The co-occurrence of an introduced biological control agent (Coleoptera: <Emphasis Type="Italic">Coccinella septempunctata</Emphasis>) and an endangered butterfly (Lepidoptera: <Emphasis Type="Italic">Lycaeides melissa samuelis</Emphasis>)

Whether a biological control agent presents a non-target risk to a native species depends if they co-occur spatially and temporally, and if the agent will harm the native species. We sampled two study sites during 1993 in Minnesota and Wisconsin to survey predators and parasitoids of the extant populations of the United States federally endangered Karner blue butterfly, Lycaeides melissa samuelis. We found the introduced coccinellid Coccinella septempuntata co-occurring spatially and temporally with eggs, larvae and adults of L. m. samuelis. The two species were also observed together on the latters sole host plant, Lupinus perennis, and in Wisconsin, an adult C. septempunctata was observed consuming second instar larvae of L. m. samuelis. Using a simple model to hypothesize the risk that C. septempunctata presents to L. m. samuelis, we showed that increases in predator density could greatly increase mortality to L. m. samuelis. At these sites, C. septempunctata were reproducing and had access to summer aphids and suitable overwintering habitat. Nearby agricultural crops could provide spring aphids for oogenesis, and assist with C. septempunctata population build-up. Maintaining a minimum isolation distance between agricultural crops known to harbor aphids and extant L. m. samuelis populations may need to be considered as part of the butterfly management program.     

Influence of Predator Presence and Prey Density on Behavior and Growth of Damselfly Larvae (Ischnura elegans) (Odonata: Zygoptera)

Foraging behavior is often determined by the conflicting benefits of energy gain and the risk of mortality from predation or other causes. Theory predicts that animals should have lower activity levels when either the risk of predation or the availability of resources in the environment is high. We investigated the adjustment of the behavior of I. elegans larvae to predator presence (Anax imperator) and prey density (Daphnia sp.) and their interaction in a completely crossed factorial experiment in the lab and the effect of behavior on growth. The foraging activity of the I. elegans larvae was significantly reduced in the presence of a free-swimming predator but not a caged predator. Abdominal movements were significantly reduced at a low prey density. Growth was significantly reduced by the presence of a free swimming predator and low prey densities. These results provide evidence that these damselfly larvae adjust their behavior to the presence of predators to increase their survival at the expense of reduced growth and development.     

Susceptibility of Delia radicum to steinernematid nematodes

Isolates of different Steinernema species (S. affine, S. bicornutum, S. feltiae and Steinernema C1) were used in mortality assays with third instar larvae of Delia radicum (L.) (Diptera: Anthomyiidae). The nematode isolates had been obtained by baiting soil regularly grown with cabbage. One isolate (S. feltiae) was the result of a natural infection of a D. radicum puparium. The highest mortality (77%) was obtained with an isolate of S. feltiae (DK1). The isolate DK1 was also used in tests with all larval stages of D. radicum. Mortality around 60% was observed for second and third instar larvae, while first instar larvae showed very low or no susceptibility. Maximum mortality of second and third instar larvae was reached applying only 25 nematodes per larva. Observations of larvae that pupated revealed that some of these puparia contained nematodes. Experiments with hatching puparia showed that a high proportion was infected by nematodes if the flies were prevented from leaving nematode-containing soil. In addition to mortality, the ability of the nematodes to successfully reproduce in the insects was studied. It was found that the species S. feltiae and S. bicornutum reproduced in D. radicum larvae and adults with S. feltiae being the most successful.     

Presence of predatory wasps and stinkbugs alters foraging behavior of cryptic and non-cryptic caterpillars on plantain (Plantago lanceolata)

