Seasonal adaptations of populations of the southwestern corn borer, Diatraea grandiosella, from tropical and temperate regions

Seasonal adaptations of populations of the southwestern corn borer, Diatraea grandiosella, obtained from south-central Mexico (19°N latitude) and southeast Missouri (37°N latitude) were compared. Day length and temperature were found to serve as environmental cues to programme the larval diapause of both populations, but different critical values were observed. The critical day length for diapause induction was about 13 hr light/day for Mexican larvae and about 15 hr light/day for Missouri larvae, and was relatively stable at 20 to 30°C. Mexican larvae displayed a less-intense diapause than did Missouri larvae. Some diapausing Mexican larvae maintained at 25 or 30°C pupated in about 15 days, regardless of the day length to which they were exposed. The rate of diapause development of Mexican larvae was high at day lengths between 14 hr and 16 hr, whereas that of Missouri larvae was accelerated at day lengths of 16 hr at 25 and 30°C. Diapause development of Mexican larvae was virtually unaffected by chilling at 10°C, whereas that of Missouri larvae continued at a low rate at 10°C. Selection of Mexican larvae for diapause showed that only four generations were needed to significantly increase the incidence of diapause.     

Characteristics of larvae of the southwestern corn borer, Diatraea grandiosella, obtained from populations present in tropical and temperate regions

A comparative study was undertaken of southwestern corn borers (Diatraea grandiosella) collected from south central Mexico (19°N latitude) and southeast Missouri (37°N latitude). All the life stages of the Mexican insects were found to be larger or heavier, or both, than were those of the Missouri insects. Mexican larvae grew at a higher rate and attained a significantly heavier body weight than did Missouri larvae. Although both Mexican and Missouri larvae underwent ecdyses during diapause, Mexican larvae ecdysed more frequently than did the Missouri larvae at 23°C light:dark 12 h:12 h. Larvae that ecdysed most frequently did not necessarily spend longer in diapause. Electrophoresis of the fat body and haemolymph proteins of Mexican and Missouri larvae revealed similar patterns. The fat body of diapausing Mexican larvae contained substantial amounts of a diapause-associated protein which has been characterized previously from the fat body of Missouri Larvae. Double immunodiffusion confirmed that the diapause-associated protein of the Mexican larvae was identical to that present in the Missouri larvae. Smaller amounts of this protein appear to be present in the fat body of diapausing Mexican larvae than are present in that of diapausing Missouri larvae.     

Über den Kannibalismus bei Larven der Baumwollblatteule

On cannibalism of the larvae of the cotton leafworm Spodoptera littoralis (Boisd.) . Some ecological studies on the larvae of the cotton leafworm Spodoptera littoralis (Boisd.) were carried out in the laboratory to prove the appearance of cannibalism under different conditions of temperature, relative humidity, population density as well as abstraction of food, and furthermore the effect of food and food quantity. Results obtained showed, that when food was sufficiently provided the different instars did not show any cannibalistic habit. Cannibalism only appeared in case of insufficient quantity of food and reached its maximum at total withdrawal of food. The cannibalism rate was different for the various instars, the fourth stage showed the highest rate. During moulting time the rate was very low. The cannibalism rate was higher at 35° C than at lower temperatures and at lower relative humidity (30–40%) higher than at higher relative humidity (70–80%). In a limited space under withdrawal of food the rate was higher with greater initial numbers of larvae than with lower initial numbers. This rate was also higher for the cultures of mixed larvae instars than for the cultures of unmixed larvae instars. Records after 72 hours showed that only the eldest instars of larvae survived. The cannibalism rate increased with the length of the fasting period.     

