Behavioral Responses of Coccinella septempunctata and Diaeretiella rapae under the Influence of Semiochemicals and Plant Extract in Four Arm Olfactometer

Bushra Siddique1,*, Muhammad Tariq1, Muhammad Naeem1 and Muhammad Ali2

1Department of Entomology, PMAS-Arid Agriculture University, Rawalpindi

2Institute of Agricultural Sciences, University of the Punjab, Lahore

ABSTRACT

Natural enemies are more effective at controlling herbivores in diverse botanical ecosystems. Different chemical cues help to correspond in diversity of associations between prey and host plant species. Recent studies exhibited that the use of natural enemy is an ecofriendly measure to control pests. The Seven spotted ladybird beetle, Coccinella septempunctata play a prominent role in aphid management. It exploits several different cues released by plants to increase the efficiency of foraging. Aphid endoparasitoid, Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae) have an ability to locate its hosts by responding to odours from aphid host plants or by visual searching. The treatments with different combinations of plant extracts and semiochemicals were used for natural enemy preference experiment. The experiment was conducted with seven treatments and five replications at Glass house situated in Pir Mehr Ali Shah Arid Agriculture University, Rawalpindi field area during Feb-April, 2015. The Coccinella septempunctata were collected from wheat crop plants. They remained starved for two days before Olfactometer bioassays. For D. rapae, mummified aphids were collected from wheat crop. Naive females were subjected to olfactometer tests. Seven different combined treatments of semiochemicals and plant extract were applied on filter paper strips at 3% concentration. The filter paper strips were placed in arms of olfactometer. The control arms were treated with n-hexane. Data pertaining to preference of C. septempunctata and D. rapae after treatment application were recorded and analysed statistically. It was found that T6 (β-pinene + E-β-Farnesene) exhibited highest mean number entries of C. septempunctata (6.13%) and highest mean time spend (6.23%) as compared to two other treatments applied. The results revealed that alarm pheromone component effective kairomone for aphid predatory beetles. It was found that T6 (β-pinene + E-β-Farnesene) exhibited highest mean number entries of D. rapae (7.50%) and highest mean time spend (6.39%) as compared to other treatments applied. The results revealed that release of insect derived semiochemicals can enhance visual searching and efficiency of parasitoid D. rapae.

Article Information

Received 29 January 2018

Revised 22 July 2018

Accepted 13 February 2019

Available online 06 May 2019

Authors’ Contribution

BS conducted the research and wrote the manuscript. MT provided techical support. MN and MA analysed the data.

Key words

Coccinella septempunctata, Treatments, Concentration, Semiochemicals, Olfactometer.

DOI: http://dx.doi.org/10.17582/journal.pjz/2019.51.4.1403.1411

* Corresponding author: bushraentomologist@gmail.com

0030-9923/2019/0004-1403 $ 9.00/0

Copyright 2019 Zoological Society of Pakistan

Introduction

The four arm olfactometer was designed by Pettersson (1970). It is a volatile based instrument having central arena with food source boxes which are connected with each other through connected tubes. It is designed to study the oviposition preference behavior of insect pest and its predator via screening experiments. Volatiles are emitted from the plant parts or body of prey. Insect pests or predators are confined in the central arena to test it for food preference (Riddick et al., 2000).

The term ‘parasitoid’ for the first time was introduced by Reuter (1913). Parasitoids have the ability to respond plant odors (Moraes et al., 2005). The volatile profile of plant odor also play a vital role to increase parasitoid attraction (Röse et al., 1998; Bukovinszky et al., 2005). It was found that volatiles released immediately from damaged plant attract parasitoids instantaneously (Mattiacci et al., 2001; Hoballah and Turlings, 2005).

Responses of natural enemies towards volatiles released from aphid infested plants are often specific in terms of plant species, plant developmental stage, herbivore species and developmental stage of herbivore (Moraes et al., 2005; Sabelis et al., 2007). But sometimes, the host specificity is not universal (Shiojiri et al., 2001; van Poecke et al., 2003).

