IPM for the Western Bean Cutworm
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Pheromone Issue Special Volume XXXVI, Number 9/10 (Published May 2019) IPM for the Western Bean Cutworm By William Quarles estern bean cutworm Photo courtesy of Adam Sisson, Iowa State University, Bugwood.org (WBC), Striacosta albicos- Wta, is a pest created by modern agriculture, as monocul- tures, genetically engineered crops, and climate change encourage it (Hutchinson et al. 2011; Blicken- staff and Jolley 1982; Dorhout and Rice 2010). WBC was found in Arizona in 1887, and it was a low intensity western pest of corn and beans for 75 years (Dorhout 2007; Archibald et al. 2017). In the 1970s and 1980s “intensified cropping and modern agriculture” accelerated its dispersal and increased its pest status. It spread throughout the Great Plains and to Texas, Mexico, and Canada (Blickenstaff and Jolley 1982; Sanchez-Pena et al. 2016). Introduction of genetically engineered corn in 1996 (see below) led to an explosive range expansion. The western bean cutworm moth, Striacosta albicosta, can be identified It spread throughout the Midwest by cream colored stripes and two characteristic spots on the forewings. It corn belt and into corn producing is a strong flier and has recently invaded the Midwest and Northeast. areas of eastern states in a period of just 10 years (Dorhout 2007; et al. 2018), and may be getting (Michel et al. 2010). (See Box A for Dorhout and Rice 2010; Michel et resistant to pyrethroids (Archibald WBC Biology). al. 2010). et al. 2017). Neonicotinoid seed WBC is a late season pest, WBC appeared in Minnesota treatments may make the problem directly damaging bean pods and in 1999, Iowa and South Dakota worse by killing biocontrols (Sea- corn kernels. The pest can signifi- in 2000; Illinois and Missouri in graves and Lundgren 2012; Difonzo cantly reduce yields and quality of 2004; Michigan and Ohio in 2006; et al. 2015). This article discusses field corn and fresh corn. Larvae finally reaching Pennsylvania and an IPM program that can reduce or eat kernels of corn, ruining it for New York in 2009. In 10 years it eliminate pesticide applications. the fresh market and otherwise colonized 11 new states (Smith et lowering yields and quality. Several al. 2018). Damage larvae can infest the same ear of Rapid expansion into new Western bean cutworm is ecological areas has presented misnamed. WBC is no longer just challenges for management. Con- a western pest, and it does not In This Issue ventional pest management is by act like a cutworm that clips plant genetically engineered corn, neon- stems. Furthermore, it prefers Bean Cutworm 1 icotinoid seed treatments, and pyre- corn to beans, and most economic throid sprays. But WBC is resistant Calendar 8 damage is done through feeding on to genetically engineered Cry1F Conference Notes 9 plant seeds. WBC acts more like a corn (Michel et al 2010; Smith corn earworm than a bean cutworm Update Photo courtesy of Professor J. Obermeyer, Purdue Cooperative Extension WBC larvae eat corn kernels. WBC feeding, shown here, can cause fungal infections that produce mycotoxins. corn. Field damage of 30-40% has Why Did it Spread? been seen. Some fields in Iowa have Pests become serious through had a 96% loss (Michel et al. 2010; a number of reasons. For instance, Paula-Moraes et al. 2012). an alien invasive pest can spread Damage includes fungal in- into areas where there are no fections that reduce quality of the natural enemies. This is the case grain. For instance, WBC infesta- for the emerald ash borer, Agrilus tion significantly increases Gib- planipennis. It has killed millions of berella ear rot. Fungal infections trees and spread through 35 states produce mycotoxins that can make in about 20 years (Herms and livestock sick when infected corn is McCullough 2014). Another factor used as a feed (Parker et al. 2017). is pesticide resistance and muta- Average infestations of one lar- tion. According to Metcalf (1983), va per plant can reduce corn yields widespread dispersal of the western by 3.7 to 15 bu/acre (Appel et al. corn rootworm, Diabrotica sp., was 1993; Paula-Moraes et al. 2013). encouraged by chlorinated pesti- One larva per plant could result in cides. Pesticide applications led to a yield loss of 8.6%, or about $55/ resistance and a genetic mutation acre (Macrotrends 2019). linked with dispersal (Wang et al. WBC prefers corn, but it 2013). But WBC is a native pest, can also be an economic pest of and its spread is not the result of a dry beans, Phaseolus vulgaris. It pesticide induced mutation (Lin- damages pods and developing bean droth et al. 2012). seeds. Damage in beans can be up WBC has a natural tenden- to 8-10%. It is difficult to separate cy