Compatibility with Pesticides and other Bioagents

Entomopathogenic nematodes have certain advantages over chemicals as biocontrol agents. They are non-polluting and thus environmentally safe and acceptable, although some countries do not allow the release of non-indigenous species. IJ3 can be applied with conventional equipment (Georgis, 1990) and are compatible with most pesticides (Forschier, et al., 1990; Rovesti, 1990; 1991). They find their hosts either actively or passively and in cryptic habitats and sometimes in soil, they have proven superior to chemicals in controlling the target insect (Gaugler, 1981). They are not well-suited for foliar application since they are sensitive to desiccation and UV radiation. The effective host range of a given species or strain is usually rather narrow, thus they do not cause indiscriminate mortality. The narrow host range means that one must select the appropriate nematode just as one must select the appropriate chemical insecticide to control the target insect.

Wang (2007) reported that the combined use of 48% chlorpyrifos EC (1000 mg/litre), 70% imidacloprid (500 mg/litre) and S. carpocapsae (4000 IJs/ml), against Rhabdoscelus lineaticollis [Rhabdoscelus lineatocollis], a new invasive pest attacking palms and sugarcanes, showed 98% mortality after 7 days, which was significantly higher than individual treatments with chlorpyrifos (68.96%), imidacloprid (0) and S. carpocapsae (68.42-78.57%) treatments. Mortality of the weevil adults in the combined treatment (88.89%) was also significantly higher than those in the individual chlorpyrifos (72%), imidacloprid (2.50%) and S. carpocapsae (27.78% 52.63%) treatments.

Rovesti and Deseo (1990) found that 2% w/v concentration of neem seed kernel extract affected third instar larvae of Heterorhabditis spp. causing mortality while Seinernema spp. were less susceptible. However, infectivity tests showed that treated Steinernema spp. killed all G. mellonella larvae while treated Heterorhabditis spp. were unable to parasitize. While Sirjusingh et al. (1991) showed that S. glaseri had higher survival, greater ability to recover and maintain infectivity after pesticide exposure than Heterorhabditis spp.

The interspecific competition of EPN with B. thuringiensis is dependent upon the timing of Bt exposure to the host (Kaya and Burlando, 1989; Poinar et al., 1990). Lepidopteran host infected with EPN 24 h prior to Bt have normal nematode development, while nematode growth is poor or negligible when Bt is inoculated 24 h prior to the nematode. When both are inoculated simultaneously, a few cadavers exhibit dual infection, with Bt occupying the anterior part, while nematode restricted to the posterior part of the insect. The nematode growth is however poor in dual infection.

Thurston (1998) compared efficacy of B. thuringiensis tenebrionis (Novodor-FC) (Btt) protected elm (Ulmus americana) foliage from damage by elm leaf beetle, Xanthogaleruca luteola [Pyrrhalta luteola]. Untreated trees lost up to 40% of their total foliage due to elm leaf beetle feeding in 3-week, while Btt-treated trees suffered only 10% defoliation. The entomopathogenic nematode S. carpocapsae, when incorporated into tree bands containing cellulose mulch, proved effective at killing high proportions of migrating larvae.

Interactions between H. bacteriophora isolate JPM4 and M.anisopliae isolates LPP45 and LPP39 with respect to mortality, production of IJs and production of conidia were studied during dual infections of sugarcane borer, Diatraea saccharalis. A positive effect was demonstrated for host mortality in duel infections of JPM4 and LPP39, causing 100%, however, the combination of JPM4+LPP39 caused a significant reduction in IJ production. The results showed that for faster time to death, a moderately virulent fungal isolate could be combined with the nematode at the expense of IJ production (Aceved et al., 2007).

Barberchek and Kaya (1990) demonstrated the suppression of entomopathogenic fungus, Beauveria bassiana, when inoculated simultaneously on Galleria with S. carpocapsae or H. bacteriophora, however, the nematodes had an antagonistic effect when the fungus was applied prior to the nematodes.The effects of the agitation system, initial temperature of the spray liquid, EPN concentration and additional air injection on the viability of EPN were studied by Aczynski et al.(2007). The results illustrated that the hydraulic agitation caused significantly more reduction in viability than the mechanical agitation. A lower temperature of the initial spray liquid yielded a significantly higher EPN viability compared to a higher temperature after hydraulic mixing and so did air injection, while EPN concentration did not significantly influence viability.