Natural enemies including Coccinellid beetles, parasitoid wasps, lacewings, and hoverflies are attracted by plant volatiles which are induced by aphid attack (Hatano et al., 2008). Endoparasitic wasps undergo obligatory development inside arthropod host. During the development phase, parasitoids can be influenced by chemical stimuli perceived from its host and the environment (Turlings et al., 1993; Godfray, 1994). It was found that experienced A. ervi and D. rapae exhibit a significant response to aphid induced plant volatiles as compared to naive individuals (Girling et al., 2006).

Natural enemies play a crucial role in pest management programs and ecological studies. Natural enemies are sensitive towards chemical cues released in multitrophic environment, with regard to host location (Poppy, 1997; Vet and Dicke, 1992). Predatory ladybeetle, Coccinella septempunctata (L.) is aphidiophagus and polyphagous (Pettersson et al., 2008; Ninkovic et al., 2011). It is best known aphid predator. It can consume more than 100 aphids per day (Capinera, 2008). It exploits the cues released by plants (Honek and Martinkova, 2008). The C. septempunctata has specialized olfactory cells in its compound eye (Pickett et al., 1998). The olfactory and visual cues play an important role to locate aphids (Sengonca and Liu, 1994).

The alarm pheromone is released by many aphid species, but the subfamily Aphididae releases particularly sesquiterpene EβF (Pickett and Griffiths, 1980). It is released when aphids are attacked by natural enemies. It induces avoidance behaviour among aphids (Gibson and Pickett, 1983) and increase the foraging behaviour of parasitoids (Foster et al., 2005). It acts as kairomone for predators such as ladybirds (Francis et al., 2004; Pettersson et al., 2008). It acts as valuable tool in aphid pest-control strategies (Roditakis et al., 2000). Therefore, this experiment was carried out to study the behavioural responses of D. rapae under the influence of seven different combinations of semiochemicals and plant extract by using four arm olfactometer.

Different chemical cues are related to diverse associations between prey and its host plant. It was found that Coleomegilla maculate, Adalia bipuncata and C. septempuncata responses were related to semiochemicals released from aphid species and their host plants (Zhu et al., 1999; Al-Abassi et al., 2000); they use chemical cues to locate their preys. Alarm pheromone component EBF is an effective kairomone for aphid predators, i.e. two spotted ladybeetle (Francis et al., 2004).

Therefore, present study was carried out to see the olfactory responses of predatory beetles towards semiochemicals and plant extract. Al-Abassi et al (2000) found that the semiochemicals have been intensively studied for their use in insect biocontrol programs.

 

Materials and methods

This experiment was conducted at Laboratories situated in Department of Entomology, Pir Mehr Ali Shah-Arid Agriculture University, Rawalpindi field area. The experiment was conducted comprising seven treatments with five replications.

Collection and rearing of insects

The C. septempunctata were collected from wheat crop plants. They were reared on 50% sugar solution. They remained starved for two days before Olfactometer bioassays.

Mummified aphids of D. rapae were collected from wheat crop in vials individually. On emergence, females were reared on 50% aqueous solution of honey for 2 days. Naive females were subjected to olfactometer tests.

Olfactometer bioassays

The behavioural responses of C. septempunctata and D. rapae under seven different treatments of plant extract and semiochemicals were determined by using a four-arm olfactometer (Pettersson, 1970; Kalule and Wright, 2004; Webster et al., 2010). The bioassay consists a pairwise treatment comparison. All bioassays for predator response were performed at 20±2°C with 0.04 W / m2 light intensity (Young et al., 1987).

Treatments were applied on filter paper strips at 3% concentration. The control arms were treated with n-hexane. Filter paper strips were placed in arms of olfactometer. Two arms are kept as control and rest of two arms are kept as treatment arms. These treatments are: T1, Turmeric; T2, β-pinene; T3, E-β-Farnesene; T4, Turmeric and β-pinene; T5, Turmeric and E-β-Farnesene; T6, β-pinene and E-β-Farnesene and T7, Turmeric, β-pinene and E-β-Farnesene.

