Recent work on selected topics of particular interest for understanding insect life-cycles is reviewed, including habitat patterns, kinds of variation, the spreading of risk and prolonged diapause, trade-offs and developmental plasticity, circannual rhythms, the concept of life cycles as developmental choices, and development or delay as the default response. Seasonal adaptations have a wider range of components than has often been appreciated. Variation in life-cycle traits, including the duration of development and the timing of emergence, can be wide, narrow, or discontinuous. Trade-offs encompass multiple simultaneous traits and are not always structured as might be expected. Diapause, cold hardiness, reproductive pattern, and other traits have evolved many times independently. Such complex interactions can be understood only by examining the detailed features of a species' habitat, because how developmental decisions are made and whether continuous development or delays are programmed reflect the predictability of habitats and the environmental signals they supply. Ecological context is important, not just mechanisms of adaptation. Therefore, although most previous studies have paid more attention to insect response than to habitat, interpreting the seasonal relevance of life-cycle patterns requires measurement and analysis for individual species of habitat characteristics and their variation, on a range of temporal and spatial scales, in much more detail than has been customary.
Recent work on anhydrobiosis in invertebrates is reviewed. I introduce definition and classification of cryptobiosis, and review the distinctive features and extremely high stress tolerance of anhydrobiotic invertebrates. Most anhydrobiotic invertebrates have evolved various kinds of behavioral, morphological, physiological and physical adaptations to reduce water loss during induction of anhydrobiosis. Trehalose is known as a common compatible solute in anhydrobiotic organisms from unicellular organisms to invertebrates and higher plants. Trehalose may provide effective protection against desiccation because it has superior biochemical and physicochemical properties for stabilizing membranes and biomolecules including proteins and lipids. Recent work also indicates several possible kinds of molecules involved in induction of anhydrobiosis. The adaptations necessary for successful induction of and recovery from anhydrobiosis vary greatly among taxa of invertebrates. Understanding the diversity of anhydrobiosis in invertebrates would be a key to elucidate evolutionary scenarios in anhydrobiosis.
The experiments were conducted to learn about the relative toxicity of insecticides against the two parasite wasps of citrus leafminer (CLM), Phyllocnistis citrella. The relative toxicity of 12 common insecticides against the eggs and first instar larvae of the pest, and its parasitoids of Chrysocharis pentheus and Sympiesis striatipes, which are dominant species in Ehime Prefecture, was compared in 2003. Corrected mortalities were evaluated by dipping or spraying methods for the CLM eggs and larvae, and by clip-cage bioassay for the parasitoid wasps. All the insecticides tested showed almost over 90% mortality to the first instar larvae of citrus leafminer, but a lesser effect to the eggs. Against the adult parasitoids, imidacloprid (a.i. 0.005%), thiamethoxam (a.i. 0.003%) and acetamiprid (a.i. 0.005%) of the nicotinoide insecticides were less toxic, but dinotefuran (a.i. 0.02%) showed rather high mortalities. Of the IGRs, teflubenzuron (a.i. 0.05%) and diflubenzuron (a.i. 0.012%) were safe or less toxic to adult wasps. These three nicotinoide and two IGRs insecticides will be suitable candidates for use in the IPM program. Isoxathion (a.i. 0.025%) and primiphose-methyl (a.i. 0.056%) of the organophosphate and alanycarb (a.i. 0.04%) of carbamate were highly toxic. Bifenthrin (a.i. 0.0015%) of the pyrethroid and petroleum oil (a.i. 1.05%) were moderate in toxicity. Clothianidin (a.i. 0.005%) of the nicotinoide showed low toxicity to Chrysocharis pentheus but moderate toxicity to Sympiesis striatipes.
Larvae of armyworm, Spodoptera litura, a polyphagous leaf-eater and the monophagous Milionia basalis pryeri feed more on a diet gel containing chlorophyll b in the light. Chlorophyll b acts as a visual stimulus to feeding rather than as a gustatory or odor stimulus. Furthermore, the larvae are found significantly more frequently on gels placed on silhouettes of gels containing chlorophyll b than on that of colorless gels. This reveals that the larval response to the color of chlorophyll b is orthokinetic rather than tactic. S. litura and M. b. pryeri larvae are able to distinguish between colors since consumption varied according to the wavelength of the green silhouettes. Feeding differences between the two species may be due to the color of their host plants. These are novel findings that indicate lepidopteran larvae recognize the green colors of their host plants.
