- Email: [email protected]
Impact of varietal resistance in rice and predation on the mortality of Sogatella furcifera (Horváth) (Homoptera: Delphacidae)
CROP P R O T E C T I O N (1986) 5 (6), 395-399
Impact of varietal resistance in rice and predation on the mortality of Sogatella furcifera (Horvhth) (Homoptera: Delphacidae) M . SALIM AND
E. A. HEINRICHS*
International Rice Research Institute, PO Box 933, Manila, Philippines Highly resistant, resistant and susceptible rice cuhivars were tested in the greenhouse to determine their effect on Sogatella furcifera (Horvfith) populations. The highly resistant cultivar IR2035-117-3, with resistance genes IVbph 1 and IVbph 2, caused the highest S. furcifera mortality. When the effects of varietal resistance and predation were combined the increase in mortality due to predators was additive. The spider Lycosa pseudoannulata Boes. et Str., mirid bug Cytorhinus lividipennis Reuter, ladybird beetle Harmonia oetomaculata(F.) and rove beetle PaederusfuscipesCurt. were effective predators ofS. furcifera and generally caused 30% mortality on the various cultivars. Results indicate that the integration of varietal resistance and predation would provide effective control of S. furcifera populations under field conditions. ABSTRACT.
Introduction
The whitebacked planthopper, Sogatella furcifera (Horvfath) (Delphacidae: Homoptera) is distributed throughout South, South-East and East Asia (Nasu, 1967). S. furcifera is emerging as a serious pest of rice in many Asian countries, especially in areas where varieties resistant to Nilaparvata lugens have been grown successfully (Heinrichs and Rapusas, 1983; Khan and Saxena, 1985). Outbreaks ofS. furcifera in Asia have recently been reported in Pakistan, Bangladesh, Nepal, India, Vietnam, Malaysia and Indonesia (Mochida et al., 1982). Both nymphs and adults of the pest suck sap from leaves and leaf sheaths, which results in yellowing of leaves, reduced tillering and plant height and an increase in the percentage of unfilled grains. High populations of S. furcifera cause hopperburn (Pathak, 1968). S. furcifera has not been reported to transmit rice diseases, but feeding punctures and ovipositional injuries predispose rice plants to bacterial and fungal diseases and honeydew excretion encourages sooty mould. Using the seedbox screening test, more than 53 000 rice accessions from the International Rice Research Institute (IRRI) germplasm collection from throughout the world have been screened for resistance to S. furcifera. Out of these, nearly 400 accessions have been found to be resistant to S. furcifera at the seedling stage (Heinrichs, Medrano and Rapusas, 1985).
Genetic analysis of resistant cultivars indicated four dominant genes, designated Wbph 1, Wbph 2, Wbph 3, and Wbph 5, and one recessive gene (wbph 4) (Sidhu, Khush and Medrano, 1979; Angeles, Khush and Heinrichs, 1981; Hernandez and Khush, 1981; IRRI, 1984). No cultivar with a high level of resistance to S. furcifera has been released for commercial cultivation. However, four of the IR cultivars (IR48, IR52, IR60 and IR62) have moderate levels of resistance at IRRI (Heinrichs et al., 1985). In the management of S. furcifera populations, resistant cultivars should be integrated with other methods of pest control to achieve stable pest suppression. Resistant cultivars are compatible with biological control agents (Adkisson and Dyck, 1980). Predators help to control target as well as other pests to which the cultivar is not resistant (Maxwell, 1972). Plant resistance has no direct detrimental effect on predators (Kogan, 1982). Insects feeding on resistant cultivars often lack virility and are small in size and slow in development. Restless behaviour on resistant cultivars exposes insects more and increases their mortality due to predators (De Bach, 1974). Mortality of Nilaparvata lugens due to predators was comparatively higher on resistant than on susceptible cultivars (Kartohardjono and Heinrichs, 1984). Predators have been reported to be important in the regulation of rice planthopper populations (Hinckley,
* Present address: Department of Entomology, 402 Life Sciences Bldg., LSU Agricultural Center, Baton Rouge, Louisiana 70803, USA. 0261-2194/86/06/0395-05 $03.00 © 1986 Butterworth & Co (Publishers) Ltd
396
S. furcifera martality: impact of varietal resistance and predation
1963). The wolf spider Lycosa pseudoannulata Boes. et Str. (Lycosidae: Araneae) has a high pest-killing capacity and is considered to be one of the predominant spiders for the control of rice pests (Kawahara et al., 1969). The mirid bug Cyrtorhinus lividipennis Reuter (Hemiptera: Miridae) is considered to be mainly an egg predator ofS. furcifera but can feed on nymphs and adults as well (Kamal, 1981). C. lividipennis can destroy on average five eggs, one nymph and 0.6 adults of S. furcifera per predator per day (Dyck et al., 1981). The ladybird beetle Harmonia octomaculata (F.) (Coleoptera: Coccinellidae) is considered to be an important predator of rice hoppers including S. furcifera (Kamal, 1981; Hinckley, 1963; Chandra, 1978). The rove beetle Paederus fuscipes Curt. (Coleoptera: Staphylinidae) is a voracious feeder on hoppers and has a high searching ability (Manley, 1977). Bearing in mind the importance of host-plant resistance and of predators as two components in integrated control, studies were conducted to determine their impact on the mortality orS. furcifera. Materials and m e t h o d s
The effect on the mortality of S. furcifera of the predators L. pseudoannulata, C. lividipennis, H. octomaculata, and P. fuscipes, on rice cultivars with different levels of S. furcifera resistance, was determined in separate tests conducted in a greenhouse at IRRI, Los Bafios, Laguna, Philippines. Experiments were laid out in a randomized complete block design with four replications. Treatments of each experiment consisted of one predator and six rice cultivars: these were IR2035-117-3, highly resistant with two genes Wbph 1 and Wbph 2; WC 1240, resistant with Wbph 1 + 1 recessive gene; Colombo, resistant with Wbph 2+ 1 recessive gene; ARC 10239, resistant with the Wbph 2 gene; N22, resistant with the Wbph 1 gene, and TN1, susceptible (Heinrichs and Rapusas, 1983). Seeds of selected rice cultivars were sown in soil in seedboxes. One week after sowing, seedlings were transplanted into soil in clay pots (14cm diameter) at the rate of four plants per pot. At 25 days after transplanting (DT) all insects and natural enemies were removed and rice plants were covered with Mylar film cages ( l l c m × 1 0 8 c m ) . After 5 days the plants were again checked for the presence ofarthropods and then the predator and prey (S. furcifera) were released in the cages. S. furcifera mortality was determined by counting the number of live insects. Total mortality of S. furcifera was based on a combination of that caused by the predator and varietal resistance. Mortality due to varietal resistance was based on mortality in cages without the predator.
aeration. Moisture was supplied on small swabs of cotton. After the last moult, spiders of uniform age were used for the feeding studies.
