Bacillus thuringiensis is a Gram-positive bacterium that produces crystalline endotoxins and is widely considered an environmentally safe insecticide to control mosquitoes and a number of agriculture pests. Bacteria closely related to B. thuringiensis have recently been discovered in association with diseased sponges, which has raised concerns that Bacillus insecticides may be harmful to tropical marine invertebrates. We exposed coral larvae and juvenile corals to the insecticides VectoBac ® G (containing B. thuringiensis israelensis) and VectoLex ® G (containing B. sphaericus). VectoBac G and VectoLex G had no effect on the survival and metamorphosis of Acropora millepora and A. tenuis larvae at very high concentrations (5000 µg l -1). The juvenile corals of the same species were also unaffected after 4 sequential 48 h exposures to B. thuringiensis israelensis and B. sphaericus at different stages of development. Adult corals (A. millepora) and sponges (Ianthella basta) were exposed to a single 6 h pulse of 1000 µg l -1 VectoBac G. Although B. thuringiensis israelensis was detected in the seawater using denaturing gradient gel electrophoresis, it was not detected in association with the corals or sponges. No evidence of coral or sponge disease was observed during the following 2 wk. These results indicate that insecticides containing endotoxin-producing Bacillus spp. are unlikely to be acutely pathogenic to corals and sponges. However, the effect on most tropical marine invertebrates remain untested and the risks of seed populations of alien Bacillus becoming established on reefs and horizontal transfer of toxin genes to native bacteria also need to be addressed.

Exploring the Role of Microorganisms in the Disease-Like Syndrome Affecting the Sponge Ianthella basta

“…The authors of that study speculate that bacterial pesticide pollution from agriculture may have introduced new bacteria that were pathogenic to sponges. Subsequent research with sponges and corals showed that addition of up to 5,000 g of the pesticides VectoBac G (containing B. thuringiensis israelensis) and VectoLex G (containing B. sphaericus) per liter could not induce symptoms of disease in I. basta (28). In addition, the Bacillus strain from the present study was readily cultured from both healthy and diseased I. basta in similar densities, suggesting that it is an unlikely primary pathogen.…”

“…All clone sequences from I. basta had low similarity to sequences in the NCBI database, indicating that I. basta hosts a novel microbial community. Similarly, Webster and coworkers (28) found that ca. 25% of the 16S rRNA-V6 tag sequences from I. basta were below the threshold for reliable assignment and may in fact represent previously unknown microbes.…”

Peer Review #1 of "Toxicity thresholds of three insecticides and two fungicides to larvae of the coral Acropora tenuis (v0.1)"

“…The first used a commercial formulation of chlorpyrifos and reported coral mortality at 6 µg L -1 of the active ingredient (Te 1998). Negri et al (2009) found no effects of the biological insecticide Bacillus thuringiensis on adult and larval corals and sponges at 5000 µg L -1 . A recent study from Wecker and colleagues (2018) reported that the organochlorine insecticide chlordecone caused PeerJ reviewing PDF | (2020:05:48551:2:0:NEW 1 Jul 2020)…”

Chemical Pollution on Coral Reefs: Exposure and Ecological Effects

“…In contrast, another study on adult colonies of P. damicornis demonstrated 50% mortality (LC50) to occur after 96-h exposure to 6 µg/L chlorpyrifos [92]. While most insecticides tested appear to negatively affect corals or their larvae, a recent study indicates that the "eco-friendly" larvicidal agent, Bacillus thuringiensis ssp israelensis (Bti), used extensively to control mosquitoes in the tropics, is harmless to coral larvae [93].…”