INTERACTION OF ENTOMOPATHOGENIC NEMATODES (STEINERNEMATIDAE) WITH SELECTED SPECIES OF IXODID TICKS (ACARI, IXODIDAE)

Entomopathogenic nematodes, currently used for biological control of v arious insect pests, were tested for their ability to penetrate and ki ll replete females of several species of ticks including Dermacentor v ariabilis (Say), Rhipicephalus sanguineus (Latreille), Amblyomma macul atum Koch, and A. cajennense (F.). These species were found to be susc eptible to the entornopathogenic nematodes, Steinernema feltiae (Filip jev) or S. riobravus (Cabanillas & Poinar), shown in previous studies in our laboratory to be attracted to and kill replete A. americanum. S . ribravus killed D. variabilis (96%), R. sanguineus (89%),A, maculatu m (24%), and A, cajennense (88%), and S. feltiae killed D. variabilis (91%) and R. sanguineus (71%). Of the ticks that survived, mean egg ma ss weights were significantly lower than those of the unexposed contro ls. When nematode-exposed ticks were examined with light microscopy, n ematodes were found to have entered ticks but did not multiply or prod uce subsequent generations of infective juveniles. The nematodes were separated from surrounding tissues by a clear space, suggesting that t hey produced protective compounds. Bacteria, thought to be symbiotes r eleased from the nematodes, multiplied initially in the hemocoel of th e tick and subsequently were found throughout the degenerating tick ti ssues. These bacteria eventually filled the tick and appeared to be th e cause of tick death. Nematode guts were filled with the bacteria, su ggesting that the bacteria were a food source. When ticks were exposed to nematodes while feeding on cattle, partially engorged females were most susceptible to the nematodes. Tick mortality and reduced egg pro duction resulted when the ticks had fed 6 and 9 d before nematode expo sure but not when ticks were exposed after 3 d of feeding. Exposure of feeding female ticks demonstrated that the nematodes were able to pen etrate tick orifices other than via the hypostome, which was embedded in the bovine epidermis for the duration of the feeding process.