We investigated the possibility of overwintering of the diamondback moth, Plutella xylostella L., in central Michigan. In the spring of 1993, counts of immature stages on brassicaceous weeds in a field previously planted to broccoli revealed a small but significant number of late instars that could not be attributed to oviposition of immigrant moths from the southern United States. We suggest that crop debris and snow cover played an important role in sheltering the larvae, which are known to tolerate sub·freezing temperatures. There was no indication of adult survival

Grafius, Edward J

Idris, A. B

English

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Evidence of Pre-Imaginal Overwintering of Diamondback Moth, \u3ci\u3ePlutella Xylostella\u3c/i\u3e (Lepidoptera: Plutellidae) in Michigan

Valparaiso University

The Great Lakes Entomologist Volume 29 Number 1 - Spring 1996 Number 1 - Spring 1996 Article 4 April 1996 Evidence of Pre-Imaginal Overwintering of Diamondback Moth, Plutella Xylostella (Lepidoptera: Plutellidae) in Michigan A. B. Idris Universiti Kebungsaan Edward J. Grafius Michigan State University Follow this and additional works at: https://scholar.valpo.edu/tgle  Part of the Entomology Commons Recommended Citation Idris, A. B. and Grafius, Edward J. 1996. "Evidence of Pre-Imaginal Overwintering of Diamondback Moth, Plutella Xylostella (Lepidoptera: Plutellidae) in Michigan," The Great Lakes Entomologist, vol 29 (1) Available at: https://scholar.valpo.edu/tgle/vol29/iss1/4 This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. -1996 25THE GREAT LAKES ENTOMOLOGIST EVIDENCE OF PRE·IMAGINAL OVERWINTERING OF DIAMONDBACK MOTH, PWTELLA XYLOSTELLA (LEPIDOPTERA: PlUTELUDAE) IN MICHIGAN A B. Idris1 and Edward 1. Grafius2 ABSTRACT We investigated the possibility of overwintering of the diamondback moth, Plutella xylostella Lo, in central Michigan. In the spring of 1993, counts of immature stages on brassicaceous weeds in a field previously planted to broccoli revealed a small but significant number of late instars that could not be attributed to oviposition of immigrant moths from the southern United States. We suggest that crop debris and snow cover played an important role in sheltering the larvae, which are known to tolerate sub·freezing tempera­tures. There was no indication of adult survival. The diamondback moth, Plutella xylostella L., is a major cabbage pestworldwide. In Michigan, it commonly occurs at elatively low population den­sities, rarely reaching outbreak levels. This is probably due to the abundance ofDiadegma insulare (Cresson)(Hymenoptera: Ichneumonidae), a larval par­asitoid, that regulates diamondback th populations. Parasitism rates of 70-100 percent have been reported in th  US (Biever et at 1992, Idris & Grafius 1993) and Canada (Harcourt 1986). The diamondback moth is believed not to overwinter in th  Great Lakes region. For example, i  southwestern Ontario, Smith & Sears (1982) found that no life stages survived winter conditions i  the field, or simulate  winter conditions in the laboratory. In southeastern Ontario, populations are thought to die out completely each year to be replaced in spring by migrants from the south (Harcourt 1986). Recent observations have indicated that pre-imaginal stages of the diamondback moth may successfully overwinter in western Canada, and that volunteer canola plants provided an early larval food source (Dosdall 1994). In temperate areas of the United States, the diamondback moth overwin­ters as adults. In the upper midwestern states (Michigan, Wisconsin and Minnesota), diamondback moth populations are not thought to overwinter but early infestations often occur near cabb debris, indicating that overwin­tering of adults in protected areas is p Ie (Mahr et al. 1993). The objectives of our study were to determine whether the diamondback moth overwinters in Michigan, and to identifY possible overwintering life stages. IDr. Idris Abd. Ghani, Dept. of Zoology, Faculti Saims Hayat, Universiti Ke­bungsaan, Malaysia, 43600 UKM, Bangi, Selangor MALAYSIA. 2Department of Entomology, Michigan State University, East Lansing, Michigan 48824-1115. 