Susceptibility of the Sod Webworm Pediasia Trisecta to Biological Control Agents
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University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Faculty Publications: Department of Entomology Entomology, Department of 1-1970 Susceptibility of the sod webworm Pediasia trisecta to biological control agents E. A. Heinrichs C. J. Southards Follow this and additional works at: https://digitalcommons.unl.edu/entomologyfacpub Part of the Entomology Commons This Article is brought to you for free and open access by the Entomology, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Faculty Publications: Department of Entomology by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. E. A. Heinrichs, C. J. Southards. 1970. Susceptibility of the sod webworm Pediasia trisecta to biological control agents. Tennessee Farm and Home Science Progress Report Number Progress Report Number 73 January, February, March 1970: 30-32. Keywords: biological control, lawn pest control, insect pathogens as biopesticides, Bacillus thuringiensis, Beauveria bassiana, entomophagous nematode Neoplectana carpocapsae Susceptibility of the Sod Webworm Pediasia trisecta To Biological Control Agents by E. A. Heinrichs and C. J. Southards· omeowners in Tennessee have (Sevin and Diazinon) have not those w h i c hare eomniercially observed complete destruction been implicated in causing web available are about equal to costs ofH their lawns by the sod webworm worm increases, but they probably of insecticides. a few months after applying an in do have an adverse effect on the secticide to control sod webworms natural enemy population. There is Materials and Methods or white grubs. The reason for also a possibility that webworms this increase rather than a de may develop resistance to these Three pathogens, a bacterium crease in the webworm population chemieaIs. In addition, these chemi Bacillus thuringienis Berliner, a is not perfectly understood. cals have the disadvantage of hav fungus Beauveria bassiana (Bals.), We believe, however, that the ing to be applied every 3 weeks and a nematode referred to as the natural enemies of the webworm during the summer because of their DD-136 strain of Neoplectana car may be reduced to sueh low popu short activity period. Because of pocapSae, were tested to determine lation levels that they exert very the above-mentioned disadvantages their ability to kill sod webworms. little control on the webworm. of chemicals, we are searching for Mode of action of .the three Thus, once the natural enemies are new means of sod webworm con agents varies. The bacterium acts destroyed in a lawn, it may require trol. as a stomach poison which enters several months or even years for Biological control, which in the insect through the mouth as them to increase to a population volves the dissemination of large the larva feeds on grass infested level necessary to exert a satis numbers of parasites, predators, with bacteria. Once in the gut, a factory control on the webworms. and/ or insect pathogens, may offer toxic crystalline protein is formed, In the absence of their natural promise in sod webworm control. causing gut paralysis a few hours enemies, which serve to control We have conducted preliminary after feeding. Feeding then ceases. their population, the webworms, studies utilizing biological control Bacteria pass through the gut wall because of their high reproductive agents which are non-toxic to into the body cavity and death potential, increase rapidly and humans, birds, wildlife, and fish. follows. lawn destruction follows. Some of these agents are so spe The fungus infection is obtained Insecticides which cause an in cific as to insects attacked that by body contact and enters the crease of webworm numbers are certain ones can be selected that insect through the body wall; the ehlorinated hydrocarbons such destroy the target insect pest but therefore, feeding is not necessary as dieldrin and chlordane. These leave unharmed other insects and as with the bacterial pathogen. are excellent insecticides for the mites which are predators and Once the fungus is inside the body control of soil insects such as white parasites. Biological control agents cavity, blood cells are destroyed grubs which feed on grass roots cause no phytotoxicity at high and blood circulation halted. Sev but have not been satisfactory in rates as some insecticides do. eral days after death, the host webworm control in Tennessee. Insect pathogens, which were insect may become covered with a Insecticides that are recom the subject of this study, are man white powdery mass of fungal men d e d b y the Institute 0 f ufactured in various formulations fruiting bodies if moisture con Agriculture for webworm control such as wettable powders, dusts, ditions are suitable. *Assistant