Air was drawn in through the four orifices which passes in each quadrant by vacuum pump. Predator, C. septempunctata was released in central olfactometer chamber for 8 minutes and was allowed move freely within each region. Olfactometer was rotated at 90° after every two minutes interval. The number of entries and time spent by C. septempunctata in each region of olfactometer was recorded using Olfa software (Nazzi, 1996). After every 10 specimens, washed with Lipsol detergent (5% v/v; Bibby Sterilin Ltd., UK), rinsed with 80% ethanol and air dried. Data pertaining to number of entries and time spent by C. septempunctata in each region of olfactometer were recorded. Similar experiment was performed with D. rapae

Statistical analysis

Data pertaining to number of entries and time spent by C. septempunctata and D. rapae in each region of olfactometer was were analysed using Wilcoxon test. The HSD test at 5% level of significance to compare the difference between the means.

 

Table I.- Number of entries (Mean ± SEM) by male and female Coccinella septempunctata in control and treatment arm of olfactometer.

Treatment	No of entries		Wilcoxon test (P-value)
	Control arm	Treatment arm
Male
T1	3.10 ± 0.23	4.90 ± 0.23	0.0004572
T2	3.0 ± 0.26	5.90 ± 0.28	0.0001485
T3	3.40 ± 0.22	6.80 ± 0.25	0.0001358
T4	3.20 ± 0.25	5.40 ± 0.16	0.0001239
T5	3.20 ± 0.25	5.80 ± 0.20	0.0001286
T6	3.10 ± 0.23	7.20 ± 0.25	0.0001399
T7	3.20 ± 0.25	6.0 ± 0.26	0.0001459
Female
T1	3.20 ± 0.20	5.20 ± 0.25	0.0002962
T2	3.30 ± 0.15	6.0 ± 0.26	0.000115
T3	3.30 ± 0.26	6.60 ± 0.22	0.0001383
T4	2.90 ± 0.23	5.50 ± 0.17	0.0001247
T5	3.10 ± 0.23	6.0 ± 0.21	0.000127
T6	3.40 ± 0.22	7.0 ± 0.26	0.0001383
T7	3.30 ± 0.21	5.90 ± 0.28	0.0001383

***, P<0.001; **, P<0.01; *, P<0.05, P< 0.1 and P<1. C. septempunctata response was measured as (Mean±SEM) number of observations in the arms of four-way olfactometer. n=80 individuals tested in each treatment.

 

Results

Number of entries in arm of olfactometer

Male C. septempunctata

It was found that C. septempunctata exhibited a significant response to choose treatment arm over the control arm in all treatments tested in olfatometer bioassay. From Table I, it was found that male C. septempunctata exhibited the maximum significant preference towards treatment T6 (Wilcoxon’s test, T = 7.20; N = 80; P = 0.000139) as compared to other treatments applied. It was found that the treatment T4 (Wilcoxon’s test, T = 5.40; N = 80; P = 0.000127) was statistically similar to T5 (Wilcoxon’s test, T = 5.80; N = 80; P = 0.000128) which was statistically at par with T2 (Wilcoxon’s test, T = 5.90; N = 80; P = 0.000148). It was observed that C. septempunctata exhibited the minimum significant preference towards treatment T1 (Wilcoxon’s test, T = 4.90; N = 80; P = 0.024) as compared to other treatments applied. The preference of C. septempunctata towards treatment T7 was (Wilcoxon’s test, T = 6.0; N = 80; P = 0.000124) which was statistically similar to T3 (Wilcoxon’s test, T = 6.80; N = 80; P = 0.000138) (Table I).

