Row CROPS, FORAGE,ANDSMALLGRAINS Fall Armyworm (Lepidoptera: Noctuidae) and Diatraea lineolata (Lepidoptera: Pyralidae): Impact of Larval Population Level and Temporal Occurrence on Maize Yield in Nicaragua ALLAN J. HRUSKAl ANDFRED GOULD Department of Entomology, North Carolina State University,Box 7634, Raleigh, NC 27695 Downloaded from https://academic.oup.com/jee/article/90/2/611/806948 by guest on 01 October 2021 J. Econ. Entomo!. 90(2): 611-622 (1997) ABSTRACT Four experiments were conducted in Nicaraguaover a 3-yrperiod to determine the effect of whorl-stage infestations of Spodoptera frugiperda (J. E. Smith) and Diatraea lineo/ata (Walker) on maize grain yields. The experiments separated the effects of period of infestation from level of infestation. Results from all experiments demonstrated that maize is more tolerant of lepidopteran infestation during early growth stages than at later stages. In- festation during mid-through late whorl caused yield losses of 15-73% when 55-100% of the plants were infested with S.frugiperda. D. lineolata infestations were highly correlated with S.frugiperda. D. /ineolata infestations were highly correlated with S.frugiperda infestation. Economic injury levels ranged from 23 to 63% of the plants infested with S.frugiperda and D. lineo/ata over a range of potential yields, using mean yield reduction from the 4 experi- ments, and an average 75% insecticide effectiveness. KEY WORDS Spodoptera frugiperda, Diatraea lineolata, maize, Nicaragua,economicinjury level Two OF THE more important biological constraints In Nicaragua, van Huis (1981) found a 33% in- to maize production throughout Latin America are crease in dry maize grain yield when plants were Spadoptera frugiperda (J. E. Smith) and Diatraea protected with an insecticide application to the linealata (Walker) (Andrews 1980, 1988; Rodri- whorl. The application decreased S.frugiperda in- guez-deI-Bosque et al. 1988; Evans and Stansly festation from 59 to 2% of the plants, and D. li- 1990). Subsistence fanners sometimes use multi- nealata infestation from 3.3 to 1.3 perforations per ple applications of insecticides to treat for these plant. In a study using cages to exclude S. frugi- pests, especially when governments subsidize ag- perda, van Huis (1981) found that D. linealata in- ricultural inputs. In 1989 on the Pacific plain of festation reduced maize grain yield from 3 to 6% Nicaragua, 99.6% of small fanners applied insec- per borer per plant. ticides to maize, with an average of 6.3 applications Obando (1976) did not find a significant corre- per season (A.J.H., unpublished data). lation between the presence of Diatraea spp. and Quantifying the effects of timing and level of yield, when other pests, including S. frugiperda, infestation of these 2 pests on maize yield is es- were not controlled. sential for developing economic thresholds and im- Other studies in North and Central America plementing rational pest management strategies. have found yield losses ranging from 7 to 35% at- Few studies have examined the impact of these 2 tributed to natural infestations of Diatraea spp., species on maize yield in Latin America, and fewer but none of these studies (Daniels and Chedester still have examined the separate effects of level and 1977, Alvarez and Morales 1979, Rodriguez-del- timing of infestation. Bosque et al. 1988) examined the effect of maize Hruska (1995) reviewed the data on maize yield growth-stage infestation on the extent of yield loss. losses from S. frugiperda infestation in 6 studies Throughout the Pacific plain of Nicaragua, S. done in Latin America. Linear regressions of the frugiperda and D. linealata occur together and in- relationship between S.frugiperda infestation and fest maize in similar patterns. van Huis (1981) yield loss predicted between 15 and 100% yield found a higWy significant correlation (,2 > 0.70) loss when all of the plants were infested during between D. linealata and S.frugiperda infestation mid- to late-whorl stage. in 3 studies carried out in 3 locations. Other stud- ies in Central America have found similar results I Current address: Department of Crop Protection, Zamorano, from experiments with insecticide-treated and un- Box 93, Teguci~,tlpa, Honduras. treated plants (Fuentes 1969, Obando 1976, Leyva 0022-0493/97/0611-0622$02.00/0 © 1997 Entomological Society of America 612 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 90, no. 2 1988). Both insects are found in the whorl of the were targeted at D. lineolata (van Huis et al. 1982). maize plant as early instars, especially during mid- In 1989, only 5% of Nicaraguan maize farmers in to late whorl stage. There are no insecticides that the Pacific region mentioned D. lineolata as 1 of are selective for one but not the other; thus, com- the 3 more important pests in maize, whereas mercial and experimental