Phase-dependent locomotor activity in first-stadium nymphs of the desert locust, Schistocerca gregaria: effects of parental and progeny rearing density

This study examined the effects of parental and progeny rearing density on locomotor activity of 1st-stadium nymphs of the desert locust, Schistocerca gregaria, using an actograph. Progeny obtained from solitarious (isolated-reared) or gregarious (crowd-reared) locusts were reared in isolation or in a group of 30 nymphs. Crowding after hatching had a slight influence on mean activity shortly after the start of measurements, but no clear effect was detected until day 2, when maximum activity during the 6-24 h of observation was significantly higher than that of the nymphs kept in isolation. On the other hand, the effects of parental rearing density on locomotor activity manifested at all ages examined (0-2 days old). Progeny of gregarious locusts showed consistently higher activity than those of solitarious locusts. In newly hatched nymphs, the effect of parental rearing density was explained by variation in body size at hatching, one of the phase-dependent characteristics. Hatchling body color was also correlated with locomotor activity and body weight. Similar levels of locomotor activity were exhibited when green, solitarious and black, gregarious nymphs were similar in body weight. These results suggested that parental rearing density indirectly influences locomotor activity in the progeny shortly after hatching by affecting their body size as eggs or hatchlings.     

Density-dependent accumulation of phase characteristics in a natural population of the desert locust Schistocerca gregaria

Abstract. Phase characteristics of locusts from parents that experienced different population densities were investigated under field conditions in Morocco. The density experienced by adults induced a marked phase change in colour, behaviour and morphometry of their offspring. A high-density subpopulation gave rise to a preponderance of black hatchlings that exhibited a high level of aggregation as later stage nymphs and showed gregarious morphometric features as adults, whereas a low-density subpopulation produced a majority of green hatchlings with a lesser tendency to group as final-instar nymphs and more solitarious morphometry as adults. The constrained isolation of insects from the low-density subpopulation, or crowding of insects from the high-density subpopulation, resulted in a behavioural and morphometric change towards even more solitarious characteristics in the former and more pronounced gregarious characteristics in the latter, relative to field-caught insects of the same age. These results from the field are consistent with those in the laboratory and provide more evidence for the dual roles of an individual locust's experience of crowding as well as that of its parents in density-dependent phase change.     

Body‐color and behavioral responses by the mid‐instar nymphs of the desert locust,Schistocerca gregaria (Orthoptera: Acrididae) to crowding and visual stimuli

The effects of crowding and isolation on body color and behavior were observed for the mid‐instar nymphs of the desert locust, Schistocerca gregaria. Some of the solitarious (isolation‐reared) nymphs that were crowded for 1 or 4 h during the third instar developed black patterns at the fourth instar, but most individuals remained unaffected. Black patterns appeared in all individuals that were crowded for 1 day or longer, but even after 4 days of crowding the black patterning for some individuals was not as intense as that for the gregarious (crowd‐reared) controls. Isolation of gregarious nymphs caused the black patterns to recede or disappear at the last (fifth) nymphal instar, but it was necessary to isolate the nymphs from the beginning of the first instar to obtain body coloration looking like solitarious nymphs in most individuals. Solitarious nymphs that were allowed to see gregarious nymphs developed different intensities of black patterns depending on the body size and number of nymphs shown. The behavioral phase shift from one phase to another was observed when the nymphs were crowded or isolated for 2 days or longer, as previously reported for the last nymphal instars of the same strain. Behavioral gregarization was induced for isolated nymphs that were allowed to see a group of nymphs through a transparent double wall. These results suggested that body‐color phase shift occurred more rapidly for mid‐instar nymphs than for late instar nymphs but the rate of behavioral phase shift was similar for the two instars.     

