Cereal yield losses caused by lepidopterous stemborers at different nitrogen fertilizer rates in Ethiopia

Abstract: Field trials were carried out at three locations in the cool‐wet western and one location in the semiarid eastern ecozones of the Amhara State of Ethiopia to determine the effects of nitrogen fertilizer on pest infestation and yield losses caused by lepidopterous stemborers in maize and sorghum. Three N fertilizer levels, i.e. 60, 120 and 180 kg/ha for maize, and 41, 64, and 87 kg/ha for sorghum, were compared with a zero N treatment. The dominant pest species were the noctuid Busseola fusca (Fuller) and the invasive crambid Chilo partellus (Swinhoe). Leaf N content was positively related to N fertilizer dosage. In general, pest density, parasitism, plant growth and borer damage variables increased with crop growth stage. On sorghum, in the cool‐wet western Amhara, increasing levels of N fertilizer also tended to increase pest density, plant growth and damage variables. In the semiarid ecozone, parasitism by the exotic parasitoid Cotesia flavipes Cameron tended to increase with N level. In the cool‐wet ecozone, sorghum yields increased by up to 74% because of fertilization; losses caused by stemborers decreased linearly with N dosage from 49% to 36%. In maize, because of low borer densities, there were no discernable trends for pest infestation and yield losses. In the cool‐wet ecozone, sorghum yields were positively related to insecticide application and plant height, and negatively to damage variables such as tunnelling and peduncle damage. In semiarid eastern Amhara, the effects of fertilizer on pest, damage and yield were low on both crops because of the higher soil fertility. The results indicate that the profitability of nitrogen fertilizer as an integrated pest management tactic in the control of cereal stemborers depends, among others, on the severity of borer damage and the soil fertility status prevailing in an area. It is concluded that N fertilizer helps minimize the impact of borers on grain yields, especially on sorghum and in the cool‐wet ecozone.     

Distribution and relative importance of cereal stem borers and their natural enemies in the semi-arid and cool-wet ecozones of the Amhara State of Ethiopia

The distribution and relative importance of lepidopteran and coleopteran stem borers and their natural enemies on maize and sorghum were studied in cereal growing zones of the Amhara State of Ethiopia from 2003 to 2004. Sorghum is the major crop in semi-arid eastern and maize in the cool-wet western zones of the Amhara state. Four administrative zones, 10 districts and 88 localities in the semi-arid ecozone (SAE) and four zones, 19 districts and 71 localities in the cool-wet ecozone (CWE) were chosen for the study. In SAE, the species composition was 91% Chilo partellus (Swinhoe) (Lepidoptera: Crambidae), 8% Busseola fusca (Fuller) (Lepidoptera: Noctuidae) and 1% Sesamia calamistis Hampson (Lepidoptera: Noctuidae). In the CWE, maize and sorghum are grown in different ecozones and thus B. fusca was the dominant species on sorghum, whereas 61% B. fusca and 39% S. calamistis were recorded on maize. Borer density generally increased with crop growth stage. C. partellus parasitism by C. flavipes Cameron (Hymenoptera: Braconidae), which occurred only in SAE, varied among districts ranging from 5% to 39%. In the CWE, unidentified nematodes parasitized medium-sized B. fusca larvae during the wet months. Population of native parasitoids was very low. The coleopteran borer, Rhynchaenus niger (Horn) (Coleoptera: Rhynchophoridae), attacked sorghum plants in both regions. Sorghum yields were negatively related to plant damage variables and positively to larval parasitism and plant growth variables. On maize, plant damage was too low to affect yields. Taylor’s power law indicated aggregated distribution for C. partellus and B. fusca larvae and pupae combined.     

Reduction of insect pest attack on sorghum and cowpea by intercropping

Two experiments to establish the relationship between insect suppression by intercropping and grain yield in sorghum and cowpea were conducted under field conditions. Treatments consisted of monocrops and intercrops of sorghum and cowpea and an additional pair of monocultures and mixtures protected by insecticides. Intercropping reduced the numbers of stem borer,Chilo partellus in sorghum and thrips,Megalurothrips sjostedti in cowpea. In the monocropped, unprotected sorghum, yield was reduced by 28% compared to the protected monocrop, while reduction in the unprotected intercropped sorghum was 15% compared to the protected intercrop. Similarly, in the unprotected cowpea, monocrop yield was reduced by 94% and intercrop yield was reduced by 51%. Thus, there are yield advantages under conditions where intercropping reduces insect pest density. Intercropping can form a component of an integrated pest management programme.     