Test 1. Sixteen freshly emerged S. furcifera brachypterous female adults and one L. pseudoannulata were released per cage. Observations on the mortality orS. furcifera with and without L. pseudoannulata were recorded daily and continued for 10 consecutive days. The predator, if dead, and all S. furcifera adults were replaced after each observation. Test 2. Fifty S. furcifera adults (brachypterous females) and one L. pseudoannulata adult were released per cage. Observations on the mortality ofS. furcifera were recorded at 4 days after infestation. Three separate trials were conducted by using fresh prey and predators on fresh plants for each trial. H. octomaculata Pupae of H. octomaculata were collected from the rice field at IRRI and kept in a cage in the laboratory. Moisture was supplied with wet cotton swabs. Adults of uniform age were used for predation studies.
Test 1. Four H. octomaculata adults and ten S. furcifera adults (brachypterous females) were released per cage. Observations on the mortality ofS. furcifera were recorded daily. All prey were replaced after each observation.
Test 2. Forty S. furcifera adults (female) and two H. octomaculata adults were placed in each cage. Observations on the mortality of S. furcifera were recorded at four days after infestation. Three separate trials were conducted by using fresh prey and predators on fresh plants for each trial. The cultures of C. lividipennis and S. furcifera were maintained in the greenhouse. Fifty first-instar S. furcifera nymphs and four C. lividipennis adults were released per cage. Mortality of S. furcifera was recorded 10 days after infestation. Both prey and predators were collected from the cages at 10 days after infestation and transferred into labelled glass tubes. S. furcifera were counted in the laboratory and mortality was calculated. P. fuscipes Fifty first-instar S. furcifera nymphs and four P. fuscipes adults were released per cage. Mortality of S. furcifera was recorded 10 days after infestation. Results and discussion
L. pseudoannulata
Last-instar spiderlings of L. pseudoannulata were collected from the screenhouse at IRRI and kept singly in glass tubes, covered with caps having small holes for
L. pseudoannulata In test 1 where all S. furcifera were replaced daily to maintain a population of 16 adults, the effect of varietal
M. SALIMAND E. HEINRICHS
397
TABLE 1. Predation efficiency ofL. pseudoannulata against S. furclfera on rice cultivars with different levels o f resistance. IRRI greenhouse, 1984
S. furcifera mortality (%)t Days after infestation
IR2035-117-3
WC 1240
31-2a (a) 2.8 c(b) 28-1a (a) 14.1 bc(b) 2 3 . 4 a b (a) 2 5 ' 0 a b (ab) 9.4 c(b) 29.7a (a) 15.6 bc(c) 26.6a (a)
25'0ab (ab) 23.4abc (a) 7.8 d(b) 32"8a (a) 12.5 cd(ab) 32"2a (a) 14.1 bcd(b) 14-1 bcd(b) 25.0ab (ab) 14"1 bcd(b)
Colombo
ARC 10239
N22
TN 1
21"gabc(ab) 17-2abc(ab) 10.9 c(b) 2 1 ' 9 a b (ab) 15'6abc(ab) 23"4ab (ab) 12.5 bc(b) 28.1 a (a) 20"3abc(abc) 18.8abc(ab)
20.3abc(ab) 14.1 bc(ab) 10.9 c(b) 23-4ab (ab) 10.9 c(b) 9-4 c(c) 29-7a (a) 15.6 bc(b) 14.1 bc(bc) 31.2a (a)
17.2abc(b) 9.4 c(b) 17-2abc(ab) 14.1 bc(b) 15.6 bc(ab) 2 3 . 4 a b (ab) 2 3 . 4 a b (a) 14.1 bc(b) 29.7a (a) 9.4 c(b)
Varietal resistance + predation 1
2 3 4 5 6 7 8
9 10
14"1 b (b) 12"5 b (ab) 15.6ab (b) 23-4ab (ab) 12.5 b (ab) 15.6ab (bc) 25.0 bc(a) 2 0 . 3 a b (ab) 12.5 b (c) 28.1a (a)
Predation (with L. pseudoannulata - without L. pseudoannulata)t 1 2 3 4 5 6 7 8 9 10
26.5** 3' 1 NS 18.7"* 7"9* 18"7"* 20-3** 3"2 NS 20-3** 7-8 NS 18"8"*
20'3** 17.2"* 1'6 NS 26"6** 6"3* 23'4** 9"4* 11'0"* 18"8"* 6"3 NS
1l'0"* 6' 3 NS 10'9"* 15"6"* 7"8** 10"9"* 23"4** 14-1 ** 7"8* 23"4**
17-2"* 12.5"* 6'2 NS 18"8"* 12.5"* 18.7"* 6'3 NS 25.0** 15.6"* 14'1"*
17.2"* 8.2 NS 6-2* 20"3** 7'8** 6"3* 25"0** 10.9"* 9.4"* 28'1 **
15-6"* 4.7 NS 17.2 ~* 11.0"* 14'0"* 17"2 "* 20"3** 9"4** 26"6 ** 4'7 NS
tAnalysis is based on values transformed to arcsin ~/-x+ 0.5. In a column, and in a row (in parentheses) means followedby a common letter are not significantlydifferent at the 5oA level by Duncan's multiple range test (Gomez and Gomez, 1984). Average of four replications. *NS=non-significant; * =significant at 5% level; * * =significant at 1% level.
resistance did not have sufficient time to be an important factor in S. furcifera mortality (Table 1). Average mortality over the 10-day period on the highly resistant cv. IR2035-117-3 was 21% whereas in susceptible TN1 it was 17%. To calculate the extent of the effect of predation on the total mortality (varietal resistance + predation) the mortality without L. pseudoannulata was subtracted from the mortality with L. pseudoannulata (Table 1). The degree of S. furcifera mortality attributable to predation ranged from 3% to 27% on a daily basis and was significantly higher than the mortality without L. pseudoannulata in most cases. In test 2, where S. furcifera mortality was recorded four days after infestation, there was sufficient time for the adverse effect of the resistant cultivars to be observed. Results of the three trials were similar (Table 2). Mortality of S. furcifera when caged in the absence of the predator was highest (74-78%) on the highly resistant cv. IR2035-117-3 and lowest (8-10%)
on susceptible TN1. Mortality in the resistant cvs WC 1240, ARC 10239 and Colombo was intermediate, ranging from 53% to 62%. On the basis of the results of the three trials, it is evident that when one predator was added to the cage of 50 S. furcifera adults, S. furcifera mortality in a 4-day period increased from 10% to 33% on the various cultivars (Table 2). The increase was simply an additive effect and there was no evidence of a higher predation rate on the highly resistant cultivar compared with the resistant or susceptible cultivars. In fact, the mortality increased 33% when the predator was added to the susceptible TN1 cages, whereas the increase was 19% on the higly resistant cv. I R 2 0 3 5 117-3.
