Effect of Semiochemicals and Plant Extracts on Performance of Aphid Parasitoid, Diaeretiella rapae

S. Bushra1,*, M. Tariq1, M. Naeem1, M. Ashfaq1, I. Bodlah1 and M. Ali2

1Department of Entomology, Pir Mehr Ali Shah Arid Agriculture University, Rawalpindi

2Institute of Agricultural Sciences, University of Punjab, Lahore

ABSTRACT

Aphids are the major pests of plant crops in temperate areas of the world. They are monophagous as well as polyphagous and damage wheat, oilseeds, vegetables and fruit crops. This study was carried out to observe the effect of plant extracts and semiochemicals on physiology and performance of endoparasitoid of aphids, Diaeretiella rapae. Seven different treatments of semiochemicals and plant extract were applied on aphid pests, Sitobion avenae and Rhopalosiphum padi and parasitoid was released. The data regarding emergence, parasitism, sex ratio, tibia length, adult weight and adult longevity of parasitoid D. rapae after the application of treatments was studied and analyzed statistically. The study revealed that plant extract can be toxic to paprasitoid D. rapae. This study will help us to use those insecticide formulations, which not only kill the aphid pests but are also eco-friendly to natural enemies and our environment.

Article Information

Received 18 October 2015

Revised 09 November 2016

Accepted 20 November 2016

Available online 28 March 2017

Authors’ Contributions

MT and MN conceived and designed the study. SB performed all the experiments and wrote the article. IB and MA analyzed the data.

Key words

Beauveria bassiana, Musca domestica, Biological aspects, Sublethal effects.

DOI: http://dx.doi.org/10.17582/journal.pjz/2017.49.2.615.621

* Corresponding author: bushraentomologist@gmail.com

0030-9923/2017/0002-0615 $ 9.00/0

Copyright 2017 Zoological Society of Pakistab

INTRODUCTION

About 5000 aphid species are crop pests (Morrison and Peairs, 1998). They weaken the plant growth by sucking sap, transmit viruses in their host and result the yield losses (Dehkordi et al., 2013; Asiry, 2015). Aphid pests Sitobion avenae and Rhopalosiphum padi coexist in spring wheat crop and cause economic damage (Chen et al., 2007). Several insecticides are used to control these aphids which are also harmful. The adverse effects of insecticides on mammals are caused by insecticide residues left on edible crops when they are consumed (Bale et al., 2008). One the other hand, some plants consist of valuable active chemicals such as alkaloids, semiochemicals, terpenoids, glycosides, flavonoids and cucurbitacins, which are toxic to insect pests (Koul and Walia, 2009). These extracts are used to reduce the losses caused by agricultural pests by killing them. These include neem, turmeric, garlic etc. These plant extracts are used in IPM, medicine and industry. Some of the plant extracts have a negative impact on natural enemies like parasitiods (Sohail et al., 2012).

The braconid wasp, Diaeretiella rapae is an endoparasitoid of aphids (Fathipour et al., 2006). But, parasitoid performance also increases with increase in aphid population (Holling, 1959). Aphid parasitoids need chemical volatiles to find suitable hosts and reproduce. These chemical volatiles are semiochemicals that indicate the presence of their hosts (Blande et al., 2007). Semiochemicals are volatile chemical compounds which are emitted by plants as alarming signals, when they are damaged. They repel herbivores (Francis et al., 2004; Verheggen et al., 2007). They attract parasitoid wasps which are antagonistic to aphid pests (El-Sayed et al., 2006). Among semiochemicals, aphid alarm pheromone has the direct influence on aphid density (Xiangyu et al., 2002). This pheromone consists α-pinene, β-pinene and E-β-farnesene (Eβf) and some trace compounds. These compounds attract natural enemies of aphids (Sasso et al., 2007; Leroy et al., 2012).

