Daily Rhythm, Factors Controlling Oviposition Behavior and Dispersal of Reproducing Adults of the Leaf Beetle Gastrophysa atrocyanea (Coleoptera: Chrysomelidae)

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以下資料感謝 Dr. Seiji Tanaka 田中誠二博士提供:
Overwintered leaf beetles (Gastrophysa atrocyanea) lay eggs on the leaves of dock plants in spring. Due to the simultaneous hatching of numerous larvae and their intensive feeding on the leaves, they often cause significant defoliation in individual dock plants. This beetle has been considered a potential candidate for biological control against dock plants, known as troublesome plants in farmland and poorly managed grassland. The present study investigated the oviposition behavior of G. atrocyanea, focusing on three subjects.
The first subject examined the daily rhythm of oviposition activity. The second subject explored why the beetles laid eggs on the undersides of leaves. The final subject investigated adult dispersal concerning the presence of larvae.
The beetles were observed laying eggs continuously during both light and dark periods under semi-natural conditions at 25°C, indicating around-the-clock oviposition activity. This continuous activity may lead to the rapid deposition of egg masses on a host plant within a short period, potentially favoring better survival of eggs and larvae.
G. atrocyanea adults have been observed depositing egg masses on the undersides of host plant leaves in field conditions. This behavior is considered adaptive due to the susceptibility of eggs to desiccation and leaf friction caused by strong winds. Additionally, the detection and predation rates of eggs by other insects and animals are likely lower on the undersides of leaves than on the front sides.
However, adults deposited egg masses on the front and undersides at similar rates either under light-dark cycles or in darkness when leaves were glued to the ceiling of Petri dishes. This suggests that the adults did not discriminate between the two sides of the leaf for oviposition, irrespective of the presence or absence of light. Nevertheless, when the beetles and dock plants were placed in a box covered with a blackout curtain and illuminated from the floor, most of the egg masses were found on the undersides of the leaves. This pattern resembled observations made under semi-outdoor conditions, indicating a strong preference for laying eggs on the undersides of leaves.
Preliminary observations indicated that adults laid eggs on the underside of a partially detached leaf disc from the floor, suggesting that this beetle may prefer to lay eggs by bending its abdomen underneath a substrate. This behavior may explain why the beetles frequently lay eggs on the undersides of leaves, even though they do not show a preference for laying eggs on either side of the leaf when both sides are presented.
During the present study, dock plants seriously defoliated by crowded larvae were frequently observed in April. Given the high lifetime fecundity of this beetle, it is not surprising that reproducing adults have evolved mechanisms to avoid overcrowding in their offspring. In late March, when numerous larvae were growing on dock plants, it was noted that most adults were found on plants without larvae. Conversely, most dock plants infested by larvae were without adults. These findings suggest the possibility that adults dispersed in response to cues associated with larvae or severely defoliated plants.
文章來源 : Seiji Tanaka。2024。日常節律,控制臺灣斑馬葉甲蟲 (Gastrophysa atrocyanea,鞘翅目:金花蟲科 ) 成年産卵行為和散佈的因素。台灣昆蟲 Formosan Entomol. 44: 1-14 (2024). DOI: 10.6662/TESFE.202401_44(1).001