Cannibalism of Helicoverpa zea (Lepidoptera: Noctuidae) from Bacillus thuringiensis (Bt) transgenic corn versus non-Bt corn

Because of the importance of cannibalism in population regulation of Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) in corn, Zea mays L., it is useful to understand the interactions between Bacillus thuringiensis (Bt) transgenic corn and cannibalism. To determine the effects of Bt corn on cannibalism in H. zea, pairs of the same or different instars were taken from Bt or non-Bt corn and placed on artificial diet in proximity. Cannibalism occurred in 91% of pairs and was approximately 7% greater for pairs of larvae reared from Bt transgenic corn (95%) than from non-Bt corn (88%). Also, first instar by first instar pairs had a lower rate of cannibalism than other pairs. Time until cannibalism was not different for larvae from Bt corn versus non-Bt corn. Pupation rate of cannibals and surviving victims was not different for pairs from Bt corn versus non-Bt corn. Finally, cannibalism increased pupation rate of cannibals from both Bt and non-Bt corn by approximately 23 and 12%, respectively, although the increases were not significant. Thus, negative effects of Bt on larvae were compensated by increased cannibalism in comparison with larvae reared on non-Bt corn, which increased larval survival to levels comparable with larvae reared on non-Bt plants.     

Seasonal adaptations of different geographical populations of the sunflower moth, Homoeosoma electellum

A photothermogram constructed for a central Missouri population (ca. 39°N latitude) of the sunflower moth, Homoeosoma electellum (Hulst) predicted that this population has a seasonal life cycle of 2 complete and a partial third generation per year, and that daylengths of less than 13 h 30 min light/day and mean temperatures of less than 20°C induce the mature larval diapause. A test of the predicted life cycle revealed that larvae entered diapause when they were exposed from their first instar onwards to natural conditions in central Missouri beginning September 15, 1982. Sunflower moths obtained from northwest Texas (ca. 35°N latitude) and northeast South Dakota (ca. 45°N latitude) displayed shorter critical photoperiods for diapause induction at 20°C (12 h 30 min light/day and 12 h 15 min light/day, respectively) than did those from Missouri. The population of the sunflower moth obtained from South Dakota does not, therefore, appear to be adapted to local conditions, and moths might disperse from lower latitudes to establish transiet populations each year.     

Phenological adaptations of a colonizing insect: The southwestern corn borer,Diatraea grandiosella

Summary The developmental rate, critical photoperiod, and diapause intensity were determined for three populations of the southwestern corn borer, Diatraea grandiosella, from Missouri, Mississippi and Kansas. Mississippi larvae grew at the highest rate and Missouri larvae grew at the lowest rate. The zero developmental temperatures (°C) for the Missouri population were estimated from regression lines as follows: 10.5° (eggs), 10.8° (diapausing larvae), 13.3° (non-diapausing larvae) and 11.4° (pupae). The required heat units were: 85° (eggs), 588° (diapausing larvae), 333° (non-diapausing larvae) and 149° days (pupae). However, the observed low temperature limit for larval growth under constant temperature regimes was approximately 17°C.The critical day lengths for diapause induction observed at 25°C were: 15 h 11 min (Missouri); 15 h 20 min (Mississippi); and 15 h 22 min (Kansas). The photoperiodic response of the Mississippi larvae was more or less retained at 30°C, whereas the response of the Missouri larvae was completely suppressed at this temperature. Diapause was most easily terminated in the Kansas larvae. The most intense diapause was observed in the Mississippi larvae.Model seasonal life cycles of the three geographic populations were constructed using photothermograms. Although the models showed good agreement with the field situation for the Missouri and the Kansas populations, some unknown factor(s) remains to account for an extremely long critical photoperiod in the Mississippi population.Contribution from the Missouri Agricultural Experiment Station, as journal series no. 9001     

HYBRID BREAKDOWN IN DEVELOPMENTAL TIME IN THE COPEPOD TIGRIOPUS CALIFORNICUS

Laboratory crosses were carried out among three genetically differentiated Los Angeles populations (all located within approximately 15 km) and one San Diego population (approximately 150 km away) of the intertidal copepod Tigriopus californicus. Despite high levels of allozyme differentiation, all crosses produced viable F₁ progeny. Most F₁ progeny had shorter developmental times and reduced variance in developmental times compared to the parental populations. Only one pair of populations failed to produce viable F₂ progeny; when the central Los Angeles population (AB) was crossed to the San Diego (SD) population, most larvae died during the late naupliar stages. Developmental times in the F₂ generation of the other Los Angeles × San Diego crosses were typically 40% longer than developmental times of the parental populations. Among the Los Angeles populations, only one cross (and not its reciprocal) showed a similarly large increase in developmental time. Variance in F₂ developmental times was greater than the parental variance in 5 of 10 crosses. These results are discussed with regard to the evolution of coadapted gene complexes and population differentiation in T. californicus.     