H. octomaculata Prey mortality in test 1 was little affected by the level of resistance of the various cultivars because all prey
TABLE 2. S. furczfera mortality due to varietal resistance and L. pseudoannulata predationt. IRRI greenhouse, 1985
S. furcifera mortality (%) Trial II
Trial I
Cuhivar IR2035-117-3 WC 1240 Colombo
ARC 10239
N22 TN1
With predator
Without predator
96a 82 b 80 b 77 b 78 b 43 d
78 b 60 c 56 cd 53 cd 54 cd 10 e
With predator
96a 84 b 82 b 80 b 80 b 42
e
Trial III
Without predator
With predator
Without predator
74 bc 61 d 62 cd 56 d 57 d 8 f
96a 82 b 80 b 77 b 78 b 43 d
78 b 60 c 56 c 53 cd 54 cd 10 e
t Analysisis based on values transformed to arcsin ~/-xwhere N = 50. All means in two columns within each trial (with predator and without predator) followed by a common letter are not significantly different at the 5% level by Duncan's multiple range test (Gomez and Gomez, 1984).
398
S. furcifera mortality: impact of varietal resistance and predation
TABLE 3. S. furc(fera p o p u l a t i o n as affected b y levels o f varietal resistance a n d H. octomaculata predation. I R R I g r e e n h o u s e , 1984
S. furcifera m o r t a l i t y ( % ) / d a y t Cultivar IR2035-117-3 W C 1240 Colombo A R C 10239 N22 TN1
With predator
Without p r e d a t o r Difference:l:
39.0 a 39.5 a 38.0 a 36.5 a 37.5 a 39.0a
6.8 5.8 6"0 5.2 5.0 3.8
a ab a ab ab b
32' 2 * * 33.7** 32"0** 31-3** 32"5** 35"2**
t
Data are averages of 10 days' observations. Analysis is based on values transformed to arcsin fix/100. In a column, means followed by a common letter are not significantly different at the 5°70level by Duncan's multiple range test (Gomez and Gomez, 1984). Average of four replications. :1: * * =significant at the 1% level. TABLE 4.
the other cultivars. Mortality on Colombo, ARC 10239 and N22 was intermediate. In the presence of the predator C. lividipennis there was a simple additive effect; the increase in mortality due to predation was 19-24% on the various cultivars (Table 5). These results agree with those of Kartohardjono and Heinrichs (1984), who reported that resistant cultivars did not increase the predation rate ofC. lividipennis over that on susceptible cultivars. The feeding rate of C. lividipennis of 0.4 nymphs per day was lower than that observed in previous studies (Dyck et al., 1981). However, the differences may have been due to a different age of prey, and different prey:predator ratio.
S. furcifera m o r t a l i t y d u e to varietal resistance a n d H. octomaculata p r e d a t i o n t . I R R I greenhouse, 1985 S. furcifera m o r t a l i t y (%) Trial I
Cultivar IR2035-117-3 WC1240 Colombo A R C 10239
N22 TN1
With predator 98 81 81 84 81 46
a b b b b f
T r i a l II
Without predator 72 50 54 59 55 10
c ef def d de g
With predator 98 81 80 84 81 46
T r i a l III
Without predator
a b b b b e
With predator
69 c 52 de 54 de 60cd 55 de 12 f
99 81 80 84 80 48
a b b b b c
Without predator 79 b 49 c 53 c 56 c 56 c 11 d
t Analysis is based on values transformed to arcsin ~/-x where N = 40. All means in two columns within each trial (with predator and without predator) followed by a common letter are not significantly different at the 5% level by Duncan's multiple range test (Gomez and Gomez, 1984).
were replaced daily and there was not sufficient time for the resistance factors to act (Table 3). The combined mortality due to predation and varietal resistance was the same on all cultivars. Mortality with H. octomaculata was 37-39%. The increase in mortality with the predator was significant for all cultivars, being 31-35%. Prey mortality in the three trials of test 2 was recorded 4 days after infestation and thus there was a significant effect of varietal resistance on the S. furcifera population (Table 4). S. furcifera mortality without the predator on IR2035-117-3 ranged from 69% to 79% in the three trials, 49-60% on the resistant cultivars and 10-12% on TN1. S. furcifera mortality in the presence of the predator H. octomaculata increased by about 30% on all cultivars. Mortality on IR2035-117-3 was 98-99%, about 80% on WC 1240, Colombo, ARC 10239, and N22, and 46-48% on susceptible TN1. The combined prey mortality due to varietal resistance and predation on IR2035-117-3 was about twice that on TN1. C. lividipennis The mortality of S. furcifera nymphs at 10 days after infestation in the C. lividipennis test was lower than that of the adults at 4 days after infestation in the previous tests. However, there was an effect of varietal resistance on mortality, as indicated in the 'without predator' column in Table 5, mortality being significantly higher on IR2035-117-3 and WC 1240 than on
TABLE 5. Effect o f levels o f varietal resistance a n d C. h'vidipennis p r e d a t i o n on S. furcifera n y m p h s . I R R I g r e e n h o u s e , 1984
S. furcifera mortality ( % ) t Cultivar IR2035-117-3 W C 1240 Colombo ARC10239
N22 TN1 Predator means
With predator 58"0 56"5 48.5 41'0 42.5 36'5 47.2
a a b bc bc c
Without p r e d a t o r Difference4: 39.0 a 37.5 a 25.0 b 21.0 b 19.5 b 12'5 c 25.8
19.0" * 19.0"* 23"5** 20.0** 23.0** 24"0** 36.5
t Mortality was recorded at 10 days after infestation. Analysis is based on values transformed to arcsin if-x/100. In a column, means followed by a common letter are not significantly different at the 5% level by Duncan's multiple range test (Gomez and Gomez, 1984). * * =significant at the 1% level.
TABLE 6. S. furcifera p o p u l a t i o n as affected by levels o f varietal resistance a n d P. fuscipes predation. I R R I g r e e n h o u s e , 1984
S. furcifera m o r t a l i t y ( % ) t Cuhivar IR2035-117-3 W C 1240 Colombo A R C 10239 N22 TN1 Predator means
With predator 65"0 62"5 49-5 51.0 41.0 42.0 51 • 8
a a b b c c
Without p r e d a t o r Difference# 37-5 a 34-0 a 22.5 b 1 9 . 5 bc 16.5 c 8"5 d 23.1
27.5** 28"5** 27.0** 31.5"* 24.5** 33.5** 28.8
t Analysis is based on values transformed to arcsin if-x/100. In a column, means followed by a common letter are not significantly different at the 5°70 level by Duncan's multiple range test (Gomez and Gomez, 1984). Average of four replications. * * =significant at the 1°70level.