Female C. septempunctata

It was found that C. septempunctata exhibited a significant response to choose treatment arm over the control arm in all treatments tested in olfatometer bioassay. From Table I, it was found that female C. septempunctata exhibited the maximum significant preference towards treatment T6 (Wilcoxon’s test, T = 7.0; N = 80; P = 0.000138) as compared to other treatments applied. It was found that the treatment T2 (Wilcoxon’s test, T = 6.0; N = 80; P = 0.000138) was statistically similar to T5 (Wilcoxon’s test, T = 6.0; N = 80; P = 0.000127) which was statistically at par with T3 (Wilcoxon’s test, T = 6.60; N = 80; P = 0.000138). It was observed that C. septempunctata exhibited the minimum significant preference towards treatment T1 (Wilcoxon’s test, T = 5.20; N = 80; P = 0.024) as compared to other treatments applied. The preference of C. septempunctata towards treatment T4 was (Wilcoxon’s test, T = 5.50; N = 80; P = 0.000124) which was statistically similar to T7 (Wilcoxon’s test, T = 5.90; N = 80; P = 0.000138) (Table II).

 

Table II.- Number of entries (Mean ± SEM) by Diaeretiella rapae in control and treatment arm of olfactometer.

Treatment 3% concentration	No. of entries		Wilcoxon test (P-value)
	Control arm	Treatment arm
T1	2.20 ± 0.25	3.90 ± 0.28	0.00109
T2	2.30 ± 0.26	5.50 ± 0.34	0.0001494
T3	2.40 ± 0.22	7.10 ± 0.28	0.0001383
T4	2.50 ± 0.27	5.70 ± 0.21	0.0001086
T5	2.10 ± 0.28	6.50 ± 0.17	0.0001301
T6	2.60 ± 0.27	7.50 ± 0.18	0.0001254
T7	2.0 ± 0.21	5.90 ± 0.23	0.000127

***, P<0.001; **, P<0.01; *, P<0.05; P< 0.1 and P<1. D. rapae response was measured as (Mean±SEM) number of observations in the arms of four-way olfactometer. n=80 individuals tested in each treatment.

 

Diaeretiella rapae

It was found that D. rapae exhibited a significant response to choose treatment arm over the control arm in all treatments tested in olfatometer bioassay. Among the seven treatments tested, D. rapae exhibited the maximum significant preference in treatment T6 (Wilcoxon’s test, T = 7.50, N = 80, p=0.00012), which was statistically at par with T3 (Wilcoxon’s test, T = 7.10, N = 80, p=0.00013). Whereas, the preference of D. rapae towards treatment T5 was (Wilcoxon’s test, T = 6.50; N = 80; P = 0.00013). It was found that the treatment T2 (Wilcoxon’s test, T = 5.50; N = 80; P = 0.00014) was statistically similar to T4 (Wilcoxon’s test, T = 5.70; N = 80; P = 0.00010) which was statistically at par with T7 (Wilcoxon’s test, T = 5.90; N = 80; P = 0.000148). Preference of D. rapae towards treatment T1 was minimum (Wilcoxon’s test, T = 3.90; N = 80; P = 0.00109) (Table II).

Time spent in arm of olfactometer

Male C. septempunctata

It was found that Coccinella septempunctata exhibited a significant response to choose treatment arm over the control arm in all treatments tested in olfatometer bioassay. From Table III, it was found that male C. septempunctata exhibited the maximum significant preference towards treatment T6 (Wilcoxon’s test, T = 6.13; N = 80; P = 1.083) as compared to other treatments applied. It was found that the treatment T6 was statistically similar to T3 (Wilcoxon’s test, T = 6.05; N = 80; P = 0.00018). It was observed that C. septempunctata exhibited the minimum significant preference towards treatment T1 (Wilcoxon’s test, T = 3.30; N = 80; P = 0.024) as compared to other treatments applied. The preference of C. septempunctata towards treatment T4 was (Wilcoxon’s test, T = 4.71; N = 80; P = 0.000179) which was statistically similar to T2 (Wilcoxon’s test, T = 4.55; N = 80; P = 0.00018). The preference of C. septempunctata towards treatment T7 was (Wilcoxon’s test, T = 5.21; N = 80; P = 0.000179) which was statistically similar to T5 (Wilcoxon’s test, T = 5.50; N = 80; P = 0.00018) (Table III).

