ABSTRACT

Population dynamics of two species of aphids, i.e., Lipaphis erysimi and Myzus persicae were studied on six species of Brassicas i.e., Brassica campestris, Brassica juncea, Brassica carinata, Brassica napus, Synapsis alba and Eruca vasicaria from 1992-93 to 1997-98 at Bathinda Punjab. The data on population of the aphids on leaves as well as flowers was recorded at weekly to fortnightly intervals. The aphid individuals appeared on various species in first week of January and population peaks reached in end February to mid March. In different years, on different species the peak population of both the aphids were recorded mostly in the same observations, showing that the same environmental factors regulate the population build up of both the species. The aphids L. erysimi and M. persicae are earlier reported to be having maximum population on B. compestris and E. vasicaria respectively. But during the present investigation, their peak populations were observed on other species also in many years indicating that the population build up of the species is regulated more by plant phenophase specific factors than plant species specific factors. The most suitable stage of plant for aphid population build up was seen to be the flowering stage. Similar trends of population build up of both the aphid species on different Brassicas on same plant parts indicate that these species during evolution have adapted to inhabit the same nich with minimum competition.

INTRODUCTION

The aphids are the most destructive pests of rapeseed mustard in India. Its nymphs and adults suck sap from leaves, stem, flowers and pods resulting in poor pod formation and reduced oil content in grains. Under severe aphid attack the loss may be as high as 75.7% (Sekhon et al., 1996). In Punjab two species of aphids appear on Brassicas, i.e., Lipaphis erysimi and Myzus persicae. Different species of aphids are reported to have different growth pattern on different Brassica cultivators (Ronquist and Ahman,1990). These two species of aphids are also reported to have differential preferences for different species of Brassica. The most preferred reported host of M. persicae is Eruca vasicaria and of L.erysimi, Brassica campestris. In the present study the population dynamics of the two aphids was studied on six species of closely related Crucifers.

MATERIAL AND METHODS

Six species of Crucifers i.e., Brassica campestris, Brassica juncea, Brassica carinata, Brassica napus, Synapsis alba and Eruca vasicaria were sown in thrice replicated randomized block design in the normal sowing time i.e., third week of October to first week of November in each year and raised as per the recommendations of Punjab Agricultural University except that the trial was kept unsprayed. The population of the aphids was recorded from ten plants in each replication and from each plant 3 leaves and 10cm top of central shoot was observed at weekly to fortnightly interval. The mean population on leaves and flowers based on these 90 leaves and 30 shoots were calculated.

RESULTS AND DISCUSSION

The aphid individuals appeared on various species in first week of January and population peaks reached in end February to mid March. In different years, on different species the peak population of both the aphids were recorded mostly in the same observations, out of 63 pairs of maximum population observations related with L. erysimi and M. persicae (Table 1), in 35 pairs the two species reached the peak population at the same date, in rest of the pairs in 18, M. persicae and in 10, L. erysimi population peaks were earlier. But even in almost all the cases the difference in period of peak population was not more than one week. It shows that the same environmental factors regulate the population build up of both the species.

The trial was sown in end October or first week of November and in all the years B. campestris was having flowers from mid of January to mid of February, B. juncea and E. vasicaria from first week of Feb. to first week of March and S. alba, B. carinata and B. napus started flowering in third week of February which remained up to third week of March on napus and up to end of March in alba and carinata . Normally during the period of study the environmental conditions were favorable for aphids late in the season i.e., middle of March and these coincided with the flowering of late maturing types. The maximum population was observed in these varieties (Table 2), though the earlier reported well known susceptible species B. campestris was also sown in the trials, in most of the years, it escaped the aphid attack. It was only during 1996-97 when the population peaks were earlier that the earlier reported favorable species of the aphids i.e. B. campestris for L. erysimi and E. vasicaria for M. persicae supported maximum population of the aphids. It shows that the population build up of the species is regulated more by plant phenophase specific factors than plant species specific factors. The most suitable stage of plant for aphid population build up was seen to be the flowering stage. Peak population of both these species reached at the same time on leaves and flowers.