M. SALIMAND E. A. HEINRICHS
P. fuscipes Without P. fuscipes, mortality of S furcifera nymphs at 10 days after infestation was significantly highest on IR2035-117-3 and WC 1240 at 38% and 34% respectively, intermediate on Colombo, ARC 10239 and N22, and lowest (9%) on T N I (Table 6). There was about a 30% increase in mortality when the predator P. fuscipes was added to the caged plants and the combined effect of predation and varietal resistance resulted in 65°70 mortality on IR2035-117-3 and 42°70 on TN1. Conclusions
The highly resistant cv. IR2035-117-3 and the resistant cvs WC 1240, Colombo, ARC 10239 and N22 all had a significant impact on S. furcifera populations. The degree of mortality depended on the stage of S. furcifera which was exposed. When predation was combined with the effect of varietal resistance, S. furcifera mortality increased for the four predators tested. Increase in mortality due to predators was generally 30% for all predator species. The additive effect of varietal resistance and predation in the integrated control of S. furcifera is expected to be an effective means of managing S. furcifera populations. It is important that these predators, which are abundant in rice fields in tropical Asia, should be conserved through the judicious use of insecticides. Although S. furcifera-resistant cultivars have not been released, breeding lines are currently being tested. When resistant cultivars are released for commercial cultivation, the integrated effect of varietal resistance and predation is expected to provide effective control of S. furcifera populations. References ADKISSON, P. L. AND DYCK, V. A. (1980). Resistant varieties in pest management systems. In Breeding Plants Resistant to Insects, pp. 233-252 (ed. by F. G. Maxwell and P. R. Jennings). New York: John Wiley and Sons. ANGELES, E. R., KHUSH, G. S. AND HEINRICHS,E. A. (1981). New genes for resistance to whitebacked planthopper in rice. Crop Science 21, 47-50. CHANDRA, G. (1978). Natural enemies of rice leaflaoppers and planthoppers in the Philippines. International Rice Research Newsletter 3(5), 20-21. DE BACH, P. (1974). Biological Control by Natural Enemies. Cambridge: Cambridge University Press. 323 pp. DYCK, V. A., KAMAL,N. Q., KENMORE, P. E., DULAY,A. C. AND PALLS, F. V. (1981). Suppression of planthopper and leafhopper populations by natural enemies, especially predators. Presented at IRRI Saturday Seminar, 25 April 1981, Inter-
national Rice Research Institute,
Los Ba~os, Philippines
(mimeograph, 12 pp.). GOMEZ, K. A. AND GOMEZ, A. A. (1984). Statistical Procedures for Agricultural Research, 2nd edn. New York: John Wiley and and Sons. 680 pp. HEINRICHS, E. A. AND RAPUSAS,H. R. (1983). Levels of resistance
399
to the whitebacked planthopper, Sogatella furcifera (Homoptera: Delphacidae) in rice varieties with different resistant genes. Environmental Entomology 12, 1793-1797. HEINRICHS, E. A., MEDRANO, F. G. AND RAPUSAS,H. R. (1985). Genetic Evaluation for Insect Resistance in Rice. Los Bafios, Laguna, Philippines: International Rice Research Institute. 356 pp. HEINRICHS, E. A., MEDRANO, F. G., RAPUSAS, H. R., VEGA, C. R., MEDINA, E., ROMENA, A., VIAJANTE,V., SUNIO, L., DOMINGO, F. AND CAMANAG, E. (1985). Resistance of IR varieties IR5 to IR62 to rice insect species. International Rice Research Newsletter, in press. HERNANDEZ, J. E. AND KHUSHz, G. S. (1981). Genetics of resistance to whitebacked planthopper in some rice varieties. Oryza 18, 48-50. HINCKLEY, A. D. (1963). Ecology and control of rice planthoppers in Fiji. Bulletin of Entomological Research 54, 467-481. IRRI (1984). International Rice Research Institute Annual Report for 1983. Los Bafios, Laguna, Philippines. 494 pp. KAMAL, N. Q. (1981). Suppression of IVhitebacked Planthopper, Sogatella furcifera (Horv6th) and Rice Leaffolder, Cnaphalocrocis medinalis (Guende), Populations by Natural Enemies. PhD thesis, Gregorio Araneta University, Manila, Philippines. 179 pp. KARTOHARDJONO, A. AND HEINRICHS, E. A. (1984). Populations of the brown planthopper, Nilparvata lugens (Still) (Homoptera: Delphacidae) and its predators on rice varieties with different levels of resistance. Environmental Entomology 13, 359-365. KAWAHARA,S., KIRITANI, K., SASALEA,T., NAKASUJI, F. AND OKUMA, C. (1969). Seasonal changes in abundance and faunal composition of spiders in the paddy fields with special reference to their relation to the seasonal prevalence of the rice green leafhopper, Nephotettix cincticeps Uhler. Proceedings of the Association for Plant Protection, Sikoku 4, 33-44. KHAN, Z. R. AND SAXENA, R. C. (1985). A selected bibliography of the whitebacked planthopper, Sogatella furcifera (Horv~th) (Homoptera: Delphacidae). Insect Science Applications 6, in press. KOGAN, M. (1982). Plant resistance in pest management. In: Introduction to Insect Pest Management, pp. 103-147 (R. L. Metcalfand W. H. Luckman, eds). New York: John Wiley and Sons. 587 pp. MANLEY, G. V. (1977). Paederus fuscipes (Col. Staphylinidae): a predator of rice fields in West Malaysia. Entomophaga 22, 47-49. MAXWELL, F. G. (1972). Morphological and chemical changes that evolve in the development of host plant resistance to insects. Journal of Environmental Quality 1(3), 265-270. MOCHIDA, O., PERFECT, T. J., DYCK, V. A. AND MAHAR, M. M. (1982). The whitebacked planthopper, Sogatella furcifera (Horvfith) (Homoptera: Delphacidae), its pest status and ecology in Asia. Presented at International Rice Research
Conference, 19-23 April 1982. International Rice Research Institute, Los Ba~os, Laguna, Philippines (mimeographed). NASU, S. (1967). Rice leafhoppers. In: The Major Insect Pests of Rice Plants, pp. 493-523. Baltimore: John Hopkins Press. 729 pp. PATHAK, M. D. (1968). Ecology of common pests of rice. Annual Review of Entomology 13, 257-296. SIDHU, G. S., KHUSH, G. S. AND MEDRANO, F. G. (1979). A dominant gene in rice for resistance to whitebacked planthopper and its relationship to other plant characteristics. Euphytica 28, 227-232.