 

Table III.- Time spent (Mean ± SEM) by male and female Coccinella septempunctata in control and treatment arm of olfactometer.

Treatment	Time spent		Wilcoxon test (P-value)
	Control arm	Treatment arm
Male
T1	2.8 ± 0.15	3.30 ± 0.06	0.02479
T2	2.52 ± 0.06	4.55 ± 0.11	0.0001806
T3	1.38 ± 0.06	6.05 ± 0.09	0.0001806
T4	2.65 ± 0.10	4.71 ± 0.11	0.0001796
T5	1.89 ± 0.09	5.50 ± 0.09	0.0001817
T6	2.37 ± 0.03	6.13 ± 0.03	1.083e-05
T7	2.10 ± 0.07	5.21 ± 0.04	1.083e-05
Female
T1	2.54 ± 0.17	3.69 ± 0.18	1.083e-05
T2	2.21 ± 0.10	5.02 ± 0.16	0.0001817
T3	1.34 ± 0.04	6.12 ± 0.1	0.0001806
T4	2.33 ± 0.05	4.89 ± 0.2	1.083e-05
T5	1.81 ± 0.09	5.02 ± 0.12	0.0001796
T6	1.26 ± 0.04	6.23 ± 0.11	1.083e-05
T7	1.67 ± 0.10	5.75 ± 0.13	0.0001806

***, P<0.001; **, P<0.01; *, P<0.05, P< 0.1 and P<1. C. septempunctata response was measured as (Mean±SEM) number of observations in the arms of four-way olfactometer. n=80 individuals tested in each treatment.

 

Female C. septempunctata

It was found that Coccinella septempunctata exhibited a significant response to choose treatment arm over the control arm in all treatments tested in olfatometer bioassay. From Table III, it was found that female C. septempunctata exhibited the maximum significant preference towards treatment T6 (Wilcoxon’s test, T = 6.23; N = 80; P = 1.083) as compared to other treatments applied. It was found that the treatment T6 was statistically similar to T3 (Wilcoxon’s test, T = 6.12; N = 80; P = 0.00018). It was observed that C. septempunctata exhibited the minimum significant preference towards treatment T1 (Wilcoxon’s test, T = 3.69; N = 80; P = 1.083) as compared to other treatments applied. The preference of C. septempunctata towards treatment T4 was (Wilcoxon’s test, T = 4.89; N = 80; P = 1.083). The preference of C. septempunctata towards treatment T2 was (Wilcoxon’s test, T = 5.02; N = 80; P = 0.00018) which was statistically similar to T5 (Wilcoxon’s test, T = 5.02; N = 80; P = 0.000179) which was statistically at par with T7 (Wilcoxon’s test, T = 5.21; N = 80; P = 0.000181).

 

Table IV.- Time spent (Mean ± SEM) by Diaeretiella rapae in control and treatment arm of olfactometer.

Treatment 3% concentration	Time spent		Wilcoxon Test (P-value)
	Control arm	Treatment arm
T1	2.07 ± 0.22	3.39 ± 0.14	0.0004943
T2	1.99 ± 0.23	4.48 ± 0.25	0.0001806
T3	1.31 ± 0.09	6.35 ± 0.08	0.0001817
T4	2.21 ± 0.18	4.58 ± 0.14	1.083e-05
T5	1.69 ± 0.13	5.68 ± 0.15	0.0001817
T6	1.12 ± 0.03	6.39 ± 0.03	1.083e-05
T7	1.93 ± 0.21	5.16 ± 0.3	1.083e-05

***, P<0.001; **, P<0.01; *, P<0.05; P< 0.1 and P<1. D. rapae response was measured as (Mean ± SEM) number of observations in the arms of four-way olfactometer. n = 80 individuals tested in each treatment.

