Asian Journal of Plant Sciences

Year: 2003 | Volume: 2 | Issue: 12 | Page No.: 925-931
DOI: 10.3923/ajps.2003.925.931

Effects of Two Potential Pest Management Components, Intercropping and Yellow Sticky Plastic Sheet Traps in Two Differentially Resistant Potato Cultivars for the Management of Myzus persicae (Sulzer)

A.U.R. Saljoqi and H.F. Van Emden

Abstract: Polyculture is traditionally a low-input agricultural system and is important in many developing countries. Polycultures of interplanted crops often support fewer pests at lower densities than monoculture and tend to increase number of natural enemies. Also Yellow Sticky Plastic Sheet Traps have proved useful for trapping aphids. A field study was conducted to study the effectiveness of these potential pest management techniques along with the partially resistant (Cardinal) and susceptible (Desiree) potato cultivars, by using their different combinations for the management of Myzus persicae (Sulzer). Berseem, Trifolium alexandrinum (L.) (family: Leguminosae) was used for intercropping with potatoes. The different combinations (treatments) used in this study were: 1) Cardinal-berseem mixed cropping+yellow sticky plastic sheet traps 2) Cardinal-berseem mixed cropping 3) Cardinal+yellow sticky plastic sheet traps 4) Cardinal separately+berseem (as land area equivalents in relation to the mixed cropping treatments) 5) Cardinal (sole crop). Treatments 6-10 were the same treatments, but with Desiree as the potato cultivar. All these treatments were used to evaluate their effects as management techniques for M. persicae, their percent parasitism, percent emergence rate of the parasitoid, Aphidius matricariae Haliday and yield of Cardinal and Desiree. Mixed cropping of Cardinal and berseem together with the yellow sticky plastic sheet traps reduced aphids by over 90% compared with numbers on the sole Cardinal crop. This combination proved in this experiment the most effective for reducing the aphid populations as compared with all other treatments. Maximum percent parasitism i.e. 6.97 and 6.94% (almost double that in the other treatments) was recorded in the potato berseem mixed cropping, with and without traps respectively. In the same two treatments, yield was increased significantly as compared with all other treatments. However no significant effects of any of the variable was evident on the percent emergence of A. matricariae.

Keywords: Potato, berseem, mixed cropping, yellow sticky plastic sheet traps, Myzus persicae and aphidius matricariae

Introduction

Intercropping can play an important role in reducing insect pests infestation (Root, 1973; Potts, 1990). van Emden and Wratten (1990) have given a number of examples of the effect of intercropping on insect population densities. Intercropping may reduce pest damage by attracting pests to a less valuable crop or one where the pest is less serious (van Emden, 1989). The number of aphids on potatoes undersown with grass were found generally to be smaller than the aphid numbers on potatoes not undersown with grass (McKinlay, 1985). Smith (1976a) recorded a lower number of aphids and other pest insects in cabbage plots with weeds than in weed-free plots. However, oat suffer higher infestation by cereal aphids, when intercropped with faba bean (Helenius, 1990).

Diverse agroecosystem created by multiple cropping tend to increase numbers of natural enemies (Root, 1973; O’Donnel et al., 1975). Natural enemies are attracted to diverse systems of shelter, alternative prey, humidity and flowers (Dempster and Coaker, 1974; smith, 1976b). Andow (1983) reported that natural enemy population often increase and seldom decrease in polycultural systems. By contrast Risch et al. (1983) claimed that natural enemies are rarely responsible for the herbivore reductions, which often occur, in diversified systems.

Yellow traps have been used by different previous workers and were found very effective as a management technique for aphids (Broadbent, 1948; A’Brook, 1973). Many aphids are attracted to yellow colours (Moericke, 1950; Hottes, 1951)^. Zimmerman-Gries (1979) used sticky yellow polythene sheets around potato plots and reported a remarkable reduction in the spread of aphid-transmitted potato leaf roll virus. The same result was found by Rogerson (1975) when he compared two automobile greases as the adhesive on sticky traps for aphids and found that light yellow calcium grease was superior to darker lithium grease. The information regarding the use of Yellow sticky plastic sheet traps as a management technique for Myzus persicae (Sulzer) in the potato crop is still lacking.