Accepted 31 January 1986
Impact of varietal resistance in rice and predation on the mortality of Sogatella furcifera (Horvhth) (Homoptera: Delphacidae) M . SALIM AND
E. A. HEINRICHS*
International Rice Research Institute, PO Box 933, Manila, Philippines Highly resistant, resistant and susceptible rice cuhivars were tested in the greenhouse to determine their effect on Sogatella furcifera (Horvfith) populations. The highly resistant cultivar IR2035-117-3, with resistance genes IVbph 1 and IVbph 2, caused the highest S. furcifera mortality. When the effects of varietal resistance and predation were combined the increase in mortality due to predators was additive. The spider Lycosa pseudoannulata Boes. et Str., mirid bug Cytorhinus lividipennis Reuter, ladybird beetle Harmonia oetomaculata(F.) and rove beetle PaederusfuscipesCurt. were effective predators ofS. furcifera and generally caused 30% mortality on the various cultivars. Results indicate that the integration of varietal resistance and predation would provide effective control of S. furcifera populations under field conditions. ABSTRACT.
Introduction
The whitebacked planthopper, Sogatella furcifera (Horvfath) (Delphacidae: Homoptera) is distributed throughout South, South-East and East Asia (Nasu, 1967). S. furcifera is emerging as a serious pest of rice in many Asian countries, especially in areas where varieties resistant to Nilaparvata lugens have been grown successfully (Heinrichs and Rapusas, 1983; Khan and Saxena, 1985). Outbreaks ofS. furcifera in Asia have recently been reported in Pakistan, Bangladesh, Nepal, India, Vietnam, Malaysia and Indonesia (Mochida et al., 1982). Both nymphs and adults of the pest suck sap from leaves and leaf sheaths, which results in yellowing of leaves, reduced tillering and plant height and an increase in the percentage of unfilled grains. High populations of S. furcifera cause hopperburn (Pathak, 1968). S. furcifera has not been reported to transmit rice diseases, but feeding punctures and ovipositional injuries predispose rice plants to bacterial and fungal diseases and honeydew excretion encourages sooty mould. Using the seedbox screening test, more than 53 000 rice accessions from the International Rice Research Institute (IRRI) germplasm collection from throughout the world have been screened for resistance to S. furcifera. Out of these, nearly 400 accessions have been found to be resistant to S. furcifera at the seedling stage (Heinrichs, Medrano and Rapusas, 1985).
Genetic analysis of resistant cultivars indicated four dominant genes, designated Wbph 1, Wbph 2, Wbph 3, and Wbph 5, and one recessive gene (wbph 4) (Sidhu, Khush and Medrano, 1979; Angeles, Khush and Heinrichs, 1981; Hernandez and Khush, 1981; IRRI, 1984). No cultivar with a high level of resistance to S. furcifera has been released for commercial cultivation. However, four of the IR cultivars (IR48, IR52, IR60 and IR62) have moderate levels of resistance at IRRI (Heinrichs et al., 1985). In the management of S. furcifera populations, resistant cultivars should be integrated with other methods of pest control to achieve stable pest suppression. Resistant cultivars are compatible with biological control agents (Adkisson and Dyck, 1980). Predators help to control target as well as other pests to which the cultivar is not resistant (Maxwell, 1972). Plant resistance has no direct detrimental effect on predators (Kogan, 1982). Insects feeding on resistant cultivars often lack virility and are small in size and slow in development. Restless behaviour on resistant cultivars exposes insects more and increases their mortality due to predators (De Bach, 1974). Mortality of Nilaparvata lugens due to predators was comparatively higher on resistant than on susceptible cultivars (Kartohardjono and Heinrichs, 1984). Predators have been reported to be important in the regulation of rice planthopper populations (Hinckley,
* Present address: Department of Entomology, 402 Life Sciences Bldg., LSU Agricultural Center, Baton Rouge, Louisiana 70803, USA. 0261-2194/86/06/0395-05 $03.00 © 1986 Butterworth & Co (Publishers) Ltd
396
S. furcifera martality: impact of varietal resistance and predation
1963). The wolf spider Lycosa pseudoannulata Boes. et Str. (Lycosidae: Araneae) has a high pest-killing capacity and is considered to be one of the predominant spiders for the control of rice pests (Kawahara et al., 1969). The mirid bug Cyrtorhinus lividipennis Reuter (Hemiptera: Miridae) is considered to be mainly an egg predator ofS. furcifera but can feed on nymphs and adults as well (Kamal, 1981). C. lividipennis can destroy on average five eggs, one nymph and 0.6 adults of S. furcifera per predator per day (Dyck et al., 1981). The ladybird beetle Harmonia octomaculata (F.) (Coleoptera: Coccinellidae) is considered to be an important predator of rice hoppers including S. furcifera (Kamal, 1981; Hinckley, 1963; Chandra, 1978). The rove beetle Paederus fuscipes Curt. (Coleoptera: Staphylinidae) is a voracious feeder on hoppers and has a high searching ability (Manley, 1977). Bearing in mind the importance of host-plant resistance and of predators as two components in integrated control, studies were conducted to determine their impact on the mortality orS. furcifera. Materials and m e t h o d s
The effect on the mortality of S. furcifera of the predators L. pseudoannulata, C. lividipennis, H. octomaculata, and P. fuscipes, on rice cultivars with different levels of S. furcifera resistance, was determined in separate tests conducted in a greenhouse at IRRI, Los Bafios, Laguna, Philippines. Experiments were laid out in a randomized complete block design with four replications. Treatments of each experiment consisted of one predator and six rice cultivars: these were IR2035-117-3, highly resistant with two genes Wbph 1 and Wbph 2; WC 1240, resistant with Wbph 1 + 1 recessive gene; Colombo, resistant with Wbph 2+ 1 recessive gene; ARC 10239, resistant with the Wbph 2 gene; N22, resistant with the Wbph 1 gene, and TN1, susceptible (Heinrichs and Rapusas, 1983). Seeds of selected rice cultivars were sown in soil in seedboxes. One week after sowing, seedlings were transplanted into soil in clay pots (14cm diameter) at the rate of four plants per pot. At 25 days after transplanting (DT) all insects and natural enemies were removed and rice plants were covered with Mylar film cages ( l l c m × 1 0 8 c m ) . After 5 days the plants were again checked for the presence ofarthropods and then the predator and prey (S. furcifera) were released in the cages. S. furcifera mortality was determined by counting the number of live insects. Total mortality of S. furcifera was based on a combination of that caused by the predator and varietal resistance. Mortality due to varietal resistance was based on mortality in cages without the predator.
aeration. Moisture was supplied on small swabs of cotton. After the last moult, spiders of uniform age were used for the feeding studies.