 

Diaeretiella rapae

It was found that D. rapae exhibited a significant response to choose treatment arm over the control arm in all treatments tested in olfatometer bioassay. Among the seven treatments tested, D. rapae exhibited the maximum significant preference in treatment T6 (Wilcoxon’s test, T = 6.39, N = 80, P = 1.083), which was statistically at par with T3 (Wilcoxon’s test, T = 6.35, N = 80, P = 0.00018). It was found that the treatment T7 (Wilcoxon’s test, T = 5.16; N = 80; P = 1.083) was statistically similar to T5 (Wilcoxon’s test, T = 5.68; N = 80; P = 0.00018). It was observed that the treatment T2 (Wilcoxon’s test, T = 4.48; N = 80; P = 0.00014) which was statistically at par with T4 (Wilcoxon’s test, T = 4.58; N = 80; P = 0.000148). The preference of D. rapae towards treatment T1 was minimum (Wilcoxon’s test, T = 3.39; N = 80; P = 0.00049) (Table IV).

 

Discussion

Olfactory cues play an important role in foraging behaviour of natural enemies (Dicke et al., 2003) i.e. in ladybird foraging behaviour (Pettersson et al., 2005; Zhu and Park, 2005). Seagraves (2009) reported that C. septempunctata orient themselves towards prey using olfactory cues. Aphid cornicle secretions containing semiochemicals are attracting cues for C. septempunctata. Han and Chen (2002) found that seven spotted ladybird exhibited significant differences toward odor source when it was exposed to crushed 1200 tea aphids in a Y tube olfactometer. Seagraves (2009) reported that the attraction of coccinellids is related to prey density. Therefore, ladybird olfactory response by EBF is a dose dependent factor (Bhasin et al., 2000). Francis et al. (2004) found that coccinellids do not respond towards EBF when its amount is less than 2µg. Al-Abassi et al. (2000) found that attractivity of EBF for C. septempunctata decreases with increasing amount of α-caryophyllene.

Leroy et al. (2012) found that aphid associated semiochemicals, i.e., [E]-β-farnesene, α-pinene, β-pinene, Z,E-nepetalactone and (-)-β-caryophyllene are potential attractants for Harmonia axyridis. Alarm pheromone component (E)- β-farnesene, either emitted by aphids and plants is an attractant for coccinellids, C. septempunctata (Al-Abassi et al., 2000; Ninkovic et al., 2001), Adalia bipunctata (Hemptinne et al., 2000), Hippodamia convergens (Acar et al., 2001) and H. axyridis (Verheggen et al., 2007; Mondor and Roitberg, 2000). Aphid alarm pheromone (α-pinene and β-pinene formulated in paraffin oil) are attractants for the Asian lady beetle. It was found that alarm pheromone can attract 70.0% of tested females in the wind-tunnel experiments. The volatile α-pinene can significantly attract the H. axyridis (Xue et al., 2008).

It was found that (Z)-3-hexenol and (E)-2-hexenal act as a synomone for the coccinellids C. septempunctata (Han and Chen, 2002). Alhmedi et al. (2010) found that H. axyridis do not show any behavourial response when (E)-β-farnesene, (Z)-3-hexenol and β-pinene is in amount of 5 μg in olfactory experiments.

Ladybirds can arrive in crop plants before aphid migrants via plant volatile chemicals (Honeˇk and Martinkova´, 2008; Ninkovic and Pettersson, 2003; Ninkovic et al., 2011). The continuous emission of plant volatiles affect ladybird searching behaviour. This phenomenon contributes to broader ecological significance of induced plant responses towards biotic stress (Markovic et al., 2014).