Phase-specific responses to different qualities of food in the desert locust, Schistocerca gregaria: developmental, morphological and reproductive characteristics

Solitarious female adults are known to produce smaller hatchlings than those produced by gregarious adults of the desert locust, Schistocerca gregaria. This study investigated developmental, morphological and reproductive responses to different qualities of food in hatchlings of different phases. Mortality was higher, the duration of nymphal development longer and adult body weight lighter with a low-quality food than a high-quality food. Gregarious hatchlings showed better survivorship, grew faster and became larger adults than did solitarious ones. The incidence of locusts exhibiting extra molting, which was typically observed in the solitarious phase, was dramatically increased when a low-quality food was given to the solitarious hatchlings. Low-quality food caused locusts to shift morphometric ratios toward the values typical of gregarious forms; smaller F/C (hind femur length/maximum head width) and larger E/F (elytra length/hind femur length). Solitarious hatchlings grown at either high- or low-quality foods and then given high-quality food after adult emergence revealed that food qualities during the nymphal stage influence their progeny quality and quantity via adult body size that influenced reproductive performance. Female adults showed an overshooting response to a shift from low- to high-quality food by increasing egg production that was specific to body size. This study may suggest that gregarious hatchlings are better adapted to adverse food conditions than solitarious counterparts and extra molting is induced even among gregarious hatchlings under poor food conditions.     

Tactile stimuli perceived by the antennae cause the isolated females to produce gregarious offspring in the desert locust, Schistocerca gregaria

Maternal determination of progeny body size and coloration in the desert locust, Schistocerca gregaria, depends on the crowding conditions experienced during the short sensitive period that occurs two to six days before the deposition of the egg pod. Solitarious (isolated-reared) females produce relatively small eggs that yield solitarious green hatchlings but, females that are exposed to crowded conditions during the sensitive period, produce larger eggs that yield the dark-colored hatchlings characteristic of gregarious forms. The present study aimed to determine the stimuli influencing the maternal determination of progeny characteristics as well as the site at which such stimuli are perceived. By exposing isolated female adults to various combinations of visual, olfactory and tactile stimuli from a crowd of other adults, we found that no crowding effects could be elicited without tactile stimulation. Coating of various body surfaces with nail polish followed by exposure to crowding stimulation suggested that female adults perceive crowding stimuli with their antennae. This finding was supported by another experiment in which the antennae were either removed or covered with wax before the isolated females were exposed to crowded conditions. Neither serotonin nor an antagonist of its receptor affected the density-dependent maternal determination of progeny characteristics when injected into isolated or crowded female adults.     

Syntaxin 1A modulates the sexual maturity rate and progeny egg size related to phase changes in locusts

The migratory locust (Locusta migratoria) exhibits clear phenotypic plasticity depending on its population density. Previous studies have explored the molecular mechanisms of body colour, behavior, immunity, and metabolism between high population density gregarious (G) and low population density solitarious (S) locusts. However, the molecular mechanisms underlying differences in reproductive traits remain unknown. G locusts reach sexual maturation much faster and lay larger eggs compared with S locusts. The traits of G locusts decreased significantly with isolation, whereas those of S locusts increased with crowding. Analysis of gene expression in female adults indicated that syntaxin 1A (Syx1A) was expressed significantly higher in G locusts than in S locusts. After silencing Syx1A expression in G locusts by RNA interference (RNAi), their sexual maturity rate and progeny egg size changed towards those of S locusts. Similarly, increment in the traits of S locusts with crowding was blocked by Syx1A interference. Changes in the traits were also confirmed by decrease in the level of vitellogenin, which is regulated by Syx1A. In conclusion, plasticity of the sexual maturity rate and progeny egg size of G and S locusts, which is beneficial for locusts to adapt to environmental changes, is regulated by Syx1A.     