I investigated inter- and intra-shoot distributions of the caterpillars of the ramie moth Arcte coerulea in shrubs of the host plant China ramie, Boehmeria nipononivea. The caterpillars were distributed on long shoots in the canopy of ramie, and caterpillar performance was better when they fed on leaves of the canopy shoots rather than those of the understory shoots. This was probably because the caterpillars could overcome the host plant defense to obtain nutrition from the sunlit shoots, which often contain higher concentrations of chemical defenses. Within a shoot, caterpillars were found on leaves that had just completed expansion. This leaf preference was probably affected by the change in food quality with leaf age. Caterpillars were never observed on buds, and their performances were poor when they fed on buds. This suggests that the chemical defense is heavily concentrated in buds. Outbreaks of A. coerulea frequently occur and cause defoliation of host plant shrubs; this may have resulted in accelerated evolution of host plant defense for rapid regrowth of the foliage, which contributes to the plant's tolerance of these moth caterpillars.
Effects of native ladybird females of Harmonia axyridis Pallas and Coccinella septempunctata L. on oviposition behavior of the exotic species, Adalia bipunctata (L.), were assessed by pairing females of the exotic species with conspecific or heterospecific females. Pairs of females were provided with aphids in excess for 30 days, during which time there were no significant differences in weight, rates of mortality, or selections of sites for oviposition among the treatments. However, females of A. bipunctata laid significantly fewer eggs over the 30-day experimental period when paired with females of H. axyridis or C. septempunctata than when paired with conspecifics, even though aphids were abundantly available in all three cases. The number of eggs laid by a female of A. bipunctata paired with conspecifics gradually declined over the 30-day experimental period, while egg production declined especially rapidly during the second ten-day period when females were paired with females of H. axyridis and C. septempunctata. Thus, egg production by females of the exotic species was reduced in the presence of the native ladybirds.
Four grain aphids, Sitobion spp. [S. avenae (F.), S. akebiae (Shinji), S. miscanthi (Takahashi) and S. fragariae (Walker)] on various grasses (Poaceae), nominated as Sitobion avenae-complex in this paper, were compared for their morphological and genetic characteristics. For morphological comparison, ten characters frequently used in the identification of S. avenae-complex were compared among samples from various global locations. The results from these comparisons demonstrated that the ranges of specific characteristics overlap considerably. The means of most characteristics were very similar among S. avenae, S. miscanthi and S. akebiae, indicating that the characteristics are not useful for the individual identification of these three grain aphids. Also, the intra-specific variations of the Far Eastern S. akebiae were as large as the inter-specific differences between S. miscanthi and S. avenae. In the nucleotide sequence comparison of the mitochondrial cytochrome oxidase subunit II (mt COII) gene, the pair-wise genetic distances among the populations of the three species ranged from 0.00 to 1.56%, almost equal to the intra-specific distances of Far Eastern S. akebiae (0.00–1.38%). In this context, it is suggested that S. akebiae (Shinji) syn. n. and S. miscanthi (Takahashi) syn. n. be synonymized under the senior name, S. avenae (F.).
The efficiencies of seven native species of eulophid parasitoids (Pnigalio katonis, Hemiptarsenus varicornis, Diglyphus isaea, D. minoeus, D. pusztensis, Chrysocharis pentheus and Neochrysocharis formosa) as biological control agents against Liriomyza trifolii in a greenhouse were evaluated based on their thermal tolerance in development and reproduction. All of them are solitary and idiobiont parasitoids, and their adults kill hosts directly by feeding on the hosts. Based upon their thermal tolerance, the species could be roughly classified into two groups, i.e., H. varicornis and N. formosa which are more adapted to high temperatures, and the other five species which are more adapted to low temperatures. In biological control, host killing by host-feeding is profitable in the release step, but becomes unprofitable in the mass-production step because it does not result directly in production of progeny. Hence, an evaluation method based on biological control efficiency (BCE) is proposed in this study as a comprehensive criterion for evaluating the efficiency of the parasitoids as biological control agents. The thermal tolerance and BCE clarified in this study revealed that D. isaea should be used in cool seasons and N. formosa in hot seasons, based on a borderline temperature of 20 to 25°C in the greenhouse.