Berseem, Trifolium alexandrinum (L.) belongs to the family Leguminosae, is a major fodder crop in Pakistan and it is grown at the same time as potatoes. Potato-berseem intercropping is a common practice in most of the areas in Pakistan. A field study was therefore conducted to explore the possibilities of reducing M. persicae populations on potatoes by studying the effectiveness of potato-berseem mixed cropping, land area equivalents in relation to the mixed cropping treatments and yellow sticky plastic traps as management techniques for populations of M. persicae, their percent parasitism, percent emergence rate of the parasitoid, Aphidius matricariae Haliday and yield of partially resistant (Cardinal) and susceptible (Desiree) potato cultivars.

Materials and Methods

This field experiment was laid out in a randomized complete block design on an area of 1667 m² (63.50x26.25 m) as 30 plots, representing 10 treatments in three replications, during the autumn of 1996. The size of each plot was 52.5 m². The following ten treatments were used.

Treatments 6-10 were the same treatments, but with Desiree as the potato cultivar.

In the intercropped plots the potato cultivars were mixed grown with berseem (no distinct rows for berseem). In the land area equivalents plot, the area of the plot was divided into two halves one of which was sown with potatoes and the other with berseem. Yellow sticky plastic sheet traps measuring 60x30 cm were fixed 1 m above the ground level. The traps were operated from emergence of the potato seedlings to harvest. One trap per plot was erected in the middle of each plot. Mobil engine oil (SAE 40/60) was used on these sheets as an adhesive. The aphids stuck to these traps were counted at weekly intervals. All the treatments were compared to the sole potato crop as the control.

The data recorded were: the number of M. persicae, percent parasitism, emergence rate of the parasitoid and yield of potatoes. When the aphid infestation started, aphids were counted at weekly intervals. Aphids were counted on six tagged leaves, two each in the top, middle and lower region of four randomly selected plants, avoiding the border rows, from each plot. The data were recorded on the same leaves on the different sampling occasions (Singh and Verma, 1985; Trivedi and Misra, 1989)^. Percent parasitism was recorded after every two weeks. Percent parasitism was recorded by collecting 50 leaves (fixed number) from each plot. The mummies were removed and the remaining aphids were counted and kept in polythene bags (32x46 cm) still on the leaves with two filter papers (11.0 cm) for absorbing condensation. After five days, which would have allowed parasitoids to develop to 4th and 5th instar nymphs and adult aphids to form mummies, the number of mummies formed was counted and the percentage parasitism was calculated by the following formula:

Percent emergence rate of the parasitoid was recorded once at the middle of the cropping season. Twenty mummies were collected from plants in each plot and placed in Petri-dishes, lined with filter papers. The Petri-dishes were covered and left in the laboratory. After ten days the number of emerged parasitoids, A. matricariae were recorded for each replicate and the percent adult emergence was calculated by using the following formula:

After hand harvesting the crop, the yield obtained was weighed separately for each plot in kg, which was then converted to t ha^-1. The data were analyzed by analysis of variance of Factorial Randomized Complete Block Design with repeated measures ‘split-plot in time’ approach (Mead et al., 1993) using ‘MSTAT-C’ computer programme and the means were compared by using Duncun’s Multiple Rang Test (DMRT) (Steels and Torrie, 1960).

The abbreviations used in this paper for the treatments to which the two potato cultivars were subjected are shown in Table 1.

Results

Population of M. persicae: Table 2 shows the means for the interaction of cultivarsxtreatments. The sole crop plots show as expected that Cardinal had fewer aphids than Desiree and this phenomenon was seen in the other treatments also. In some cases aphid numbers were half as large again on Desiree as on Cardinal, but the difference was fourfold with the combination of intercropping with traps, when very few aphids were found on Cardinal. All treatments gave significantly lower aphid numbers than the sole crop, but the effect of intercropping was significantly greater than the same two crops grown as land area equivalents.

The means for the interaction of cultivarsxtime intervals are given in Table 3. On both cultivars, the population of aphids increased with the passage of time up to a peak at week 7. The lowest number of aphids was recorded on the last week of the observations, after which the crop was harvested. The table also shows that again overall Cardinal had fewer aphids than Desiree.