Two's a Crowd: Phenotypic Adjustments and Prophylaxis in Anticarsia gemmatalis Larvae Are Triggered by the Presence of Conspecifics

Defence from parasites and pathogens involves a cost. Thus, it is expected that organisms use this only at high population densities, where the risk of pathogen transmission may be high, as proposed by the "density-dependent prophylaxis" (DDP) hypothesis. These predictions have been tested in a wide range of insects, both in comparative and experimental studies. We think it pertinent to consider a continuum between solitarious and gregarious living insects, wherein: (1) solitarious insects are those that are constitutively solitary and do not express any phenotypic plasticity, (2) the middle of the continuum is represented by insects that are subject to fluctuations in local density and show a range of facultative and plastic changes; and (3) constitutively gregarious forms live gregariously and show the gregarious phenotype even in the absence of crowding stimuli. We aimed to chart some of the intermediary continuum with an insect that presents solitarious aspects, but that is subject to fluctuations in density. Thus, Anticarsia gemmatalis (Lepidoptera: Noctuidae) larvae reared at higher densities showed changes in coloration, a greater degree of encapsulation, had higher hemocyte densities and were more resistant to Baculovirus anticarsia, but not to Bacillus thuringiensis. Meanwhile, with increased rearing density there was reduced capsule melanization. Hemocyte density was the only variable that did not vary according to larval phenotype. The observed responses were not a continuous function of larval density, but an all-or-nothing response to the presence of a conspecific. As A. gemmatalis is not known for gregarious living, yet shows these density-dependent changes, it thus seems that this plastic phenotypic adjustment may be a broader phenomenon than previously thought.     

Phase-specific developmental and reproductive strategies in the desert locust

Locusts modify developmental and reproductive traits over successive generations depending on the population density. A trade-off between developmental rate and body size and between progeny size and number is often observed in organisms. In this study, we present evidence that this rule is evaded by desert locusts, Schistocerca gregaria Forsk?l, which often undergo outbreaks. Under isolated conditions, large hatchlings, typical of the gregarious forms, grow faster but emerge as larger adults than do small hatchlings typical of the solitarious forms, except for some individuals of the latter group that undergo extra molting. Under crowded conditions, large and small hatchlings grow at a similar rate, but the former become larger adults than the latter. Small hatchlings show a trade-off between development time and body size at maturation, but this constraint is avoided by large hatchlings. Phase-specific, as well as body size-dependent, differences are also detected in reproductive performance. As adult body size increases, females of a solitarious line produce more but slightly smaller eggs, whereas those of a gregarious line produce more and larger eggs. Total egg mass per pod is larger in gregarious forms than in solitarious forms. A trade-off between egg size and number is shown by a solitarious line but not by a gregarious line that produces relatively large eggs with similar numbers of eggs per pod. These results suggest that phase transformation involves not just a shift of resource allocation but also an enhanced capability expressed in response to crowding.     

Phase polymorphism in Schistocerca gregaria: Assessment of juvenile hormone synthesis in relation to vitellogenesis

Juvenile hormone (JH) synthesis by the corpora allata of gregarious and solitarious phase females of Schistocerca gregaria was determined in vitro during the penultimate and last stadia as well as during the first gonotrophic period of adults. Generally, the corpora allata of solitarious females showed higher rates of JH synthetic activity. In addition, in adult females there was a temporal difference between the corpora allata activities of gregarious and solitarious locusts, the latter exhibiting relatively higher rates of JH synthesis early in the first gonotrophic period. The corpus allatum volumes of solitarious females were also generally larger than those of their gregarious counterparts; there was no synchrony between fluctuations in JH synthetic activity and changes in corpus allatum volume in either phase.The early onset of relatively high JH synthetic rates in solitarious females was correlated with the early detection, by rocket immunoelectrophoresis, of vitellogenin in the haemolymph and vitellin in the oöcytes. Vitellogenin appeared in the haemolymph on day 4 in solitarious females and on day 6 in gregarious females and vitellin appeared in the oöcytes on days 6 and 8 respectively. Oöcyte length at which vitellogenesis was first detected was 1.8 mm for gregarious and 1.3 mm for solitarious females. However, despite the accelerated onset of both vitellogenin synthesis and uptake, oöcyte maturation time of solitarious females was longer. In both gregarious and solitarious females, vitellogenin titres increased until oöcytes reached a length of about 4 mm and declined thereafter. Vitellin content of ovaries increased proportionately to oöcyte growth until they attained a length of 5.0 mm. The subsequent increase in length of oöcytes to maturity is attributed to postvitellogenic growth, possibly by hydration.     

