A new entomogenous nematode for pest management systems James E. Milstead George 0. Poinar, Jr. arget pest resurgence and second- veniles that begin leaving the host T ary pest outbreaks which result from cadavers within 8 to 10 days after host disruptive effects of chemical pesticides death. The LD, for seventh instar larvae on natural enemies have caused increased of the Greater Wax is between interest in microbial control measures in three and six invasive juveniles. An ini- pest management ecosystems. For such tial dosage of 5 to 20 invasives produces control, entomogenous nematodes offer approximately 350,000 juveniles per host promise as easily manipulatable mortali- cadaver. ty factors on pests. Of these nema- The juveniles can be stored in saline todes, members of the Neoaplecta- and have survived in a 2.5 percent Ring- nu have been the most intensively stud- ers salt solution for 14 months at 7". ied. They are amenable to mass-produc- To determine the host range of tion techniques, and in 75 percent of Heterorhabditis in laboratory trials, can- reported field trials their utilization has didate were exposed to approxi- resulted in increased parasitization mately 6000 invasive stages placed on levels and significant reductions in pest- filter pads in petri dishes. Results (table Flg. 1. Symbiotic bacteria carried by invasive population densities and/or adequate 1) indicate that the nematode can utilize juveniles d Heterorhobditis bacteriophoro Poinar. plant protection. In 1975 a new nema- many different hosts, including many of tode parasite, Heterorhabditis bacterio- major agricultural and medical importance. phora Poinar, was discoverd by D. E. Laboratory trials were conducted I Pinnock to be a significant mortality fac- to assess the effect of invasive juveniles tor in populations of Heliothis punctigera on fifth-instar larvae of the red-humped inhabiting alfalfa fields near Brecon, caterpillar, , a pest of South Australia. This nematode has been walnut, Liquidambar and red bud plant- studied in the laboratory, and the ings. For these trials nemas were uniform- present report discusses its biology, ly distributed on the surface of a 7-cm- pathogenicity, and potential as a biologi- deep stratum of U.C. Soil Mix overlaying cal control agent. a 2-cm-deep layer of coarse moist sand. The life cycle of Heterorhabditis Results of two experiments (table 2) bacteriophora Poinar has been studied suggest a graded mortality response to by utilizing laboratory populations of the varying nema dosages. It appears that 1 Fig. 2. Invasive juveniles inside the body of a Greater Wax Moth, Galleria mellonella square foot of a comparable soil would hermaphroditic female. The nematode exists in a symbiotic rela- require application of approximately tionship with a gram-negative asporous 2000 invasive juveniles, and that a single rod-shaped bacterium (figure 1) which is host cadaver could yield enough invasives released when invasive juvenile stages of for treatment of 100 square feet of soil. the nematode penetrate into the Laboratory evidence suggests that hemocoel of a host. Host mortality occurs Heterorhabditis usually replicates in sus- in 16 to 48 hours, depending on the initial ceptible host cadavers, so it is conceiv- nema dosage and ambient temperature. able that the invading nematodes might A temperature range of 16.8 to 29.5"C fa- produce epizootics and thus eliminate vors nematode development in the host. the need for frequent treatment. After gaining entry into the host, Continuing research will assess the the invading juveniles develop into her- impact of Heterorhabditis on non-target maphroditic females, which then deposit organisms and the action of biotic and some of their eggs in the fatty tissue of abiotic factors on survival of this nema- the host cadavers. These eggs develop in- tode in various soil ecosystems, but pre- to males and females. The remaining liminary studies suggest that Hetero- eggs are retained in the body of the her- rhabditis may prove to be a valuable maphroditic females where they utilize adjunct in non-disruptive pest manage- parental tissue and develop into mature ment systems. juveniles (figure 2) before escaping into the fatty tissue where further develop- James E. Milstead is Staff Research As- ment to second generation hermaphro- sociate 111 and George 0. Poinar, Jr., is ditics takes place. Insect Pathologist, Division of Entom- Both sexual and subsequent her- ology and Parasitology, University of maphroditic females produce invasive ju- California, Berkeley.

12 CALIFORNIA AGRICULTURE,MARCH 1978