Effect of daylength and temperature on the larval diapause of the sunflower moth, Homoeosoma electellum

The effect of daylength and temperature on the regulation of the larval diapause of a central Missouri population of the sunflower moth, Homoeosoma electellum, was examined. Fully grown fourth-instar larvae exhibit a facultative diapause. Measurements of the effect of photoperiod on diapause induction revealed critical photoperiods of about 13 h 30 min light/day at 20°C, and between 11 h 45 min and 12 h light/day at 23°C. Third and fourth-instar larvae were shown to be the main sensitive stages for diapause determination. Daylength was also shown to be an important regulator of the rate of diapause development. A short day of LD 10:14 h permitted only a low rate of diapause development, whereas long days of LD 14:10 h and LD 16:8 h accelerated diapause development at 25 and 30°C. When long days were alternated with short days at 30°C the accelerating effect of long days on diapause development was not found. Systematic transfers of chilled diapausing larvae revealed an accelerated diapause development in groups transferred from 10 to 30°C LD 10:14 h, but diapause development was not accelerated in groups transferred from 10 to 30°C LD 16:8 h.     

Plasticity in the timing of a major life‐history transition and resulting changes in the age structure of populations of the salamander Hynobius retardatus

Variation in age and size at life‐history transitions is a reflection of the diversifying influence of biotic or abiotic environmental change. Examples abound, but it is not well understood how such environmental changes influence the age structure of a population. I experimentally investigated the effects of water temperature and food type on age and body size at metamorphosis in larvae of the salamander Hynobius retardatus. In individuals grown at a cold temperature (15 °C) or given Chironomidae as prey, the time to metamorphosis was significantly prolonged, and body size at metamorphosis was significantly enlarged, compared with individuals grown at a warmer temperature (20 °C) or fed larvae. I also examined whether larval density (a possible indicator of cannibalism in natural habitats) generated variation in the age structure of natural populations in Hokkaido, Japan, where the climate is subarctic. Natural ponds in Hokkaido may contain larvae that have overwintered for 1 or 2 years, as well as larvae of the current year, and I found that the number of age classes was related to larval density. Although cool water temperatures prolong the larval period and induce later metamorphosis, in natural ponds diet‐based enhancement of development translated into a shorter larval duration and earlier metamorphosis. Geographic variation in the frequency of cannibalism resulted in population differences in metamorphic timing in H. retardatus larvae. It is important to understand how environmental effects are ultimately transduced through individual organisms into population‐level phenomena, with the population response arising as the summation of individual responses. Without a thorough comprehension of the mechanisms through which population and individual responses to environmental conditions are mediated, we cannot interpret the relationship between population‐level and individual‐level phenomena. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 100–114.     

Seasonal and geographical variation in diapause and cold hardiness of the Asian corn borer,Ostrinia furnacalis

Asian corn borer, Ostrinia furnacalis (Guenée), is a key corn pest in the Asian‐Western Pacific countries. It overwinters as full‐grown larvae in plant stalks or in a spun‐silk covering located in the plant debris in the temperate regions of China. Supercooling point (SCP) and survival rate after low sub‐zero temperature treatment were assessed for field‐collected populations in the laboratory using a cool bath with a 1°C/min cooling rate until ?40°C. Mean SCPs were varied among geographical populations, with a significant decline from ?22.7°C of Haikou, the multivoltine tropical population in the south, to ?28.5°C of Gongzhuling, the univoltine temperate population in the northeast of China. In addition, there was more than 1°C difference in SCP between Gongzhuling univoltine and bivoltine populations that were from the same geographic origin. Mean SCPs of the Guangzhou population fluctuated over the year, with significantly lower SCPs in winter than in other seasons, which correlated with a significantly higher proportion of diapausing larvae in winter than in other seasons. Over 41% of overwintering larvae from the northeast population could withstand to be supercooled for a few minutes to the low sub‐zero temperature of ?40°C, but only 6.7% of their southern counterparts did so. The findings from this study suggest that O. furnacalis mostly takes advantage of freeze avoidance as diapausing larvae for overwintering in the southern region, whereas it exhibits freeze tolerance in diapause in the northeastern region.     