The treatments also interacted with the time intervals (Table 4). All the treatments significantly depressed the aphids population compared with the control (P<0.05). Lower number of aphids was recorded initially in PB+YT followed by PB, P+YT and LAE and these numbers consistently increased with the passage of time up to week 7, when the highest number of aphids was recorded and the numbers then started to decline on each treatment respectively. Low numbers of aphids were recorded mostly in the last week of data recording.

Percent parasitism: Table 5 shows that the percent parasitism recorded on the intercrop, whether with or without traps was significantly higher than in all other treatments (P<0.05). The percent parasitism recorded on the intercrop was statistically higher than with land area equivalents, which gave no improvement in parasitism over the sole crops. There was a progressive increase in percent parasitism up to week 7 (P<0.05), which coincided with peak aphid numbers (Table 5).

Emergence of A. matricariae: Means for the effect of cultivars, treatments and their interactions are given in Table 6. No significant effects of any of the variables were evident.

Aphids on yellow sticky plastic sheet traps:In both PB+YT and P+YT, the number of aphids trapped on the YT increased with time up to a peak at week 7. The lowest numbers of aphids were recorded on the YT in both treatments on the last week of the observations (Table 7). These results seem to follow very closely the trend of the results described for the numbers of aphids recorded on the plants leaves at different time intervals. Fig. 1 shows the relationship of the number of aphids on the six leaves of the potato plants and on the yellow sticky plastic sheet traps in PB+YT and in P+YT at different time intervals (weeks). The model Y = 52.342X-9.9783 explained 86% variability. The t-test value (6.539) was significant at P<0.001. This suggested that there was a strong positive relationship between the number of aphids recorded on the YT and on the crop plants at different time intervals. For the number of aphids on the six leaves of the potato plants and on the yellow sticky plastic sheet traps in P+YT at different time intervals, the model Y = 33.486x-104.27 explained 96% variability. The t-test value (12.289) was significant at P<0.001, which also showed strong positive relationship.

Yield: Table 8 shows that PB+YT and PB had yields statistically inseparable from each other (P>0.05), but significantly higher than in all other treatments (P<0.05). Yellow traps gave some control but not as much as intercropping. The lowest yield was recorded from LAE, which was statistically similar to P (control) (P>0.05).

Discussion

The population of M. persicae was significantly reduced in all treatments compared to the sole crop, for both potato cultivars. PB+YT had up to 79% fewer aphids compared with the control and was the most effective treatment for reducing aphid populations in both cultivars, followed by PB, P+YT and LAE. Root (1973) and Andow (1992) suggested that herbivores were more likely to find and remain on host plants that occur in large, dense and pure stands due to the resource concentration factor. Koestoni and Sastrosiswojo (1985) also found 76% fewer aphids (M. persicae) on potato leaves when intercropped with maize or sunflower. In the present study Cardinal was superior in reducing the number of aphids compared to the Desiree.

These results suggest that partial plant resistance further increased the effectiveness of intercropping in suppressing the aphid population. No past work was found in the literature search where an experiment has previously compared partially resistant and susceptible plants in an intercropping system.

In LAE higher number of aphids was recorded compared with PB with or without traps. The reason may be the visual and olfactory effects produced by the mixed cropping which affect the behaviour and colonization of M. persicae. It may be because of the dilution effect of having more plants to choose from, because the aphids were also observed on berseem crop. Intercropping is known to have changed the micro-climate of crops and this can affect insect development (Potts, 1990). Also in LAE the bare soil was the same as in the P. The dense plant cover provided by the intercropping of potatoes with berseem was probably the main cause of the reduction in the invasion and subsequent colonization by aphids. Smith (1976a) obtained similar results on unweeded Brussels sprouts. She discussed the factors affecting insect colonization of brassicas grown on different backgrounds and concluded that insect preference for plants which stand out against bare soil is partly due to their phototactic reaction and more importantly to their optomotor reaction to the plants ‘looming up’ along their path (Kennedy et al., 1961). Thus the effect is accentuated when plants are high-lighted against a bare soil background which is characteristic of brassica crops most of the time. Plant cover might, therefore, diminish the optomotor landing response of the migrating insect with intercropping providing the appropriate level of camouflage. When clover was used as the intercrop, a larger reduction of Brevicoryne brassicae (L.) infestations was obtained than from strips of clover between the brassica rows (O’Donnell and Coaker, 1975).

