ARnrnOPODS IN RELATION TO PLA..'IT DISEASES Effect of Ear Wounding and Cultural Practices on Abundance of Carpophilu8 freemani (Coleoptera: Nitidulidae) and Other Microcoleopterans in Maize in Northeastern Mexico L. A. RODRIGUEZ-DEL-BOSQUE, J. LEOS-MARTINEZ,] AND P. F. DOWD2 Campo Experimental Rio Bravo, I!'i1IFAP-SAGAR, Apartado Postal 172, Rio Bravo, Tamaulipas, Mexico 88900 J. Econ. Enlomol. 91 (4): 796-801 (1998) ABSTRACT Field experiments were conducted from 1993 to 1997 in northern Tamaulipas, Mexico, to identify the sap beetles and other microcoleopterans attracted to maize ears, and to evaluate their abundance in relationship to growing season (spring or fall), ear wounding (caterpillars, birds, and artificial), crop phenology, cultivar, and aflatoxin contamination. During the 5-yr study, 14 species ofmicrocoleopterans in 7 families were identified. However, only 3 ofthese species comprised 97% of the total captures: Carpophilusjreemani Dobson (Nitidulidae), Cathartus quadncollis (Guerin­ Meneville) (Cucujidae), and Sitophilus zeamais Motschulsky (Curculionidae). C. jreemani was by far the predominant species, comprising nearly 90% of all collections regardless ofgrowing season, crop management, or type of ear damage. Sap beetles occurred commonly during both the spring and fall growing seasons. Compared with undamaged ears, microcoleopterans were 2- to 5-fold more abundant in caterpillar-damaged ears, and 5- to 28-fold more abundant in bird-damaged and artificially damaged ears. c.jreemalli seemed to respond more to ear wounding (5- to lO-fold) than C. quadncollis and S. zeamais (2- to 4-fold). A maximum average density of 57 sap beetles per ear was observed in artificially damaged ears during the spring of 1993. Maximum abundance of microcoleopterans occurred from dough-hard to 25% kernel moisture stages. C. jreemalli was abundant during all maize reproductive stages, whereas C. quadncollis and S. zeamais were common only when kernels were drying down (15-20% moisture). Number ofsap beetles varied significantly among cultivars in both undamaged and damaged ears. Infection by Aspergillusjlavus Link:Fr and aflatoxin contamination of maize were enhanced by ear wounding and incidence of sap beetles. KEY WORDS sap beetles, seasonality, Aspergillus jlavus, aflatoxin, ear damage SAP BEETIES OF the genus Carpophilus (Coleoptera: and are resistant to most mycotoxins compared with Nitidulidae) are cosmopolitan pests of a wide variety ear-infesting lepidopterans (Dowd 1995). Invasion of ofagricultural commodities, including fresh and dried maize sap beetlesis facilitated bybird orcaterpillarear fruits, vegetables, and grains, both before and after damage orby varieties with poor husk coverage (Con­ harvest (Hinton 1945, Dobson 1954, Kehat et al. 1983, nell 1956). Bartelt 1997). Sap beetles feed on fruits or other plant Contamination of preharvest maize with aflatoxin parts that are ripening or decomposing. In addition to B1, a potent hepatocarcinogenic secondary metabolite direct damage by sap-beetle feeding, significant losses produced by Aspergillus fiavus Link:Fr, has been a in quality may occurbecause ofinsect parts in and on major concern in the agricultural region ofnortheast­ the infested product and because the beetles serve as ern Mexico during recent years. A series of studies in carriers of microorganisms that cause additional fruit this area showed that aflatoxin contamination was spoilage (Lindgren and Vincent 1953). closely associated with high temperatures during ear Although sap beetles have been recognized as vec­ development and with ear injury by insects (Rodri­ tors of fungi (Lindgren and Vincent 1953), their role guez-del-Bosque et al. 1995, Rodriguez-deI-Bosque in vectoring mycotoxigenic fungi to crops such as maize (Zea mays L.) has been demonstrated only 1996). Although 5 species of caterpillars were col­ recently. Maize sap beetles appear to be well adapted lected from the ears, by far the most common was the for vectoring mycotoxigenic fungi, including species corn earworm, Helicoverpa zea (Boddie) (Lepidop­ in the genera Aspergillus, Penicillium, and Fusarium. tera: Noctuidae). In addition, preliminary observa­ Sap beetles are attracted to fungal and maize volatiles tions showed that several unidentified species of sap beetles and other microcoleopterans occur in this re­ gion, infesting particularly those ears injured by lep­ 1 Facultad de Agronomia, Uk'lL, Apartado Postal 358, San Nicolas idopterans. The objectives ofthis study were to iden­ de los Garza, N.L. Mexico 66450. Z National Center for Agricultural Utilization Research, USDA­ tify the sap beetles and other species attracted to ARS, 1815 North University Street, Peoria, II.. 61604. maize ears in northeastern Mexico and to evaluate