Differential cannibalism and population dynamics in a host-parasitoid system

The effects of host cannibalism on a host-parasitoid system were explored through experiment and modelling. In individual encounters between parasitized and unparasitized Plodia interpunctella larvae, parasitized larvae were more likely to be cannibalized. Inclusion of this differential cannibalism into a simple Lotka-Volterra-type model of host-parasitoid population dynamics generates alternative stable states-including stable coexistence and extinction of the parasitoid — which depend on starting conditions. Possible mechanisms for differential cannibalism, and its implications for studies of host-parasitoid populations and biological control programmes are discussed.     

Heterosis is common and inbreeding depression absent in natural populations of Arabidopsis thaliana

The importance of genetic drift in shaping patterns of adaptive genetic variation in nature is poorly known. Genetic drift should drive partially recessive deleterious mutations to high frequency, and inter‐population crosses may therefore exhibit heterosis (increased fitness relative to intra‐population crosses). Low genetic diversity and greater genetic distance between populations should increase the magnitude of heterosis. Moreover, drift and selection should remove strongly deleterious recessive alleles from individual populations, resulting in reduced inbreeding depression. To estimate heterosis, we crossed 90 independent line pairs of Arabidopsis thaliana from 15 pairs of natural populations sampled across Fennoscandia and crossed an additional 41 line pairs from a subset of four of these populations to estimate inbreeding depression. We measured lifetime fitness of crosses relative to parents in a large outdoor common garden (8,448 plants in total) in central Sweden. To examine the effects of genetic diversity and genetic distance on heterosis, we genotyped parental lines for 869 SNPs. Overall, genetic variation within populations was low (median expected heterozygosity = 0.02), and genetic differentiation was high (median F_ST = 0.82). Crosses between 10 of 15 population pairs exhibited significant heterosis, with magnitudes of heterosis as high as 117%. We found no significant inbreeding depression, suggesting that the observed heterosis is due to fixation of mildly deleterious alleles within populations. Widespread and substantial heterosis indicates an important role for drift in shaping genetic variation, but there was no significant relationship between fitness of crosses relative to parents and genetic diversity or genetic distance between populations.     

Photosynthesis and cannabinoid content of temperate and tropical populations of Cannabis sativa

Four populations of Cannabis sativa L. grown from seeds collected in Panama, Jamaica, Nepal, and east central Illinois were grown under controlled conditions in growth chambers. One set was grown under warm conditions (32° day and 23° night) and the other set was grown under lower temperatures (23° day and 16° night). CO₂ exchange and transpiration were examined under various temperatures and light intensities. Observations on growth, and analyses for chlorophyll and Δ₁THC (tetrahydrocannabinol) content were made. Under warm growth conditions, the central Illinois population had the highest photosynthetic rate at all temperatures investigated. The Nepal population had intermediate rates, while the Jamaica and the Panama populations had the lowest rate. The Jamaica and Panama populations had insignificant changes in photosynthetic response to changes in temperatures between 15° and 30°. Under cool growing conditions the central Illinois population had the highest rate of photosynthesis with a definite peak at 25°. Nepal plants had intermediate rates of photosynthesis, while the Panama and Jamaica populations had the lowest rate. Differences in chlorophyll and drug content were also significant between these populations. From these data it is suggested that the four populations can be grouped into different ecotypes genetically adapted to their respective environments.     

