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The larvae of O. furnacalis attack all parts of the maize plant. Yield losses are greatest when damage occurs at the reproductive stages. Late-instar larvae bore into the stem or branches of host plants or webbed groups of florets or branches. They bore in the shank and cob in the ear or feed on silk or kernels. The stalk is the most common feeding site for final-instar larvae.
Integrated Pest Management
IPM has been used for the control of O. furnacalis on Guam (Nafus and Schreiner, 1989).
The recommended management scheme in the Philippines is based on a control action threshold: early planting; the use of the microbial pesticide Bacillus thuringiensis subsp. kurstaki and chemical pesticides; release of the predatory earwig Euborella annulata as a biological control agent at the whorl and tassel stages; the use of moderately resistant varieties; and sanitation (Morallo-Rejesus, 1988). Restraints to the adoption of these IPM programmes outside the Philippines are discussed by Bernardo (1993).
Maize plants are detasselled in some parts of the Philippines as a control measure against O. furnacalis. Detasselling 75% of the plants in a field reduced infestation and larval tunelling primarily by removing larvae feeding in the tassels, and secondarily by reducing larval survival because of reduced amounts of pollen available as food (Felkl, 1988a; Shreiner and Nafus, 1988). Detasselling maize significantly reduced the number of O. furnacalis in Guam but did not always lead to increased yield (Schreiner and Nafus, 1988).
Detasselling is also used in combination with insecticides. In terms of grain yield, detasselling alone was sufficient and combination with a systemic insecticide was not necessary (Alolina and Catli, 1986; Felkl, 1988b); no significant difference in grain yield was observed between detasselling alone and detasselling in combination with a systemic insecticide (Alolina and Catli, 1986).
As the area being cultivated with maize in Henan, China, has declined since the 1970s, the first generation of O. furnacalis has moved to cotton (Li QiaoSi et al., 1999). The insects overwinter in maize stems, so a simple control method involves the removal of maize stubble from fields between harvesting and early May. Maize is the ideal host plant for O. furnacalis and intercropping maize (450-750 plants/ha) in cotton fields from mid-April to early May greatly reduced damage to the cotton crop. Rapid removal of harvested wheat (when intercropped with cotton) also reduces damage to cotton seedlings.
Maize varieties have been screened for resistance to O. furnacalis in Taiwan (Kuo et al., 1990; AVRDC, 1990).
Maize inbred resistance trials were conducted at 25 sites in 11 countries (Brewbaker et al., 1989); a few inbreds showed high resistance to a number of parasites, deseases, ear rots, yield and drought tolerance, and stored product pests.
A single cross maize 2D-No1 with resistance to O. furnacalis was developed with Zhidian 122 x Huangzaosi in China. The yield was 31.5% higher than in a control variant (Zhou et al., 1987).
The inheritance of resistance to O. furnacalis was investigated in Tainan-white maize inbred lines by Shieh GuangJauh et al. (1999). S2 and S5 inbred lines derived from eight Tainan-white (TNW) maize populations collected from eight differential areas were evaluated for resistance to O. furnacalis at Wufeng, Taichung. Resistance was controlled by two and three groups of genes at the whorl and silking stage, respectively. A recessive gene may be responsible for resistance to O. furnacalis because inbred lines with a higher level of resistance have more recessive genes.
Meng FanXiang (1998) found a good maize inbred line (He 344) with resistance to maize northern blight (Setosphaeria turcica), head smut (Sphacelotheca reiliana), O. furnacalis and lodging. The line had high combining ability and has been used as a parent in several lines.
A collaboration between the Central Research Institute for Food Crops (CRIFC), Bogor, Indonesia, and Garst Seed Company, Slater, Iowa, USA (previously ICI/Zeneca Seeds) exists to develop insect-resistant maize using the cryV Bt gene (Robeff and Ives, 1998).
Biological control, based on the release of egg parasitoids (Trichogramma sp.), is the most efficient method of controlling this pest, particularly in tropical regions. Evaluation of the effectiveness of biological control with Trichogramma in China indicated that costs could be reduced by not using pesticides (Li, 1988).
The rate of parasitism in the first egg stage rose to 70% following the long-term release of T. dendrolimi in Liaoning province, China. Damage to maize stabilized at about 10% (Zhang et al., 1990a). Qui HongGui et al. (1999) proved that host-acceptance of T. dendrolomi is plastic and rearing for three to four generations on specific host eggs is required to significantly change the host preference of female wasps.
The distribution and population dynamics of Trichogramma ostriniae were studied in 17 crop habitats in China by checking the rate of egg parasitism of mass-reared O. furnacalis (Zhou DaRong et al., 1997). The newly laid egg masses were placed in plant leaves and taken back 3 days later to monitor parasitism rates. Results showed that the distribution, occurrence and numbers of T. ostriniae varied in different habitats. The population of T. ostriniae was greatest and most persistent in a spring sweet potato field. Crops interplanted with legumes slightly increased the rate of parasitism. The population of T. ostriniae varied between years and was particularly affected by drought.