A wood borer, Apriona japonica, causes significant damage to young Zelkova serrata trees. Previous studies in the life cycle of some other pests suggest that weeds around the base of the host tree might have some effect on oviposition behavior of A. japonica. Here I investigated the effect of removal of weeds on A. japonica oviposition on Z. serrata during the summer of 1996. Weed removal significantly depressed the number of oviposition marks. In a plot in which weeds had been removed, the height distribution of oviposition marks significantly differed from that in a control plot, in which most oviposition marks were found below the weed height. These results suggest that A. japonica adults prefer to oviposit on host branches and stems that are covered with weeds and that removing weeds deters A. japonica from ovipositing on exposed host tree parts.
Time-temperature-mortality relationships for egg, larval, pupal, and adult stages of the cigarette beetle, Lasioderma serricorne were investigated to determine disinfesting conditions for stored tobacco. Susceptibility to low temperatures changed according to the developmental stage. Eggs were most susceptible to low temperatures that were higher than −5°C. Larvae acquired cold tolerance during exposure to 15°C for 1 mo. These acclimated larvae were the most tolerant of all. LT99 values of acclimated larvae were calculated as 7.2 h at −15°C, 23.7 h at −10°C, 376 h at −5°C, 1,140 h at 0°C, and 1,880 h at 5°C. As the most susceptible stage, egg susceptibility to moderately low temperatures (16–20°C) was specifically examined. At 20°C, most eggs (>80%) normally hatched within 4 wk, but all eggs died within 6 wk at temperatures less than 18°C. This fact indicates that the reproductive cycle can be blocked at temperatures less than 18°C, and that tobacco stored in such conditions will never become infested, even if eggs are deposited by invading adults. Consequently, if the tobacco temperature is reduced to 5°C for 3 mo in winter and is subsequently maintained below 18°C throughout the rest of the year, tobacco can become and remain pest-free without any chemical control.
Eighteen weed species were surveyed for western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), from spring through autumn in 1994 within an ornamental production area in central Japan. WFT were collected from eight weed species and occurred as the predominant thrips species on most of the weed species in April. In early April, the densities of WFT adults and thrips larvae were high on racemes of common groundsel. From April to May, the densities of WFT on flowers of narrowleaf vetch, dandelion, and white clover increased rapidly. Between June and July, WFT adults inhabited predominately the Poaceae weed, but the density of their larvae was low. Furthermore, WFT became the minor colonizers on several weed species from August onward. These results suggest that WFT inhabit and reproduce predominately on numerous weed species flowering around the fields in spring, so the removal of weeds flowering in early spring is important for the control strategy of WFT.
Females of the black chafer Holotrichia loochooana loochooana (Sawada) (Coleoptera: Scarabaeidae) release anthranilic acid, which functions as sex attractant pheromone for males and aggregation pheromone for females. When a white lure treated with anthranilic acid was placed next to an untreated black lure in the field, males were observed to make pinpoint landings significantly more frequently on the latter. When the distance between the two lures was increased from 0 to 20 cm, frequency of pinpoint landing onto the untreated black lures significantly decreased while that onto the treated white lures slightly increased. When the lures were further separated to 2.5-m intervals, males approached only to the treated lures regardless of the color but significantly more frequently landed on the black ones than on the white. These observations demonstrated that males locate and land on a female by visual cues after reaching the vicinity by olfaction.
Effects of photoperiod and temperature on the induction of adult diapause were examined in Dolycoris baccarum (L.) collected in Osaka and Hokkaido, Japan. Adults started reproduction soon after adult emergence under long-day conditions, while they entered diapause under short-day conditions. The critical photoperiod for the induction of diapause was between 13 and 14 h and between 15 and 16 h in insects of the Osaka and Hokkaido populations, respectively. Under long-day conditions, most insects of the Osaka population emerged as reproductive adults at any temperature used, whereas those in the Hokkaido population tended to show lower incidence of diapause as the temperature increased. Preoviposition periods in females of the Osaka population were shorter than those of the Hokkaido population. The duration of diapause in the Osaka population was shorter at 30°C than at 25°C under short-day conditions. In Osaka, D. baccarum is assumed to produce three generations a year, like several other seed-sucking bugs. In Hokkaido, a greater proportion of adults produces the second generation in summer under long daylengths.
To elucidate the defensive functions of the trash-package of the green lacewing Mallada desjardinsi larva against the ladybird Harmonia axyridis, the contact frequency, attack rate, and capture rate of ladybirds were compared between the ‘with trash’ or ‘naked’ treatments of the green lacewing. The contact frequency until the ladybird captured the green lacewing was significantly more in the ‘with trash’ treatment (median: four times) than in the ‘naked’ treatment (median: one time), which indicates that the trash-package of the green lacewing offers protection from predation by ladybirds. The attack rate of the ladybirds on the ‘with trash’ green lacewing larvae (55%) was significantly lower than that on the ‘naked’ ones (90%). After the ladybirds first attacked, their capture rate of the ‘with trash’ green lacewing larvae (18%) was significantly lower than that of the ‘naked’ ones (83%). Thus, the trash-package of the green lacewing affords prevention against recognition (primary defense) and subjugation (secondary defense) from the ladybird.
