Abstract
An alternative control method to the use of chemical insecticides against soil dwelling insect pests is the application of entomopathogenic nematodes formulated in alginate beads for enhanced shelf life. The aim was to compare the benefit on nematode survival and infectivity of: (i) pre-conditioning of juveniles, and (ii) coating of alginate beads. The nematodes Steinernema glaseri , Steinernema carpocapsae, and Heterorhabditis bacteriophora were reproduced in last instar larvae of the wax moth Galleria mellonella and the infective juveniles emerged were subjected to two capture treatments: white traps and plaster of Paris, the latter was utilized as a pre-conditioning treatment. A total of 1,000 infective juveniles were formulated in each sodium alginate bead with or without an alginate coating. The beads were stored at 23 ± 3°C and a bidistilled water suspension of nematodes was set as a control. The survivorship of these formulates and their infectivity on Galleria mellonella larvae were evaluated every 7 d post-formulation (dpf). In beads without pre-conditioning juveniles nor coating, Steinernema carpocapsae had the higher survival rate (58.8%), the longest survival time (28 dpf) and the higher infectivity (100%) as well. Pre-conditioning improved the survival and infectivity of Steinernema glaseri by 22.5% at 21 dpf and 70.0% at 14 dpf, respectively. Alginate coating increased survival (21.7%) and infectivity (95%) of Heterorhabditis bacteriophora for up to 28 dpf. The combination of pre-conditioning and coating slightly favored the survival (10% for up to 14 dpf) of Steinernema glaseri and infectivity (100% for up to 35 dpf) of Steinernema carpocapsae . Non pre-conditioned Steinernema carpocapsae formulated in uncoated beads was the combination with better performance in survivorship (58.8%) and infectivity (100%) at 28 dpf. It was concluded that non pre-conditioned Steinernema carpocapsae formulated in uncoated beads was the combination with better survivorship and infectivity.
Highlights
Entomopathogenic nematodes (EPNs) (Nematoda: Heterorhabditidae and Steinernematidae) are effective biological control agents of insects pests due to their ease of adaptation, high lethality against major pests and safety (Grewal, 2002), are exempt from registration by the Environmental Protection Agency (EPA) in the U.S.A, are compatible with various chemical pesticides and are feasible for genetic selection (Kaya and Koppenhöfer, 2004)
The pre-conditioning of infective juveniles (IJs) in plaster of Paris prior to formulation in sodium alginate beads (ABs) may have a positive effect on their survival time and infectivity since Cortés-Martínez et al (2017) found that the survival of Steinernema glaseri mechanically pelletized in diatomaceous earth was improved if the IJs used were pre-conditioned on wet plaster of Paris after host emergence, compared to those from white trap
The survival rates per week of EPNs in ABs are presented in Table 1, which shows that Steinernema carpocapsae (Sc) had the best viability, maintaining a SR value of 58.8% for 28 d, followed by Heterorhabditis bacteriophora (Hb) with a SR of 51.4% at 21 d and Steinernema glaseri (Sg) with the shortest survival time with 7 d and 15% of SR
Summary
Entomopathogenic nematodes (EPNs) (Nematoda: Heterorhabditidae and Steinernematidae) are effective biological control agents of insects pests due to their ease of adaptation, high lethality against major pests and safety (Grewal, 2002), are exempt from registration by the Environmental Protection Agency (EPA) in the U.S.A, are compatible with various chemical pesticides and are feasible for genetic selection (Kaya and Koppenhöfer, 2004). The cooling system required to maintain its storage stability during the transportation and spray technology required for the application increase the cost of use of EPNs (Chen and Glazer, 2005). To promote the expansion of the use of EPNs as biological control agents, current research focuses on the development of low-cost formulations with: greater storage stability at room temperature, increased resistance during the transportation to the application site, where it dissolves for application in aqueous medium or it is deposited directly on moist soil (Burges, 1998; Grewal, 2000; Grzywacz et al, 2014), effective control of target insect pest and greater persistence in the field (Grewal, 2002; Shapiro-Ilan et al, 2012). The pre-conditioning of infective juveniles (IJs) in plaster of Paris prior to formulation in sodium ABs may have a positive effect on their survival time and infectivity since Cortés-Martínez et al (2017) found that the survival of Steinernema glaseri mechanically pelletized in diatomaceous earth was improved if the IJs used were pre-conditioned on wet plaster of Paris after host emergence, compared to those from white trap
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