Effect of cowpea monocultures and polycultures with sorghum and greengram on predatory arthropods

Prior to implementing biological control, knowledge on availability of the possible enemies of pest(s) is important. Therefore, as part of a larger on-farm study whose main objective was to develop a farmer-friendly package for the management of cowpea pests, the diversity and abundance of insect predators within cowpea cropping systems (sole crops and intercrops) were monitored at three diverse locations in eastern Uganda. Coccinellids, syrphid larvae, spiders, Orius sp. and earwigs were observed at all locations. Abundance of Coccinellids and syrphid larvae were not influenced by the cowpea genotype nor cropping systems. Contrastingly, the abundance of predatory Orius sp., spiders and earwigs differed significantly among the cowpea cropping systems, being more common in the cowpea pure stands and cowpea + greengram than in the cowpea + sorghum intercrops.     

Relationships of intercropped maize, stem borer damage to maize yield and land-use efficiency in the humid forest of Cameroon

Stem borers are the most important maize pests in the humid forest zone of Cameroon. Field trials were conducted in the long and short rainy seasons of 2002 and 2003 to assess the level of damage and yield reductions caused by stem borers in monocropped maize and in maize intercropped with non-host plants such as cassava, cowpea and soybean. The intercrops were planted in two spatial arrangements, i.e. alternating hills or alternating rows. All intercrops and the maize monocrop were grown with and without insecticide treatment for assessment of maize yield loss due to borer attacks. The land-use efficiency of each mixed cropping system was evaluated by comparing it with the monocrop. The temporal fluctuation of larval infestations followed the same pattern in all cropping systems, but at the early stage of plant growth, larval densities were 21.3-48.1% higher in the monocrops than in intercrops, and they tended to be higher in alternating rows than alternating hills arrangements. At harvest, however, pest densities did not significantly vary between treatments. Maize monocrops had 3.0-8.8 times more stems tunnelled and 1.3-3.1 times more cob damage than intercrops. Each percentage increase in stem tunnelling lowered maize grain yield by 1.10 and 1.84 g per plant, respectively, during the long and short rainy season in 2002, and by 5.39 and 1.41 g per plant, respectively, in 2003. Maize yield losses due to stem borer were 1.8-3.0 times higher in monocrops than in intercrops. Intercrops had generally a higher land-use efficiency than monocrops, as indicated by land-equivalent-ratios and area-time-equivalent-ratios of >1.0. Land-use efficiency was similar in both spatial arrangements. At current price levels, the net production of mixed cropping systems was economically superior to controlling stem borers with insecticide in monocropped maize. The maize-cassava intercrop yielded the highest land equivalent ratios and the highest replacement value of the intercrop. At medium intensity cropping this system is thus recommended for land-constrained poor farmers who do not use external inputs such as fertilizer and insecticides.     

Spatial and Temporal Spread of Cassava Mosaic Virus Disease in Cassava Grown Alone and when Intercropped with Maize and/or Cowpea

The spread of cassava mosaic disease (CMD) and populations of the whitefly vector (Bemisia tabaci) were recorded in cassava when grown alone and when intercropped with maize and/or cowpea. The trials were planted under conditions of high inoculum pressure in 1995 and 1996 at a site in the lowland rainforest zone of southern Cameroon. In the 1995 experiment, the maize and cowpea intercrops reduced the final incidence of CMD in the cassava cvs. Dschang White and Dschang Violet, but not in the more resistant cv. Improved. In the 1996 experiment with cv. Dschang Violet, the maize and cowpea intercrops grown alone or together decreased adult whitefly populations on cassava by 50% and CMD incidence by 20%. The monomolecular population growth model generally provided the best fit for disease progress. Areas under the disease progress curves (AUDPCs) and incidences expressed as multiple infection units were significantly (P<0.05) less for cassava intercropped with maize and/or cowpea than in cassava alone; times to 50% CMD incidence were significantly (P<0.05) longer in all intercrop systems. In 1995 the basic infection rates (r) were similarly low (0.010 per month) in the moderately resistant cv. Dschang Violet intercropped with maize and in all treatments in the more resistant cv. Improved. By contrast, rates were significantly higherfor cv. Dschang Violet alone or with cowpea and in all treatments for the less resistant cv. Dschang White (0.030–0.060). In 1996, r values in cassava grown alone (0.077) were significantly larger (P<0.05) than in the other cropping systems (0.042–0.052). There were no significant differences in the symptom severity in the different cropping systems. Disease foci were isodametric and more compact in plots containing cowpea than in other cropping systems.     