Cold hardiness of larvae of the southwestern corn borer, Diatraea grandiosella

The cold-hardening capacity of field-collected larvae from southeast Missouri and laboratory-reared larvae of the southwestern corn borer, Diatraea grandiosella Dyar, was examined. Supercooling points of non-diapause and diapause larvae collected from maize plants grown in Missouri (36°30 N lat.) were ca.-7.0°C. The hemolymph melting points of diapause field larvae (-0.8°C) were significantly lower than those of non-diapause larvae collected in July (-0.5°C). The supercooling points of hemolymph from non-diapause and diapause field larvae ranged randomly from-10° to-18°C. Supercooling points of non-diapause laboratory larvae increased from-13° to-10°C prior to pupation, whereas those of diapause larvae increased similarly before the onset of diapause, but then decreased during diapause to ca.-17°C. No change in supercooling points or capacity to survive in the presence of ice was observed in diapause laboratory larvae acclimated at 4°C for 63 days. Laboratory and field larvae began to freeze at ca.-1.5°C in the presence of ice, but survived to several degrees below their melting points. The high supercooling points of field larvae appeared to be due to the presence of an environmental ice-nucleator. Although data for laboratory larvae indicate sufficiently low supercooling points to permit winter survival in southeastern Missouri, considerable larval mortality occurs in the field due to inoculative freezing and the presence of an ice-nucleator.     

Effect of emigration on cannibalism and intraguild predation in aphidophagous ladybirds

Abstract.  1. The incidence and timing of emigration, cannibalism, and intraguild predation of larvae of three aphidophagous ladybirds (Coleoptera: Coccinellidae), Harmonia axyridis Pallas, Coccinella septempunctata brucki Mulsant, and Propylea japonica Mulsant, relative to the presence of prey was determined in the laboratory in single- and mixed-species populations.
2. In single-species populations, 80% of the larvae of C. s. brucki emigrated prior to the extinction of the aphid population and no larvae were lost due to cannibalism; however > 80% of the larvae of the other two species were still present when the aphid became extinct and the losses due to cannibalism for H. axyridis and P. japonica were 25% and 14% respectively. Finally, 28% of the P. japonica larvae completed their development, whereas no larvae of the other two species became adult.
3. In mixed-species populations, mortality of P. japonica attributable to cannibalism or intraguild predation increased greatly to 60%, whereas that of the other two species remained about the same. Consequently, survival of H. axyridis larvae improved and survival of P. japonica worsened; however the survival of C. s. brucki larvae was not affected by the other two species. Early emigration by C. s. brucki larvae may have enabled them to escape intraguild predation by H. axyridis in this system.     

The required day number and timely induction of diapause in geographic strains of the mosquito Aedes atropalpus

Diapause is triggered in A. atropalpus from 14°N lat when 9 or more short-day photoperiod cycles occur during the photosensitive 4th instar and pupa. Temperatures of 22°C and higher cause part or all of this population to complete the photosensitive period in less than 9 days thereby avoiding diapause. In contrast, 4 short-day cycles during the photosensitive period are sufficient to trigger diapause in A. atropalpus from 45°N lat. This population experiences the 4 required days at temperatures as high as 28°C. A strain from an intermediate location of 34°N lat must “see” 7 short days during the photosensitive stages for induction of diapause. This requirement is met at temperatures of 24°C and less. These results suggest that southern strains of A. atropalpus have evolved a means of avoiding short-day induced diapause if temperatures are high and other requirements for growth are available.A correlation between critical daylength for induction of diapause and geographic origin has been shown for several insect species. The evolution of a requirement for different numbers of diel cycles during the photosensitive period is another means of modifying the diapause response in populations from different latitudes and geographic areas.     

Relationship between transmission ratio distortion and genetic divergence in intraspecific rice crosses

The strength of reproductive isolation often correlates positively with parental divergence in both animals and plants. Here, we assess the relationship between transmission ratio distortion (TRD) of marker loci and parental divergence in intraspecific rice (Oryza sativa L.) crosses. We produced 10 diverse F(2) populations by crossing a temperate japonica reference accession with each of 10 donor accessions belonging to subpopulations different from the reference accession, and then genotyped the F(2) populations using molecular markers distributed across the entire genome. Significant TRDs (α?=?0.05) were detected in 9 of the 10 F(2) populations. TRD regions on chromosomes 3 and 6 were common to several populations; in contrast, other TRD regions were unique to a single population, indicating the diversification of genomic location of TRDs among the populations. The level of TRD (estimated from the overall number and magnitude of TRDs) was significantly correlated with the genetic distance between the donor accessions and the reference accession. Our results suggest that in intraspecific rice crosses, parental divergence may result in diversification of the TRD pattern, followed by an increase in the level of TRD.     