In this study the effect of different semiochemicals and plant extracts was studied on the performance and physiology of aphid parasitoid, Diaeretiella rapae. This study will help us to use those insecticide formulations, which not only kill the aphid pests but they are also eco-friendly to natural enemies and environment. Long term studies on the effect of semiochemicals and plant extracts towards pests and natural enemies are required before recommending their use as pesticide (Asiry, 2015; Arshad et al., 2016). In this way, we can conserve natural enemies and manage the aphid pests.

MATERIALS AND METHODS

Wheat seeds of variety Fareed-06 were sown in pots in glass house under controlled conditions (25±2°C) and 65% RH under an LD 16:8 h. About 25 plants per pot were sown. After 6 weeks of germination the plants were subjected to aphid culture of Sitobion avenae and Rhopalosiphum padi separately. About 100 aphids per pot were released. These plants were covered with ventilated polythene sheets to avoid accidental aphid infestation and escape of applied culture. Two weeks later, three hundred aphids per pot were left behind and rest of them were removed via camel hair brush.

Mummified aphids were collected from wheat field crops. They were placed in glass vials till hatching. Newly emerged Diaeretiella rapae females were paired into a 2.5 x 8 cm glass tube and were reared on 1droplet honey+1 droplet water per day.

Seven treatments having combination of semiochemical and plant extracts were applied to these plants in 3% concentration. Five pairs of D. rapae were released under polythene sheets just after the application of seven treatments. These combinations are presented in Table I.

Table I.- Treatments of plant extracts and semiochemicals.

Treatments | Semiochemical and plant extract | Concentration
T 1 | Turmeric | Control, 3%
T 2 | β-pinene | Control, 3%
T 3 | E-β-Farnesene (E β f) | Control, 3%
T 4 | Turmeric, β-pinene | Control, 3%
T 5 | Turmeric, E-β-Farnesene | Control, 3%
T 6 | β-pinene, E-β-Farnesene | Control, 3%
T 7 | Turmeric, β-pinene and E-β-Farnesene | Control, 3%

Parasitoids were removed after 24 h. Aphids were allowed to develop for 10-14 days for mummy formation. Mummies were collected in individual gelatine capsules. The data regarding emergence, parasitism, sex ratio, tibia length, adult weight and adult longevity of D. rapae after the application of seven treatments as mentioned above.

Statistical analysis

The data pertaining to emergence, parasitism, sex ratio, tibia length, adult weight and adult longevity of D. rapae after the application of seven significant treatments were subjected to Statistical package R with CRD design.

Table II.- Emergence (%), sex ratio (%) and parasitism (%) of D. rapae on Sitobion avenae and Rhopalosiphum padi.

| Emergence % | Sex ratio % | Parasitism % | Tibia length
Sitobion avenae
Control | 83.81±1.88 | 35.27±2.32 | 56.2±1.59 | 0.52 ± 0.02
T 1 | 77.0±2.57 | 35.18±2.01 | 30.4±1.33 | 0.46 ± 0.01
T 2 | 86.82±0.51 | 35.25±5.04 | 54.4±1.72 | 0.54 ± 0.01
T 3 | 86.37±1.49 | 42.09±1.61 | 42.8±1.66 | 0.40 ± 0.02
T 4 | 75.63±1.89 | 43.89±3.47 | 28.8±1.85 | 0.43 ± 0.01
T 5 | 85.81±1.37 | 36.99±2.44 | 35.6±1.99 | 0.46 ± 0.02
T 6 | 90.67±0.70 | 36.69±2.45 | 66.8 ±1.8 | 0.55 ± 0.01
T 7 | 87.43±1.8 | 39.24±2.39 | 44.8 ±1.8 | 0.42 ± 0.02
Rhopalosiphum padi
Control | 84.02±0.92 | 45.96±3.92 | 55.2±1.59 | 0.53 ± 0.02
T 1 | 77.18±2.33 | 37.44±4.01 | 31.8±1.98 | 0.44 ± 0.02
T 2 | 91.62±0.98 | 34.22±1.04 | 56.8±1.88 | 0.52 ± 0.01
T 3 | 87.73±0.96 | 36.54±4.76 | 46.2±2.27 | 0.47 ± 0.01
T 4 | 80.21±2.32 | 37.98±2.00 | 50.86±2.7 | 0.45 ± 0.02
T 5 | 83.16±2.83 | 37.44±2.24 | 33.0±2.39 | 0.47 ± 0.01
T 6 | 91.06±0.47 | 43.88±3.70 | 64.8±1.93 | 0.54 ± 0.02
T 7 | 85.07±1.44 | 41.13±2.85 | 43.2±1.66 | 0.44 ± 0.01