1. Screening of bioinsecticides against the cotton bollworm on cotton. Carrano-Moreira-AF; All-J. Pesquisa-Agropecuaria-Brasileira. 1995, 30:3, 307-312; 22 ref.
Four bioinsecticides and a synthetic pyrethroid were evaluated against Heliothis zea [Helicoverpa zea] in the laboratory. Treatments were: cypermethrin; Bacillus thuringiensis subsp. kurstaki; Steinernema feltiae; nuclear polyhedrosis virus; Beauveria bassiana (Bals) and an untreated check, applied over 2.8 cm2 cotton leaf discs in 3 concn. Mortality rate was recorded 1, 2, 7 and 9 days after treatment. The efficiency of the bioinsecticides was also tested in a green house. Treatments were the same but instead of the virus an experimental formulation of B. thuringiensis (Mycogen) was used. Each treatment consisted of 4 plants (Coker 310) sprayed with insecticide and infested with 9 neonate larva. Results were evaluated 7 days after treatment. In the laboratory, cypermethrin and B. thuringiensis were significantly different from the untreated control at day 1, despite concentrations. They did not differ statistically from each other. S. feltiae showed a significant higher mortality rate than the control after day 2. The virus was highly effective between 2 and 7 days after treatment, killing all larvae. In the greenhouse, cypermethrin was significantly more effective than no treatment.
2. Kaya-HK; Burlando-TM. 1989. Infectivity of Steinernema feltiae in fenamiphos-treated sand. Journal-of-Nematology, 21:3, 434-436.
The presence of fenamiphos in sand adversely affected the ability of S. feltiae [Neoaplectana carpocapsae] to infect larvae of Galleria mellonella. When S. feltiae and Galleria were placed on the sand surface on the same day as the fenamiphos granules, nematode activity was totally suppressed. Placement of the Galleria larvae on the sand surface 7 days after nematode and fenamiphos treatment resulted in nematodes killing significantly fewer Galleria larvae as fenamiphos concentrations increased from 4.5 to 18.0 mg a.i./kg dry sand. Fenamiphos was nematostatic in sand over a 4-7 day exposure period, but the nematodes were infectious when they were extracted from sand.
3. Gaugler-R; Campbell-JF. 1991. Behavioural response of the entomopathogenic nematodes Steinernema carpocapsae and Heterorhabditis bacteriophora to oxamyl. Annals-of-Applied-Biology, 119:1, 131-138; 22 ref.
Infective juveniles of Steinernema carpocapsae showed a low level of locomotory activity that is presumed to limit their usefulness as biological insecticides. A 30 µg ml-1 solution of oxamyl reduced the proportion of non-mobile nematodes by nearly two thirds to 35%, while stimulating a 7.5-fold increase in sinusoidal movement. This increase in activity did not result in a corresponding increase in host-finding. Oxamyl treatment did not enhance infective juvenile pathogenicity to Galleria mellonella larvae. At higher concentrations, oxamyl caused aberrant nematode movement and partial paralysis. Heterorhabditis bacteriophora infective juveniles maintained a high level of locomotory activity. Treatment with 30 µg ml-1 oxamyl increased the proportion of sinusoidal over non-sinusoidal movements, but infective juvenile host-finding and pathogenicity were significantly reduced. Higher rates impaired movement and induced complete paralysis. It is concluded that oxamyl is incompatible with S. carpocapsae and H. bacteriophora. The concept of chemically activating infective juveniles to increased locomotory activity and thereby achieving enhanced efficacy is inconsistent with these results.
4. Gordon-R; Chippett-J; Tilley-J. 1996. Effects of two carbamates on infective juveniles of Steinernema carpocapsae all strain and Steinernema feltiae Umeao strain. Journal-of-Nematology, 28:3, 310-317; 26 ref.
Laboratory bioassays were conducted to determine the effects of two carbamates, carbofuran (an acetylcholinesterase inhibitor) and fenoxycarb (a juvenile hormone analog), on survival and infectivity of the infective juveniles (IJ) of Steinernema feltiae Umea strain and Steinernema carpocapsae all strain. Both insecticides caused mortality of IJ in a dose-related fashion. The two nematode species were equally sensitive to fenoxycarb (LD50 ca. 0.03 mg/ml). Whereas IJ of S. feltiae were several orders of magnitude more sensitive to carbofuran (LD50 _ 0.2 µg/ml) than to fenoxycarb. S. carpocapsae IJ displayed approximately the same degree of sensitivity to carbofuran (LD50 0.01-0.03 mg/ml) as they did toward fenoxycarb. Toxicity of the carbamates was the same at all exposure periods from 24 to 168 hours' duration. Determinations of infective doses of nematodes required to cause 50% mortality of Galleria mellonella larvae showed that the infectivity of IJ that survived exposure to either of the two carbamates was not compromised by treatment.
5. Koppenhofer-AM; Brown-IM; Gaugler-R; Grewal-PS; Kaya-HK; Klein-MG 2000 Synergism of entomopathogenic nematodes and imidacloprid against white grubs: greenhouse and field evaluation.
Biological-Control, 19:3, 245-251; 27 ref.

Synergism between entomopathogenic nematodes and imidacloprid against scarabaeid larvae was tested in the greenhouse and field in California during 1997. Heterorhabditis bacteriophora, Steinernema glaseri and S. kushidai were tested with 200 g a.i. imidacloprid/ha against Cyclocephala hirta, Popillia japonica, C. borealis, Exomala orientalis and C. pasadenae in the laboratory and H. bacteriophora, S. glaseri and H. indica were tested against C. hirta and P. japonica in the field. In greenhouse experiments, the strongest and most consistent synergism occurred in combinations of imidacloprid and S. glaseri. In an experiment with several scarabaeid species, a significant increase in mortality in the combination treatment compared to the agents alone was observed for all scarabaeid species with imidacloprid and S. glaseri combinations. In field experiments with C. hirta, interactions between imidacloprid and H. bacteriophora were additive, while those with S. glaseri were synergistic. However, in field experiments with P. japonica synergistic interactions were observed between imidacloprid and both nematode