We examined the foraging patterns of two species of caterpillar (Junonia coenia: Nymphalidae and Spilosoma congrua: Arctiidae) that contrast in feeding specialization and crypticity on plantain (Plantago lanceolata) in the absence and presence of two different insect predators [stinkbugs, Podisus maculiventris (Pentatomidae) and wasps, Polistes fuscatus (Vespidae)]. Junonia larvae were quite apparent to human observers, feeding on upper leaf surfaces during daylight, whereas Spilosoma larvae were relatively cryptic, often hiding under leaves and in soil crevices during daylight. In the presence of either predator species, the non-cryptic Junonia caterpillars more quickly left the plant on which they were initially placed and were less apparent than Junonia larvae not exposed to predators. The presence of predators had no detectable influence on where the caterpillars occurred on the plants (new, intermediate-aged or mature leaves, or reproductive stalks). Surprisingly, the predators influenced the behavior of the inherently cryptic Spilosoma: the apparency of these larvae at night increased when wasps had access to the plots during the day. Survivorship of the non-cryptic Junonia was less than 12% when stinkbugs were present compared to 60% in their absence. Although the presence of wasps resulted in a lower relative growth rate for the non-cryptic Junonia larvae, the indirect effect of predators on reduction in survivorship due to alterations in prey growth rate through behavioral changes was less than 3%. After taking into account the decline in caterpillars per plot through predation, we found that both the amount of leaves eaten and the proportion of plants eaten were altered on plots with predators present, which suggests that the caterpillars' increased consumption countered increased maintenance costs due to the presence of predators. Overall, our results indicate that hostplant size, level of predation and type of predator can influence the degree to which these caterpillars react to the presence of insect predators. In contrast, degree of inherent feeding specialization and cryptic behavior seemed to have little effect on the expression of reactive behaviors of these caterpillars to predators.     

Influence of Dimilin on a microsporidian infection in the gypsy moth Lymantria dispar (L.) (Lepidoptera: Lymantriidae)

Bioassay studies were conducted to investigate the influence of Dimilin (diflubenzuron), a chitinsynthetase inhibitor used for insecticidal control of the gypsy moth, Lymantria dispar, on the development and viability of a microsporidian pathogen of L. dispar. Before or after an infection with a Nosema species, L. dispar larvae were fed Dimilin in sublethal dosages. Dimilin fed to L. dispar larvae at 0.65 ng/cm² diet surface resulted in a total larval mortality of 53%. Although the microsporidian infection alone did not cause high mortality rates (9%), mortality increased to 96% when L. dispar larvae were inoculated with both Dimilin and Nosema spores. When Dimilin was fed to the larvae 24 h before or 6 days after inoculation with the microsporidium, the number of mature spores produced was significantly reduced. When Dimilin was fed to the larvae 24 h after microsporidian inoculation, the number of spores produced was not significantly reduced. Spores that were produced in larvae after Dimilin had been ingested with the diet were less infectious than spores produced in control larvae; the experimental infection rate decreased from 94% when spores obtained from control larvae were used, to 48 or 10% when spores obtained from larvae fed Dimilin 24 h or 6 days after Nosema inoculation, respectively, were used. Mature microsporidian spores washed in Dimilin solution prior to oral inoculation, however, were as infectious as spores stored in liquid nitrogen. We have shown that Dimilin interferes with the establishment of the parasite in its host. In addition, when Nosema sp. succeeds in infecting the L. dispar host despite treatment with Dimilin, the microsporidium does not develop optimally and spore production is reduced.     

The choice of oviposition site and the effects of density and oviposition timing on survivorship in<Emphasis Type="Italic"> Rana japonica</Emphasis>

In species that lack parental care and whose larvae are restricted to a given space throughout development, choice of egg-laying or reproductive sites often greatly influences fitness. Furthermore, reproductive success of individuals may be affected not only by conditions of the breeding area but also by the time when they start to breed, because intraspecific variation in the timing of breeding may result in asymmetric competition between larvae. We addressed these issues in an experimental and field study of the Japanese brown frog, Rana japonica. We tested whether the survival success of larvae decreased with an increase in the number of deposited egg masses and with a greater delay in oviposition. We found that the number of egg masses and timing of oviposition together significantly predicted larval survival per clutch. Moreover, we observed the natural oviposition of R. japonica to examine the prediction that if the density of larvae and the timing of oviposition affect survivorship of larvae, R. japonica will avoid depositing eggs in pools in which egg masses have already been deposited. We found that for small pools only, R. japonica tended to favor oviposition at unoccupied pools (those lacking egg masses and larvae) in the spawning season. For large pools, however, adults favored those already occupied by egg masses in the spawning period. The density of egg masses and tadpoles or the timing of oviposition may have less effect on spawning or the survival of tadpoles in large pools than in small pools.     