All values are Mean±SEM. T1, Turmeric; T2, β-pinene; T3, E-β-Farnesene (Eβf); T4, (Turmeric, β-pinene); T5, (Turmeric E-β-Farnesene; T6, (β-pinene E-β-Farnesene; T7, Turmeric, β-pinene and E-β-Farnesene.

RESULTS AND DISCUSSION

Emergence of D. rapae reared on aphids

The comparison of means of D. rapae emergence at 5% level of probability is shown in Table II. The D. rapae exhibited 83.81% emergence in untreated controls when it was reared on S. avenae. It was found that D. rapae exhibited minimum mean emergence (75.63%) in T4 and maximum mean emergence (90.67%) after the application of T6. The mean emergence of D. rapae was found 85.81% after the application of T5, which was statistically similar to T3 (86.37%) which was statistically at par with T2 (86.82%). The mean emergence of D. rapae was found to be 77.0% and 87.43% after the application of T1 and T7, respectively. The overall emergence of D. rapae, ranged from 75.63-90.67% after the application of seven different treatments (Table II). This shows that T6 was the combination of semiochemicals which enhanced the total emergence of parasitoids significantly as compared to other six treatments. While semiochemical alone also exhibited the significant results (T2, T3). The treatment with turmeric and Ebf exhibited significantly higher emergence in T5.

The D. rapae exhibited 84.02% emergence in untreated controls when it was reared on R. padi. It was found that D. rapae exhibited minimum mean emergence (77.18%) in T1 and maximum mean emergence (91.62%) after the application of T2. The mean emergence of D. rapae was found to be 87.73% after the application of T3, followed by T7 (85.07%), which was statistically similar to T5 (83.16%), which was statistically at par with T4 (80.21%), respectively. The overall emergence of D. rapae ranged from 77.18-91.62% after the application of seven different treatments Table II.

It was found that treatment T6 having combination of two semiochemicals exhibited the higher level of significance. Similarly treatment T2 which consisted of only one semiochemical, also exhibited higher level of significance. The treatment with only turmeric exhibited significantly lowest level of emergence as compared to other treatments (T1).

Analysis of variance of the data revealed significant differences among both aphid species, parasitoid and treatments applied. It exhibited a non significant effect of aphid species and treatments on the emergence of D. rapae (F=1.254, df=7, P<1). A highly significant effect of treatments on the emergence of D. rapae was found (F=16.329, df=7, P<0.001). A non-significant effect was found between aphid species and emergence of D. rapae (F=0.848, df=1, P<1).

Parasitism (%) of D. rapae reared on aphids

The comparison of means of D. rapae parasitism rate at 5% level of probability is shown in Table II. The D. rapae exhibited 56.2% parasitism rate in untreated controls when it was reared on Si. avenae. It was found that D. rapae exhibited minimum mean parasitism rate (28.8%) in T4 and maximum mean parasitism (66.8%) after the application of T6. The mean parasitism of D. rapae was found 30.4% and 35.6% after the application of T1 and T5, respectively. The D. rapae exhibited mean parasitism after the application of T3 was 42.8%, which was statistically at par with T7 (44.8%) followed by T2 (54.4%), respectively. The overall parasitism of D. rapae ranged from 28.8-66.8% after the application of seven different treatments (Table II). It was found that treatment T6 having combination of two semiochemicals exhibited the higher level of significance. The treatment with turmeric and β-pinene exhibited significantly low level of parasitism (T4). The treatment with only turmeric exhibited significantly low level of parasitism as compared to other treatments (T1).