In the interaction of cultivarsxtime intervals (weeks) and also treatmentsxtime intervals, the population of aphids increased with time, up to week 7, when the peak population of aphids was recorded. After this numbers started to decline, perhaps due to poor foliar growth, very low temperature (0 to-3°C) and heavy rainy weather conditions. These results agree with those of Hughes (1963) and Way (1968), who reported that plants become unsuitable for aphids, either by aging or by the damage inflicted by the insects and reproductive rate of the population declines. Carter (1972) and Watt and Dixon (1981) reported that adverse changes in weather and food quality can result in very poor survival of aphids. Adams (1962) stated that the critical low temperature for survival of apterae of M. persicae is 2 °C. Heie and Peterson (1961) also suggested that M. persicae can survive only at above 4 °C temperature.

Yellow sticky plastic sheet traps were found a good management technique for suppressing the aphid populations. In both treatments the number of aphids stuck on the YT was strongly correlated with the number of aphids on the crop plants on each time interval. Previous researchers, Rehman and Shahid (1988), who also used yellow plastic sheets and found them very effective against aphids.

The highest percent parasitism was recorded on PB with or without traps which was significantly higher than on all other treatments (P<0.05). A likely reason for these differences in percent parasitism is that the berseem crop may have been releasing some volatile compounds stimulating parasitism. Khan et al. (1997) investigated the effectiveness of combined cropping regimes of cultivated and wild plants for reducing stem-borer damage. In a field trial a non-host molasses grass, Melinis minutiflora P. Beauv. planted in alternate rows with maize resulted in a significant increase in parasitism by the larval braconid parasitoid, Cotesia sesamiae (Cameron). They attributed this increase to the attraction of C. sesamiae by the λ volatile component released by intact M. minutiflora, which attracts parasitoids and is produced by herbivore-damaged plants and is implicated more widely as a cue for stimulating parasitism and predation. Raymundo and Alcazar (1983) also noted an increase in the numbers of Diglyphus spp. which parasitised the leaf miner fly Liriomyza huidobrensis Blanchard in a potato-wheat intercrop.

They attributed this increase to the attraction of Diglyphus by the sweet smell of wheat at anthesis.

Among the time intervals (weeks), maximum percent parasitism was recorded in week 7, maybe because of favourable temperature (20-25°C) and weather conditions. Initially the temperature was high, gradually becoming cool and in the last week there was freezing temperature and very heavy rain. These results agree with those of Campbell and Mackauer (1977) and Tamaki et al. (1980), who suggested that among the biotic and abiotic factors influencing the natural enemy and its host in the field, temperature would have the greatest effect on the parasitoid, Diaeretiella rapae (M’Intosh), because temperature greatly influences parasitoid biology and abundance. Shijko (1989), who studied the different parameters for mass rearing of A. matricariae under different constant temperatures, recorded 36.2, 78.3 and 121.9 eggs per female at temperatures of 15, 20 and 25 °C respectively. He also found a deterioration of all the biological parameters of A. matricariae when the temperature rose above 30 °C. He reported that at 25 °C, the optimal temperature for the parasitoid, the parasitoid increased 7.5-fold per week. Aphidius smithi Sharma and Subba Rao was exposed to six constant temperatures by Wiackowski (1961), who also reported no development at 1.7 or 32.2 °C.

The highest yield was recorded when aphid numbers were lowest i.e. in the intercropped plots. Moreover, berseem belongs to family Leguminosae, which stores nitrogen in the nodules present on the roots. It is possible that this nitrogen might have been used by the potato crop for growth and development. Wilson and Burton (1938) reported that in pot studies, legumes could produce nitrogen during growth and so benefit an associated non-legume. Willey and Osiru (1972) also observed higher yield of maize per plant in the maize-bean intercrop than monocrop maize.

REFERENCES