Response of cereals to nitrogen in sole cropping and intercropping with different legumes

The response of sole and intercropped cereal to nitrogen fertilization was compared in three contrasting cropping systems, sorghum/pigeonpea, maize/groundnut, and sorghum/cowpea. The cereal in these systems responded to nitrogen similarly as in sole cropping, although different legumes affected the cereal differently. There was no current season benefit from the legume, whether it matured earlier or later than the cereal, and for high yields the cereal in intercropping needs fertilizer application. Response to nitrogen varied with the amount and distribution of seasonal rainfall. With increased nitrogen fertilizer applied to the intercropped cereal, the legume yields were suppressed. The optimum dose for the intercropped cereal was similar to that for sole cropping but it was 50% less in a dry year particularly, on a shallow Alfisol. The combined yields of both crops made intercropping more profitable than sole cropping. The relative advantage of intercropping was high in the sorghum/pigeonpea system (40 to 70%) because of the greater temporal difference between species, and moderate in the maize/groundnut (13 to 35%), and sorghum/cowpea (18 to 25%) systems. Although the relative advantage of intercropping (expressed as Land Equivalent Ratio (LER)) decreased with N, the economic value, of the advantage was little affected within the optimum N range because absolute yields increased with fertilization.     

The role of intercropping different cereal species in controlling lepidopteran stemborers on maize in Kenya

Abstract:  The effects of mixed cropping systems containing maize, sorghum, millet and beans on infestations of cereals by lepidopteran stemborers and on associated parasitoids, as well as on yields and land equivalent ratios (LER) were assessed during four consecutive rainy seasons at two sites in the semi-arid eastern region of Kenya. Systems containing the non-host bean were more efficient in reducing pest densities than those with millet or sorghum only. Higher parasitism in diversified systems compared to monocrops was due to density-dependent effects rather than superior suitability of such systems to parasitoids. The maize–bean system, which had the highest proportion of bean plants, had LERs >1.65 while most other systems had LERs <1. It is concluded that mixed cropping with several cereal species has little advantages in terms of yield loss abatement due to stemborers and land use efficiency. However, including the drought-tolerant crops such as sorghum and millet in the system stabilizes food security in drought-prone areas such as eastern Kenya.     

Suitability of brachiaria grass as a trap crop for management of Chilo partellus

The cereal stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) is a major insect pest of sorghum (Sorghum bicolor L. Moench) and maize (Zea mays L.) in Africa. Trap cropping systems have been shown to be a valuable tool in management of this pest. To optimize trap cropping strategies, an understanding of host‐plant preference for moth oviposition and host suitability for larval survival on potential trap plants is a prerequisite. Therefore, we assessed seven brachiaria accessions (Poaceae) for preference by C. partellus moths and subsequent larval performance. In two‐choice tests with a local open‐pollinated maize variety (cv. Nyamula), significantly higher numbers of eggs were deposited on brachiaria accessions Marandu, Piata, and Xaraes than on maize, whereas fewer eggs were recorded on plants of Mulato II, Mulato I, and Cayman. There was a significant and negative correlation between the trichome density on plant leaves and C. partellus oviposition preference for brachiaria. In addition to poor larval performance on brachiaria, there was no clear ranking in the accessions regarding larval orientation, settling, arrest, and food ingestion and assimilation. First instars did not consume leaf tissues of brachiaria plants but consumed those of maize, which also suffered more stem damage than brachiaria plants. No larvae survived on brachiaria plant tissue for longer than 5 days, whereas 79.2% of the larvae survived on maize. This study highlights the preferential oviposition of C. partellus on brachiaria plants over maize and the negative effects that these accessions have on subsequent larval survival and development. Our findings support the use of brachiaria as a trap crop for management of C. partellus through a push‐pull technology.     

Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae) a new invasive species in Israel

Chilo partellus, the spotted stem borer (SSB), is reported for the first time from the fields of sorghum and corn in Israel. Spotted stem borer larvae were first discovered in July 2010 on sorghum and corn plants in the Western Galilee. The new pest had spread all over northern Israel by the end of 2011. The identity of the new pest was confirmed using the morphology of the dissected male genitalia and its attraction to SSB sex pheromone.     

Effects of rhizobial inoculation, cropping systems and growth stages on endophytic bacterial community of soybean roots

Interspecific interactions and soil nitrogen supply levels affect intercropping productivity. We hypothesized that interspecific competition can be alleviated by increasing N application rate and yield advantage can be obtained in competitive systems. A field experiment was conducted in Wuwei, Gansu province in 2007 and 2008 to study intercropping of faba bean/maize, wheat/maize, barley/maize and the corresponding monocultures of faba bean (Vicia faba L.), wheat (Triticum aestivum L.), barley (Hordeum vulgare L.) and maize (Zea mays L.) with N application rates of 0, 75, 150, 225 and 300 kg N ha^?1. Total land equivalent ratios (TLER) were 1.22 for faba bean/maize, 1.16 for wheat/maize, and 1.13 for barley/maize intercropping over the 2-year study period. Maize was overyielding when intercropped with faba bean, but underyielding when intercropped with wheat or barley according to partial land equivalent ratios (PLER) based on grain yields of individual crops in intercropping and sole cropping. There was an interspecific facilitation between intercropped faba bean and maize, and interspecific competition between maize and either wheat or barley. The underyielding of maize was higher when intercropped with barley than with wheat. Fertilizer N alleviated competitive interactions in intercrops with adequate fertilizer N at 225 kg ha^?1. Yield advantage of intercropping can be acquired with adequate nitrogen supply, even in an intensive competitive system such as barley/maize intercropping. This is important when using intercropping to develop intensive farming systems with high inputs and high outputs.     

First report of Chilo partellus in Turkey,a new invasive maize pest for Europe

The spotted stem borer, Chilo partellus (Swinhoe, 1885) (Lepidoptera: Crambidae), an invasive pest of wild and cultivated grasses in Asia and Africa, was found for the first time during periodic surveys of maize fields in the East Mediterranean region of Turkey in September and October 2014. The pest was recorded in maize fields of three of four provinces surveyed (Adana, Hatay and Osmaniye; it was not detected in Icel province). The Mediterranean corn stalk borer, Sesamia nonagrioides Lefebvre (Lepidoptera: Noctuidae), is the dominant maize pest in the East Mediterranean region of Turkey, followed by the European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae). The new invasive species comprised 4.9% of the total number of collected lepidopteran pests collected from maize stems and cobs in locations infested by C. partellus. No natural enemies of the new pest were recorded during our surveys. We discuss possible interactions among these three lepidopteran pests sharing the same habitat, prospects for control of C. partellus by the control methods currently used against S. nonagrioides and O. nubilalis, and also speculate on the path of invasion taken by C. partellus into Turkey.     

Distribution,relative importance,and agro-climatic preferences of cereal stem borers in Eastern Ethiopia

Abstract

The distribution and relative importance of lepidopteran stem borers attacking maize and sorghum were investigated in farmers’ fields during the main cropping seasons of 2015 and 2016 across three main agro-climatic zones (ACZs) of eastern Ethiopia. Three stem borer species, namely Busseola fusca Fuller, Chilo partellus Swinhoe and Sesamia calamistis Hampson were found attacking these crops with different levels of distribution and abundance among ACZs. Busseola fusca was the only borer species in the highlands and dominant (67%) in the midhighland zones, while C. partellus was predominant (75%) in the lowlands. The abundance of S. calamistis was low across its distribution range. Across both years, mean plant infestation by B. fusca ranged from 20.38 in lowlands to 42.97% in highlands. Chilo partellus resulted in a mean infestation of 27.38% in the midaltitude to 68.24% in lowlands. Mean density of larvae per plant was higher for C. partellus (2.85), followed by B. fusca (1.41) and S. calamistis (0.46). Moreover, within each ACZs, variation in plant damage variables was observed between the study periods. These spatio-temporal differences in community structures of stem borers are discussed particularly in relation to agro-climatic requirements.     