Test 1. Sixteen freshly emerged S. furcifera brachypterous female adults and one L. pseudoannulata were released per cage. Observations on the mortality orS. furcifera with and without L. pseudoannulata were recorded daily and continued for 10 consecutive days. The predator, if dead, and all S. furcifera adults were replaced after each observation. Test 2. Fifty S. furcifera adults (brachypterous females) and one L. pseudoannulata adult were released per cage. Observations on the mortality ofS. furcifera were recorded at 4 days after infestation. Three separate trials were conducted by using fresh prey and predators on fresh plants for each trial. H. octomaculata Pupae of H. octomaculata were collected from the rice field at IRRI and kept in a cage in the laboratory. Moisture was supplied with wet cotton swabs. Adults of uniform age were used for predation studies.
Test 1. Four H. octomaculata adults and ten S. furcifera adults (brachypterous females) were released per cage. Observations on the mortality ofS. furcifera were recorded daily. All prey were replaced after each observation.
Test 2. Forty S. furcifera adults (female) and two H. octomaculata adults were placed in each cage. Observations on the mortality of S. furcifera were recorded at four days after infestation. Three separate trials were conducted by using fresh prey and predators on fresh plants for each trial. The cultures of C. lividipennis and S. furcifera were maintained in the greenhouse. Fifty first-instar S. furcifera nymphs and four C. lividipennis adults were released per cage. Mortality of S. furcifera was recorded 10 days after infestation. Both prey and predators were collected from the cages at 10 days after infestation and transferred into labelled glass tubes. S. furcifera were counted in the laboratory and mortality was calculated. P. fuscipes Fifty first-instar S. furcifera nymphs and four P. fuscipes adults were released per cage. Mortality of S. furcifera was recorded 10 days after infestation. Results and discussion
L. pseudoannulata
Last-instar spiderlings of L. pseudoannulata were collected from the screenhouse at IRRI and kept singly in glass tubes, covered with caps having small holes for
L. pseudoannulata In test 1 where all S. furcifera were replaced daily to maintain a population of 16 adults, the effect of varietal
M. SALIMAND E. HEINRICHS
397
TABLE 1. Predation efficiency ofL. pseudoannulata against S. furclfera on rice cultivars with different levels o f resistance. IRRI greenhouse, 1984
S. furcifera mortality (%)t Days after infestation
IR2035-117-3
WC 1240
31-2a (a) 2.8 c(b) 28-1a (a) 14.1 bc(b) 2 3 . 4 a b (a) 2 5 ' 0 a b (ab) 9.4 c(b) 29.7a (a) 15.6 bc(c) 26.6a (a)
25'0ab (ab) 23.4abc (a) 7.8 d(b) 32"8a (a) 12.5 cd(ab) 32"2a (a) 14.1 bcd(b) 14-1 bcd(b) 25.0ab (ab) 14"1 bcd(b)
Colombo
ARC 10239
N22
TN 1
21"gabc(ab) 17-2abc(ab) 10.9 c(b) 2 1 ' 9 a b (ab) 15'6abc(ab) 23"4ab (ab) 12.5 bc(b) 28.1 a (a) 20"3abc(abc) 18.8abc(ab)
20.3abc(ab) 14.1 bc(ab) 10.9 c(b) 23-4ab (ab) 10.9 c(b) 9-4 c(c) 29-7a (a) 15.6 bc(b) 14.1 bc(bc) 31.2a (a)
17.2abc(b) 9.4 c(b) 17-2abc(ab) 14.1 bc(b) 15.6 bc(ab) 2 3 . 4 a b (ab) 2 3 . 4 a b (a) 14.1 bc(b) 29.7a (a) 9.4 c(b)
Varietal resistance + predation 1
2 3 4 5 6 7 8
9 10
14"1 b (b) 12"5 b (ab) 15.6ab (b) 23-4ab (ab) 12.5 b (ab) 15.6ab (bc) 25.0 bc(a) 2 0 . 3 a b (ab) 12.5 b (c) 28.1a (a)
Predation (with L. pseudoannulata - without L. pseudoannulata)t 1 2 3 4 5 6 7 8 9 10
26.5** 3' 1 NS 18.7"* 7"9* 18"7"* 20-3** 3"2 NS 20-3** 7-8 NS 18"8"*
20'3** 17.2"* 1'6 NS 26"6** 6"3* 23'4** 9"4* 11'0"* 18"8"* 6"3 NS
1l'0"* 6' 3 NS 10'9"* 15"6"* 7"8** 10"9"* 23"4** 14-1 ** 7"8* 23"4**
17-2"* 12.5"* 6'2 NS 18"8"* 12.5"* 18.7"* 6'3 NS 25.0** 15.6"* 14'1"*
17.2"* 8.2 NS 6-2* 20"3** 7'8** 6"3* 25"0** 10.9"* 9.4"* 28'1 **
15-6"* 4.7 NS 17.2 ~* 11.0"* 14'0"* 17"2 "* 20"3** 9"4** 26"6 ** 4'7 NS
tAnalysis is based on values transformed to arcsin ~/-x+ 0.5. In a column, and in a row (in parentheses) means followedby a common letter are not significantlydifferent at the 5oA level by Duncan's multiple range test (Gomez and Gomez, 1984). Average of four replications. *NS=non-significant; * =significant at 5% level; * * =significant at 1% level.
resistance did not have sufficient time to be an important factor in S. furcifera mortality (Table 1). Average mortality over the 10-day period on the highly resistant cv. IR2035-117-3 was 21% whereas in susceptible TN1 it was 17%. To calculate the extent of the effect of predation on the total mortality (varietal resistance + predation) the mortality without L. pseudoannulata was subtracted from the mortality with L. pseudoannulata (Table 1). The degree of S. furcifera mortality attributable to predation ranged from 3% to 27% on a daily basis and was significantly higher than the mortality without L. pseudoannulata in most cases. In test 2, where S. furcifera mortality was recorded four days after infestation, there was sufficient time for the adverse effect of the resistant cultivars to be observed. Results of the three trials were similar (Table 2). Mortality of S. furcifera when caged in the absence of the predator was highest (74-78%) on the highly resistant cv. IR2035-117-3 and lowest (8-10%)
on susceptible TN1. Mortality in the resistant cvs WC 1240, ARC 10239 and Colombo was intermediate, ranging from 53% to 62%. On the basis of the results of the three trials, it is evident that when one predator was added to the cage of 50 S. furcifera adults, S. furcifera mortality in a 4-day period increased from 10% to 33% on the various cultivars (Table 2). The increase was simply an additive effect and there was no evidence of a higher predation rate on the highly resistant cultivar compared with the resistant or susceptible cultivars. In fact, the mortality increased 33% when the predator was added to the susceptible TN1 cages, whereas the increase was 19% on the higly resistant cv. I R 2 0 3 5 117-3.