T. dendrolimi and T. ostriniae are the most effective Trichogramma egg parasitoids of O. furnacalis (Zhang, 1988). T. dendrolimi produced >90% parasitism of O. furnacalis in Tonghua, Jilin, China (Gao and Duan, 1992).
T. chilonalis is the most important parasitoid of O. furnacalis on Guam, but does not keep the pest below the economic threshold level (Nafus and Schreiner, 1986).
T. evanescens was successfully released in the Philippines (Tran et al., 1988). Parasitism reached 40-76.9% and the pest population was reduced by 35-67.8%. Parasitized eggs were found in maize fields 25-30 km away from the original release site. Staggered planting, leaving a standing maize crop in the field all year round, and the presence of alternative food plants of O. furnacalis during the dry season, were beneficial for the establishment of T. evanescens (Tran et al., 1988).
Field experiments were conducted in China using Trichogramma dendrolimi and T. chilonis reared on artificial host eggs to control summer generations of O. furnacalis (Feng JianGuo et al., 1999). Egg parasitism in O. furnacalis was 65.44-68.16%. A releasing container for Trichogramma reared on artificial host eggs was designed and the emergence rate was >90%.
He KangLai et al. (2002) surveyed parasitoids and pathogens of overwintering O. furnacalis larvae in 11 locations in maize-growing areas in nine provinces of China. A tachinid fly, Lydella grisescens, a braconid wasp, Macrocentrus cingulum and an ichneumon wasp, Eriborus terebrans [Diadegma terebrans] were the major parasites. Beauveria bassiana, Bacillus thuringiensis and two microsporidia, Nosema furnacalis and Nosema sp., were the major pathogens. In general, the pathogens caused higher mortality of O. furnacalis than the parasitic insects. Muscardine was the most prevalent disease, particularly in the spring maize area.
The nematode, Steinerma feltiae agriotos, showed promise against O. furnacalis in the laboratory and in the field in China (He et al., 1991).
Formulations of Bacillus thuringiensis are used in combination with Trichogramma sp. to control O. furnacalis (Padua et al., 1987; Tandan and Nillama, 1987).
Wang ZuNan (1996) bred three entomogenous fungi (Beauveria amorpha, Beauveria sp. and Paecilomyces tenuipes) collected in the wild on dead insects in Taiwan and assessed their potential as control agents on different pests. The potential of B. bassiana as a control agent for O. furnacalis in Taiwan is discussed by Hou (1997).
In Japan, Kageyama at al. (1998) looked at the inheritance of sex ratio distortion towards females and its underlying mechanism in O. furnacalis. He suggested that chromosomal males are feminized by a cytoplasmic agent(s). Kageyama et al. (2002) later investigated the possibility of using Wolbachia as a control agent as it can affect cytoplasmic incompatibility, parthenogenesis, male-killing, hybrid breakdown and feminization. This phenomenon has until now only been observed in isopods. The results suggest an indepent evolutionary origin for Wolbachia-induced feminization in O. furnacalis and in isopods.
Xu Jing et al. (1998) evaluated an engineered endophytic bacterium 12#Bt/CXC (cryIA (c) gene from Bacillus thuringiensis subsp. kurstaki introduced into the chromosome of Clavibacter xyli subsp. cynodontis) as a biological control agent. Strain 12# had higher insecticidal activity than B. thuringiensis strain HD-73 and a PBS-treated control, causing 63% mortality at the highest concentration tested, while the mortality rate of larvae ingesting wild-type HD-73 was 53% at the same concentration. The concentration-mortality curves of the two strains showed a linear correlation. On plants, the insecticidal activity of maize injected with 12# was obviously greater than that of maize seed treated with 12#. At different injection concentrations, larval mortality varied from 70 to 96%, being significantly different from that of PBS controls. At the same time, strain 12# restrained the development of O. furnacalis so that the weight of living larvae was reduced by 26.4 to 44.5%. Larvae on inoculated maize did not develop to the second instar, while those on the control developed to the fourth instar.
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:
O. furnacalis is mainly a pest of maize and sweetcorn. Reduction of maize yield was assessed in Taiwan by Hsu et al. (1988). Each larva caused 1.7% yield reduction of field maize in the spring crop and 4.4, 5.6 and 2.5% loss of sweetcorn in the autumn, winter and spring crops, respectively. The number of cavities was a more reliable indicator of yield loss than the number of larvae or pupae.
An economic threshold of not more than one larva per plant was established in the Philippines (Morallo-Rejesus et al., 1990). Field losses of 4.8-30.9% were recorded, depending on location (Teng et al., 1992).
The time of appearance of adults in cotton fields in China could be forecast on the basis of the rate of development of the larvae in the fields. The threshold for control was 0.9-1.1 egg masses/100 plants in the first generation and 3.1 egg masses/100 plants in the second (Liu et al., 1983).
Wang XuePing et al. (2001) conducted a study at Rugao, Jiangsu, China to evaluate the damage caused by the larvae of second generation O. furnacalis on summer maize sown at different times. Larval attack was found to be dependent on the sowing periods of summer maize.