Ecological aspect of a new insect pest of tomato Lasioptera sp. (Diptera: Cecidomyiidae)

In 2010, stem damage was detected in tomato grown in greenhouses at Yoichi, Hokkaido, Japan. It was reported that larvae of Lasioptera sp. (Diptera: Cecidomyiidae) developed in the damaged stems. We studied the ecology of the species with the ultimate aim of developing its control measures. To identify the host plants, the number of larvae in the wounded stems of cucumber, green pepper, eggplant, and tomato grown in a greenhouse in Yoichi, Hokkaido was recorded. Since no larvae were found in the stems of green pepper and cucumber, it appeared that these plants were not the hosts of the species. In contrast, three and 63 larvae were found in one of the 17 stems of eggplant, and 11 of the 15 stems of tomato, respectively. Therefore, this Lasioptera species appeared to be highly dependent on tomato for laying eggs. Subsequently, the first emergence period after overwintering was studied. The adults emerged from the residue of stems that had remained under the snow. They were captured in the emergence trap during the last 10 days of May and early June. Although the first reports of damage to tomato by this species emerged around mid-June in 2014, 2015 and 2016, which was very close to the first emergence period, the insects were not observed very frequently. Successful capture of adults started from mid-August with the suction traps installed in the greenhouse. These findings suggest that this species of Lasioptera might have several generations per year, and their numbers can increase rapidly from first emergence (June) to the end of the cropping season (September). Since it would be difficult to control the species spreading over a wide region, the species should be controlled while it is not widely found. Moreover, sampling with the suction trap and continuous observation of the plant revealed that activity of the adults was confined to daytime. However, even during daytime, the number of larvae in the stems cut during dry weather was lesser than that in stems cut during rainy conditions. It was inferred that rapid drying of the stem wound owing to dry weather would hinder egg laying. Thus, the biology and behavior of the adults of the harmful species of Lasioptera revealed in this study might contribute significantly in developing new control methods in future.