Do desert locust hoppers develop gregarious characteristics by watching a video?

Various sensory stimuli have been suggested to induce gregarious body coloration in locusts, but most previous studies ignored the importance of substrate color. This study tested the effects of visual, olfactory and tactile stimuli from other locusts on the induction of gregarious body coloration in single (isolated-reared) Schistocerca gregaria nymphs housed in yellow-green cups. Odor from gregarious (crowd-reared) locusts, which is believed to induce black patterns in single locusts, had little effect when applied to visually isolated nymphs at the 2nd stadium onward, and all test nymphs remained green without black patterns at the last stadium, as in controls reared without odor and visual stimuli. Visual stimuli alone induced black patterns when a single solitarious nymph was allowed to see other locusts in another cup. The degree of black patterns increased as the number of locusts shown increased, and some test nymphs developed body coloration typically observed in gregarious forms. A classical morphometric ratio (hind femur length/head width) shifted toward the value typical of gregarious forms when the single nymphs were allowed to see 5 or 10 locusts. Single nymphs also developed black patterns when presented green conspecific nymphs and adults of two hemipteran species kept in another cup. No synergetic effects of visual and odor stimuli were detected. Movies of locusts, crickets and tadpoles were found effective in inducing black patterns in single locusts. Ontogenetic variation in the sensitivity to crowding and experimental methodology might be responsible for some discrepancies in the conclusions among different researchers.     

Is juvenile hormone involved in the maternal regulation of egg size and progeny characteristics in the desert locust?

The role of juvenile hormone (JH) in the maternal regulation of progeny characteristics was examined in the desert locust, Schistocerca gregaria. Female adults of this species are known to produce smaller but more eggs when reared in isolation than do those reared in a group. Eggs laid by isolated females develop green hatchlings typical of solitarious forms, whereas those laid by the latter produce black hatchlings typical of gregarious forms. Topical application of a juvenile hormone analog (JHA), fenoxycarb, or implantation of corpora allata (CA) taken from the migratory locust, Locusta migratoria, caused crowded S. gregaria females to deposit smaller eggs, but did not have a significant effect on the number of eggs per egg pod except at high doses of JHA. The production of smaller eggs by treated and untreated crowded females was closely associated with earlier deposition of the egg pods and shorter oviposition intervals. However, neither JHA application nor CA implantation influenced the progeny characteristics in actively reproducing aged females under crowded conditions, while untreated control females started producing smaller and more eggs upon transfer to isolated conditions. These results may suggest that JH is not directly involved in the maternal regulation of phase-dependent progeny characteristics.     

Adult female desert locusts require contact chemicals and light for progeny gregarization

Crowding causes many organisms to express phenotypic plasticity in various traits. Phase polyphenism in desert locusts represents one extreme example in which a solitary form (solitarious phase) turns into a gregarious form (gregarious phase) in response to crowding. Conspicuous differences in body size and colour occur even in hatchlings. The phase‐specific differences in hatchling characteristics are caused by the tactile stimuli perceived by the antennae of their mother. However, the nature of the tactile stimuli and the mechanism by which the perceived stimuli are processed as a gregarizing signal remain unknown. To explore this problem, the antennae of solitarious adult females of the desert locust Schistocerca gregaria are touched with the bodies of conspecific locusts at different physiological stages and those of other species. The results suggest that a cuticular chemical factor at a specific developmental stage of conspecific locusts causes the solitarious females to produce large eggs that give rise to black hatchlings characteristic of gregarious forms (progeny gregarization), and that this or a similar compound occurs in other acridids, crickets and cockroaches but not in beetles. The involvement of a chemical substance is also supported by hexane extracts of cuticular surfaces of locusts that induce the same effects. Interestingly, crowding induces such gregarizing effects only when the female receives the appropriate stimulus in the presence of light. Solitarious female S. gregaria with their head capsule coated with phosphorescent paint exhibit progeny gregarization in response to crowding and light pulses in darkness, whereas those treated in the same way without light pulses fail to do so.     