The D. rapae exhibited 55.2% parasitism rate in untreated controls when it was reared on R. padi. It was found that D. rapae exhibited minimum mean parasitism rate (31.8%) in T1 and maximum mean parasitism (64.8%) after the application of T6. The D. rapae exhibited mean parasitism after the application of T2 (56.8%), followed by T4 (50.86%) and T3 (46.2%), which was statistically similar to T7 (43.2%), followed by T5 (33.0%). The overall parasitism of D. rapae ranged from 31.8-64.8% after the application of seven different treatments (Table II). It was found that treatment T6 having combination of two semiochemicals exhibited the higher level of significance. The treatment with turmeric and Eβf significantly low level of parasitism (T5). The treatment with only turmeric exhibited significantly lowest level of parasitism as compared to other treatments (T1).

A non-significant effect was observed between aphid species and treatments on the parasitism rate of D. rapae (F=0.613, df=7, P<1). The treatments have highly significant effect on parasitism rate of D. rapae (F=82.961, df=7, P<0.001). The aphid species have non significant effect on parasitism rate of D. rapae (F=0.014, df=1 P<1).

The D. rapae exhibited 35.27% male proportion in untreated controls when it was reared on S. avenae. It was found that D. rapae exhibited minimum mean male emergence (35.18%) in T1 and maximum male emerged (43.89%) after the application of T4. The male population of D. rapae was found to be 35.25% after the application of T2, which was statistically similar to T6 (36.69%) which was statistically at par with T5 (36.99%). It was found that mean male population of D. rapae after T4 (43.89%) is statistically similar to T3 (42.09%). The overall male emergence of D. rapae ranged from 75.63-90.67% after the application of seven different treatments (Table II). The treatment with turmeric and β-pinene exhibited significantly highest level of male emerged (T4). The treatment with only turmeric exhibited significantly lowest level of emerged males as compared to other treatments (T1).

A non-significant effect of aphid species and treatments was found on the sex ratio of D. rapae (F=1.568, df=7, P<1). Similarly, a non-significant effect of treatments on sex ratio of D. rapae was found (F=1.162, df=7, P<1). Both aphid species exhibited non significant effect on D. rapae (F=0.503, df=1, P<1).

Sex ratio of D. rapae reared on R. padi

The comparison of means of D. rapae sex ratio at 5% level of probability is shown in Table II. The D. rapae exhibited 45.96% male proportion in untreated controls when it was reared on R. padi. It was found that D. rapae exhibited minimum mean male emergence (34.22%) in T2 and maximum male emerged (43.88%) after the application of T6. The male population of D. rapae after the application of T1 and T5 was found similar to each other (37.44%), which was statistically similar to T4 (37.98%) which was statistically at par with T3 (36.54%). It was found that mean male population of D. rapae after T6 (43.88%) is statistically similar to T7 (41.13%). The overall male emergence of D. rapae ranged from 34.22-43.88% after the application of seven different treatments (Table II).

The treatment T4 having β-pinene alone exhibited significantly lowest level of male emerged. The treatment T6 was the combination of two semiochemicals enhanced the total emergence of male parasitoids significantly as compared to other six treatments.

Tibia length of D. rapae reared on S. avenae

The D. rapae exhibited 0.52% tibia length in untreated controls when it was reared on S. avenae. It was found that D. rapae exhibited minimum mean tibia length (0.40%) in T3 and maximum mean tibia length (0.55%) after the application of T6. The mean tibia length of D. rapae was found to be 0.42% after the application of T7, which was statistically similar to T4 (0.43%), which was statistically at par with T1 (0.46%). The mean tibia length of D. rapae after the application of T2 (0.54%) was statistically similar to T6 (0.55%). The overall tibia length of D. rapae ranged from 0.40% to 0.55% after the application of seven different treatments (Table II). The treatment T6 which was the combination of two semiochemicals enhanced the tibia length of female parasitoids significantly compared to other six treatments. The tibia length of female parasitoids reduced significantly in Eβf (T3) compared to other six treatments.