Various studies on growth of different species of aphids on different Brassica cultivators have shown different growth pattern on different Brassica cultivators (Ronquist and Ahman,1990). L. erysimi is reported to be having better growth on B. campestris than on B. juncea (Weibulls and Melin, 1990) But in this case these field studies show similar trends of population build up of both the aphid species on different crucifers on same plant parts though with different magnitudes, indicating that these species during evolution have adapted to inhabit the same nich with minimum competition. and that M. persicae and L. erysimi are both oligophagus, adapted during evolution to feed on many types of crucifers and their population build up on different species is governed more by coincidence of favorable environmental conditions with plant phenophase and less by the genetic differences between different related group of species of crucifers. Thus any genotype in which peak flowering coincides with favorable environmental conditions of the aphids would be heavily infested and its yield reduced drastically.

Table 2. Species supporting maximum and minimum population at peak infestations of Lipaphis erysimi and Myzus persicae in different years.

Year	Pest	Maximum population*						Minimum population
		on leaves			on flowers			on leaves		on flowers
		W/M**	Population	Species	W/M	Population	Species	Population	Species	Population	Species
92-93	L***	1 M	321.0	S. alba	1 M	161.9	S. alba	0.0	B. campestris	15.2	B. juncea
D1@	M	1 M	12.2	S. alba	1 M	3.2	S. alba	2.4	B. napus	0.5	B. juncea
92-93	L	3 M	245.5	S. alba	4 F	163.5	S. alba	72.0	B. napus	31.5	B. campestris
D2	M	3 M	62.2	S. alba	3 M	10.0	B. carinata	22.2	B. napus	0.0	B. juncea
93-94	L	3 M	5.5	S. alba	3 M	48.0	S. alba	0.0	B. campestris	0.0	E. vasicaria
	M	3 M	55.1	B. carinata	3 M	14.4	E. vasicaria	0.9	B. campestris	5.8	B. carinata
94-95	L	1 A	4.1	S. alba	1 A	4.1	S. alba	0.0	B. campestris	0.0	B. campestris
	M	4 M	29.3	S. alba	2 M	43.5	S. alba	0.6	B. campestris	0.3	B. carinata
95-96	L	2 M	8.2	B. carinata	2 M	13.4	B. napus	0.2	E. vasicaria	0.2	E .vasicaria
	M	2 M	59.6	B. alba	4 F	42.8	E .vasicaria	17.2	E. vasicaria	0.9	B.carinata
96-97	L	-	-	-	2 F	68.0	B. campestris	-	-	0.0	B. carinata
	M	-	-	-	2 F	22.2	E. vasicaria	-	-	0.0	B. carinata
97-98	L	-	-	-	3 M	226.7	S. alba	-	-	5.5	E. vasicaria
	M	-	-	-	2 M	64.4	S. alba	-	-	2.8	B. carinata

* Number of aphids per 3 leaves or per 30 cm top of central shoot for flowers. **W/M = week /month, as 1M= first week of march, F= February, A= April

*** L = Lipaphis erysimi M= Myzus persicae . @ In the year two trials were laid D1 early and D2 was late sown

Table 1. Period of peak population of L.erysimi and M. persicae on different varieties in various years