Innate phase behavior in the desert locust,Schistocerca gregaria

Abstract Detailed aspects of the transition from the solitarious to the gregarious phase in the framework of locust ecology are undoubtedly most important for understanding locust phase polyphenism. Nevertheless, due to obvious difficulties in studying the solitarious phase in nature, such information is limited and mostly available from research carried out under laboratory conditions. In the current study, we examined the dispersal patterns of newly hatched locust nymphs in a laboratory setup that simulated seminatural conditions. This was carried out with no previous manipulation of the nymphs other than controlling their parental density. We comparatively tested the spatial distribution of newly hatched nymphs on perches located at different ranges within an emergence arena, and the expected Poisson (random) distribution. Hatchlings were found to disperse among the perches in a pattern significantly different from that expected by random. Irrespective of their parents’ phase, the observed distributions of all nymphs were clearly clumped, similar or close to those expected for gregarious locusts. It seems that rather than emerging with a parentally derived and predetermined phase, hatchlings have an independent default or innate behavioral state, which reflects at least tolerance if not attraction to conspecifics. The typical phase behavior may later become dominant under the appropriate environmental conditions. These results imply novel perspectives on locust phase transformation, which contribute to our understanding of the formation of locust crowds under field conditions. These should be considered in any rationale for developing a preventative management strategy of locust populations.     

Knockdown of the corazonin gene reveals its critical role in the control of gregarious characteristics in the desert locust

The two plague locusts, Schistocerca gregaria and Locusta migratoria, exhibit density-dependent phase polyphenism. Nymphs occurring at low population densities (solitarious forms) are uniformly colored and match their body color to the background color of their habitat, whereas those occurring at high population densities (gregarious) develop black patterns. An injection of the neuropeptide, corazonin (Crz) has been shown to induce black patterns in locusts and affect the classical morphometric ratio, F/C (F, hind femur length; C, maximum head width). We herein identified and cloned the CRZ genes from S. gregaria (SgCRZ) and L. migratoria. A comparative analysis of prepro-Crz sequences among insects showed that the functional peptide was well conserved; its conservation was limited to the peptide region. Silencing of the identified SgCRZ gene in gregarious S. gregaria nymphs markedly lightened their body color and shifted the adult F/C ratio toward the value typical of solitarious forms. In addition, knockdown of the gene in solitarious nymphs strongly inhibited darkening even after a transfer to crowded conditions; however, these individuals developed black patterns after being injected with the Crz as a rescue treatment. SgCRZ was constitutively expressed in the brains of S. gregaria during nymphal development in both phases. This gene was highly expressed not only in the brain in both phases, but also in the corpora allata in the gregarious phase. This conspicuous phase-dependent difference in SgCRZ gene expression may indicate a functional role in the control of phase polyphenism in this locust.     

Effects of isolation and crowding on the haemolymph pigment composition of the desert locust, Schistocerca gregaria (Orth., Acrididae)