chemical control of one 100% mentioned S. frugiperda (A.J.H., unpub- species results in control of both, when applied lished data). from mid- to late-whorl. Economic threshold recommendations for S. Eighty percent of D. lineolata eggs are laid dur- frugiperda in maize vary from 11% (Evans and ing late whorl stage in Nicaragua (van Huis 1981). Stansly 1990) to 40% of the plants infested (An- S.frugiperda begins oviposition earlier than D. li- drews and Rueda 1986, Hruska et al. 1988), with neolata, with 80% of D. lineolata oviposition oc- most recommendations in the 20-30% range (Sar- curring during mid-through late-whorl stages (van miento and Casanova 1975, Obando 1976, van Huis 1981). Both species move quickly into the Huis 1981). Although economic thresholds are giv- Downloaded from https://academic.oup.com/jee/article/90/2/611/806948 by guest on 01 October 2021 whorl on eelosion, with D. lineolata burrowing en in terms of S.frugiperda infestation, it is likely deeper than S.frugiperda. Damage to maize leaves that the recommendations are for the combined by early instars of 2 pests, a skeletonization of leaf infestation of S.frugiperda and D. lineolata, in ar- areas, cannot be distinguis,hed. Seven days after eas where the ranges of 2 pests overlap. eelosion, D. lineolata causes distinctive damage as This study was carried out to determine the im- it burrows into the unwhorled leaves, leaving a row pact of S. frugiperda and D. lineolata infestation of holes when the leaf expands. By 4th instar, D. on maize grain yields in Nicaragua. In contrast to lineolata begins to burrow into the stem, where it previous studies, the effects of timing of infestation is no longer accessible by foliar insecticides. As lar- and level of infestation were separated to deter- vae burrow downward, they make small holes in mine the impact of level of infestation during dif- the stem. Before entering diapause or pupating, ferent periods of infestation, leading to recommen- and exit hole is made in the stem, leaving a thin dations for both timing of control and economic layer of epidermis intact. injury levels. Most S. frugiperda larvae stay in the whorl, feeding on new leaves (Morrill and Greene 1973). Materials and Methods The damage to newly expanding leaves and frass is easily observed by visual examination of the Four experiments were carried out at 2 field sta- whorls. Late instars are cannibalistic, usually re- tions within 5 km of each other on the eastern sulting in only 1 large S. frugiperda per plant edge of Managua, Nicaragua. The sites are on the (Wiseman and McMillian 1969). Pacific plain of Nicaragua at 70-100 m above sea The effect of timing of S.frugiperda infestation level and are characterized by distinct wet and dry on maize yield has been examined in 2 studies. seasons. An average of 1,030 mm of rain falls dur- Gross et al. (1982) found that S. frugiperda infes- ing the wet season, from May through November, tation during early- and late-whorl stages caused when both 1st and 2nd planting cyeles occur, and yield reduction, but not during midwhorl stage. an average 80 mm falls during the dry season from van Huis (1981) conducted an artificial defoliation December through April. These conditions are experiment, simulating S.frugiperda damage from similar to much of the Pacific plain, where annual early-whorl stage to tasseling. He found signifi- rainfall ranges from 600 to 1,400 mm. Maize also cantly greater yield reductions when defoliation may be produced during the dry season, using ir- occurred during mid- to late-whorl stages, com- rigation. Two experiments were carried out during pared with early-whorl or tasseling. the 1st rainy season, 1 during the 2 rainy season, The critical period of protection for D. lineolata and 1 under irrigation. has been studied for some growth stages of maize. Experiment 1: First Rainy Season 1986. The van Huis (1981) worked with the 1st half of the 1st experiment was planted in June 1986 at the whorl stage and found that in a long-cyele variety, "Las Mercedes" Experimental Station of the Univ- application of chlorpyrifos of the whorl at 15 d af- ersidad Nacional Agraria, located at Kilometer 10 ter planting did not affect infestation by D. lineo- of the Carretera Norte, Managua, Nicaragua. lata. There was a tendency toward reduced infes- Maize variety NB-lOO, a locally developed open tation with application at 30 d after planting. pollinated inbred line, with maturity at 90 d, was Another experiment (van Huis 1981) showed that planted by hand. Distance between rows was 92 insecticide application in tassel stage maize signif- cm and between plants 20 cm, for a planting den- icantly lowered infestation by D. lineolata. sity of 54,000 plants per hectare. Final plant den- Despite the fact that D. lineolata can cause sig- sity was =42,000 plants per hectare.