| The diamondback moth (DBM), Plutella xylostella L. (Lepidoptera:Plutellidae) is one of the most destructive cosmopolitan insect pest of cruciferous vegetables and requires-US $4-5 billion globally in estimated annual management costs. It has shown significant resistance to almost every synthetic insecticide applied in the field because of overusing chemical pesticide, and the environment was then great damaged. The DBM uses glucosinolates as host recognition cues for oviposition, and oviposition preference is different among the various cruciferous vegetables. Along with pesticides, various pest management tools have been used and/or proposed to manage this species, incuding intercropping and crop rotation with various cruciferous vegetables. Therefore, researches on the olfactory behavior and mechanism of the diamondback moth have a very important practical significance.We studied the mating, feeding and oviposition preferences of the DBM in Shanxi region, the antennae are the main olfaction organ in insects, and play a key role in mating and oviposition behaviors. The ultrastructure and function of the sensilla on the antennae of DBM were preliminary studied to investigate the olfactory identification mechanism. The main results are as follows:1 The effects of adult age and temperature on the mating of DBMThe mating capability and behavior of the DBM were investigated under laboratory conditions, the age of the DBM significantly affected their mating rate. Both males and females were able to mate at the first day after emergence, the highest mating rates at the lrst and 2nd day were above 70%. From the 3-day, the diamondback moth mating rate decreased with increasing age, and the moth mating rate reached the lowest (9.67±0.47%) at 8th-day. The temperature also affects the mating capability. At 25℃ the mating rate was the hightest(85.0±4.36%) and mating peak occurred at the earlist(1.86±0.08 d). When the temperature was either below 25℃ or higher than 25℃, the DBM mating rate was reduced, and mating peak was delayed. At 19℃ the mating rate was 54.69±4.93% and the mating peak occurred at 3.52±0.32 d. At 34℃ the mating rate was 32.57±3.06% and the mating peak at 3.97±0.13 d.2 The feeding and oviposition preference of DBM in ShanxiFeeding behavior of the DBM larvae among the seven species of cruciferous vegetables were investigated in the laboratory and in the field. We found that the larva feeding preference was different, the preference order was as follows:Brassica napus> B. juncea>B. chinensis L>B. parachinensis Bailey≥B. oleracea L.> Raphanus sativus L>B. aleracea L. var. botrytis L. We also investigated that the oviposition preference of DBM among the seven species of cruciferous vegetables. The result showed that oviposition preference was different, the preference order was as follows:Brassica campestris L.>B. napus>B.juncea L.> Raphanus sativus L.> B. parachinensis Bailey> B. oleracea L.>B. aleracea L. var. botrytis L.3 Effects of low concentration of avermectin on DBM olfactory behaviorsThe effects of spraying low concentrations avermectin on DBM mating behavior, host-finding and oviposition preference were conducted. Our findings are as follows:(1) The mating success rate was 81.79±4.61%, the mating peak was 1.82±0.47d without avermectin application. When abamectin was sprayed, the mating behavior was remarkably disturbed, the mating success rate dropped to 54.26±4.87%, the peak mating period was delayed to 2.87±0.42d. (2) The DBM larva feed the seedlings of B. napus-B. napus, B. napus-Raphanus sativus, B. Napus-B. juncea, the average feeding area ratios were 1:0.98,1.53:1,2.10:1, respectively. When abamectin was respectively sprayed to B. napus in the three groups, the larva feeding activity were converted, the average feeding area ratios were 1:0.35,0.10:1, 0.08:1, respectively. The feeding preference of P. xylostella was altered by insecticide, the larva intended to feed the cruciferous plants without the insecticide. (3) The DBM adults laid eggs on the plants of B. chinensis-B. chinensis, B. napus-B. chinensis, R. sativus-B. chinensis, their average ratios of laying eggs were 1:1.03,1:1.73,1:3.84, respectively. When abamectin was respectively sprayed to B. chinensis in the three groups, oviposition preference were converted, their average ratios of laying eggs were 1:0.19,1:0.30,1:0.40, respectively. The oviposition preference to host plants was altered after spraying of avermectin, DBM laid more eggs on the plants without avermectin application. It demonstrated that insecticide application played a more important role in oviposition preference than host plants, and both factors were integrated to affect the oviposition preference of the moth. In addition, avermectin also influence oviposition site selection, DBM tried to select avermectin-free plant sites to lay eggs.4 The importance of antennae in the olfactory behaviorIn this study, we ablated the antennae of the DBM in various ways, with the aim of understanding the influences on the mating and oviposition behaviors. We found that the mating success rate was 84.44±3.85%, the mating peak was at 1.92±0.64d and the number of eggs laid on B. campestris was three times more than on R. sativus in a control group containing intact antennae. Neither oviposition preference nor mating behaviors changed significantly when less than 1/4 of both antennae were removed. However, there was a significant behavioral change when the antennae were ablated by more than half. With a decrease in antenna length, the successful mating rate decreased, mating peak was delayed and oviposition preference became weaker. When both antennae were completely removed, the mating success rate dropped to 11.11±3.84%, the peak mating period was delayed to 9±0.89d and oviposition preference was eliminated. Although the group with unilateral antenna removal and the group in which 2/4 of both antennae were removed retained similar numbers of sensilla, the former maintained a significantly higher degree of oviposition preference and lower rate of successful mating, but mating peak times did not differ between the two groups.5 Types and ultrastructures of olfactory sensilla in DBM antennaeWith scanning and transmission electron microscopic and focused ion beam-scanning electron microscopic the examinations revealed that the DBM antenna was filiform, the length of antenna, scape, pedicel and flagellum were all greater in males than in females. Sixteen types of sensilla were identified on the antennae:trichodea (two subtypes), basiconica, coeloconica (three subtypes), styloconica (two subtypes), squamiformia, auricillica, Bohm, furcatea (three subtypes), cupuliform organs and terminal sensory pegs. Some of the sensilla possessed sexual dimorphism. The trichoid sensilla type Ⅰ and Ⅱ were the most numerous sensilla type on the antennae, the male antennae had more trichodea sensilla than the female antennae, and trichoid sensilla type Ⅰ have 2-3 dendritic profiles in each sensillum. Basiconic and coeloconic sensilla were more numerous in female than in male antennae, and basiconic sensilla type I have 2-6 dendritic profiles in each sensillum. The terminal sensory pegs have 3 sensory cells in male and 4 sensory cells in female.6 The olfactory function of the main antennal sensillaCorrelations between sensilla distributions and olfactory behaviors were examinated. Our studies showed that DBM trichoid sensilla Ⅰ and Ⅱ were highly correlated with mating rate and oviposition preference, but negatively correlated with mating peak. Basiconic and coeloconic sensilla were not correlated with mating rate and peak, but highly correlated with oviposition preference. These findings suggest that the trichoid sensilla probably respond to sex pheromones and plant volatiles, whereas the basiconic and coeloconic sensilla were sensitive to plant odors. |
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