Legume Hosts of Macrophomina phaseolina in Kenya and Effect of Crop Species on Soil Inoculum Levels

Studies were conducted in eastern Kenya to determine the common legume crop and weed hosts of Macrophomina phaseolina (Tassi) Goid., the inciter of charcoal rot disease. The effect of maize, sorghum, bean, and cowpea on the soil inoculum level was also investigated after field inoculation. All the legume crops and weeds tested were found to be infected by the pathogen after artificial inoculation. Common bean, soybean, cowpea were the most susceptible while pigeonpea, green gram, and hyacinth bean were moderately susceptible. Groundnut, chickpea. Cassia spp. and Crotalaria spp. were least susceptible after artificial inoculation, Monocropping of sorghum, maize, cowpea and common bean for three consecutive crop seasons increased M. Phaseolina soil inoculum in ascending order.     

Effects of crop diversification levels and fertilization regimes on abundance of Brevicoryne brassicae (L.) and its parasitization by Diaeretiella rapae (M’Intosh) in broccoli

1 The effects of intercropping via competition on crop yields, pest [cabbage aphid Brevicoryne brassicae (L.)] abundance, and natural enemy efficacy were studied in the Brassica oleracea L. var. italica system. 2 From May to December 2004, insect populations and yield parameters were monitored in summer and autumn in broccoli monoculture and polyculture systems with or without competition from Brassica spp. (mustard), or Fagopyrum esculentum Moench (buckwheat), with addition of organic (compost) or synthetic fertilizer. 3 Competition from buckwheat and mustard intercrops did not influence pest density on broccoli; rather, aphid pressure decreased and natural enemies of cabbage aphid were enhanced in intercropping treatments, but this varied with the intercropped plant and season (summer vs. autumn). 4 In compost‐fertilized broccoli systems, seasonal parasitization rates of B. brassicae by Diaeretiella rapae (M’Intosh) increased along with the expected lower aphid pressure compared with synthetically fertilized plants.     

Invasive maize spotted stem borer Chilo partellus Swinhoe 1885 (Lepidoptera: Crambidae) is the dominant pest in maize agro-system in the Mediterranean Region of Turkey

The maize spotted stem borer Chilo partellus Swinhoe 1885 (Lepidoptera: Crambidae) was recorded for the first time in Turkey in 2014. This pest is described as invasive, especially in the current climate change dispensation. It is important to investigate the population dynamics of C. partellus for better management practices. We studied the species abundance distribution (SAD) models and some biodiversity indices of three major stem bores, C. partellus, Ostrinia nubilalis and Sesamia nonagrioides as these are the most common and major stem borers of maize in the Mediterranean Region. With the help of light traps, weekly catches of the three major maize stem borers were collected during two maize growing seasons (first cropping and second cropping seasons) in 2018 and 2019. The results showed that C. partellus emerged earlier (April-May) and was very dominant throughout the first cropping season of maize. Ostrinia nubilalis and S. nonagrioides emerged late in June-July, and its population remained low throughout the first cropping season. The population structure of all three stem borers was similar throughout the second cropping season of maize. The relative abundance (RA) of C. partellus was significantly higher than that of O. nubilalis and S. nonagrioides in the first cropping (p <.0001) when compared to the second cropping season (p >.05) for both years. In the first cropping season for both years, no SAD model fitted the observed species distribution, although Fisher’s log series was relatively similar. In the second cropping for both years, the geometric series distribution model fitted the observed SAD. The Berger-Parker dominance index was greater for the first cropping season than that of the second, whereas the opposite was true for the Simpson’s evenness and evenness of Pielou. High RA of C. partellus and the geometric series distribution observed in the second cropping are indicative of a possible dominant status of the C. partellus in the Mediterranean Region of Turkey. Our findings indicated that seasonality is a fundamental driving factor influencing the distribution of the three major stem borers of maize in the Mediterranean Region. In addition, the long and warmer winters could be the reason for the dominance of C. partellus as indicated by the diversity indices.     