H. octomaculata Prey mortality in test 1 was little affected by the level of resistance of the various cultivars because all prey
TABLE 2. S. furczfera mortality due to varietal resistance and L. pseudoannulata predationt. IRRI greenhouse, 1985
S. furcifera mortality (%) Trial II
Trial I
Cuhivar IR2035-117-3 WC 1240 Colombo
ARC 10239
N22 TN1
With predator
Without predator
96a 82 b 80 b 77 b 78 b 43 d
78 b 60 c 56 cd 53 cd 54 cd 10 e
With predator
96a 84 b 82 b 80 b 80 b 42
e
Trial III
Without predator
With predator
Without predator
74 bc 61 d 62 cd 56 d 57 d 8 f
96a 82 b 80 b 77 b 78 b 43 d
78 b 60 c 56 c 53 cd 54 cd 10 e
t Analysisis based on values transformed to arcsin ~/-xwhere N = 50. All means in two columns within each trial (with predator and without predator) followed by a common letter are not significantly different at the 5% level by Duncan's multiple range test (Gomez and Gomez, 1984).
398
S. furcifera mortality: impact of varietal resistance and predation
TABLE 3. S. furc(fera p o p u l a t i o n as affected b y levels o f varietal resistance a n d H. octomaculata predation. I R R I g r e e n h o u s e , 1984
S. furcifera m o r t a l i t y ( % ) / d a y t Cultivar IR2035-117-3 W C 1240 Colombo A R C 10239 N22 TN1
With predator
Without p r e d a t o r Difference:l:
39.0 a 39.5 a 38.0 a 36.5 a 37.5 a 39.0a
6.8 5.8 6"0 5.2 5.0 3.8
a ab a ab ab b
32' 2 * * 33.7** 32"0** 31-3** 32"5** 35"2**
t
Data are averages of 10 days' observations. Analysis is based on values transformed to arcsin fix/100. In a column, means followed by a common letter are not significantly different at the 5°70level by Duncan's multiple range test (Gomez and Gomez, 1984). Average of four replications. :1: * * =significant at the 1% level. TABLE 4.
the other cultivars. Mortality on Colombo, ARC 10239 and N22 was intermediate. In the presence of the predator C. lividipennis there was a simple additive effect; the increase in mortality due to predation was 19-24% on the various cultivars (Table 5). These results agree with those of Kartohardjono and Heinrichs (1984), who reported that resistant cultivars did not increase the predation rate ofC. lividipennis over that on susceptible cultivars. The feeding rate of C. lividipennis of 0.4 nymphs per day was lower than that observed in previous studies (Dyck et al., 1981). However, the differences may have been due to a different age of prey, and different prey:predator ratio.
S. furcifera m o r t a l i t y d u e to varietal resistance a n d H. octomaculata p r e d a t i o n t . I R R I greenhouse, 1985 S. furcifera m o r t a l i t y (%) Trial I
Cultivar IR2035-117-3 WC1240 Colombo A R C 10239
N22 TN1
With predator 98 81 81 84 81 46
a b b b b f
T r i a l II
Without predator 72 50 54 59 55 10
c ef def d de g
With predator 98 81 80 84 81 46
T r i a l III
Without predator
a b b b b e
With predator
69 c 52 de 54 de 60cd 55 de 12 f
99 81 80 84 80 48
a b b b b c
Without predator 79 b 49 c 53 c 56 c 56 c 11 d
t Analysis is based on values transformed to arcsin ~/-x where N = 40. All means in two columns within each trial (with predator and without predator) followed by a common letter are not significantly different at the 5% level by Duncan's multiple range test (Gomez and Gomez, 1984).
were replaced daily and there was not sufficient time for the resistance factors to act (Table 3). The combined mortality due to predation and varietal resistance was the same on all cultivars. Mortality with H. octomaculata was 37-39%. The increase in mortality with the predator was significant for all cultivars, being 31-35%. Prey mortality in the three trials of test 2 was recorded 4 days after infestation and thus there was a significant effect of varietal resistance on the S. furcifera population (Table 4). S. furcifera mortality without the predator on IR2035-117-3 ranged from 69% to 79% in the three trials, 49-60% on the resistant cultivars and 10-12% on TN1. S. furcifera mortality in the presence of the predator H. octomaculata increased by about 30% on all cultivars. Mortality on IR2035-117-3 was 98-99%, about 80% on WC 1240, Colombo, ARC 10239, and N22, and 46-48% on susceptible TN1. The combined prey mortality due to varietal resistance and predation on IR2035-117-3 was about twice that on TN1. C. lividipennis The mortality of S. furcifera nymphs at 10 days after infestation in the C. lividipennis test was lower than that of the adults at 4 days after infestation in the previous tests. However, there was an effect of varietal resistance on mortality, as indicated in the 'without predator' column in Table 5, mortality being significantly higher on IR2035-117-3 and WC 1240 than on
TABLE 5. Effect o f levels o f varietal resistance a n d C. h'vidipennis p r e d a t i o n on S. furcifera n y m p h s . I R R I g r e e n h o u s e , 1984
S. furcifera mortality ( % ) t Cultivar IR2035-117-3 W C 1240 Colombo ARC10239
N22 TN1 Predator means
With predator 58"0 56"5 48.5 41'0 42.5 36'5 47.2
a a b bc bc c
Without p r e d a t o r Difference4: 39.0 a 37.5 a 25.0 b 21.0 b 19.5 b 12'5 c 25.8
19.0" * 19.0"* 23"5** 20.0** 23.0** 24"0** 36.5
t Mortality was recorded at 10 days after infestation. Analysis is based on values transformed to arcsin if-x/100. In a column, means followed by a common letter are not significantly different at the 5% level by Duncan's multiple range test (Gomez and Gomez, 1984). * * =significant at the 1% level.
TABLE 6. S. furcifera p o p u l a t i o n as affected by levels o f varietal resistance a n d P. fuscipes predation. I R R I g r e e n h o u s e , 1984
S. furcifera m o r t a l i t y ( % ) t Cuhivar IR2035-117-3 W C 1240 Colombo A R C 10239 N22 TN1 Predator means
With predator 65"0 62"5 49-5 51.0 41.0 42.0 51 • 8
a a b b c c
Without p r e d a t o r Difference# 37-5 a 34-0 a 22.5 b 1 9 . 5 bc 16.5 c 8"5 d 23.1
27.5** 28"5** 27.0** 31.5"* 24.5** 33.5** 28.8
t Analysis is based on values transformed to arcsin if-x/100. In a column, means followed by a common letter are not significantly different at the 5°70 level by Duncan's multiple range test (Gomez and Gomez, 1984). Average of four replications. * * =significant at the 1°70level.
