Abstract
The wheat stem sawfly, (Cephus cinctus Norton) Hymenoptera: Cephidae, has been a major pest of winter wheat and barley in the northern Great Plains for more than 100 years. The insect’s cryptic nature and lack of safe chemical control options make the wheat stem sawfly (WSS) difficult to manage; thus, biological control offers the best hope for sustainable management of WSS. Entomopathogenic nematodes (EPNs) have been used successfully against other above-ground insect pests, and adding adjuvants to sprays containing EPNs has been shown to improve their effectiveness. We tested the hypothesis that adding chemical adjuvants to sprays containing EPNs will increase the ability of EPNs to enter wheat stems and kill diapausing WSS larvae. This is the first study to test the ability of EPNs to infect the WSS, C. cinctus, and test EPNs combined with adjuvants against C. cinctus in both the laboratory and the field. Infection assays showed that three different species of EPNs caused 60–100% mortality to WSS larvae. Adding Penterra, Silwet L-77, Sunspray 11N, or Syl-Tac to solutions containing EPNs resulted in higher WSS mortality than solutions made with water alone. Field tests showed that sprays containing S. feltiae added to 0.1% Penterra increased WSS mortality up to 29.1%. These results indicate a novel control method for WSS, and represent a significant advancement in the biological control of this persistent insect pest.
Highlights
The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), has been an important pest of cereal crops in the northwest region of North America for more than 100 years [1, 2]
Entomopathogenic nematodes (EPNs) related differences in wheat stem sawfly (WSS) mortality suggest that WSS is more susceptible to infection and death from H. indica and S. feltiae, compared to S. kraussei
Plugs were saturated quickly in Syl-Tac and Adigor (6.5 ± 0.85 and 12.4 ± 3.58 sec, respectively). This result indicates that chemical additives would allow EPN suspensions to absorb into the plug >50× more rapidly than EPN suspensions made with water alone
Summary
The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), has been an important pest of cereal crops in the northwest region of North America for more than 100 years [1, 2]. Managing Wheat Stem Sawfly Using Nematodes losses caused by the WSS are most prevalent in the northern Great Plains, including Montana, North Dakota, South Dakota, Minnesota, Saskatchewan, Alberta, and Manitoba [5, 6]. Infestation levels of more than 70% have been reported [7] and economic loss from crop damage caused by this insect has been estimated at $250 million USD per year in the state of Montana alone [8]. The larvae construct a plug from frass and plant particles to close up the exposed stem lumen when the weakened stalks break off and fall away [4]. WSS causes severe crop loss because infested wheat plants produce lower quality kernels and fallen stems cannot be gathered by combine harvester machines [6]
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