The D. rapae exhibited 0.53% tibia length in untreated controls when it was reared on R. padi. It was found that D. rapae exhibited minimum mean tibia length (0.44%) in T1 and maximum mean tibia length (0.54%) after the application of T6. The mean tibia length of D. rapae was found to be 0.47% after the application of T3 and T5, which was statistically similar to T4 (0.45%), which was statistically at par with T6 (0.54%) followed by T2 (0.52%). The overall tibia length of D. rapae ranged from 0.40-0.55% after the application of seven different treatments (Table II). It was found that treatment T6 having combination of two semiochemicals exhibited higher level of significance. The treatment with turmeric exhibited significantly reduced tibia length (T1, T7) compared to other treatments.

A non-significant effect of aphid species and treatments was found on the tibia length of D. rapae (F=0.975, df=7, P<1). The treatments have highly significant effect on tibia length of D. rapae (F=15.82, df=7, P<0.001). The aphid species have non significant effect on parasitism rate of D. rapae (F=0.162, df=1 P<1).

Table III.- Adult longevity and adult weight of Diaeretiella rapae on Sitobion avenae.

Treatments | Means ± SEM
Adult longevity (days) |  | Adult weight (mg)
♂ | ♀ | ♂ | ♀
Sitobion avenae
Control | 8.80±0.58 | 14.6±0.51 |  | 0.15±0.01 | 0.23±0.01
T 1 | 5.40±0.40 | 9.80±0.49 |  | 0.12±0.01 | 0.20±0.01
T 2 | 8.20±0.58 | 13.0±0.89 |  | 0.18±0.01 | 0.25±0.01
T 3 | 9.40±0.68 | 12.0±0.71 |  | 0.16±0.01 | 0.24±0.01
T 4 | 6.0±0.45 | 11.0±0.71 |  | 0.11±0.01 | 0.23±0.01
T 5 | 6.0±0.45 | 11.0±0.71 |  | 0.15±0.01 | 0.26±0.01
T 6 | 9.8±0.58 | 16.2±0.37 |  | 0.18±0.01 | 0.20±0.01
T 7 | 7.40±0.51 | 11.4±0.51 |  | 0.20±0.01 | 0.32±0.01
Rhopalosiphum padi
Control | 9.2±0.37 | 13.2±0.86 |  | 0.17±0.01 | 0.24±0.01
T 1 | 6.2±0.37 | 9.6±0.40 |  | 0.12±0.01 | 0.22±0.01
T 2 | 8.4±0.51 | 11.8±0.97 |  | 0.17±0.01 | 0.27±0.01
T 3 | 9.8±0.58 | 14.6±0.51 |  | 0.13±0.01 | 0.27±0.01
T 4 | 6.0±0.32 | 10.4±0.51 |  | 0.12±0.01 | 0.24±0.01
T 5 | 5.8±0.37 | 10.4±0.68 |  | 0.16±0.01 | 0.27±0.01
T 6 | 9.4±0.68 | 14.4±0.51 |  | 0.18±0.01 | 0.29±0.01
T 7 | 7.2±0.58 | 12.0±0.84 |  | 0.19±0.01 | 0.30±0.01

For statistical detail and abbreviations, see Table II.

Adult weight of male D. rapae reared on aphids

The comparison of means of D. rapae adult weight at 5% level of probability is shown in Table III. The D. rapae exhibited 0.15% adult weight in untreated controls when it was reared on S. avenae. It was found that D. rapae exhibited minimum mean adult weight (0.11%) in T4 and maximum mean adult weight (0.20%) after the application of T7. It was found that mean adult weight of D. rapae after the application of T2 and T6 was similar to each other (0.18%), which was statistically similar to T3 (0.16%) at par with T5 (0.15%). The overall adult weight of D. rapae ranged from 0.11-0.20% after the application of seven different treatments (Table III).

