Effect of soil salinity on entomopathogenic nematode survival and behaviour

Abstract

Soil salinity, measured as electroconductivity (dS m −1 ), is a major problem in crop production, including areas where entomopathogenic nematodes (EPN) are applied as biological control agents. EPN species, primarily Heterorhabditis, have been isolated from coastal areas and agricultural soils with high salinity (>4.0 dS m −1 ). Given the aqueous nature of their environment, soil salinity may play an important role in EPN movement and host finding. We assessed the survival of Steinernema riobrave, S. glaseri, Heterorhabditis indica, H. sonorensis and H. bacteriophora exposed to saline soils within the range found in agricultural soils. Survival and infectivity were generally unaffected by salinities ranging from 0 to 50 dS m −1 (50 dS m −1 is similar to the salinity of seawater). Salinity had been shown to negatively impact foraging in S. riobrave so additional experiments analysing the behaviour and attraction to host cues by S. riobrave and H. indica were conducted. Agar-based behavioural assays revealed species-specific responses to salinity. At the higher salinity levels (30 and 50 dS m −1 ) movement of H. indica decreased, the path taken was more circuitous and individuals did not move toward a host. There was a strong antagonistic effect on H. indica motility and host-finding behaviour. No significant differences were observed for S. riobrave exposed to any of these salinity levels. However, under simulated field conditions, high saline conditions (30 and 50 dS m −1 ) reduced the distance both H. indica and S. riobrave travelled toward a host. Both species are used for biological control of weevil pests in orchards where salinities have been recorded up to 20 dS m −1 . Field efficacy of EPN applied for biological control in saline soils may be improved by timing applications to avoid late season build-up of salts in irrigated crops and applying the appropriate EPN species.

Effects of some inorganic fertilizers on entomopathogenic nematodes, Steinernema feltiae (Tur-S3) and Heterorhabditis bacteriophora (Hb.H)

“…The excessive use of inorganic fertilizers causes a variety of environmental problems such as soil salinity, heavy metal accumulation, greenhouse effect, eutrophication in water bodies and nitrate accumulation (Sönmez et al 2008). When exposed to soil salinity, the movement of EPNs is restricted and their ability to find and recognize their host is reduced (Nielsen 2011). There is more accumulation of heavy metals in the areas where agricultural activities such as fertilizing are conducted than in natural areas (Campos-Herrera et al 2010).…”

Optimizing Sampling and Extraction Methods for Plant-Parasitic and Entomopathogenic Nematodes

“…Biological control of PPNs using an introduced BCA may not be as effective in various settings as that of indigenous BCA due to ecological validity. Soil moisture and texture [ 10 ], salinity [ 11 ], mulching [ 12 ], and pH [ 13 ] were also found to modulate EPN populations directly or indirectly by influencing their hosts or enemies [ 4 ].…”

Optimizing for taxonomic coverage: a comparison of methods to recover mesofauna from soil

“…Moreover, the loss of saprophytic soil fungal and bacterial propagules during the sieving and rinsing process of SC is advantageous because primarily fungi and bacteria intimately associated with nematodes, mites, and collembola are retained. This property has been exploited in studies that utilized qPCR tools to estimate the occurrence and dynamics of fungal and bacterial natural enemies of entomopathogenic nematodes (Campos-Herrera et al, 2014;Pathak et al, 2017). Sucrose centrifugation appears to be uniquely suited to study species assemblages affecting soil nematodes, given the breadth of natural enemy guilds it can capture.…”

“…According to Petersen and Luxton (1982), passive extraction methods are more efficient than active methods such as Berlese funnels. Nevertheless, Berlese funnels are the most frequently used extraction method for soil microarthropods.…”

“…Relationships measured between biotic and abiotic variables in soil food web surveys can reveal potential key natural enemies of nematodes as well as cultural practices that manipulate the soil in ways to exploit the services of biological control agents of harmful nematodes and arthropod pests ( Duncan et al, 2013 ; Campos-Herrera et al, 2015, 2019 ). For example, surveys of naturally occurring communities of entomopathogenic nematodes and some of their natural enemies have identified soil properties such as pH ( Hara et al, 1991 ; Campos-Herrera et al, 2013a ), salinity ( Hara et al, 1991 ; Nielsen et al, 2011 ), texture and moisture ( Campos-Herrera et al, 2013b ) that potentially modulate EPN populations directly, or indirectly by affecting their hosts ( Gazit et al, 2000 ) or natural enemies ( Duncan et al, 2013 ; Campos-Herrera et al, 2019 ).…”