Sibling cannibalism in Koi carp, Cypvinus carpio L., larvae and juveniles reared under controlled conditions

The potential impact of sibling cannibalism on the size and population structure of captive populations of Koi carp, Cyprinus carpio L., which were fed only dry foods, was determined. The rate of cannibalism was found to be positively density-dependent, with the highest rate being recorded at initial stocking densities of 40 larvae 1 (33.3% of the fish had been eaten by cannibals by day 52). Two types of cannibalism could be distinguished: type I, where the head of the prey was rejected once the caudal region of the prey had been progressively ingested; type II, where the prey were caught either head-first or tail-first and were ingested completely. The first type was limited to the period from the ninth to the 15th day of rearing, and the second type started on the 18th day. Measurement of the mouth, head and tail allowed the calculation of predicted cannibal -prey relationships. The consequences and implications of coeval sibling cannibalism in culture systems are discussed.     

Cannibalism of parasitoid‐attacked conspecifics in a non‐carnivorous caterpillar

Cannibalism, the killing and consumption of conspecifics, can even occur in insect species typically considered to be non‐carnivorous. Of particular interest is the cannibalism of parasitoid‐attacked conspecifics, which could reduce parasitism levels in subsequent generations for that conspecific population. This study reports on the occurrence and some of the consequences of cannibalism in parasitoid‐attacked obliquebanded leafroller, Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae). We show that larvae of C. rosaceana, which is considered to be an herbivorous caterpillar species, did not prey upon live conspecifics, but readily consumed conspecifics attacked by Habrobracon gelechiae Ashmead (Hymenoptera: Braconidae). Further examination found that C. rosaceana larvae feeding on parasitoid‐attacked conspecifics, since their fourth instar, suffered a higher mortality and reduction in body size than those fed on plant material only. The cannibalism of attacked conspecifics did not appear to offer any nutrient benefits for the cannibal. To our best knowledge, this is the first empirical example of the occurrence and some of the consequences of cannibalism by a non‐carnivorous insect on its parasitoid‐attacked conspecifics. We discuss the adaptive significance of such cannibalism on parasitoid‐attacked conspecifics with respect to a trans‐generational fitness gain for the population through the killing of the parasitoids, thereby reducing parasitism in subsequent generations.     

Predator–prey interactions and the cannibalism of larvae of Armigeres subalbatus (Diptera: Culicidae)

Predation and cannibalism can affect the co-existence of mosquito species or the assemblage of mosquito species (i.e., community structure). In this study, predatory feeding patterns and cannibalism of larvae of Armigeres subalbatus mosquitoes were quantified under laboratory conditions using Aedes albopictus and Culex uniformis larvae as prey organisms. Rate of consumption of prey larvae and the rate of cannibalism of 1st to 4th instar larvae of Armigeres subalbatus were reported at 24 h intervals with and without alternative food supplement. Both the 3rd and 4th instar larvae of Ar. subalbatus showed a substantial predation on the larvae of Ae. albopictus (33.6 ± 4.4) and Cx uniformis (47.3 ± 7.6). The cannibalism of the predatory larvae was strongly correlated to the larval density (r = 0.9). The predator and the prey density and the given food type were significant factors that determined the rate of pupation, death and the emergence as adults. A significant relationship was shown for the co-occurrence of predatory larvae and the prey larvae at the 85 natural breeding habitats observed at the field (χ² = 74.4, p < 0.001). Nine breeding sites (10.6%) were positive for both prey and predatory larvae. Our study showed robust information about the predatory and cannibalistic behavior of Ar. subalbatus larvae emphasizing their role in managing the population structure of mosquito communities.