Management of rice bug, Leptocorisa oratorus (F.) (Hemiptera: Alydidae) using white muscardine fungus Beauveria bassiana (Bals.) Vuill. in upland rice-based cropping systems

Date

6-1995

Abstract

Leptocorisa oratorius (F.) is the most serious insect pests of rice at milking stage. Control strategies in current use against the pests are largely based on chemical insecticides which are prohibitively expensive to farmers in addition to the accumulation of toxic residues in the environment.

Laboratory and field experiments were conducted to screen and select isolates of B. bassiana most pathogenic to L. oratorius; to evaluate the development and infection of B. bassiana on L. oratorius in an intercropping systems; to assess the effects of B. bassiana on other insects pests of rice, legumes and its natural enemies including effects on vertebrates; and to determine the effects of sucrose, plant extracts and exposure to direct sunlight on the germination and survival of B. bassiana conidia.

Three isolates of Beauveria bassiana were evaluated for pathogenicity against Leptocorisa oratorius. GLH isolate was most potent with LC50 of 4.65 x 109 ; 2.22 x 109 and 1.3 x 109 conidia/ml for third instar, fourth instar, fifth instar and adults, respectively. LT50 was 7.95 days (third instar); 5.52 days (fourth instar); 3.37 days (fifth instar) and 2.89 days (adults). The test also revealed that immature stages (3rd-4th instar) were more resistant to fungal infection than late instar (5th) and adults.

Field application of B. bassiana suspension at the rate of 1.0 x 1013 conidia/ha regulated the population of L. oratorius in rice and R. linearis in legumes. Natural enemy population was likewise regulated to a lesser degree. Acid fuchsin test showed that the use of B. bassiana as myco-insecticide did not influence the extent of damage caused by L. oratorius on rice grains. Intercropping systems had less influence on the development and infection of B. bassiana against L. oratorius but enhanced the management of insect pests affecting upland rice including L. oratorius.

Abraded skin of albino mice treated with B. bassiana conidia showed no apparent clinical, pathological and historical abnormalities.

Laboratory tests revealed that 1,000ppm sucrose added to agar-medium enhanced germination of conidia. Conidia germinated on different extracts tested, but germination rate was inversely proportional to extract concentration. Viability of B. bassiana conidia was substantially and totally inactivated after one and three hours exposure under bright sunlight, respectively.

B. bassiana is highly pathogenic to L. oratorius, less virulent to natural enemies and safe to other organisms including humans. Efficacy under field conditions, however, was inhibited by unfavorable environmental conditions such as low relative humidity in upland agroecosystem and inactivation of conidia presumably caused by exposure to direct sunlight.

Document Type

Dissertation

Degree

Doctor of Philosophy in Entomology

College

Graduate School (GS)

Adviser/Committee Chair

Bernardo P. Gabriel

Committee Member

Eliseo P. Capadan, Jose R. Medina, Restituta P. Robles

Language

English

LC Subject

Rice bug

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

LG 996 1995 E75 T83

Notes

Doctor of Philosophy (Entomology)

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