Host plant selection behaviour of Chilo partellus and its implication for effectiveness of a trap crop

Female lepidopterans can display a hierarchy of preference among potential host species, a trait thought to arise from the balance between attractants and deterrents to which the insects respond. Host plant ranking by moths and larvae of Chilo partellus Swinhoe (Lepidoptera: Crambidae), an important pest of cereals in Africa, was investigated, and whether eggs deposited on specific host plants yield larvae of particular host preferences. Trap plants are used in management of this pest. However, any ‘disagreement’ in host ranking between moths and larvae could potentially reduce effectiveness of trap crops as larvae emigrate to the main crop from the parent’s preferred trap plant. We also investigated whether host plant preference is influenced by the diet upon which larvae fed as part of an integrated assessment of the relationship between host plant selection and learning in C. partellus. Five host plants (all Poaceae) were used: maize (Zea mays L.), sorghum (Sorghum bicolor Moench), Napier grass (Pennisetum purpureum Schumach), and two varieties of signal grass [Brachiaria brizantha (A. Rich.) Stapf], viz., local (henceforth signal grass) and improved (‘Mulato’). In multiple choice tests, C. partellus female moths preferentially oviposited on Napier grass, followed by sorghum, maize, and signal grass, and least preferred ‘Mulato’. Larvae however equally orientated and settled on leaf cuts of maize, sorghum, signal grass, and Napier grass, but least preferred ‘Mulato’. Moreover, eggs from specific host plants did not yield larvae of particular host preferences. Furthermore, oviposition preference was not altered by the larval food. These results imply only a slight ‘disagreement’ in host ranking behaviour between moths and larvae, which is beneficial for trap cropping as larvae would not ‘reject’ the trap plant and appreciably disperse to the neighboring plants. Moreover, absence of larval learning behaviour indicates that regardless of the larval food C. partellus moths would still be attracted to the selected trap plant.     

Onion fly egg distribution in soil: a new sampling method and the effect of two granular insecticides

Tests were carried out in a screenhouse to determine the potential of a microsporidian pathogen,Nosema marucae (Microspora: Nosematidae), for the control of the spotted stalk borer,Chilo partellus (Lepidoptera: Pyralidae), on sorghum. Foliar application of an aqueous suspension ofN. marucae spores on egg batches pasted on the sorghum plants reduced leaf-damage in plants in the protected plots, and increased the proportion of plants with fully- and partially formed heads compared to unsprayed plots. Further, there was less tunnelling and fewer larvae in the sprayed plots. The pathogen also reduced pest infestation and damage to plants when the plots were infested with newly emerged larvae instead of eggs.N. marucae has a potential to controlC. partellus.     

Using competitive and facilitative interactions in intercropping systems enhances crop productivity and nutrient-use efficiency

This paper reviews recent research on the processes involved in the yield advantage in wheat (Triticum aestivum L.)/maize (Zea mays L.), wheat/soybean [Glycine max (L.) Merr.], faba bean (Vicia faba L.)/maize, peanut (Arachis hypogaea L.)/maize and water convolvulus (Ipomoea aquatica Forsk.)/maize intercropping. In wheat/maize and wheat/soybean intercropping systems, a significant yield increase of intercropped wheat over sole wheat was observed, which resulted from positive effects of the border row and inner rows of intercropped wheat. The border row effect was due to interspecific competition for nutrients as wheat had a higher competitive ability than either maize or soybean had. There was also compensatory growth, or a recovery process, of subordinate species such as maize and soybean, offsetting the impairment of early growth of the subordinate species. Finally, both dominant and subordinate species in intercropping obtain higher yields than that in corresponding sole wheat, maize or soybean. We summarized these processes as the `competition-recovery production principle'. We observed interspecific facilitation, where maize improves iron nutrition in intercropped peanut, faba bean enhances nitrogen and phosphorus uptake by intercropped maize, and chickpea facilitates P uptake by associated wheat from phytate-P. Furthermore, intercropping reduced the nitrate content in the soil profile as intercropping uses soil nutrients more efficiently than sole cropping.     

Binding of Bacillus thuringiensis Cry1A toxins with brush border membrane vesicles of maize stem borer (Chilo partellus Swinhoe)

Maize stem borer (Chilo partellus) is a major insect pest of maize and sorghum in Asia and Africa. Bacillus thuringiensis (Bt) δ-endotoxins have been found effective against C. partellus, both in diet-overlay assay and in transgenic plants. Gene stacking as one of the resistance management strategies in Bt maize requires an understanding of receptor sharing and binding affinity of δ-endotoxins. In the present study, binding affinity of three fluorescein isothiocyanate labeled Cry1A toxins showed high correlation with the toxicity of respective δ-endotoxins. Competitive binding studies showed that Cry1Ab toxins share some of the binding sites with Cry1Aa and Cry1Ac with low affinity and that Cry1Ab may have additional binding sites that are unavailable to the other two toxins tested.