Koji Mishiro

Double meaning of courtship song in a moth

Males use courtship signals to inform a conspecific female of their presence and/or quality, or, alternatively, to ‘cheat’ females by imitating the cues of a prey or predator. These signals have the single function of advertising for mating. Here, we show the dual functions of the courtship song in the yellow peach moth, Conogethes punctiferalis, whose males generate a series of short pulses and a subsequent long pulse in a song bout. Repulsive short pulses mimic the echolocation calls of sympatric horseshoe bats and disrupt the approach of male rivals to a female. The attractive long pulse does not mimic bat calls and specifically induces mate acceptance in the female, who raises her wings to facilitate copulation. These results demonstrate that moths can evolve both attractive acoustic signals and repulsive ones from cues that were originally used to identify predators and non-predators, because the bat-like sounds disrupt rivals, and also support a hypothesis of signal evolution via receiver bias in moth acoustic communication that was driven by the initial evolution of hearing to perceive echolocating bat predators.

Male courtship ultrasound produced by mesothoracic tymbal organs in the yellow peach moth Conogethes punctiferalis (Lepidoptera: Crambidae)

Insect sound-producing apparatuses are mostly classified into two types: file–scraper and tymbal. Structures and locations of these organs are conserved in some phylogenetic groups, e.g., crickets, grasshoppers, and cicadas. However, moths have evolved diversified sound-producing organs, such as wing castanets and proboscis, in addition to the file–scraper and tymbal, in each species. Here we demonstrate that the yellow peach moth Conogethes punctiferalis (Guenée) (Lepidoptera: Crambidae) has developed mesothoracic tymbal organs never reported so far in insects. Tymbals are male specific and used for generating ultrasonic clicks in mating. We found eight to nine striae on the smooth surface of the tymbal membrane, suggesting the production of several clicks by a single buckle of the membrane in association with contraction/relaxation of the mesothoracic muscles. Acoustic data from click sequences support the idea that the series is generated by side-to-side asynchrony with an active/passive half cycle by an inward/outward buckle, and thus in click group (pulse) production, males emit 28 clicks with the right and left tymbals. The click-producing mechanism is similar, but not homologous, to those of other clicking species in five moth families. Thus, moths have acquired tymbal organs through independent and convergent evolution.

Sticky Traps Baited with Synthetic Aggregation Pheromone Predict Fruit Orchard Infestations of Plautia stali (Hemiptera: Pentatomidae)

ABSTRACT The brown-winged green bug, Plautia stali Scott, mainly reproduces on Japanese cedar or cypress cones in Japanese plantation forests during summer and autumn. It often depletes its food sources in forest habitats and moves to cultivated crops in large numbers. To establish an easy method for assessing the risk of fruit orchard infestation by P. stali, we conducted a 3-yr field survey that monitored the attraction of bugs to the synthetic P. stali aggregation pheromone using a sticky trap.We used a morphological indicator, variable body size depending on food intake, to estimate the nutritional status in nymphs, which showed that nymphs attracted to the synthetic pheromone were starving. Comparisons between increasing changes in the number of stylet sheaths left on the cones by P. stali and the number of trapped nymphs show that monitoring nymphs with the pheromone-baited sticky trap is useful for inferring conditions regarding food resources in forest habitats. The trend toward trapping second instars can provide a timely overview of resource competition for cones. Trapping middle-to-late (third—fifth) instars is a warning that the cones are finally depleted and that there is a high probability that adults will leave the forests and invade the orchards. In addition, trends in trapping adults suggest that there is a potential risk of orchard infestation by the pest and predict the intensity and period of the invasion. The pheromone-baited sticky trap is an easy but useful survey tool for predicting P. stali orchard infestations.

Developmental response of the brown-winged green bug, Plautia stali (Heteroptera: Pentatomidae), to food shortage

To study developmental response of the brown-winged green bug, Plautia stali Scott, to food shortage we reared nymphs under restricted feeding conditions produced by shortening the feeding period after molt or withholding food from second to fifth instars. For second instars, molting rates were significantly reduced as the feeding period was shortened. Shortening the feeding periods for third to fifth instars also reduced molting rates, but less so; some nymphs were able to complete their developments even if no food was given to any of the instars. Compared with controls for which feeding was not restricted, nymphs that successfully reached the next instar had reduced postmolt body size as a result of restricted feeding for all instars except the fifth (2-day feeding for second instar, and 1-day feeding for third and fourth instars), whereas instar duration was unchanged or only slightly prolonged for all instars. These results suggest that only nymphs with nutritional accumulation over a specific threshold in each instar can progress to the next instar, and that, particularly for second to fourth instars, nymphs develop on schedule without prolonging instar durations to compensate for reduced growth under conditions of food shortage.

High duty cycle pulses suppress orientation flights of crambid moths

Bat-and-moth is a good model system for understanding predator-prey interactions resulting from interspecific coevolution. Night-flying insects have been under predation pressure from echolocating bats for 65Myr, pressuring vulnerable moths to evolve ultrasound detection and evasive maneuvers as counter tactics. Past studies of defensive behaviors against attacking bats have been biased toward noctuoid moth responses to short duration pulses of low-duty-cycle (LDC) bat calls. Depending on the region, however, moths have been exposed to predation pressure from high-duty-cycle (HDC) bats as well. Here, we reveal that long duration pulse of the sympatric HDC bat (e.g., greater horseshoe bat) is easily detected by the auditory nerve of Japanese crambid moths (yellow peach moth and Asian corn borer) and suppress both mate-finding flights of virgin males and host-finding flights of mated females. The hearing sensitivities for the duration of pulse stimuli significantly dropped non-linearly in both the two moth species as the pulse duration shortened. These hearing properties support the energy integrator model; however, the threshold reduction per doubling the duration has slightly larger than those of other moth species hitherto reported. And also, Asian corn borer showed a lower auditory sensitivity and a lower flight suppression to short duration pulse than yellow peach moth did. Therefore, flight disruption of moth might be more frequently achieved by the pulse structure of HDC calls. The combination of long pulses and inter-pulse intervals, which moths can readily continue detecting, will be useful for repelling moth pests.

Thermal response and reversibility of prolonged larval diapause in the chestnut weevil, Curculio sikkimensis.

Curculio sikkimensis undergoes prolonged larval diapause that is terminated by chilling and warming cycles. To examine the effects of warming temperatures and their duration on diapause termination, we exposed diapause larvae that had not been reactivated after chilling at 5 degrees C to 20 or 25 degrees C and chilled them again before incubation at 20 degrees C. With increasing warming duration at 20 degrees C, diapause termination after chilling increased and shorter chilling durations became effective. In contrast, few or no larvae warmed at 25 degrees C terminated diapause after chilling, irrespective of the warming duration. To investigate the effect of warming temperature on diapause intensity, larvae with diapause weakened by initial incubation at 20 degrees C after the first chilling were subsequently incubated at 15, 20, or 25 degrees C, then chilled at 5 degrees C before incubation at 20 degrees C. Diapause termination increased significantly after the larvae were treated at 15 or 20 degrees C but decreased significantly after they were treated at 25 degrees C. The intensification of prolonged diapause at 25 degrees C was reversed when the larvae were transferred to 20 degrees C. Diapause intensity in C. sikkimensis therefore decreases at 20 degrees C, increases at 25 degrees C, and can be reversed by alternately exposing diapause larvae to 20 and 25 degrees C. In C. sikkimensis, prolonged diapause does not always proceed in one direction, and its intensity fluctuates in response to ambient temperature conditions.