The D. rapae exhibited 0.17% adult weight in untreated controls when it was reared on R. padi. It was found that D. rapae exhibited minimum mean adult weight (0.12%) in T1 and T4 and maximum mean adult weight (0.19%) after the application of T7. It was found that mean adult weight of D. rapae after the application of T3 (0.13%), which was statistically similar to T5 (0.16%) at par with T6 (0.18%). The overall adult weight of D. rapae ranged from 0.12-0.19% after the application of seven different treatments (Table III). It was found that treatment T7 having combination of two semiochemicals and turmeric exhibited the highest level of significance. The treatment with only turmeric (T4, T1) exhibited significantly lowest male weight compared to other treatments.

Adult weight of female D. rapae on aphids

The comparison of means of D. rapae adult weight at 5% level of probability is shown in Table III. The D. rapae exhibited 0.23% adult weight in untreated controls when it was reared on S. avenae. It was found that D. rapae exhibited minimum mean adult weight (0.20%) in T4 and T6 and maximum mean adult weight (0.32%) after the application of T7. It was found that mean adult weight of D. rapae after the application of T4 was 0.23%, which was statistically similar to T3 (0.24%) and T2 (0.25%), which statistically was at par with T5 (0.26%). The overall adult weight of D. rapae ranged from 0.20-0.32% after the application of seven different treatments (Table III).

The D. rapae exhibited 0.24% adult weight in untreated controls when it was reared on R. padi. It was found that D. rapae exhibited minimum mean adult weight (0.22%) in T4 and maximum mean adult weight (0.30%) after the application of T7. The mean adult weight of D. rapae after the application of T2, T3 and T5 was similar to each other (0.27%). It was found that mean adult weight of D. rapae after the application of T6 was 0.29%, followed by T4 (0.24%). The overall adult weight of D. rapae ranged from 0.22% to 0.30% after the application of seven different treatments (Table III). It was found that treatment T7 having combination of two semiochemicals and turmeric exhibited the highest level of significance. The treatment with only turmeric (T1) exhibited significantly lowest female weight compared to other treatments.

A non significant effect of aphid species and treatments on the adult weight of D. rapae was exhibited (F=0.153, df=7, P<1). A highly significant effect of treatments on adult weight of D. rapae was found (F=5.398, df=7, P<0.001). A non-significant effect was found between aphid species and adult weight of D. rapae (F=0.188, df=1, P<1).

Adult longevity of male D. rapae reared on aphids

The comparison of means of adult D. rapae longevity at 5% level of probability is shown in Table III. The D. rapae exhibited 8.80% adult longevity in untreated controls when it was reared on S. avenae. It was found that D. rapae exhibited minimum mean adult longevity (5.40%) in T1 and maximum mean adult longevity (9.8%) after the application of T6. It was found that mean adult longevity of D. rapae after the application of T4 and T5 was similar to each other (0.6%). The mean adult longevity of D. rapae after the application of T6 was 9.8%, which was statistically similar to T3 (9.40%), which was statistically at par with T2 (8.20%). The overall adult longevity of D. rapae ranged from 5.40-9.8% after the application of seven different treatments (Table III). It was found that treatment with Eβf alone and Eβf with β-pinene (T3, T6) have highest longevity of male parasitoids compared to other treatments. The treatment with only turmeric exhibited significantly lowest level of male longevity compared to other treatments (T1).

A non significant effect of aphid species and treatments on the adult longevity of D. rapae was exhibited (F=0.228, df=7, P<1). A highly significant effect of treatments on adult longevity of D. rapae was found (F=8.059, df=7, P<0.001). A non-significant effect was found between aphid species and adult longevity of D. rapae (F=0.001, df=1, P<1).