1Idris and Grafius: Evidence of Pre-Imaginal Overwintering of Diamondback Moth, <i>PlPublished by ValpoScholar, 199626 THE GREAT LAKES ENTOMOLOGIST Vol. 29, No.1 MATERIALS AND METHODS In early spring 1993, volunteer plants of three weed species, Barbarea vulgaris R. Br., Thalspi arvense L. and Capsella bursa-pastoris (L.) Medic were abundant in a field previously planted in broccoli at the Michigan State University Collins Road Entomology Research farm and in other areas at the Michigan State University Farm. On 10, 15, 2  and 25 May, we selected 50 to 70 plants of each species at random. The plants were pulled out ofthe ground and inspected for the presence of diamondback moth larvae or pupae by plac­ing individual weeds on white paper placed on the ground. We recorded the number oflarvae and pupae found on each weed species separately. We reared larvae in 25 x 15 x 10 cm covered rearing pans in the laboratory at 25 ± 2'C and photoperiod of 16:8 (L:D) h until pupation, to evaluate parasitism. Th determine the presence of diamondback moth eggs, we randomly se· lected and detached leaves from each plant collected above. These were kept in the laboratory as described above and checked daily for 5 d for egg hatch. Overwintering of adults was evaluated in early April of 1993 by setting up five cages (180 x 165 x 165 cm) in and near a field previously planted with broccoli. We pulled u  the residue of 50 to 70 broccoli plants by hand and placed them in each cage. Th trap emerging moths we hung white sticky traps (Pherocon™ lC - bottom; Trece Inc., Salinas, CA) on wooden stakes within each cage. These were inspected every other day. We also put five potted broc­coli plants in each cage as a substrate for oviposition. The presence of eggs or larvae on broccoli leaves was checked using a lOx magnifying glass once every 3 d until the end of May 1993. The Michigan Stat  University Climatological Resources Center (Dr. Jeff Andresen) provided air and soil temperature data. Degree-Days (DD) accu­mulation above 7.3'C, developmental threshold for he diamondback moth (Butts & McEwen 1981), was calculated following Zalom et al. (1983). RESULTS Most of the life stages were found on B. vulgaris. We found a total of 24 fourth instars on the four sampling dates (Table 1). They were found begin­ning on the first sample date, 10 May. In addition, one late th rd instar was found on 10 May. No eggs were collected before 20 May (based on the larvae from detached leaves collected on this date, Table 1). We did not find any first or second instars before 25 May, when three first instars were recorded from B. vulgaris. On the same day we found a total of four pupae (three from B. vul­garis and one from C. bursa-pastoris). There were 11 and 23 first insta  from the detached leaves collected on 20 and 25 May, respectively. No diapausing Diadegma insulare or other parasitoids were recorded from weeds inspected in the field or reared from diamondback moth larvae. No diamondback moth adults were caught by the sticky traps in the field cages. We did not find eggs or larvae on the broccoli plants placed inside th cages. The average daily maximum air temperatures and soil surface tempera­tures were similar during the winter of 1992-1993 (Fig. 1 A & B). However, the surface minimum temperature above debris was higher than the air tem­perature. From December 1992 through March 1993, air and soil surface tem­perature were below 7.3'C, and there were more days below freezing than in the fall of 1992 and the spring of 1993 (Fig. 1, A to C). In February 1993, it snowed for 17 d causing an accumulation of snow and soil surface tempera­tures were warmer than air temperatures (Fig. lC). The total degree-days ac­cumulated (DD) above 7.3·C was 45.8 from December through March, as op­2The Great Lakes Entomologist, Vol. 29, No. 1 [1996], Art. 4https://scholar.valpo.edu/tgle/vol29/iss1/41996 27THE GREAT lAKES ENTOMOLOGIST Table 1. Diamondback moth stages recorded from weeds and detached weed leaves, Michigan State University Farm, 1993. Larvae First instars from Weed species Dates 1st 2nd 3rd 4th Pupae detached leaves* Barbarea vulgaris 10 May 0 0 1 2 0 0 15 May 0 0 0 3 0 0 20 May 0 0 0 6 1 11 25 May 3 0 0 4 2 23 Thalspi arvense 10 May 0 0 0 1 0 0 15 May 0 0 0 0 0 0 20 May 0 0 0 1 0 3 25 May 0 0 0 2 0 6 CapseUa 10 May 0 0 0 0 0 0 bU1'8a-pastDris 15 May 0 0 0 1 0 0 20 May 0 0 0 0 0 2 25 May 0 0 0 1 1 8 TOTAL 3 0 0 24 4 53 *Diamondback moth first instars from eggs laid on weed leaves that were detached and brought to the laboratory on the stated date. posed to 217 DD from October through December plus January through April(Fig.1D). DISCUSSION The above results indicate that larvae may have overwintered in the study plots. There were no eggs or early instars found until long after the third or fourth Gate) instars (Table 1), which supports this. The late instars are reported to have very low super cooling points (-14.3'C), indicating that some of them can tolerate sub-freezing temperatures (Hayakawa et al. 1988). Higher temperatures in or below the crop debris and higher accumulations of snow in February