Hiroe Yasui, Nao Fujiwara-Tsujii, Seiji Tanaka, Sadao Wakamura

Insect Interactions Research Unit

［Abstract］

The characteristic mating behaviour of the white grub bettle (Dasylepida ishigakiensis), a serious insect pest of sugarcane, has led to the identification of (R)-2-butanol (R2B) as a major sex pheromone component. The present study revealed the effects of R2B and racemic 2-butanol (rac-2B) in mating disruption both in the laboratory and in the field. Infestation can be effectively controlled by releasing either synthetic R2B or rac-2B in the field to facilitate disruption of the sexual communication in the white grub beetle.

［Keywords］

sex pheromone, 2-butanol, flight tunnel experiment, mating disruption, pest control methods

［Background］

The white grub beetle, Dasylepida ishigakiensis (Coleoptera: Scarabaeidae) is one of the most destructive pests plaguing the sugarcane crop in the Miyako Islands in Okinawa. Sugarcane roots and underground stems are voraciously eaten by third instar larvae and the plants often die just prior to harvesting (Fig. 1). The application of pesticides has not been effective against soil insects and could even lead to pollution of underground water. During the cold months of February and March, these insects appear above the ground for mating at around 18:00 in the evening with temperatures above 18°C. Mating usually lasts for only half an hour after which both male and female insects return to the soil before dawn. During such a short period of mating activity, the male insects are attracted to the female sex pheromone. Therefore, we used synthetic sex pheromones to interfere with mating activity of white grub beetle and to develop an efficient method for abating this pest insect.

［Results and Discussion］

1. The white grub beetle has been found to undergo diapause at the 3rd stadium larvae and adult stages which are both thermally regulated. The diapause at the adult stage effectively serves to synchronize the time of sexual maturation and the sex pheromone is emitted only by the mature females.
   
2. The female sex attractant pheromone has been identified as 2-Butanol (2B), a low molecular weight highly volatile alcohol. It has been identified for the first time as a sex pheromone component of insects (Fig. 2).
   
3. Two enantiomers of 2-Butanol, (R)- and (S)-2-butanols (R2B and S2B) have been identified. However, insects can be attracted only to R2B which is quite costly to use as communication disrupting agent. Conversely, racemic 2-butanol (mixture of R2B : S2B 1:1, rac-2B) is much less expensive and is thus more practical than R2B for this purpose. The effectiveness of aerial permeation with R2B and rac-2B as communication disrupting agents was compared by spraying in a flight tunnel and directly in sugarcane fields in order to evaluate the feasibility using rac-2B in the field.
   
4. In the flight tunnel experiment, males could not reach a female model with a R2B lure under permeation with either R2B or high concentration of rac-2B.
   
5. The field experiment was performed using synthetic compounds sealed either in tube dispensers 20 cm in length or rope-type dispensers 25 m in length provided by ShinEtsu Chem. Co. We compared the mating rates of female and male trap catches between treated plots and untreated control plots (Fig. 3). There was no difference between tube- and rope-type dispensers. Either R2B or high concentrations of rac-2B prevent their mating and male attraction to pheromone trap.
   
6. This result may indicate that the flight tunnel assay is useful in evaluating the efficacy of chemicals as mating-disruption agents and in estimating the approximate amounts required for mating disruption.

1. Mating disruption method for management of pest insects is commonly used in Lepidopteran insects but not among Coleopteran insects. Our results may lead to further application of mating disruption in a wide variety of insect pests. In the case of Coleopteran insects, detailed characterization of the life cycle will be necessary for efficient application of this method.

Fig.1. Sugarcane field severely damaged by white grub beetle.	Fig.2. The male beetles attracted to a pheromone trap.

Fig.3. Effects of pheromone components, dispenser types and concentrations on the mating rates of D. ishigakiensis females and relative percentages of male trap catches in the sugarcane fields on Miyako Island. A: Mating rate of females. B: Relative trap catch of males. T: tube-type dispenser, R: rope-type dispenser. Histograms and vertical bars indicate the back-transformed means and SE, and the means designated by the same letter are not significantly different at P = 0.05. The numbers in parentheses indicate the number of plots tested/day.

 

[Collaborator]
Norio Arakaki, Atsushi Nagayama and Hiroaki Oroku (Okinawa Prefectural Agricultural Research Center)

[Reference]

1. Arakaki N, Hokama Y, Nagayama A, Yasui H, Fujiwara-Tsujii N, Tanaka S, Mochizuki F, Naito T, Hongo T, Wakamura S (2013) Mating disruption for control of the white grub beetle Dasylepida ishigakiensis (Coleoptera: Scarabaeidae) with synthetic sex pheromone in sugarcane fields Applied Entomology and Zoology 48(4):441-446
   
2. Yasui H, Wakamura S, Fujiwara-Tsujii N, Arakaki N, Nagayama A, Hokama Y, Mochizuki F, Fukumoto T, Oroku H, Harano K, Tanaka S (2012) Mating disruption by a synthetic sex pheromone in the white grub beetle Dasylepida ishigakiensis (Coleoptera: Scarabaeidae) in the laboratory and sugarcane fields Bulletin of Entomological Research 102(02):157-164