M. SALIMAND E. A. HEINRICHS
P. fuscipes Without P. fuscipes, mortality of S furcifera nymphs at 10 days after infestation was significantly highest on IR2035-117-3 and WC 1240 at 38% and 34% respectively, intermediate on Colombo, ARC 10239 and N22, and lowest (9%) on T N I (Table 6). There was about a 30% increase in mortality when the predator P. fuscipes was added to the caged plants and the combined effect of predation and varietal resistance resulted in 65°70 mortality on IR2035-117-3 and 42°70 on TN1. Conclusions
The highly resistant cv. IR2035-117-3 and the resistant cvs WC 1240, Colombo, ARC 10239 and N22 all had a significant impact on S. furcifera populations. The degree of mortality depended on the stage of S. furcifera which was exposed. When predation was combined with the effect of varietal resistance, S. furcifera mortality increased for the four predators tested. Increase in mortality due to predators was generally 30% for all predator species. The additive effect of varietal resistance and predation in the integrated control of S. furcifera is expected to be an effective means of managing S. furcifera populations. It is important that these predators, which are abundant in rice fields in tropical Asia, should be conserved through the judicious use of insecticides. Although S. furcifera-resistant cultivars have not been released, breeding lines are currently being tested. When resistant cultivars are released for commercial cultivation, the integrated effect of varietal resistance and predation is expected to provide effective control of S. furcifera populations. References ADKISSON, P. L. AND DYCK, V. A. (1980). Resistant varieties in pest management systems. In Breeding Plants Resistant to Insects, pp. 233-252 (ed. by F. G. Maxwell and P. R. Jennings). New York: John Wiley and Sons. ANGELES, E. R., KHUSH, G. S. AND HEINRICHS,E. A. (1981). New genes for resistance to whitebacked planthopper in rice. Crop Science 21, 47-50. CHANDRA, G. (1978). Natural enemies of rice leaflaoppers and planthoppers in the Philippines. International Rice Research Newsletter 3(5), 20-21. DE BACH, P. (1974). Biological Control by Natural Enemies. Cambridge: Cambridge University Press. 323 pp. DYCK, V. A., KAMAL,N. Q., KENMORE, P. E., DULAY,A. C. AND PALLS, F. V. (1981). Suppression of planthopper and leafhopper populations by natural enemies, especially predators. Presented at IRRI Saturday Seminar, 25 April 1981, Inter-
national Rice Research Institute,
Los Ba~os, Philippines
(mimeograph, 12 pp.). GOMEZ, K. A. AND GOMEZ, A. A. (1984). Statistical Procedures for Agricultural Research, 2nd edn. New York: John Wiley and and Sons. 680 pp. HEINRICHS, E. A. AND RAPUSAS,H. R. (1983). Levels of resistance
399
to the whitebacked planthopper, Sogatella furcifera (Homoptera: Delphacidae) in rice varieties with different resistant genes. Environmental Entomology 12, 1793-1797. HEINRICHS, E. A., MEDRANO, F. G. AND RAPUSAS,H. R. (1985). Genetic Evaluation for Insect Resistance in Rice. Los Bafios, Laguna, Philippines: International Rice Research Institute. 356 pp. HEINRICHS, E. A., MEDRANO, F. G., RAPUSAS, H. R., VEGA, C. R., MEDINA, E., ROMENA, A., VIAJANTE,V., SUNIO, L., DOMINGO, F. AND CAMANAG, E. (1985). Resistance of IR varieties IR5 to IR62 to rice insect species. International Rice Research Newsletter, in press. HERNANDEZ, J. E. AND KHUSHz, G. S. (1981). Genetics of resistance to whitebacked planthopper in some rice varieties. Oryza 18, 48-50. HINCKLEY, A. D. (1963). Ecology and control of rice planthoppers in Fiji. Bulletin of Entomological Research 54, 467-481. IRRI (1984). International Rice Research Institute Annual Report for 1983. Los Bafios, Laguna, Philippines. 494 pp. KAMAL, N. Q. (1981). Suppression of IVhitebacked Planthopper, Sogatella furcifera (Horv6th) and Rice Leaffolder, Cnaphalocrocis medinalis (Guende), Populations by Natural Enemies. PhD thesis, Gregorio Araneta University, Manila, Philippines. 179 pp. KARTOHARDJONO, A. AND HEINRICHS, E. A. (1984). Populations of the brown planthopper, Nilparvata lugens (Still) (Homoptera: Delphacidae) and its predators on rice varieties with different levels of resistance. Environmental Entomology 13, 359-365. KAWAHARA,S., KIRITANI, K., SASALEA,T., NAKASUJI, F. AND OKUMA, C. (1969). Seasonal changes in abundance and faunal composition of spiders in the paddy fields with special reference to their relation to the seasonal prevalence of the rice green leafhopper, Nephotettix cincticeps Uhler. Proceedings of the Association for Plant Protection, Sikoku 4, 33-44. KHAN, Z. R. AND SAXENA, R. C. (1985). A selected bibliography of the whitebacked planthopper, Sogatella furcifera (Horv~th) (Homoptera: Delphacidae). Insect Science Applications 6, in press. KOGAN, M. (1982). Plant resistance in pest management. In: Introduction to Insect Pest Management, pp. 103-147 (R. L. Metcalfand W. H. Luckman, eds). New York: John Wiley and Sons. 587 pp. MANLEY, G. V. (1977). Paederus fuscipes (Col. Staphylinidae): a predator of rice fields in West Malaysia. Entomophaga 22, 47-49. MAXWELL, F. G. (1972). Morphological and chemical changes that evolve in the development of host plant resistance to insects. Journal of Environmental Quality 1(3), 265-270. MOCHIDA, O., PERFECT, T. J., DYCK, V. A. AND MAHAR, M. M. (1982). The whitebacked planthopper, Sogatella furcifera (Horvfith) (Homoptera: Delphacidae), its pest status and ecology in Asia. Presented at International Rice Research
Conference, 19-23 April 1982. International Rice Research Institute, Los Ba~os, Laguna, Philippines (mimeographed). NASU, S. (1967). Rice leafhoppers. In: The Major Insect Pests of Rice Plants, pp. 493-523. Baltimore: John Hopkins Press. 729 pp. PATHAK, M. D. (1968). Ecology of common pests of rice. Annual Review of Entomology 13, 257-296. SIDHU, G. S., KHUSH, G. S. AND MEDRANO, F. G. (1979). A dominant gene in rice for resistance to whitebacked planthopper and its relationship to other plant characteristics. Euphytica 28, 227-232.
Accepted 31 January 1986