Non-host plant odor (Tanacetum vulgare; Asteracea) affects the reproductive behavior ofLobesia botrana Den. et Schiff (Lepidoptera: Tortricidae)

Females ofLobesia botrana Den. et Schiff. (Lepidoptera Tortricidae) are attracted in natural conditions by volatiles released by a nonhost plant: tansy (Tanacetum vulgare L.; Asteracea). We have shown that both tansy flowers and their odor inhibit oviposition behavior and mating behavior and reduce adult longevity. The mean number of eggs laid per female isolated with tansy flowers was reduced by up to 50% every 2 days during the 6 days of exposure. This reduction was maintained after the tansy was removed. In the presence of tansy essential oil, the egg-laying reduction ranged from about 30 to 80% according to the odor concentration. The number of spermatophores found in females isolated with tansy flowers was also reduced twofold compared to the control treatment, indicating that the presence of tansy reduced mating activity. This mating activity is strongly reduced, by two-thirds, when adults face the highest dose of essential oil compared to controls. The number of eggs laid by the controls cannot be explained by the number of spermatophores. Therefore, the reduction in oviposition has been attributed to the presence of tansy flowers or to the tansy odor. Tansy flowers and tansy odor increased male mortality during the exposure (10% in the control, 50% in the tansy treatment, and up to 98% in the odor treatment). The highest rates of male mortality occurred during the 4- to 6-day period of exposure to flowers or odor. Repellence resulting in sustained locomotor activity is a possible cause of such a mortality. Female mortality was increased only in response to the highest dose of odor. This increase might be due to egg retention, and not directly to a plant effect. We discuss the effects of tansy flower odor on different patterns relative to the reproductive behavior ofL. botrana and, especially, on oviposition behavior in the ecological context of plant selection and polyphagy.     

Behavioral and physiological responses of susceptible and resistant diamondback moth larvae to Bacillus thuringiensis

To determine whether field-selected resistance of diamondback moth (Plutella xylostella L.) (Lepidoptera: Plutellidae) to Bacillus thuringiensis is based on behavioral or physiological adaptation, we measured mortality, consumption, and movement of larvae from a susceptible and a resistant colony when placed on untreated and B. thuringiensis treated cabbage. Colonies did not differ in mortality, consumption, or movement on untreated cabbage. However, for a given amount of consumption of treated cabbage, resistant larvae had lower mortality than susceptible larvae, demonstrating that resistance had a physiological basis. The movement patterns could not account for the differences between colonies in survival. Resistant larvae did not avoid B. thuringiensis more than did susceptible larvae. Thus, we found no evidence for behavioral resistance.     

Development and reproduction of Stratiolaelaps scimitus (Acari: Laelapidae) with fungus gnat larvae (Diptera: Sciaridae), potworms (Oligochaeta: Enchytraeidae) or Sancassania aff. sphaerogaster (Acari: Acaridae) as the sole food source

Stratiolaelaps ( = Hypoaspis) miles (Berlese) (Acari: Mesostigmata: Laelapidae) is a polyphagous soil-dwelling predatory mite that is widely marketed for use in greenhouse production systems to manage populations of dark-winged fungus gnats, Bradysia spp. (Diptera: Sciaridae) and for supplemental control of thrips. The suggestion by Walter and Campbell (2003, Biol. Control 26: 253–269) that North American commercial cultures of S. miles may actually be S. scimitus was confirmed. The development and reproduction at 21–23 °C of S. scimitus provided ad libidum with one of three different prey – the fungus gnat Bradysia aff. coprophila (Lintner), potworms (Enchytraeidae), or Sancassania aff. sphaerogaster (Zachvatkin, 1937) (Acari: Astigmata: Acaridae) – were compared. Developmental duration of the egg and non-feeding larval stages were 2.47 and 1.11 days, respectively; mortalities were 8.3 and 5.5%. Stratiolaelaps scimitus failed to develop beyond the protonymphal stage when provided with S. aff. sphaerogaster alone, although some feeding was observed. Development and reproduction of S. scimitus was successful on both fungus gnat larvae and enchytraeids, with no influence of prey on protonymphal duration (4.70 days) and mortality (8.3%), or on deutonymphal duration (4.61 days) and mortality (6.1%). Adult female S. scimitus feeding on potworms, compared to those feeding on fungus gnat larvae, had a significantly shorter pre-oviposition period (2.69 vs. 4.59 days). However, diet did not influence other adult female developmental or reproductive characteristics (oviposition period, 18.6 days; post-oviposition period, 6.2 days; total adult longevity, 27.3 days; total number of eggs, 26.5). S. scimitus reared on potworms tended (p = 0.06) to have a higher intrinsic rate of increase, a higher finite rate of increase and a shorter doubling time (r _m = 0.142 day⁻¹, λ = 1.153, Dt = 4.85 days) than those reared on fungus gnat larvae (r _m = 0.105 day⁻¹, λ = 1.110, Dt = 6.58 days), but differences in net reproductive rate (R ₀) and generation time (G) were not significant.     