August 1998 RODRlGliEZ-DEL-BosQVE IT AL.: ABlINDAc'lCE OF MIQ1.0COLEOPIERANS 797 their abundance in relationship to ear wounding and In the 3rd experiment, the hybrids Ceres-2452 and crop management practices. H-433 were planted in each ofO.l-haadjacent plots on 20 August 1995 (fall growing season). Forty ears of each hybrid were sampled at 20% kernel moisture Materials and Methods stage in each of4 categories: undamaged, caterpillar­ A series of field experiments was carried out from damaged, bird-damaged, and artificially damaged ears. 1993 to 1997 at the National Institute of Forestry, Aflatoxin Contamination. This experiment was car­ Agricultural and Livestock Research Experiment Sta­ ried out during the spring gro\ving season of 1997 to tion located near Rio Bravo, Tamaulipas, a subtropical test the influence of ear damage and the presence of region in northeastern Mexico. The Experiment Sta­ microcoleopterans on ear infection by A. jlavus and tion (100 ha) is surrounded by commercial fields contamination with aflatoxin. A 0.25-ha plot was planted with either maize or grain sorghum, Sorghum planted with the hybrid H-433 on 16 ApriL Four treat­ bicolor (L.). Moench, the main crops in this area Most ments (with 4 replicates of 20 ears each) were in­ of the agricultural area (1 million hectares) is culti­ cluded: undamaged ears, caterpillar-damaged ears, ar­ vated only during thespringgrowing season (January­ tificially damaged ears (uncovered), and artificially July), although a small proportion is planted for a 2nd damaged ears covered with a cloth bag after the crop during the fall growing season (August-Decem­ wounding to prevent infestation by microcoleopter­ ber). In all experiments, crop management was per­ ans. Sampling took place 10 d after inflicting the ar­ formed according to the Rio Bravo Station recom­ tificial damage, when ears had =25% of kernel mois­ mendations for maize (Reyes et al. 1990), except that ture. Ears were harvested and transported to the no insecticide was applied during the maize repro­ laboratory for inspection of microcoleopterans as ex­ ductive stages. plained above. All ears also were examined for visible Maize Phenology. Two experiments were con­ A. jlavus (frequency of ear infection determined by ducted to determine the influence of crop phenology macroscopic symptoms). Grain (both symptomatic and ear damage on the abundance ofmicrocoleopter­ and nonsymptomatic kernels) ofthe same ears exam­ ans in maize ears. The 1st experiment was carried out ined for visible A. jlavus was mixed in 20-liter plastic during the spring growing season of 1993 in a 0.25-ha containers. A I-kg grain sample was dried at 75°C in a plot planted on 22 February with the 'H-422'. Fifty paper bag for 24 h in a forced-air oven. A 250-g sub­ undamaged ears and 50 ears showing damage by lep­ sample ofthe dried grain was finely ground in a Wiley idopteran larvae (natural infestation) were sampled mill (Model 4 with a 20-mesh screen, A. H. Thomas, randomly during each of3 maize stages: physiolOgical Philadelphia) and placed in a paper bag. After mbdng maturation (indicated by the black layer) and 20 and again, a 50-g subsample was weighed and extracted for 15% kernel moisture. Ears were transported to the aflatoxin by using the Aflatest (Vicam, Watertown, laboratory and inspected for microcoleopteran adults MA) immunoaffinity column (Candish et al. 1991, that were then placedin vials with 70% ETOH for later Trucksess et al. 1991). Aflatoxin level (ppb) was mea­ identification. The same procedure was used for all sured in a Torbex fluorometer, Model FX-I00 (Vi­ subsequent experiments. cam). A 2nd experiment was carried out during the fall Statistics. Differences in abundance of microco­ growing season of1996 in a 0.25-ha plot planted on 12 leopterans and aflatoxin levels among types of ear August with the hybrid Asgrow-9622. Twenty ears of damage and cultivars were determined with analysis each of 4 categories were sampled: undamaged, cat­ of variance (ANOVA) (SAS Institute 1988) followed erpillar-damaged, bird-damaged, and artificially dam­ by the Fisher protected least significant difference aged with a nailboard (Rodriguez-del-Bosque 1996) (LSD) test (P < 0.05). The interaction between cul­ 10 d before each sampling date. Sampling maize stages tivars and ear damage was tested by chi-square con­ were milk, dough-hard, physiological maturation, and tingency tables (P < 0.05) (SAS Institute 1988). 25, 20, and 15% kernel moisture. Cultivars. The interaction ofvarieties and ear dam­ Results age in relation to abundance of microcoleopterans in maize ears was tested in 3 experiments. The 1st ex­ A total of 4,889 and 7,945 adult microcoleopterans periment consisted of planting two O.I-ha adjacent was collected