In order to solve the long-standing problem as to whether the eyes of Scutigera coleoptrata were functional and responded to flashes of light, we carried out electrophysiological recordings from them with glass electrodes pushed into the eye's retina. The electroretinograms were typical cornea-negative responses, similar in shape and duration to those seen in other arthropods, including those with cryptic lifestyles. We located two sensitivity peaks: one in the vicinity to light of 448 nm wavelength and a second 0.25–0.5 log unit lower one in the ultraviolet region (UV) of the spectrum around 350 nm and we expect at least two kinds of visual pigments to be present. We can only speculate on the surprisingly well-developed UV-sensitivity and suggest that it could serve the animal as an alarm colour to avoid open, illuminated spaces or to detect exits from concealed hiding places in soil crevices and from under boulders.
Adult Platypus quercivorus beetles were artificially inoculated into Japanese oak trees (Quercus crispula). Two inoculation methods were used: uniform inoculation through pipette tips, and random inoculation by release into netting. Four of the five trees that were inoculated uniformly died, as did all five trees that were inoculated at random. Seven of the nine dead trees showed the same wilting symptoms seen in the current mass mortality of oak trees. Raffaelea quercivora, which has been confirmed to be the pathogenic fungus that causes wilt disease and is usually isolated from the mycangia of P. quercivorus, was isolated from all of the inoculated dying trees. Trees that died faster showed a higher density of beetle galleries that succeeded in producing offspring. We found positive relationships between the density of beetle galleries that succeeded in producing offspring and the rate of discoloration in the sapwood and the isolation rate of R. quercivora. Therefore, we clearly demonstrated that P. quercivorus is a vector of R. quercivora, and that the mass mortality of Japanese oak trees is caused by mass attacks of P. quercivorus.
In Japanese populations of the pea aphid Acyrthosiphon pisum, four types of facultative endosymbiotic bacteria, Serratia symbiotica, Regiella insecticola, Rickettsia sp. and Spiroplasma sp., have been identified in addition to the essential endosymbiont Buchnera aphidicola. On the vetch Vicia sativa and other leguminous plants, Aphis craccivora, Megoura crassicauda and A. pisum frequently co-occur and form mixed colonies. In this study, the endosymbiotic microbiotae in A. craccivora and M. crassicauda collected from different localities in Japan were investigated in comparison with the endosymbiotic microbiotae in sympatric samples of A. pisum. While the A. pisum samples frequently contained one or more of the four symbionts, the A. craccivora samples were infected with only Serratia and the M. crassicauda samples contained none of the facultative symbionts. When the four symbionts were artificially transferred from A. pisum to M. crassicauda by hemolymph injection, Regiella and Spiroplasma established heritable infections in the novel host while Serratia and Rickettsia did not. The Regiella infection in M. crassicauda was stably maintained with 100% fidelity for over 50 generations, whereas the Spiroplasma infection was unstable. On the basis of these results, we discussed the possible mechanisms whereby the different infection patterns with the facultative symbionts are maintained in the sympatric aphid communities.
Aphelinus asychis from Kyoto and A. albipodus from Kobe, which enter weak diapause, strictly oligopause sensu Mansingh (1971), as adults and diapause as larvae, respectively, were reared under natural conditions in Kyoto to validate their overwintering dormancy and to compare previous laboratory results with dormancy-inducing and terminating photoperiods and temperatures in the field. In A. asychis, 30% of the females that had emerged in late October to early November survived until late March, but all males that had emerged in the same time died by mid-January. Some of the females oviposited in early and mid-November, but the females were likely to stop oviposition between late November and late January because no aphids that were exposed to the females were mummified. The surviving females oviposited from early February to late March, and adults of the first generation emerged in mid- to late April. Adult oligopause appeared to be induced by the photoperiod in mid- to late October and to be maintained for more than two months. In A. albipodus, mature larvae of the generation beginning in mid-October overwintered within the mummies, and adults emerged in mid- to late April. Larval diapause appeared to be induced by the photoperiod in mid-October and to be terminated by cold temperatures experienced at the end of January.
