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The widespread use of transgenic plants imposes selection pressure on insect pest populations to develop insecticide resistance. Evaluation of effectiveness of resistance management strategies is very important in resistance management programs. Resistance management to insecticides is widely believed to depend in part on associated fitness costs. Fitness costs can delay the development of resistance. In the present study, the effects of two entomopathogenic nematode species, Steinernema carpocapsae and Heterorhabditis bacteriophora were studied on the fitness of first insect population of Heliothis virescens selected with Vip3A in the laboratory. It was found that both nematodes species increased the fitness cost of Vip3A selected insects. The mortality of the Unsel subpopulation after exposure to either nematode species was significantly lower than that of the Vip3A-Sel subpopulation. Likewise, the reproduction of both nematode species was significantly greater in cadavers of the Unsel compared with the Vip3A-Sel subpopulation of H. virescens. There was positive correlation between nematode reproduction and the larval instar infected with nematodes. The penetration of infective nematode juveniles (IJ) was greater in the Vip3A-Sel subpopulation than in the Unsel subpopulation of H. virescens. It is concluded that entomopathogenic nematodes could increase the fitness costs and subsequently delay the resistance. [ABSTRACT FROM AUTHOR]

In laboratory experiments, we investigated how media with varying ratio of peat:sand and two levels of compaction influence dispersal success of entomopathogenic nematode (EPN) species with different foraging strategies: Steinernema carpocapsae (ambusher), Heterorhabditis downesi (cruiser) and Steinernema feltiae (intermediate). Success was measured by the numbers of nematodes moving through a 4 cm column and invading a wax moth larva. We found that both compaction and increasing peat content generally decreased EPN infective juvenile (IJ) success for all three species. Of the three species, H. downesi was the least affected by peat content, and S. carpocapsae was the most adversely influenced by compaction. In addition, sex ratios of the invading IJs of the two Steinernema species were differentially influenced by peat content, and in the case of S. feltiae, sex ratio was also affected by compaction. This indicates that dispersal of male and female IJs is differentially affected by soil parameters and that this differentiation is species-specific. In conclusion, our study shows that organic matter: sand ratio and soil compaction have a marked influence on EPN foraging behaviour with implications for harnessing them as biological pest control agents. [ABSTRACT FROM AUTHOR]

Among the species of banana borers, black weevil (Cosmopolites sordidus) is the most economically important pest in Costa Rica and worldwide. The control of C. sordidus in intensive production systems is mainly based on application of insecticides; therefore the search for biological alternatives, such as the use of entomopathogenic nematodes (EPN), is needed. The susceptibility of Cosmopolites sordidus to Heterorhabditis atacamensis CIANE07 was evaluated. The effect of inoculating H. atacamensis on larvae and adults of C. sordidus, in vitro and in artificially infected corms, was evaluated. Larvae inoculated with EPN had a mortality of 88% on the second day and 100% on the third day; no mortality was observed in adults. The treatments of 100, 500 and 1000 IJ.larvae-1 showed statistically significant differences from the control and theLD50 was 52 IJ.larvae-1. When the larvae were placed within the corms the LD50 increased to 375 IJ.larvae-1. The results indicate that the strain H. atacamensis CIA-NE07 is capable of locating and infecting weevil larvae within the banana corm and reach infection levels over 80%, 10 days after inoculation at doses of 1000 and 2000 IJ.larvae-1. The entomopathogenic nematodes are a viable alternative to be considered in the Integrated Pest Management programs of black weevil, in crops such us banana and plantain. [ABSTRACT FROM AUTHOR]

Entomopathogenic nematode infective juveniles are likely to encounter both uninfected and infected insects and host quality depends on the stage of the infection. We hypothesized that nematode response to infected hosts will change over the course of an infection. Here, we tested this hypothesis by focusing on the influence of host infection status on long-range attraction to host volatile cues. The attraction response of 3 nematode species (Steinernema carpocapsae, S. glaseri and S. riobrave) with different foraging strategies to infected and uninfected insects (Galleria mellonella and Tenebrio molitor) was tested at 24 h intervals from start of infection to emergence of infective juveniles from depleted host. As expected, based on their foraging strategies, S. carpocapsae was not very responsive to hosts, S. glaseri was highly responsive and S. riobrave was intermediate. Generally, the level of attraction did not change with time after infection and was similar between infected and uninfected hosts. An exception was S. glaseri infected T. molitor, which tended to be less attractive to S. glaseri than uninfected hosts. These results suggest that any influence of host infection status on infection behaviour is occurring at subsequent steps in the host-infection process than host attraction, or involves non-volatile cues. [ABSTRACT FROM PUBLISHER]

Exposure to hydrodynamic stresses during flow through a hydraulic nozzle can cause permanent damage to biological pesticides during spray application. Aqueous suspensions of a benchmark biological pest control agent, entomopathogenic nematodes (EPNs), were passed through three different hydraulic nozzles (standard fiat fan, Spraying Systems XR8001VS; hollow cone, Spraying Systems TXA8001VK; and full cone, Spraying Systems FL5-VS) within an experimental opposed-pistons flow device. Computational fluid dynamics (CFD) was used to numerically simulate the internal flow within the XR8001VS and TXA8001VK nozzles, and important flow field parameters from the CFD simulations were compared to the observed EPN relative viability after treatment. Overall greater reductions in EPN relative viability were observed for the flat fan (9.5%) compared to the cone type nozzles (≤2.8%). The average energy dissipation rates within the exit orifices were significantly higher for the XR8001VS flat fan compared to the TXA8001VK hollow cone, which was consistent with the greater reductions in EPN relative viability observed for the XR8001VS. These differences in EPN damage were due to the distinct characteristics of each nozzle's flow field. The reduced flow area of the narrow, elliptical exit orifice of the flat fan generates an extensional flow regime, where it was found that the tensile stresses developed were large enough to cause nematode damage. However, with the cone nozzles, the high rotational flow component did not produce hydrodynamic conditions conducive to causing nematode damage. Overall, common hydraulic nozzles were found to be acceptable for spray application of EPNs following the manufacturer's recommendations. However, it is recommended that an appropriately sized (i.e., larger than the organism) cone nozzle is more suitable for spray application than a fan nozzle to avoid damage to the biopesticide. [ABSTRACT FROM AUTHOR]