Effects of gall volume on survival and fecundity of gall-making aphidsAdelges japonicus (Homoptera: Adelgidae)

The number of larvae reaching maturity within the gall of Adelges japonicus was positively related to gall volume, and the relationship between the number of mature larvae and gall volume did not change with different densities of colonized larvae. The population changes in the bud galls of A. japonicus were surveyed by collecting the galls, which did not suffer predation or parasitism within the galls, from young artificial plantations of Picea jezoensis over two years. In the year when the density of colonized larvae was high, they suffered a 42% mortality within the galls, whereas mortality was nearly zero in the low density year. The numbers of larvae per gall were positively correlated with gall volume. The regression lines of the number of colonized larvae on gall volume did not differ significantly in the regression coefficients between the two years, whereas the intercept was significantly higher in the year when the density of colonized larvae was higher. However, different within-gall mortality nullified this difference, and the regression lines of the number of mature larvae on gall volume had no significant difference both in the regression coefficients and the intercepts. This suggests that the number of mature larvae per gall was limited by available resources within the gall which were positively related to gall volume. In 25% of the galls in which mature larvae inhabited, the space within the galls were completely filled by the larvae, indicating that space was one of the limiting resources. Gall volume also affected the number of adults that emerged from the gall and the potential number of their progeny.     

Predator induced life-history shifts in a freshwater cladoceran

Summary Life-history theory predicts that maturity and resource allocation patterns are highly sensitive to selective predation. Under reduced adult survival, selection will favour genotypes capable of reproducing earlier, at a smaller size and with a higher reproductive effort. When exposed to water that previously held fish, (size selective predators which prefer larger Daphnia), individuals of Daphnia hyalina reproduced earlier, at a smaller size and had a higher reproductive investment. Hence the prey was able to switch its life history pattern in order to become less susceptible to predation by a specific predator. The cue that evokes the prey response is a chemical released by the predator.     

The Effects of Water,Season, and Colony Composition on Foraging Preferences of <Emphasis Type="Italic">Pheidole ceres</Emphasis> [Hymenoptera: Formicidae]

Field colonies of the ant Pheidole ceres were presented with a choice between a protein source and a carbohydrate source, under wet and dry conditions, at three different times in the year. These time periods corresponded with different reproductive (the production of sexuals) and growth (the production of workers) stages of the colony. Moisture had no effect on the forging behavior of P. ceres but the colonies did change their foraging preferences during different times of the year. This behavior correlated with the amount of larvae in the colony. However, lab experiments demonstrated that larvae did not directly influence the foraging decisions of the workers but that adult reproductives did.     

Adult feeding affects fecundity of the predator,Calosoma sycophanta (Col.: Carabidae)

Calosoma sycophanta L. adults were fed either gypsy moth (Lymantria dispar L.) larvae or split grapes for set periods of time while their reproduction was monitored. Few female beetles reproduced unless fed gypsy moth larvae during the first week after they ended hibernation. Even females initially fed grapes that were later fed larvae had reduced reproduction. The implications these results have for relationships between beetle and gypsy moth populations are discussed.     

Oviposition choice by the Onopordum capitulum weevil Larinus latus (Coleoptera: Curculionidae) and its effect on the survival of immature stages

Female Larinus latus lay eggs into the capitula of their Onopordum spp. host plants from the onset of capitulum development until the completion of flowering. This tight linkage between insect life-history and plant development optimised larval survival, apart from some initial asynchrony between the readiness of the females to oviposit and the suitability of the very small capitula to physically support eggs. Eggs were laid on bracts and stems of capitula or directly in the florets, when these became available. Both the location of the egg and time of oviposition influenced mortality factors such as egg and larval parasitism, egg desiccation and larval establishment. Overall, survival of eggs laid later in the season into florets was higher, although the adults that emerged were smaller. The change in choice of oviposition site that occurs at the onset of flowering, not only favours survival, but ensures more efficient resource use by the larvae. This occurs because sequential flowering of Onopordum spp. drives a sequential oviposition pattern and spreads the egg load more evenly over the available capitula, reversing a trend earlier in the season to clump eggs that were laid directly on the bracts. Other potential constraints, such as capitulum size, absolute egg density and previous egg-laying do not play a major role in determining the oviposition pattern of L. latus. Larval survival was positively correlated with capitulum size and not strongly influenced by egg density. Competition for resources only appeared to play a role in smaller capitula, and manifested itself in a reduction in the size of emerging adults rather than the death of immatures. In the absence of strong interspecific competition, the oviposition behavior of L. latus has become geared to maximising resource use for larvae (i.e. its own potential competitiveness) rather than minimising interactions with other members of the capitulum endophage guild.     