than in the other months (Fig. 1C) may have protected the larvae. The surviving individuals may have begun to enter diapause or be­came inactive in No mber when weeds were dead (no food available), and the minimum and maximum air temperatures were less than 7.3°C (Fig. lA). The larvae then continued their development in late April 1993, when early sea­son weeds flourished (food became abundant) and temperatures were moder­ate (Fig. 1A). The developmental period of diamondback moth larvae from hatch to the third or fourth insta  requires 110 or 170 DD above 7.3'C (Butts & McEwen 1981). The degree-days base 7.3°C accumulated in late April was 80.2 DD and in May was 422.8 DD ('C)(Fig. 1 D). According to these heat unit accumula­tions, the third and fourth instars we found in May could have come from overwintered first or second instars. In th  laboratory, however, we observed these two larval stages survived for only a week when placed in empty 15.0 cm diam Petri dishes and kept at 4'C, while the third and fourth instars sur­3Idris and Grafius: Evidence of Pre-Imaginal Overwintering of Diamondback Moth, <i>PlPublished by ValpoScholar, 1996A. Air temperature 	 tv C. Below freezing or snowing 	 c::ou---­~ 30 30 -• , , , ......c....... .i I !jI-'-'-:!j!" I ':ljl i eni 20 ~ 'Ci 20B 10 is -""-0"-"'0_. tr' 	 10 I~ OJ 	.-'S---0!-IO 	 i ~ -20 ... l) .c '2 i:;-	 .c '2 i:;- ~ <: 1l 11 ia ia 	 0 11 '"11 ia ~ 0.. ms S = = ~ ~ ::E 	 S ~ 8 = 2 ~ « ::E u 5 :iii i'l ::E 	 .0 ::E Q0 8 ..., " <> > .,u ....a 	 AI~ ~ 	 Ifz 8 	 i 8 ~ u 	 s; 0G B. Soil surface temperature 	 D. Degree-days A('I")~ 30 500 	 (flr.: 	 m m(!) ;>- 400 	 Z 0 	 o~ 300 en ~ ~ 200 "0 0 100 	 8 a 	 ~~ -­l) l) i:;-	 '2 ;>.11 ia 	 c:l ~ 0 .8 ia ~ -5S 5 1 ~ 7S i 1 « i ::E 	 j j j = ~ '" la ~ ~ fa ::E ..... Il..8 Il.. " z ~ 	 2: Figure 1. Average daily air (A) and soil surface (B) temperatures, numbers of days snowing or below 	 tv ,<>freezing (C) and the Degree-Days accumulation (0) from October 1992 to May, 1993 (Michigan State University Horticulture Farm, 1.5 kIn southeast of Collins Road Entomology Farm). 	 Z ? i 20 i 10 ;:... 0 ~ ~-IO! -20 1 ____________________......................................................................................................................................~ 4The Great Lakes Entomologist, Vol. 29, No. 1 [1996], Art. 4https://scholar.valpo.edu/tgle/vol29/iss1/41996 29THE GREAT lAKES ENTOMOLOGIST vived over two months (unpublished data). This suggests that the third and fourth instars were t e ones that successfully overwintered. However, fourth instars require only 40 DD to become pupae (Butts & McEwen 1981); they should have been pupae by May 1 but we didn't find pupae until 20 May. The development of diamondback moth during April an  early May may have been prolonged because of poor quality food. Diamondback moth pupae could possibly overwinter within or under the crop debris. They can also tolerate super-cooling down to -19.2"C (Hayakawa et al. 1988). However, at above 7.3"C, the development from pupae to adultwould require 100 DD (Butts & McEwen 1981). Mortality ofan egg is 100% at below 10'C (Hardy 1938)(the maximum air temperature between mid-October 1992 to week three of April 1993 was lower than 10'C, Fig. lA) or if exposed to cold temperature for 60 d (Honda 1992). This suggests that our field col­lected larvae did not originate from adults emerged from pupae. In our field cage study, there were no diamondback moth eggs observed or adult caught even though they were monitored until the end of May. This suggests that adult moths did not overwinter in Michigan in 1992-1993. Sim­ilarly, in Alberta, Canada, diamondback moth adults were first caught by the emergence traps on 26 May, indicating adults may originate from the suc­cessful overwintering larvae (DosdallI994). In southern Ontario, where temperatures are similar to mid-Michigan, di­amondback moth adults arrive from the s uthern United States around mid­May (Harcourt 1986). In our study, considerable numbers of first instars were recorded from the detached leaves collected on 20 and 25 May (Table 1), sug­gesting that oviposition began in mid-May. If oviposition occurred at this time, the developmental time from egg hatch to third or fourth instars would have been 23 d at 20'C (Salinas 1986). This indicates that larvae collected in this study were the offspring of these migrants. The average daily maximum air temperatures were below 7'C in March 1993 (Fig. lA), and no oviposition has been observed at this temperature (Hardy 1938). Oviposition by the successful overwintered diamondback moth adults could occur in late April when the