Professor and Associate baits, and aqueous suspensions, and Nematodes en t e r the host Professor, respectively, Department of can be applied with the same equip through the mouth with food as do Agricultural Biology. ment as insecticides. Costs for the bacteria or they may enter Page Thirty Tennessee Farm and Home Science Figure 1. Front half of a dead sod webworm larva covered with white through natural openings. Pene Beauveria tration of the gut wall occurs as bassiana they move into the body cavity. mycelia .. Bacteria associa ted wi th nema todes are then released - causing death of the host insect. N ema todes reproduce within the dead host body and may be present by the thousands .. Mature webworm larvae used in this study were collected from an infested lawn in Norris, Tennes see. Five larvae per replicate were placed in a plastic petri dish which Table 1.. Percent mortality of sod webworm larvae, Pediasia trisecto, placed on contained excised bluegrass blades grass sprayed with pathogenic organisms on filter paper. Bacteria and fungi were applied at rates of 250, 25, Days after treabnent and 2.5 million spores per milliliter Biological agent Rate/ml 2 3 (mI) of water and nematodes at 1,900, 1,000, 500 Fungi rates of and lar 7 vae per ml of water. One ml of B. bassiana 25,,10 31 a 85 9S each rate was sprayed onto the B. bassiana 2Sxl()6 31 36 51 bluegrass with an atomizer; sod B. bassiana 2.5xl00 6 30 60 webworm larvae were then added and the dish placed in total dark Bacteria ness in an 80°F. incubator. Each 8. thuringiensis 25xl0'" 90 100 100 treatment was replicated f 0 u r B. thuringiensis 25xl08 31 75 9S times. B. thuringiensis 2.5xl00 16 46 70 Nematodes Results N. corpocapsae 1900 25 90 95 Sod webworm larvae were ap N. carpocapsae 1000 21 80 95 parently susceptible to all three N. carpocapsae SOD 21 80 85 agents. Some of the larvae ex posed to fungi were practically Check, no treatment 11 38 55 covered with white mycelia about L.S.D ...05 for difference between: a week after death (Figure 1) • About a week after application, Two rates of one biological agent 16 17 20 the bodies of larvae infected with Two biological agents 32 34 23 nematodes were teeming wit h Check YS. treatment means thousands of nematodes; this indi (Dunnettls procedure) 29 33 23 cated that reproduction had taken aEach number is average of 4 replications. place within the body of the host larva. Nematodes could be ·seen moving within the body cavity and the second day after treatment Dosage rate is apparently a very in a few days they began leaving (T a b I e 1). Treatments sprayed important factor affecting mortal... the host body and were visible in with the high rate of fungus and ity in the bacterial and fungal the fluid surrounding the dead of nematodes reached 95% mor... treatments (Table 1). The fungal larva (Figure 2). tality 3 days after treatment. There treatment at the high rate caused Bacteria at the high rate was was no statistical difference among significantly g rea t e r mortality the fastest acting of the three the high rates of the three treat than the check 8 days after treat- organisms with 100% mortality ments after 3 days. ( Continued on Page 32) January, February, March, 1970 Page Thirty-One Figure 2. Part Biological Control of a dead sod webworm larva (Cont1~nued fron~ Page 31) surrounded by nematodes ment while lower rates did not. (arrow) which All nematode rates caused greater have left the mortality than the check. It is carcass. apparent that the dosage rate is apparently an important factor for fun g i and bacteria treatments while it does not appear to be as important for nematodes. How ever, nematode rates less than 500 larvae per ml might prove to be too low. lligh mortality in the untreated check was probably due to exces sive moisture in the petri dishes and/or t he presence of natural pathogens in the larvae. Conclusions reliminary laboratory investi Pgations indicate that the three biological agents tested success fully invade the body and destroy larvae of the sod webworm, P. trisecta. Further laboratory as well as field testing is necessary before the effect of factors such as moisture and temperature on Reprint from the agents can be determined and Tennessee Farm & Home Science their practical value assessed. It Progress Report Number 73 is known, for example, that nema January, February, March 1970 todes are s usceptihle to drying. The University of Tennessee, Knoxville Thus a .question that needs to be answered is whether or not nema todes sprayed on grass would be ingested before death by drying. Hall (1954) demonstrated that Crambus bonifatellus, a common sod webworm species in California, was susceptible to B. bassiana in field trials but stated that B. thur ingiensis was more effective be cause it was not as limited by moisture and temperature.