The D. rapae exhibited 9.2% adult longevity in untreated controls when it was reared on R. padi. It was found that D. rapae exhibited minimum mean adult longevity (5.8%) in T5 and maximum mean adult longevity (9.8%) after the application of T3. It was found that mean adult longevity of D. rapae after the application of T3 (9.8%) was statistically similar to T6 (9.4%), which was followed by T2 (8.4%), which was statistically at par with T7 (7.2%). The overall adult longevity of D. rapae ranged from 5.8-9.8% after the application of seven different treatments (Table III). It was found that treatment with Eβf alone and Eβf with β-pinene (T3,T6) have highest longevity of male parasitoids as compared to other treatments. The treatment with only turmeric, turmeric with β-pinene exhibited significantly lowest level of male longevity as compared to other treatments (T4, T1).

Adult longevity of female D. rapae reared on aphids

The comparison of means of adult D. rapae longevity at 5% level of probability is shown in Table III. The D. rapae exhibited 14.6% adult longevity in untreated controls when it was reared on S. avenae. It was found that D. rapae exhibited minimum mean adult longevity (9.80%) in T1 and maximum mean adult longevity (16.2%) after the application of T6. It was found that mean adult longevity of D. rapae after the application of T4 and T5 was similar to each other (11.0%), which was statistically at par with T7 (11.0%). The mean adult longevity of D. rapae after the application of T2 was 13.0%, which was statistically similar to T3 (12.0%). The overall adult longevity of D. rapae ranged from 9.80-16.2% after the application of seven different treatments (Table III). It was found that treatment T6 having combination of two semiochemicals exhibited the higher level of significance. The treatment with only turmeric exhibited significantly lowest level of female longevity as compared to other treatments (T1).

The D. rapae exhibited 13.2% adult longevity in untreated controls when it was reared on R. padi. It was found that D. rapae exhibited minimum mean adult longevity (9.6%) in T1 and maximum mean adult longevity (14.6%) after the application of T3. It was found that mean adult longevity of D. rapae after the application of T4 and T5 was similar to each other (10.4%), which was statistically similar to T2 (11.8%), which was statistically at par with T7 (12.0%). The overall adult longevity of D. rapae ranged from 9.6-14.6% after the application of seven different treatments (Table III). The treatment with only turmeric exhibited significantly lowest level of female longevity compared to other treatments (T1). It was found that treatment having Eβf alone and combination of two semiochemicals (T3,T6) exhibited the highest level of significance.

Gowling and van Emden (1994) observed the variation in parasitism rate of B. brassicae by D. rapae in various cultivars in the field experiments. Bayhan et al. (2007) reported the highest level of parasitism of B. brassicae in cabbage (40.20%), and the lowest level of parasitism in turnip (32.64%). Mölck et al. (2000) found that plant volatiles facilitate or enhance parasitoid foraging efficiency to respond towards these odors. Fernandez and Nentwig (1997) found that development time, fecundity, sex ratio, longevity, parasitization rate and size of A. colemani are significantly affected by nutritional value of host plant.

Insect parasitoids need suitable hosts to reproduce. Parasitoids use cues that indicate the presence of their hosts (Blande et al., 2007). Successful host foraging behavior by insect parasitoids includes host-habitat location, host location, host acceptance, host suitability, and host regulation provided by olfactory cues (Vinson, 1985).

It was found that D. rapae takes 9 to 15 days to complete its life cycle in laboratory. Adult female longevity was 10-15 days, while male can live for 7-10 days (Reed et al., 1992). Females live significantly longer than males (Bayhan et al., 2007). Bernal and Gonzales (1997) found that the longevity of female D. rapae was 11.5 days at 21.1°C on Diuraphis noxia.

CONCLUSION

This study suggested that long term studies on the effect of semiochemicals and plant extracts towards pests and natural enemies are required before recommending their use as pesticide. In this way, we can conserve natural enemies and manage the aphid pests.

Statement of conflict of interest

Authors have declared no conflict of interest.

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