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Striped grass looper

Mods latipes (Guenee) (Lepidoptera: Noctuidae)

Natural History

Distribution. Striped grass looper is native to the western hemisphere, where it occurs commonly from the southern United States south to Brazil, including the Caribbean. On occasion, it is reported from as far north as Labrador and as far south as Argentina, but its occurrence always is limited to east of the Rocky Mountains and Andes Mountains. In the United states it is damaging only in the Gulf Coast region, where warm weather favors the survival of this tropical insect. Other species of the genus occur in the same area, but are not thought to be important pests.

Host Plants. As implied by its common name, this species feeds only on grasses. Several crops support striped grass looper, including bahiagrass, Bermuda-grass, corn, guineagrass, millet, oat, pangolagrass, paragrass, rice, ryegrass, St. Augustine grass, Sudan grass, sugarcane, sorghum, and wheat. Among vegetable crops, only sweet corn is injured. Wild grasses reported as hosts include barnyardgrass, Echinochloa crusgalli; bluestem, Andropogon spp.; crabgrass, Digi-taria spp.; goosegrass, Elusine indica; Johnsongrass, Sorghum halepense; panicum, Panicum spp.; and others.

Natural Enemies. Although there is extensive information on natural enemies affecting striped grass looper in Central and South America (e.g., Cave, 1992), data from North America are limited. Hall (1985) reported larval and pupal parasitism rates of 7.0-44.6% with a mean value of 29% in southern Florida sugarcane fields. Sarcophagid and tachinid flies seem to be most important, and include Sarcodexia sternodon-tis Townsend and Sarcophaga sp. (both Diptera: Sarco-phagidae); Archytas marmoratus (Townsend), Attacta brasiliensis Schiner, Belvosia bicincta Robineau-Desvoidy, Chetogena sp., Eucelatoria armigera (Coquil-lett), Euphorocera claripennis (Macquart), and Lespesia aletiae (Riley) (all Diptera: Tachinidae). Among the wasp parasitoids are Brachymeria ovata (Say), B. robusta (Cresson), Spilochalcis sanguineiventris (Cresson), Spilo-chalcis n. sp. (Hymenoptera: Chalcididae); Copidosoma truncatellum (Dalman) (Hymenoptera: Encyrtidae); Apanteles scitulus Riley, Meteorus autographe Muese-beck, Microplitis maturus Weed (Hymenoptera: Braco-nidae); Coccygomimus aequalis (Provancher), Enicospilus purgatus (Say), Gambrus ultimus (Cresson) (Hymenoptera: Ichneumonidae); and Trichogramma sp. (Hymenoptera: Trichogrammatidae). The ectoparasi-tic nematode, Noctuidonema guyanense (Nematoda: Aphelenchoidea) is found on the bodies of moths (Rogers and Marti, 1993), but causes few detectable effects on the insects.

Predation may be an important factor, if overlooked element in striped grass looper population dynamics. In addition to predation by such usual predators as lady beetles (Coleoptera: Coccinellidae), there are frequent reports of predation by Anolis spp. lizards and songbirds such as eastern meadowlark, Sturnella magna, and redwing blackbird, Agelaius phoeniceus.

Pathogens associated with striped grass looper include the fungi Beauveria bassiana and Nomuraea rileyi and a virus, but the importance of these microorganisms has not been determined.

Life History and Description. Striped grass looper is found throughout the year in southern Florida and Puerto Rico; elsewhere in the United States it is abundant principally during late summer and autumn. There is no period of diapause in this species. Duration of the complete life cycle has been given by most authors as 40-60 days, though it varies with temperature. The developmental threshold for this insect is reported to be 13.7?C, and it tolerates temperature of 20-30? C readily. Thus, several generations occur annually in the south.

Egg. The eggs are deposited singly or in small groups of up to five or six eggs on either the upper or lower leaf surface, usually just before midnight. The egg is pale green initially, darkening with age. It is hemispherical, with the base flattened. The egg is marked by the presence of 29-33 ridges, which radiate from the center. It measures about 0.65 mm in diameter and 0.55 mm in height. Duration of the egg stage is 3-5 days at 25-28?C.

