Aart van Schoonhoven

A review of insect prevalence in maize (Zea mays L.) and bean (Phaseolus vulgaris L.) polycultural systems

Abstract Tropical agroecosystems often include two or more crops arranged in diverse polycultural patterns. Experimental evaluation of the pest situation in polycultural systems was carried out in several field experiments at CIAT (Centro Internacional de Agricultura Tropical, Palmira, Colombia) with maize and beans in monoculture and polyculture. Beans grown as maize/bean polycultures had 26% fewer Empoasca kraemeri Ross and Moore adults than monoculture beans. Similarly the populations of Diabrotica balteata Le Comte were 45% less in polycultures. Spodoptera frugiperda (Smith) incidence as cutworm in maize was reduced 14% in polycultures. Also these systems had 23% less infestation of fall armyworm as whorl feeder. Date of planting affects pest interactions in these systems. For example, maize planted 30 and 20 days earlier than beans reduced leafhoppers on beans by 66% as compared to simultaneous planting. Fall armyworm damage on maize was reduced 88% when beans were planted 20 to 40 days earlier than the maize. Diversification of monocultural systems with other crops, especially non-host plants, seems to be one effective strategy in tropical pest management. Further research will provide a basis for incorporating practical pest control schemes into the most important intercropping systems in the tropics.

Structure and Composition of the White Grub Complex (Coleoptera: Scarabaeidae) in Agroecological Systems of Northern Cauca,Colombia

Abstract The larvae of some species of Scarabaeidae, known locally as “chisas” (whitegrubs), are important pests in agricultural areas of the Cauca, Colombia. They form a complex consisting of many species belonging to several genera that affect the roots of commercial crops. The objective of the present study was to identify the members of the complex present in two localities (Caldono and Buenos Aires) and collect basic information on their biology, economic importance, and larval morphology. The first of two types of sampling involved sampling adults in light traps installed weekly throughout one year. The second method involved larval collections in plots of cassava, pasture, coffee, and woodland. Each locality was visited once per month and 10 samples per plot were collected on each occasion, with each sample from a quadrants 1 m2 by 15 cm deep, during 1999-2000. Light traps collected 12,512 adults belonging to 45 species and 21 genera of Scarabaeidae within the subfamilies Dynastinae, Melolonthinae, and Rutelinae. Members of the subfamily Dynastinae predominated with 48% of the species (mostly Cyclocephala), followed in decreasing order by Melolonthinae (35%) and Rutelinae (15%, principally Anomala). Melolonthinae comprised 60% of the specimens (Plectris spp. 59.5% and Phyllophaga spp. 35.9%). A total of 10,261 larvae of 32 species was collected, including 12 species each of Melolonthinae (Phyllophaga, Plectris, Astaena, Macrodactylus, Ceraspis, Barybas, and Isonychus), Rutelinae (Anomala, Callistethus, Stigoderma, and Leucothyreus) and Dynastinae (principally Cyclocephala). At least a third of the species sampled as larvae are rhizophagous pests. Taken together, adult and larval sampling methods permitted a more precise definition of the whitegrub complex in Caldono and Buenos Aires.

THE INFLUENCE OF LEAFHOPPER (EMP0ASCA KRAEMERI) ATTACK DURING VARIOUS BEAN (PHASEOLUS VULGARIS) PLANT GROWTH STAGES ON SEED YIELD

Bean plants (Phaseolus vulgaris L.) variety Diacol‐Calima, were protected with insecticides from Empoasca kraemeri R. & M. attack during various growth stages. When the leafhopper attack occurred late in the growing season, the most critical period for control was from 45–62 days after planting. When leafhopper attack was severe during the entire growing season, the period from 27–44 days was most critical, followed in importance by the 45–62‐day period. Insecticidal control before 27 days and after 62 days after planting did not influence final seed yield.

The mechanisms of resistance in common beans to the leafhopper Empoasca kraemeri

Greenhouse and field studies were conducted to determine the mechanisms of resistance (tolerance, antibiosis and antixenosis) in common beans Phaseolus vulgaris L. to the leafhopper Empoasca kraemeri Ross & Moore (Homoptera: Cicadellidae). No antibiosis effects were detected in any of the bean lines investigated. However, in both free choice and no choice tests in the greenhouse, ovipositional antixenosis was detected, and appeared to increase with increasing plant age in resistant bean lines. The results of the field study were similar to those obtained in the greenhouse and suggested that bean line EMP 81 possessed only tolerance as a mechanism of resistance to leafhoppers, while EMP 89, EMP 94, EMP 97 and EMP 82 were non‐preferred by ovipositing leafhoppers.

A post‐Green Revolution strategy for the improvement of small farmer‐grown common beans

Abstract Since 1973, the CIAT Bean Progam has focused on disease resistance breeding, with selection for performance under low input conditions and adaptation to farmers’ current production systems. This strategy was chosen to make new bean technology more accessible to resource poor farmers in low income countries than had been the products of the Green Revolution approach of selecting for maximum yield under optimum high input conditions. A case study of adoption of new disease resistant bean varieties among small farmers in Costa Rica shows that the disease resistance strategy has resulted in varieties that improve productivity even in farmers’ traditional shifting cultivation system. However, many small farmers are finding it advantageous to intensify management in order to raise the gains from the new varieties. Such success in a disease resistance, small farm‐oriented crop improvement program, depends critically on strong national agricultural research capacity, and a continuing commitment to deploy...