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The overwintering biology of the black cutworm, Agrotis ipsilon, in field cages (Lepidoptera: Noctuidae) [Missouri].

1982; Kansas (Central States) Entomological Society; Volume: 55; Issue: 3 Linguagem: Inglês

1937-2353

R. N. Story, Armon J. Keaster,

Insect and Arachnid Ecology and Behavior

The survival of lab reared and feral black cutworms, Agrotis ?psilon (Hufnagel), was monitored separately in field cages in Columbia, Missouri, during the fall and winter of 1977-1978. Lab reared cutworms did not survive beyond October. Feral cut worms completed a generation within the cage, mated, and ovi posited viable eggs during October. In late December 14% of the eggs were viable, but by early January the number of viable eggs was only 1%, and in February none were viable. The moths did not survive beyond December and viable larvae or pupae were not found during the winter or spring. The overwintering stage(s) of the black cutworm (BCW), Agrotis ?psilon (Hufnagel), in the North-central region of the United States has not been determined. Although pupae have been carried successfully through the winter in Tennessee (Crumb, 1929), similar attempts in northern regions have been unsuccessful (Apple, 1967; Carey and Beegle, 1975). The inability of the cutworms to survive in these studies may have been attributable to an incompatible habitat, a lack of time to acclimate to the environment, or an inability of the cutworm to overwinter. An overwintering study was therefore initiated in which cutworms were established in a natural habitat during the summer and their survival monitored throughout the fall and winter. Materials and Methods During the winter of 1977-78 the survival of lab reared and feral BCW was monitored separately in 3.7 X 6.1 X 1.8m saran cages at the University of Missouri South Farms, Boone County, Missouri. Cages were erected dur ing July, 1977, and metal barriers (20 cm tall) inserted around the inside perimeter to prevent larval escape. Several plant species were seeded inside 1 Contribution from the Missouri Agricultural Experiment Station. Journal Series No. 8756. This work was supported in part by the U.S. Environmental Protection Agency grant no. R-805 429 Development of Pest Management Strategies for Soil Insects on Corn. 2 Present address: Department of Entomology, Louisiana State University, Baton Rouge 70803. Received for publication 24 September 1981. This content downloaded from 157.55.39.58 on Sat, 30 Jul 2016 05:26:47 UTC All use subject to http://about.jstor.org/terms 622 JOURNAL OF THE KANSAS ENTOMOLOGICAL SOCIETY the area: bluegrass (Poa pratensis L.), clover (Trifolium pr?lense L.), lambs quarters (Chenopodium album L.), wheat (Triticum aestivum L.), soybeans (Glycine max L.), and fescue (Fesiuca arundinacea Schreb.). Laboratory reared BCW (125 pupae, 200 1st instar, and 200 4th instar) were placed in a single cage during early August. A total of 68 feral moths captured in a walk-in black-light trap were released in a second cage between August 10 and August 30. A 90% beer and 10% honey solution was continually provided for the moths during August and September, but beginning in October the solution was no longer placed in the cages. Larvae and adults were monitored periodically through the fall. The cages were removed in late December and returned to the plots again on March 18. On March 23 a Phercon? 1C trap containing a rubber septa impregnated with the BCW pheromone, (Z)-7 dodecen-1-yl acetate and (Z)-9-tetradecen-l-yl acetate, was placed in each cage to detect the presence of emerging males. It was apparent in October that the lab reared BCW had not survived; subsequent observations (November-January) were restricted to the feral population. In late December ten 15 X 15 X 25 cm soil samples, including the vegetation, were taken in the cage with the feral population. One sample was divided laterally into 5 cm sections and each washed separately with a soil washing device which would retain eggs (Chandler et al., 1966). The nine remaining soil samples were examined for larvae and pupae by washing them through a series of sieves. To determine the approximate location of eggs on plants, six 15 X 15 cm plots were randomly selected, the vegetation removed at the soil surface, and the plants cut laterally into four sections: 0-8, 8-16, 16-24, and > 24 cm in height. Each section was washed separately in the soil washing device reported by Chandler et al. (1966). The viability of eggs through the winter was monitored by sampling the egg population on December 27, January 4, and February 24. The data also provided an estimate of the egg population. On each sampling date eight 15X15 cm plots were randomly selected, the vegetation removed at the soil surface, and the samples washed together in the soil washing device. Using daily max-min temperatures from the UMC South Farms, the cen tigrade degree day unit accumulation