Year		Aphid Species						Cruciferous Species
		B.campestris		B. juncea		B. napus		B.carinata		S.alba		E .vasicaria
		W/M**	Max pop*	W/M	Max pop	W/M	Max Pop	W/M	Max Pop	W/M	Max Pop	W/M	Max pop
								on leaves
92-93	L***	2F	0.01	1M	57.3	1M	20.8	1M	57.6	1M	321.0	-	-
D1@	M	-	0.0	1M	4.9	1M	2.4	1M	3.2	1M	12.2	-	-
92-93	L	4 F	22.7	3M	147.5	3M	72.0	3M	137.9	3M	245.5	-	-
D2	M	4F	1.2	3M	24.7	3M	22.2	3M	110.7	3M	186.6	-	-
93-94	L	1M	1.5	1M	1.0	1M	2.8	3M	3.5	3M	5.5	3M	0.9
	M	3M	0.9	3M	33.8	3M	21.6	3M	55.1	3M	25.5	3M	6.3
94-95	L	-	0.0	4M	0.9	4M	1.3	1A	2.1	1A	4.1	1A	0.6
	M	2M	0.8	4M	24.0	4M	9.1	4M	17.1	4M	29.3	4M	1.1
95-96	L	2M	1.9	2M	4.4	4M	3.9	2M	8.2	2M	4.9	2M	0.2
	M	2M	26.2	2M	37.7	2M	30.1	2M	38.0	2M	59.6	4F	28.3
								on flowers
92-93	L	1M	18.9	1M	15.2	1M	78.8	1M	51.4	1M	161.9	-
D1	M	4 J	0.7	1M	0.5	1M	2.4	1M	3.7	1M	3.2	-
92-93	L	4F	31.5	4F	53.7	4F	44.4	3M	76.0	4F	163.5	-
D2	M	2F	2.0	3M	3.1	4F	1.7	3M	10.0	3M	9.0	-
93-94	L	3F	11.7	1M	2.3	3M	14.6	3M	14.9	3M	48.0	3M	0.5
	M	3M	7.9	3M	8.7	3M	6.5	3M	5.8	1M	6.9	3M	14.4
94-95	L	4M	0.1	1A	0.4	4M	0.7	1A	2.2	1A	4.1	1A	0.6
	M	2M	3.8	1A	32.3	4M	8.5	4M	11.0	2M	43.5	1A	7.9
95-96	L	2M	2.7	2M	2.9	2M	13.4	2M	7.4	2M	4.8	2M	1.7
	M	2M	20.8	2M	24.8	2M	12.3	2M	7.9	4F	41.1	4F	42.8
96-97	L	3F	68.0	3M	24.2	3M	29.4	2M	13.7	4F	14.1	3M	11.4
	M	3F	10.8	3F	13.0	4F	3.8	4F	1.9	4F	9.5	3F	22.2
97-98	L	1M	61.8	3M	168.2	3M	176.7	3M	127.0	3M	226.7	4M	5.5
	M	2M	19.5	4M	37.8	4M	46.7	2M	48.2	2M	64.4	4M	22.4

* Number of aphids per 3 leaves or per 30cm top of central shoot for flowers.

**W/M = week /month, as 1M= first week of march, F= February, A= April

*** L = Lipaphis erysimi M= Myzus persicae .

@ In the year two trials were laid D1 early and D2 was late sown

REFERENCES

1. Ronquist F. and Ahman A. 1990. Reproduction rate of Indian mustard aphid (Lipaphis erysimi pseudobrassicae) on different Brassica oilseeds: comparasions with Swedish strain of mustard (Lipaphis erysimi erysimi) and cabbage aphid (Brevicoryne brassicae). Annals of applied Biology. 116: 425-430.

2. Sekhon B. S., Bakhetia D.R.C. and Arora R. 1996. Yield losses due to mustard aphid, Lipaphis erysimi (Kaltenbach) in some Brassica species in the Punjab. Journal of aphidology. (In press).

3. Weibull J. and Melin G. 1990. Free amino acid content of phloem sap from Brassica plants in relation to the performance of Lipaphis erysimi (Hemiptera: Aphididae) . Annals of applied Biology. 116: 417-423.

PUNJAB AGRICULTURAL UNIVERSITY

REGIONAL RESEARCH STATION

BATHINDA

Dr B. S. Sekhon Dated: 26.3.99

Sr Entomologist (Professor)

Ref: 1480

Dr Mandy Smith

Conference coordinator

10^th International Rapeseed congress

C/- Australian Convention & Travel Services Pty Ltd

GPO Box 2200

Canberra ACT 2601

AUSTRALIA

Dear Dr Smith ,

RE: 10^TH INTERNATIONAL RAPESEED CONGRESS

Please find enclosed herewith my full paper accepted for poster presentation entitles `Population dynamics of Lipaphis erysimi and Myzus persicae on different species of Brassica’. I hope you will find it in order. One hard copy is being sent by a separate envelop and in this envelop one copy on floppy disc typed as per instructions are being sent.

From this station hard copies of two research papers by Dr S. S. Dhillon et al

related with breeding having reference numbers 1478 and 1479 were sent. Their files on floppy are also on this floppy disc.

Kindly acknowledge the receipt of the papers.

With best wishes and kind regards,

Yours sincerely,

(B. S. Sekhon)