The Phyto trap is an artificial microstructure that permits the easy collection of live predacious phytoseiid mites in the field. Neoseiulus californicus is a well-established indigenous phytoseiid mite in Japanese pear tree orchards in Japan. We examined whether or not the population size of N. californicus on Japanese pear trees can be estimated using Phyto traps attached to twigs in two Japanese pear orchards. The results suggest that the density of a prey mite, Tetranychus kanzawai, on leaves influenced the number of N. californicus trapped by the Phyto traps. When the density of T. kanzawai was high on the leaves, many N. californicus were observed on the leaves and the pattern of density change synchronized between T. kanzawai and N. californicus. Under this condition, no N. californicus were found in the Phyto traps. On the other hand, when the density of T. kanzawai was low on the leaves, N. californicus were found in the Phyto traps as well as on the leaves. The number of N. californicus collected by the Phyto traps also increased as the extent of leaf withering increased, and reached a peak after leaf fall was complete. This suggests that the movement of N. californicus on the pear trees during leaf-fall season can be elucidated in some detail by using the Phyto trap. The survey by the Phyto trap attached to twigs can eventually clarify the population fluctuation and movement of N. californicus on trees that are been overlooked in the investigation of the leaves alone.
The timing of diapause induction and overwintering success in the cotton bollworm Helicoverpa armigera were studied outdoors in Chiba (35°N, 140°E) and Kyoto (35°N, 135°E) prefectures, Japan, using local populations collected from Chiba and Mie (34°N, 136°E) Prefectures, respectively. For comparison, a similar experiment was performed in Chiba using a closely related species, H. assulta. Diapause induction in H. armigera was stimulated by low temperatures in autumn, and the incidence of pupal diapause increased sharply with little change in photoperiod. In Kyoto, pupae of H. armigera overwintered successfully in a state of diapause. However, larvae that had hatched from eggs deposited in late autumn suffered high mortality, presumably from the cold; therefore, the pattern of temperature change in autumn credibly affects overwintering success in H. armigera. In contrast, a considerable number of H. assulta pupae entered diapause well before autumn, even though those individuals had hatched from eggs deposited during the mid-summer. Thus, H. assulta appeared to prepare for overwintering earlier and more successfully than did H. armigera in this temperate zone. Differences in diapause induction between the sexes revealed in laboratory experiments with H. armigera were not detected under outdoor conditions.
As difference in food requirements of aphidophagous ladybirds might have an influence on the strength of interactions between the ladybirds and mutualistic ants, the effects of ant attacks on the foraging behavior of the two ladybird species, Coccinella septempunctata brucki and Propylea japonica, were investigated in relation to their developmental stages (adults and larvae). Large-sized C. septempunctata adults preyed on more aphids and were more frequently attacked by the ants than another species and developmental stage. Escape rates of the ladybirds after attacking tended to be higher in adults than in larvae. The percentage of C. septempunctata adults remaining on the plant in the ant-present treatments was significantly lower than in ant-excluded treatments, while there was no significant difference in the proportion of P. japonica adults between the two treatments. The proportion of larvae of both species was high even in ant-present treatments. This study revealed that the effects of ant attacks on the ladybirds differed between the two species in relation to their developmental stages, suggesting that food requirement of ladybirds would be one of important factors to understand the relationship between aphidophagous ladybirds and mutualistic ants.
The effects of temperature on the life history traits of Rhopalosiphum maidis (Fitch) were determined at 6, 10, 15, 20, 25, 30, and 35±1°C on corn leaves, Zea mays (L.). At 35°C, only a few nymphs survived and completed development, but all failed to reproduce. Total immature stages from birth to adult decreased as temperature increased from 51.7 d at 6°C to 5.2 d at 30°C, but became 8.0 d at 35°C. Overall immature development required 119.05 degree-days above 4.44°C. Adult longevity was as high as 26.7 d at 15°C, but significantly declined at 30 and 35°C. The average adult fecundity was as high as 45 offspring at 15 and 20°C, but dropped to 1.8 at 6°C and 8.6 at 30°C. In general, as temperatures increased, age-specific survivorship (lx) declined more quickly, but age-specific fecundity (mx) peaked earlier. At 25°C, the age-specific net maternity (vx=lxmx) was the highest in the early reproductive period, resulting in the highest intrinsic rates of increase (rm=0.329). At 20–30°C, the values of rm were significantly higher than those at lower temperatures. The results indicate that corn leaf aphids probably are better adapted in population growth to a wider range of high temperatures in warm regions.