L‘élevage de deux coccinelles Harmonia axyridis et Semiadalia undecimnotataà l'aide d'oeufs d’Anagasta kuehniella tués aux rayons ultraviolets

Résumé Les coccinelles aphidiphages Harmonia axyridis Pallas et Semiadalia undecimnotata Schneider (Coccinellidae) ont été élevées pendant trois générations à l'aide d'oeufs d'Anagasta kuehniella Zell. (Pyralidae) tués par une exposition à un rayonnement ultraviolet. Chez la première espèce, cette proie de substitution présente une valuer alimentaire comparable si ce n'est pas supérieure à celle du puceron Acyrthosiphon pisum (Harris). Ces résultats permettent d'envisager, dès à présent, une production massive dans ces conditions trophiques. La mise en place d'un élevage continu dépend de l'évolution sur un grand nombre de générations de certains paramètres biologiques notamment de la fertilité des femelles. Chez la seconde espèce, une telle application paraît impossible pour l'instant.

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Summary Aphidophagous coccinellids Harmonia axyridis and Semiadalia undecimnotata were reared on eggs of the pyralid moth, Anagasta kuehniella during three generations previously killed by exposure to ultra violet radiation. Incidentally, these eggs are used for the mass production of Trichogramma. For H. axyridis larvae, this prey has the same nutritional value as the aphid Acyrthosiphon pisum (control). In adults, it causes an increase in reproductive activity which persisted during three generations. Decreased egg fertility is compensated for by stimulated oviposition. However, regardless of generations, the number of larvae produced per female per day remained equal to or became larger than the control. When the adults are transferred to aphid prey after 15 days of oviposition on the substitution food, a high level of fecundity is maintained and egg fertility improved, particulary during the last two generations. In S. undecimnotata, a specific aphid predator, preying on substitute prey is associated with prolonged pre-imaginal development and increased mortality, the latter affecting up to 50% of the larvae during the third generation. In adults, it induces a deterioration of the reproductive capacities (fecundity, fertility) which however seemed to improve during the third generation. Substitute prey has negative effect on these adults. At present, only H. axyridis might be considered for temporary mass production, as suggested by the results obtained at the end of the first generation.

     

Mortality in reared hydropsychid pupae (Trichoptera: Hydropsychidae)

Cases containing pupae of Hydropsychidae (Trichoptera) were collected from sampling-stations along the length of the Credit and Humber Rivers, Ont., and reared at 18°C. Mortality was high; about 33% of the cases produced adults. Up to 24% of collected cases had been infested with chironomid larvae. Within a station, emergence success and mortality due to chironomid infestation were about the same for the species of Hydropsyche Pictet present; Cheumatopsyche Wallengren suffered less chironomid-related mortality than Hydropsyche. There were significant between-station differences in chironomid-related mortality for H. sparna Ross, H. bronta Ross, H. morosa Hagen, and H. slossonae Banks. Chironomid-related mortality was lowest for pupae from upper Credit R. stations, highest for pupae collected from a lower Credit R. station. Pupae from all Humber R. stations suffered about the same amount of chironomid-related mortality. Chironomid infestation was significantly higher for prepupae than for pupae.     

Relative performance of European grapevine moth (<Emphasis Type="Italic">Lobesia botrana</Emphasis>) on grapes and other hosts

The European grapevine moth, Lobesia botrana is a major grapevine pest, but despite the abundance of vineyards it is a generalist and uses either grapes or alternative species. Given the abundance and predictability of grape, L. botrana could be expected to have evolved towards monophagy. In order to understand why this species remains polyphagous, we hypothesized that larvae reared on rare wild host plants should have higher fitness than those reared on the more abundant grape host. For this, we compared larval performance and several life history traits on three alternative host plants (Daphne gnidium, Olea europaea, Tanacetum vulgare) and three Vitaceae (Vitis vinifera), two cultivars and one wild species (Ampelopsis brevipedunculata), and two control groups raised on either a low or a high nutritive value medium. Alternative hosts are more suitable than Vitaceae for the reproductive performance of L. botrana: larval mortality and development time was reduced, while pupal weight, growth rate, female longevity, female fecundity, duration of laying and mating success were increased. High quality food ingested by larvae promotes higher adult body weight and enhances female reproductive output. This suggests that alternative hosts provide greater nutritional value for L. botrana than Vitaceae. The use of alternative host plants could thus be maintained in the host range because they offer L. botrana a better fitness than on the Vitaceae. This could typically represent an advantage for moths behaving in plant diversity grape landscapes.     