Larva. The larvae are slender and elongate throughout development. Initially, the larvae measure only about 3 mm long, eventually attaining a length of 55-70 mm. The body is yellowish or tan, but marked with numerous, narrow, brown and black stripes. The stripes extend from the body onto the head. In many specimens a dark brown or black band encircles the body between the first and second, and second and third abdominal segments. Viewed from the side, these bands appear to be dorsal spots. The larva bears three pairs of prolegs, and moves with a looping motion. Duration of the larval stage is 20-40 days. Alvarez and Sanchez (1981) reported mean (range) development times of 2.0 (2-2), 2.5 (2-3), 2.7 (2-5), 3.5 (3-4), 1.8 (1-3), and 4.9 (4-5) days, respectively, for instars 1-6 when cultured at 30?C. They also reported a mean development time for larvae of 17.4 days, but did not include the prepupal period in this calculation. There are 6-7 instars, with mean (range) head capsule widths of 0.38 (0.33-0.41), 0.56 (0.49-0.63), 0.90 (0.79-1.01), 1.40 (1.13-1.54), 1.70 (1.64-2.00), 2.3 (2.20-2.50), and 3.01 (2.95-3.26) mm for instars 1-7, respectively (Ogunwolu and Habeck, 1975). Larvae tend to be found singly on blades of grass, and drop to the soil surface if disturbed. They are active principally at night. (See color figure 431.)

Pupa. Larvae fold the leaves and pupate within. The pupa is covered with a soft, flimsy cocoon. The pupa measures 16-21 mm long and bears a waxy bloom which imparts a whitish or bluish color. Duration of the pupal stage is 6-12 days. Alvarez and Sanchez (1981) reported a mean pupal period of 6.7 days at 30?C.

 

Adult. The moths are grayish tan or gray in general color, with dark lines and circular markings. Like other Mods spp., striped grass looper males have a dark spot on the lower margin of the forewing about one-third the distance to the outer margin. However, most specimens of M. latipes bear a dark area or spot at about the mid-point along the outer margin of the forewing, a character that helps distinguish M. latipes from the other Mods spp. Striped grass looper moths superficially resemble adults of velvetbean caterpillar, Anticarsia gemmatalis Hubner. However, the transverse stripe across the forewing of velvet-bean caterpillar moths terminates at the apex, whereas in striped grass looper it runs parallel to the outer wing margin (Gregory et ah, 1988). The wingspan of striped grass looper moths is 35-40 mm. Adults fly most actively during the early evening hours, though mating frequency is highest near midnight. Adults survive for 10-20 days when provided with food. They typically produce 200-300 eggs.

The biology of striped grass looper was summarized by Genung and Allen (1974), Reinert (1975), and Dean (1985). Larval and pupal descriptions can be found in Ogunwolu and Habeck (1979). Striped grass looper is included in the key to looper pests of vegetables found in Appendix A.

Damage

Over 40 species of grasses are fed upon, but other plants seem to be relatively immune to attack. The first and second instars feed on epidermal leaf tissue only, but later instars notch the leaf margins. When abundant, larvae completely defoliate grass plants, leaving only the midribs and stems. Larvae feed at night, and remain curled on the soil or in clumps of grass during the day. Although not regularly abundant, during some seasons they can be devastating pests, causing high levels of defoliation.

Management

Moths are attracted to light (Gregory et ah, 1988) and to sugar-based baits (Landolt, 1995). It is also possible to attract males to pheromone formulations, though velvetbean caterpillar may be attracted to the same chemicals (McLaughlin and Heath, 1989; Landolt and Heath, 1989). Larvae often are difficult to detect because they hide during the day, and their presence is observed only following damage. Grass weeds are often the site of initial infestation in crop fields, so grass weeds should be destroyed to discourage moths from ovipositing within crops. If larval numbers are high or damage is imminent, application of insecticides to crop foliage is recommended.