The highlights of the entomology section are summarized as follows:||A. Utilization of hosts plant resistance and related evaluation techniques.||V.P.S. Panwar (India) reported that the maize stalk borers, Chilo Qartellus throughout Indiaduring raining season and Sesamia inferan in Peninsular India during winter season, are serious pestsof maize in Asia and Africa causing grain yield loss from 18% to 49%. Development of resistant cultivars is very economical and one of the essential components of IPM in India. Various sources of resistant maize materials have already been identified. Mass rearing of stalk borers based on locally available and cheap ingredients has been successful. Artificial infestation techniques were standardized and evaluation of plant damage based on a rating scale of 1-9 has been perfected. Due to additive and non-additive genes involved, low gene frequency and the polygenic nature of inheritance, a recurrent selection method has been suggested. In case of hybrids, the resistance level in inbreds will influence the resistance in resultant hybrids. D. Zhou (China) introduced a successful laboratory bioassay technique for host plant resistance evaluation which can use 6 to 7 leaf stage corn seedlings as testing materials. A specially prepared lyophilized plug of diet was used to adsorb the juice of the leaf tissue. After infestation of 10 to 15 neonate ACB larvae and incubation for 5 to 7 days, there will be a significant difference in body size/weight or amount of "frass" produced between highly resistant versus susceptible testing materials. The results obtained are highly identical to that of the traditional field artificial infestation technique with grown plants, having the advantages of fast, accurate results for the non-growing season evaluation by using frozen seedlings collected from growing season.|D. Bergvinson (CIMMYT) gave a talk on current status of breeding maize germplasm tolerant to maize tropical insect-pests. His presentation is summarized as follows:|The International Maize and Wheat Improvement Center (CIMMYT) has been able to develop maize germplasm resistant to tropical stem borers through S3 recurrent selection as well as identifying tolerant elite lines by screening CIMMYT germplasm. Elite line trials consist of artificial infestations for sugarcane borer (Diatraea saccharalis) and armyworm (S1Jodo1Jterafrugi1Jesda), grown under high plant density (130,000 plants/ha). In the fIrst trial 9 white and 15 yellow lines were identified and a diallel formed to characterize the heterotic behavior and hybrid resistance to borer and armyworm. The best performing hybrids were selfed and used to form heterotic synthetics call Insect Tolerant Synthetics (ITS). This process has since been repeated to produce the second set of ITS. Lines extracted out of a CIMMYT insect resistant population, Population 390, have shown higher levels of resistance than the resistant check CML 67, while having good agronomic traits.|Research on the biochemical basis of insect resistance in tropical maize has found leaf toughness to be the most important trait. Leaf toughness in Pop. 390 has increased over cycles of selection by 15%. Mapping of leaf toughness in CIMMYT's recombinant inbred lines (CML 67 x CML 131) has identified four quantitative trait loci on chromosomes I and 8, which are identical to those for leaf feeding resistance. Leaf nitrogen content has also been identified as an important factor for stem borer establishment on maize. Reducing soil fertility can reduce stem borer damage and borer -associated losses. Work is presently underway to identify optimal fertilization practices which reduce insect establishment while maintaining high yields.|B. Behavioral study of ACB adults||Zhou (China) reported two behavioral studies in ACB adults.||B-l : Studies on behavioral response of male ACB to the lure by using calling virgin females/|synthetic pheromone indicated that the procedures of male moth responding to the trapping system can be distinguished/ described as: a) approaching, b) searching below the traps, c) orienting to the trap,|d) searching around the trap and e) contacting/ landing upon the trap. Furthermore, it was observed that leaving mated female and dead virgin female on the trap with the synthetic pheromone lure can significantly increase the rate of male contacting/ landing upon the trap. Thus reveal a visual stimulant factor governing the efficacy of pheromone trapping.|B-2: Behavioral study on ACB dispersal flight. Similar to the European corn borer 0. nubilalis,|the ACB is not a migratory insect. However, flight-mill tests under laboratory revealed that a 24 h flight could cover a total distance of more than 100 kIn. So, it was necessary to conduct a release-and-recapture experiment with the objectives of :|a) searching for scientific basis for the effectiveness of overwintering control and of the source of ACB population for each year as well. In otherwords -to determine whether or not there is the possibility of having a large amount of migratory ACB population from outer area.|b) Determination of the "Minimum Effective Area" for conducting population control experiments/ pilot tests. Two large scale release-and-recapture experiments were carried out in 1987 and 1988, with an amount of high quality labelled ACB adults of 150,000 and 600,000 respectively. Results indicated that: a) 80% to 95% of the released moth were caught at 2 to 4 kIn. from the releasing site, showing that the ACB is not a migratory insect. Therefore, the local overwintering population is the main source for the next year population. Thus, a thorough overwintering control is possible to reduce the size of insect population for the next year. Similarly, the size of local overwintering population can also be used as the main source of ACB for a forecasting research program. Also, the "Minimum Effective Area" was determined to be a 4 kIn. radius circle with a big village (the site of overwintering maize stalks, similar to a releasing site) as its center. For more important experiments, a barrier-space of lor 2 kIn. in width was recommended, which is supposed to have an effect of arresting 80 to 95% of moths from outer area to the experimental zone.|C. Utlization of Trichogramma sp.|Tseng, C.T. (Taiwan) reported an ACB biological control program started in 1984, which consists in the augmentative release of Trichof!ramma ostriniae. The stored grain pest, Corcvra cevhalonica Stainton was used as an alternate host for the mass production of T. ostriniae. For saving labor cost in the mass production of T. ostriniae, one egg card machine has been developed. The machine is 10 times as faster as that of laborer in producing egg cards (3.5 x 15 cm). Although the augmentative release of T. vstriniae can significantly increase the parasitism rate, grain yield and income when compared with conventional control, it is still necessary to combine with 2 or 3 chemical applications to obtain control on field corn. In case of sweet corn, augmentative release of T. ostriniae combined with 1 low tonic insecticide and 3 ~ treatments, plus removal of tassels in two out of three rows, could give as satisfactory control as chemicals in reducing plant damage. Furthermore, it was proved that long term augmentative release of T. ostriniae had produced accumulative effect on suppressing the corn borer population to a considerable extent. Zhou. D (China) introduced a succesful artificial host egg production system that has a good effect on parasitism rate of egg masses under field conditions. He also reported the phenomenon of a strange effect in increasing parasitism rate on ACB egg masses under field condition, when a creeping type mung bean was used in interplanting with summer corn at a rate of 1 row of mung bean to 2 rows of corn plants. However, the mechanism of mung bean effect still needs further investigation.|D.

Significant control effect of Bt-transgenic maize to the Asian corn borer Zhou D. (China) showed slides on very good control effect of different tissue of Bt transgenic maize, produced by the Monsanto Co., to ACB damage after infested by a large number of larvae, especially under laboratory conditions. The tested tissues include whorl leaf, young tassel, silk, kernel and cob.

English

0208|AGRIS 0201|AL-Maize Program|R01PROCE

Juan Carlos Mendieta

CIMMYT Publications Collection