Morphology and development of <Emphasis Type="Italic">Pteromalus cerealellae</Emphasis> (Ashmead) (Hymenoptera: Pteromalidae) on <Emphasis Type="Italic">Callosobruchus maculatus</Emphasis> (F.) (Coleoptera: Chrysomelidae)

Pteromalus cerealellae (Ashmead) (Hymenoptera: Pteromalidae) is an ectoparasitoid of several stored-product insect pests. Very little information has been published on its biology and development in host larvae, which typically are concealed within seeds. We documented the development of P. cerealellae within fourth instar larvae of its concealed host, Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae) infesting cowpea seeds. The preimaginal life stages of the parasitoid were characterized for the first time using morphological structures revealed by microscopic techniques including scanning electron microscopy. Pteromalus cerealellae produces hymenopteriform eggs and larvae. Eggs hatch into 13-segmented first instar larvae with peripneustic condition of spiracles. The larvae have simple, tusk-like mandibles, whereas the mandibles of the pupae and the adults are of the conventional toothed types. Using statistical analyses of the sizes of the larval mandibles and head capsules in conjunction with reliable characters such as the number of exuviae on the body of parasitoid larvae, cuticular folding, and excretion of the meconium, we recorded four larval instars for P. cerealellae. The data showed significant positive correlations between larval mandible lengths and widths of larval head capsules, as well as between mandible lengths and larval instars, suggesting that mandible length is a good predictor of the number of instars in P. cerealellae. Developmental time from egg to adult emergence was ∼12 d for females and ∼11 days for males at 30 ± 1°C, 70 ± 5% r.h. and 12L:12D photoperiod.     

Intraspecific competition of Glyptotendipes paripes (Diptera: Chironomidae) larvae under laboratory conditions

Glyptotendipes paripes larvae were reared in wells of tissue culture plates, in groups of 2, 4, 8, 16, and 32 (representing densities of about 1,300, 2,600, 5,200, 10,400, and 20,800 larvae per m², respectively). Larval groups were supplied with one of two concentrations (low or high) of food and larvae were individually observed to evaluate the effects of density on mortality, growth, development, behavior, and adult body size. Increased larval densities resulted in higher mortality, as well as slower larval growth and development. The distribution of developmental time became flatter at higher density, with a wider range of values, or even became bimodal. This was a consequence of the most rapidly developing individuals at higher densities emerging as adults sooner than the fastest developing individuals at lower densities, although overall mean developmental time was longer at higher densities. At higher densities, growth and development of smaller larvae were slowed, based on the relative difference in body length between competitors. When larger competitors emerged as adults or died, the growth of smaller larvae may have accelerated, resulting in increased variability of developmental times. The effect of larval density on adult body size was complex, with the largest body size found at the lowest density and a second peak of adult size at high-middle densities, with smaller adult body sizes found at low-middle, and high densities. Similarly, as with developmental time, the range of body size increased with increasing density. Examined food concentrations had no effect on larval mortality, but significantly affected developmental time, growth rate, and adult body size. At higher densities, larvae spent more time gathering food and were engaged in aggressive or antagonistic behaviors.     

Effects of spatio-temporal intervals between newly-hatched larvae on larval survival and development inMonochamus alternatus (Coleoptera: Cerambycidae)

The effects of distance between hatching larvae on survival and development were investigated inMonochamus alternatus. Two newly-hatched larvae were inoculated intoPinus densiflora bolts at a distance of 2.5 cm or 10 cm, simultaneously or at an interval of 2 weeks. Some larvae were inoculated singly as a control. When larvae were inoculated simultaneously, mortality of the closely-inoculated larvae was significantly higher than that of distantly-inoculated larvae. Such high mortality was identified as due to conspecific bites. When the two larvae were inoculated asynchronously, the first-inoculated larvae killed some second-inoculated larvae but were never killed by them. Consequently, mortality was higher in second-inoculated larvae than in first-inoculated larvae. In particular, there was a significant difference in mortality between them when the larvae had been inoculated closely. The mortality of second-inoculated larvae was higher in the closely-inoculated group than in the distantly-inoculated group although there was no significant difference between them. In the case of two simultaneously-inoculated larvae, the initial distance between them had no significant effect on the development and growth in the early larval stage. When the larvae were inoculated asynchronously, the first-inoculated larvae grew more quickly than singly-inoculated control larvae.