Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 10, 2007
Publication Date: April 21, 2007
Citation: Blackburn, M.B., Farrar, R.R., Gundersen, D.E., Lawrence, S.D., Martin, P.A. 2007. Reproductive failure of Heterorhabditis marelatus in the Colorado potato beetle: Evidence of stress on the nematode symbiont Photorhabdus temperata, and potential interference from the enteric bacteria of the beetle. Biological Control 42:207-215. Interpretive Summary: Some nematodes (tiny worms) can attack and kill insects by infecting them with disease causing bacteria. After the bacteria kill an insect, they digest it, and the nematode feeds on the bacteria. After feeding on the digested insect and bacteria, the nematodes reproduce and leave the dead insect to look for other insects to attack. The nematodes and their bacteria are attractive candidates for the biological control of insects. One nematode/bacteria combination has been shown to attack and kill Colorado potato beetle larvae, but the nematode cannot reproduce within the dead beetle. We investigated the growth of these bacteria in the Colorado potato beetle and found evidence that the insect-killing bacteria are stressed while living in the beetle. It also appears that bacteria that live in the gut of the beetle can escape the gut and inhibit the growth of the nematode's insect killing bacteria. Five different bacteria present in the gut of the beetle were found to inhibit the growth of the insect-killing bacteria. In contrast, the insect-killing bacteria had a lesser effect on the growth of the beetle's gut bacteria. These results will be of interest to those attempting to control Colorado potato beetle with nematodes, and useful to scientists searching for other nematode-bacteria combinations to control this damaging pest.
Technical Abstract: The nematode Heterorhabditis marelatus and its symbiont, Photorhabdus temperata, have been documented to successfully attack and kill, but cannot reproduce within, Leptinotarsa decemlineata (Say) (Armer et al., 2004). P. temperata cultured in vitro in L. decemlineata hemolymph did not differ in phenotype or growth rate from those cultured in nutrient broth. Microscopic examination of body fluid from P. temperata-killed L. decemlineata revealed a high incidence of P. temperata exhibiting abnormal growth characteristics, such as filamentous forms that regularly exceeded 50 'm in length, possibly indicating stress. It was also noted that many P. temperata infections were accompanied by substantial growth of competing bacteria that could interfere with growth of either P. temperata or H. marelatus. We isolated six species of enteric bacteria from our laboratory colony of L. decemlineata, and identified them as species of Serratia, Pseudomonas, Acinetobacter, Pantoea, Klebsiella, and Lactococcus. When P. temperata was grown alongside these enteric isolates on plates, all but the Lactococcus isolate inhibited the growth of P. temperata to a greater extent than P. temperata was able to inhibit their growth. Surprisingly, the Serratia isolate appeared to be slightly stimulated by the presence of P. temperata.