average daily maximum air temper­ature was at 12'C, but it would require 13 d for egg to hatch (Hardy 1938). If this happened then the diamondback moth first instars should have been in the field and collected on 10 May (our first sampling date). On this date, how­ever, only third and fourth ins tars were found (Table 1). Therefore, if anyadults successfully survived the winter they could not be the source for the larvae that we collected. This is the first evidence of diamondback moth overwintering in th  Great Lakes region. However, numbers of successful individuals may be signifi­cantly reduced in colder winters. . Our results indicate the importance of proper treatment on the previous cabbage field for managing the diamondback moth. Tilling of field before planting is a common practice that could destroy overwintering diamondback moth larvae, D. insulare pupae or parasitized larvae although no D. insulare pupae or parasitized larvae were found in this study. Fur her research on overwintering sites for the diamondback moth and D. insulare should be con­ducted. ACKNOWLEDGMENTS Thanks to Brad Scriber, Brad Ferrari and Paul Kolarik for their assis­tance. We also thank Deborah McCullough for critical comments. This study 5Idris and Grafius: Evidence of Pre-Imaginal Overwintering of Diamondback Moth, <i>PlPublished by ValpoScholar, 199630 THE GREAT LAKES ENTOMOLOGIST Vol. 29, No.1 was supported by the Michigan Vegetable Council and the Michigan Agricu1~ tural Experimental Station. LITERATURE CITED Biever, K. D. , R. L. Chauvin, G. L. Reed, & R. C. Wilson. 1992. Seasonal occurrence and abundance of lepidopterous pests and associated parasitoids on collards in the north­western United States. J Entomol. Sci. 27:5-18. Butts, R. A & F. L. McEwen. 1981. Seasonal populations of the diamondback moth Plutella xylostella (Lepidoptera: Plutellidae) in relation to day-degree accumulation. Can. EntomoL 113:127-131. Dosdall, L. M. 1994. Evidence for successful overwintering of diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), in Alberta. Can. EntomoL 126: 183­185. Hardy, J. E. 1938. Plutella maculipennis, Curt., its natural and biological control in England. Bull. EntomoL Res. 29:343-373. Harcourt, D. G. 1986. Population dynamics of the diamondback moth in southern On­tario. pp, 1-15. Diamondback Moth Management. I : Tal kar, N.S & T. D. Griggs (eds.). Proceeding of the First International Workshop, Asian Vegetable Research and Development Center, Shanhua, Taiwan, 11 -15 March 1985. Hayakawa, H., H. Tsutsui, & C. Goto. 1988. A survey of overwintering of the diamond­back moth, Plutella xylostella Linne., in the Tokachi district of Hokkaido. Ann. Rept. Plant Prot. North Japan, 39:227 - 228. (In Japanese with English Summary). Honda, K. 1992. Hibernation and migration of diamondback moth in northern Japan. pp, 43 - 50. Diamondback Moth and Other Crucifers Pests. In:Talekar, N. S. (ed.). Proceedings of the Second International Workshop, Tainan, Taiwan, 10-14 December 1990. Idris A B. & E. Gratius. 1993. Field studies on the impact of pesticides on the dia­mondback moth, Plutella xylostella (L')(Lepidoptera: Plutellidae) and parasitism by Diadegma insulare (Cresson)(Hymenoptera: Ichneumonidae). J. Econ. EntomoL 86:1196-1202. Mahr, S. E. R., D. L. Mahr, & J. A Wyman. 1993. Biological control of insect pests of cabbage and other crucifers. Cooperative Extension publication, University of Wis­consin. 55 pp. Putnam, L. G. 1978. Diapause and cold hardiness in Microplitis plutellae, a parasite of the larvae of the diamondback moth. Can. J. Plant Sci. 58:911-913. Salinas, P. D. 1986. Studies on diamondback moth in Venezuela with reference to other Latin American countries. pp, 17-24. In: Talekar, N.S & T. D. Griggs (eds.). Proceed­ing of the First International Workshop, Asian Vegetable Research and Development Center, Shanhua, Taiwan, 11 -15 March 1985. Smith, D. B. & M. K. Sears. 1982. Evidence for dispersal of diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae) into southern Ontario. Pro. Entomol. Soc. Ont. 113:21-27. Zalom, F. G., P. B. Goodell, L. T. Wilson, W. W. Barnet & w. J. Bently. 1983. Degree­Days: The calculation and use of heat units in pest management. Cooperative Exten­sion, University of California, Berkeley. Leaflet 21373. 10 pp. 6The Great Lakes Entomologist, Vol. 29, No. 1 [1996], Art. 4https://scholar.valpo.edu/tgle/vol29/iss1/4

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Evidence of Pre-Imaginal Overwintering of Diamondback Moth, \u3ci\u3ePlutella Xylostella\u3c/i\u3e (Lepidoptera: Plutellidae) in Michigan

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