during October and November was calculated for a developmental threshold of 10.44?C (Luckmann et al., 1976). The mean number of degree day units required for newly emerged females to oviposit was estimated with the data of Archer et al. (1980). Results and Discussion Cutworms obtained from the lab colony became established in early Au gust, but the population evidently did not survive beyond October. During late August, 5th and 6th instar larvae were very abundant in the cage and many dead larvae were present. They appeared to be diseased, but this was not verified. In October the soil in the cage was hand searched for larvae This content downloaded from 157.55.39.58 on Sat, 30 Jul 2016 05:26:47 UTC All use subject to http://about.jstor.org/terms VOLUME 55, NUMBER 3 623 and pupae, but none were found. The pheromone trap placed in the cage during the spring did not capture any BCW, nor were larvae found in the cage during the spring (March-June). Early instar larvae from the feral population were first observed on August 30. By mid-September most BCW were in the 5th and 6th instar, and by the end of the month moths began emerging. During the height of moth emergence there were 1-2 moths per dm2 around the edge of the cage. However, a subsequent generation of larvae evidently did not occur, for none were found. By early December live moths were no longer found in the cage. From one 15 X 15 X 25 cm soil sample collected in December, 40 eggs were recovered from the vegetation, 23 from the topmost 5 cm soil layer, 2 from a depth of from 5-10 cm, and none at further depths. No BCW larvae or pupae were found in nine 15 X 15 X 25 cm soil samples collected in December and washed in a series of sieves. Vegetation from six 15 X 15 cm plots revealed that 45% (n = 124) of the eggs were deposited at a height greater than 24 cm, while 9% (n = 25), 23% (n = 65), and 23% (n = 64) of the eggs, respectively, were obtained from height intervals of 0-8, 8-16, and 16-24 cm. The greater proportion of eggs on the terminal parts of plants was probably a reflection of the increased leaf surface area at greater heights and not a preference on the part of the moths. Because many of the grasses were not standing erect in the cage during September, plant height did not indicate their standing height at time of oviposition. The viability of eggs on three dates through the winter was estimated. On December 23, 14% (n = 275) of the eggs were viable, but by January 4 the number of viable eggs was only 1% (n = 3), and on February 24 none (n = 304) were viable. These data indicated that eggs did not survive the winter, even though the plot was covered with snow from late December to early March. The pheromone trap maintained in the cage from March 23 to late May did not capture any BCW moths. Visual searches for larvae made in the cage during the spring (March-June) did not reveal any BCW. The presence of a large number of eggs, some of which were viable during December, indicated that at least some moths emerging at the end of Sep tember mated and oviposited eggs during the fall. The soil and vegetation samples indicated an egg population of 60,652 in the 3.7 X 6.1 m cage during December, assuming 100% recovery of eggs from the samples. Although moths were not provided a beer and honey solution during late fall, Fairchild (1977) reported that BCW moths maintained on a diet of only water ovi posited a mean 300 eggs per female. According to degree day calculations, moths emerging on October 1 would start ovipositing on October 21 and by early December these eggs would have hatched and developed through the 1st instar. Moths emerging after October 14 would not be able to lay a full complement of eggs. Thus, there were sufficient heat units during the This content downloaded from 157.55.39.58 on Sat, 30 Jul 2016 05:26:47 UTC All use subject to http://about.jstor.org/terms 624 JOURNAL OF THE KANSAS ENTOMOLOGICAL SOCIETY fall for moths to oviposit most of their eggs, although not enough for many of the eggs to hatch. Kaster and Showers (1982) found that nearly all the BCW females cap tured during September and October of 1978 and 1979 in Iowa were unmated. In addition, males were not responsive to the synthetic BCW pheromone. They conclude their data suggest a reproductive diapause, in dicating the moths may overwinter in the Midwest or migrate southward during the fall. If moths actually overwinter, the eggs present in the over wintering cage were presumably oviposited by the small proportion of fe males that mate during the fall; these eggs evidently do not survive the winter in the Midwest. If moths were to migrate southward, the reproductive dia pause would presumably be short and a full complement of eggs would have been deposited in warmer regions where development would have continued. Thus, the results of this study cannot discount either hypothesis, but provide evidence that eggs are not able to overwinter in the Midwest.