Vekaria and Patel (2000) found that different treatments of neem extracts were less toxic towards D. rapae and C. septempunctata as compared to chemical insecticides. Halder et al. (2010) tested the efficacy of chloroform, methanol extracts and oils from nayantara, Vinca rosea and bottle brush against Lipaphis erysimi and C. septempunctata under laboratory condition. It was found that plant extracts and oil have not exhibited mortality to C. septempunctata up to ten days after feeding the treated L. erysimi. Chakraborty and Ghosh (2010) tested the toxicity of Bacillus thuringiensis, Beauveria bassiana, malathion and Neemactin and Avermectin on ladybeetle. It was found that Neemactin and Avermectin were least toxic as compared to six insecticide formulations tested.

The results revealed that T6 (β-pinene, E-β-Farnesene) exhibited highest mean number entries of C. septempunctata (6.13%) and highest mean time spend (6.23%) as compared to two other treatments applied. Results depicted that alarm pheromone is a promising biopesticide and attractant for several aphidophagous predators including C. septempunctata.

Hymenopteran parasitoids are important natural enemies in biological control programs of aphids in diverse crops (Araya et al., 2010). Previous studies revealed that parasitoids locate their hosts by semiochemicals emitted from their hosts and from the plants infested by their hosts (Zhu et al., 2005). Wickremasinghe and van Emden (1992) and Vet and Dicke (1992) found that a number of aphid parasitoids respond and attract towards plant volatiles in olfactometer bioassays. Aphids themselves not attractive towards all parasitoids (Micha and Wyss, 1995). Aphid release alarm pheromone from their cornicles when disturbed, which is attractive for some parasitoids (Micha and Wyss, 1996).

Micha et al. (2000) found that the parasitoid orientation behavior in olfactometer bioassay is influenced by the odours emitted from infested plant baits. Some parasitoids respond to aphid induced plant volatiles and some remain unresponsive to odors of host plant (Storeck et al., 2000; Girling et al., 2006). Heil (2008) reported that parasitoids have ability to distinguish between aphid infested and uninfested plants, and they can also distinguish between plants infested by different herbivores. Takemoto et al. (2009) found that volatiles released from Vicia faba infested by Acyrthosiphon pisum attract naive Aphidius ervi in a Y-tube olfactometer. Foster et al. (2005) reported that D. rapae spend up to 20 min time interval in the discs treated with EβF. The time spent by D. rapae in EβF treated discs increased with increase in its concentration. D. rapae can move towards high distances from untreated to EβF treated discs. Turlings et al. (2004) found that 90% of endoparasitoid Cotesia marginiventris females stay in odour treated arm. If no odour is offered in olfactometer bioassay, most of females stay in central chamber during 30 min duration. Wyckhuys and Heimpel (2007) found that response potential of aphid parasitoid Binodoxys communis towards certain stimuli was 59, 68, 67, 62, and 62% for odors from Aphis glycines, A. oestlundi, A. monardae, A. nerii, and A. asclepiadis, respectively. In olfactometer bioassays, both male and female A. ervi exhibited more significant time spent in air-stream containing β-phellandrene and caryophyllene as compared to controls (George et al., 2013).

Our study dipicted that T6 (β-pinene + E-β-Farnesene) exhibited highest mean number entries of D. rapae (7.50%) and highest mean time spend (6.39%) as compared to other treatments applied. Therefore, these semiochemicals are attractive to natural enemies, i.e., predatory beetles (Han and Chen, 2002; Osawa, 2000) and parasitoids. Guerrieri et al. (1999) found that herbivore induced volatiles are released by plants is a systemic response. Cortesero et al. (2000) found that release of plant volatiles which attract parasitoid species should be enhanced through plant breeding.

 

Acknowledgements

The authors are thankful to research support of Dr. Tobby Bruce, Rhothmstat Research Institute, UK and Pir Mehr Ali Shah Arid Agriculture University, Rawalpindi for providing an opportunity to carry out this study.

 

Statement of conflict of interest

The authors declare no conflict of interest.

 

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