Studies On The Electroantennographic And Behavioral Responses Of Eight Insects To Ricin And Arbin

Insects have a highly developed olfactory sensory system, mainly based in their antennae, for the detection and discrimination of volatile compounds in the environment. The electroantennogram (EAG) technique is an important method to rapidly investigate the activity and sensitivity of insect antennae to volatiles. Recently, several attempts have been made to expand this application into using insect antennae as biosensors for detecting selected volatile compounds in the ambient environment and some encouraging results were obtained, which is of significant importance if the EAG technique is to be used for monitoring target volatiles amidst a background of other volatiles.Ricin and arbin are the proteins of high toxicity extracted from the seeds of Ricinis communis and Abrus precatoriu, respectively. Because of their toxicity, extensive source and easy extraction, it will pose a great threat to the public health of human once the food and water are polluted by these toxins,.The present study was initialized to investigate the EAG and behavioral responses of eight insect sepecies (Helicoverpa amigera, Plutella xylostella, Ostrinia furnacalis, Spodoptera exigua, Antherea pernyi, Bombus lucorum, Periplaneta americana and Blattella germanica) to ricin and arbin. By comparing the EAG amplitude, the sensitivity and selectivity of their antennae to target toxins could be well analyzed. Our goal in this study was aimed at getting some highly sensitive and selective insect antennae to target odors, which would provide meaningful information on taking advantage of the sensitivity of insect antennae to monitor the bio-toxins in the environment for the early-warning according to the principle of EAG responses.The main results were as follows: 1. EAG responses from insects to different toxinsThe present study showed that EAG responses could be elicited from the examined insect species by tested toxins. The EAG amplitude from the control (distilled water) was lowest and it was significantly different from those amplitudes from treatments except Bombus lucorum (F=1.135,P=0.352).The EAG amplitudes from various toxins were different. Among the tested toxins, the highest EAG amplitude (-0.310±0.039 mV)from Antherea pernyi was elicited by ARA. And the EAG amplitude from Plutella xylostella elicited by raw arbin was highest (♀:-0.831±0.056 mV;♂:-0.901±0.061 mV). The EAG amplitudes from the other insects elicited by raw ricin were highest, which demonstrated that the electrophysiological activity of raw ricin to most of tested insects was the strongest. Among the 6 insects, the EAG amplitudes from Blattella germanica elicited by raw ricin were significantly different from those elicited by other toxins (P<0.05). No significant difference was observed between the EAG amplitudes from B. lucorum and Helicoverpa amigera stimulated by the tested toxins. There were significant differences between the EAG amplitudes from Ostrinia furnacalis males elicited by raw ricin and raw arbin (P<0.05), howerer, the amplitudes of females were insignificantly different when they were stimulated by the tested toxins. The EAG amplitudes from Spodoptera exigua femlaes elicited by raw ricin were significantly different from those elicited by other toxins (P<0.05) and the significant difference was only not observed between the amplitudes of males elicited by raw ricin and raw arbin. The EAG amplitudes from Periplaneta americana males elicited by raw ricin were significantly different from those elicited by other toxins, but the significant difference was only shown between the amplitudes of females elicited by raw ricin and ARA.2. EAG responses from eight insects species to raw ricinThe EAG amplitudes from the insects species examined to raw ricin were between–(0.254±0.018) mV and–(0.852±0.098) mV. And the lowest EAG amplitude was elicited from P. americana (♀: -0.254±0.018 mV,♂: -0.319±0.017 mV), which demonstrated P. americana was most insensitive to raw ricin.3. EAG responses from eight insects species to RTAThe EAG amplitudes from the insects species examined to RTA were between–(0.383±0.087) mV and–(0.768±0.061) mV. The highest EAG amplitude was stimulated by P. xylostella (♀: -0.768±0.061 mV,♂: -0.721±0.076 mV), which showed P. xylostella was most sensitive to RTA.4. EAG responses from eight insects species to raw arbinThe EAG amplitudes from the insects species examined to raw arbin were between–(0.225±0.004) mV and–(0.901±0.091) mV. The lowest and highest EAG amplitudes were elicited from P. americana (♀:-0.225±0.004 mV,♂:-0.251±0.015 mV) and P. xylostella (♀:-0.831±0.056 mV,♂: -0.901±0.091 mV), respectively. And the EAG amplitudes from P. xylostella were significantly higher than other insects (P<0.05), demonstrating it had highest sensitivity to raw arbin.5. EAG responses from eight insects species to ARAThe EAG amplitudes from the insects species examined to ARA were between–(0.209±0.008) mV and–(0.702±0.080) mV. The lowest and highest EAG amplitudes were elicited from P. americana (♀:-0.209±0.008 mV,♂: -0.218±0.005 mV) and P. xylostella (♀:0.626±0.040 mV,♂: -0.702±0.080 mV), respectively. And the amplitudes from P. xylostella were significantly higher than other insects (P<0.05), demonstrating it was most sensitive to ARA.6. Effects of sexes on EAG responsesThe sex of insects had some effects on EAG responses. The EAG amplitudes from P. xylostella, B. germanica, O. furnacalis, S. exigua and H. amigera female were all higher than males and there was no significant difference between sexes except S. exigua (F=6.557,P=0.012). However, The EAG amplitude from P. americana males was higher than females and the sexual difference was significant (F=4.636,P=0.034).7. Dose-response CurveEAG responses could be recorded from all examined insects among the range of dose, suggesting EAG response thresholds were at similar orders of magnitude, however, individual and sexual differences were observed in the present study. EAG response elicited from A. pernyi was found to be dose-dependent with a typical"S"curve. EAG amplitude from P. xylostella male was higher than that from female, which demonstrated that male antennae were more sensitive. The amplitude of EAG response from B. lucorum elicited by raw ricn, arbin and RTA increased with the increase of dose, but it reached the plateau at the dose of 10.0 ng followed by a lower EAG amplitude in spite of the increase of dose, demonstrating the detection limit of B. lucorum antennae. Dose-response curves from other insects varied with the insect species and sex with different peaks at different doses, that is to say, EAG response thresholds were variable in different antennae.8. Olfactory behavioral responsesAmong the insect species examined, the taxis of B. germanica to RTA was obvious and there was significant sexual difference between individuals (F=7.324, P=0.014). The tested insects were attracted to raw ricin except that P. xylostella oriented behaviorally to raw arbin and sexual dimorphism was not observed (P>0.05). The behavioral responses of S. exigua and A. pernyi were not positively related to the EAG responses, while the behavioral and electrophysiological data of other insects were found to be consistent.