to spread. It is a strong flier, damaged pods (“pick”) from healthy and virgin females can cover 24 ones, and “pick” lowers the pur- km (14.4 mi) in 8 hours (Dorhout chase price. Pick amounts greater 2007). Planting large monocultures than 2% could cause buyers to in the 1970s and 1980s gave it refuse entire shipments (Michel et a ready food supply that favored al. 2010; Difonzo et al. 2015). migrating populations. Introduc- 2019 Tomato is also a possible host tion of genetically engineered corn plant. Successful management in promoted cropping practices that corn and beans might cause it to encouraged WBC (see below). Cli- move to tomatoes (Blickenstaff and mate change may also have been a Jolley 1982; Antonelli and O’Keeffe factor, as it must overwinter in soil. 1981). Milder winter temperatures may have allowed the pest to invade cold IPM Practitioner, XXXVI (9/10) Published May 2019 2 Box 7414, Berkeley, CA 94707 Update Box A. Biology of the Bean Cutworm WBC is a native noctuid F. Peairs, CSU, Bugwood.org 32% are recovered in the same moth in the same guild as the row as the egg mass (Panuti et corn earworm, Helicoverpa zea, al. 2012; Michel et al. 2010). and the European corn borer, Fortunately, larval survival in a Ostrinia nubilalis. There is one corn field is low, ranging from generation per year. Life stages 4-12% in Nebraska (Paula-Mo- are eggs, larvae, prepupae, pu- raes et al. 2013). pae and adults (Dorhout 2007). WBC goes through six lar- Gray-brown moths are val instars on a plant. The first about 20 mm (0.8 in) long, and instars have black heads and wingspan is about 40 mm (1.6 are about 2.5 mm (0.1 in) long. in). They can be identified by Early larvae in beans feed on the cream-colored stripes along leaf tissue, then later larval in- the outer edges of the fore- Eggs of western bean cutworm stars chew their way into bean wings, and two characteristic J. Obermeyer, Purdue Cooperative Extn. pods. The larval stage is vari- wing spots on each forewing. able, but can last an average of Moths fly at night and rest in about 30 days. Larvae are light the crop in the daytime. Mating tan or pink with longtitudinal and egglaying is in July and stripes. Fourth instars or later August, with females producing have two black rectangles as about 300-400 eggs. Egg mass- markings directly behind the es averaging about 50 eggs are head. The 6th instars are about laid on upper leaf surfaces in 35 mm (1.4 in) long (Dorhout corn when it is near the tassel 2007; Michel et al. 2010). stage of development. Eggs are There is a prepupal and laid on the underside of bean a pupal stage in the soil. WBC leaves deep in the canopy. Eggs overwinters as a prepupa about are about 0.75 mm (0.03 in). 7.6 to 20 cm (3 to 8 in) deep Eggs are initially white, but in soil. Pupae measure about turn purple before they hatch Larva of WBC feeding at the tip of a 17 mm (0.66 in) in the lon- in about 5-7 days (Dorhout corn ear. gest direction. Sandy soils are 2007; Michel et al. 2010). preferred to clay soils. The soil Larvae eat their egg shells to plant, within and between stage makes treatment with and disperse upward to tassels rows, dispersing in a 3 m (10 nematodes a possibility (see in corn, then later crawl down- ft) circle about a hatching egg Nematodes). It completes pupa- ward and enter the ears. One mass. About 75% of hatching tion in spring and emerges as ear may contain several larvae. larvae are found within 1.7 m an adult in the summer (Dor- Larvae in corn move from plant (5.6 ft) of the egg mass. About hout 2007; Michel et al. 2010). areas such as Michigan and Minne- al. 2011). Blickenstaff (1979) had in beneficial carabid beetle larvae sota (Blickenstaff and Jolley 1982; observed that cultivation killed 90% exposed to neonicotinoid corn seed- Hutchinson et al. 2011). of overwintering WBC. lings. Neonicotinoid treatments add- BT for the western corn root- GMOs Encourage Pest ed to GMO seeds do not control late worm (WCR), Diabrotica virgifera Cropping practices associ- season pests, but can have a nega- virgifera, was introduced in 2003. ated with GMOs encourage the tive impact on biocontrols (Difonzo Plantings of BT corn for the root- pest. Roundup Ready® corn meant et al. 2015). Predator populations worm meant fewer soil insecticide growers could switch from cultiva- can be reduced by 25% (Seagraves treatments were needed. BT for the tion to no-till and apply herbicides and Lundgren 2012). In corn, treat- rootworm led to a situation where for weed control. As a result, WBC ed seeds have killed 80% of exposed WBC pupae could develop without pupating in the soil was no longer Harmonia axyridis ladybug larvae exposure to pesticides (Gassmann killed by cultivation (Hutchinson et (Moser and Obryki 2009).