Abstract:  An experimental study on the effect of isolation and crowding of the desert locust, Schistocerca gregaria (Forskål) on haemolymph pigment composition (as measured by absorbance ratios at 460 and 680 nm) was carried out at the International Centre of Insect Physiology and Ecology, Nairobi. The results showed that haemolymph absorbance ratios of gregarious and solitarious locusts were different (P < 0.05) and that there was no phase-specific sex differentiation with regard to this measure (P < 0.05). The haemolymph pigment composition changes during isolation and grouping showed contrasting trends. It changed rapidly in nymphs, but slowly and erratically in adults both resulting from isolation and grouping at hopper stage. Significant shifts in locust phase status were recorded in both situations in nymphs in F₀ generation, and in the adults by the end of the F₂ and F₃ generations of solitary and gregarious conditions, respectively. Shifting of fledglings did not induce significant changes in their mean absorbance ratios in both situations, i.e. isolation and crowding within F₀ generation. The ratio of length of posterior femur (F) to greatest width of the head capsule (C) changed either at a similar rate or more often slower than the haemolymph pigment ratio and both required more than a generation to transform fully. The study has shown that haemolymph pigment composition could be a suitable measure for monitoring phase changes at nymphal stages of the desert locust.     

Effects of juvenile hormone treatment on phase changes and pheromone production in the desert locust,Schistocerca gregaria (Forskal) (Orthoptera: Acrididae)

The roles of juvenile hormone III (JH III) on phase changes and pheromone production were examined in laboratory-reared gregarious desert locust, Schistocerca gregaria (Forskal). The hormone was applied to 5th instar nymphs and newly emerged adult locusts. Generally, the 5th instar nymphs exhibited a higher sensitivity to hormone treatments than the adults. Hormone applications inhibited pheromone production (as measured by the amounts of phenylacetonitrile released). In addition, JH III had a significant effect on the external colouration and absorbance ratios of the haemolymph pigments. It is concluded that the effects of exogenous JH III on gregarious locusts represent a shift towards the solitarious phase.     

Fever and phenotype: transgenerational effect of disease on desert locust phase state

Natural enemy attack can cause transgenerational shifts in phenotype such that offspring are less vulnerable to future attack. Desert locusts (Schistocerca gregaria) show density‐dependent variation in their resistance to pathogens, such that they are less vulnerable to pathogens when in the high‐density gregarious phase state (when they would probably be more exposed to pathogens) than when in the solitarious phase state. We therefore hypothesized that infected gregarious parents would maintain this phenotype in their offspring. We infected gregarious desert locust nymphs with the fungal pathogen Metarhizium anisopliae var. acridum, and allowed them to survive to reproduction by means of behavioural fever. The phase state of the locust offspring was assessed by their colouration and behavioural assays. Contrary to our hypothesis, we found an increase in solitarization in the infected population (14.6% solitarious offspring from infected parents, vs. <2% from uninfected counterparts at equivalent density). In a second experiment, we simulated behavioural fever temperatures and obtained a similar result (13.6% solitarious offspring vs. 4.4% from controls), implying that the phenomenon is probably a side‐effect of the hosts’ fever response. Identification of this novel environmental factor affecting locust phase state could have important implications for the biological control of these major pests.     

Measurements of locomotor activity in hatchlings of the migratory locust Locusta migratoria: effects of intrinsic and extrinsic factors

Abstract. The effects of intrinsic and extrinsic factors on locomotor activity in crowd‐reared first‐stadium nymphs of the migratory locust Locusta migratoria are investigated under continuous light conditions using an actograph apparatus. Nymphs show monomodal or bimodal patterns of locomotor activity with respect to the time after the start of measurements, depending on the age. Locomotor activity is suppressed by the presence of grass in nymphs aged 0–2 days old but a peak of activity observed shortly after hatching is not suppressed. The results suggest that newly‐hatched nymphs may try to disperse from the hatching site. Nymphs show higher locomotor activity levels under moist conditions than under dry conditions during the first 5‐h period of measurements. This enhanced locomotor activity may constitute attempts to avoid high humidity. Under dim‐light conditions (2 × 10^?2 Wm^?2), locomotor activity is suppressed during the first half day and increases to a high level thereafter in both grass‐fed and unfed individuals. This increased activity might indicate a possible involvement of circadian rhythms. Background colour has no significant effect on the locomotor activity. The present study provides new aspects of behaviour in nymphs as well as baseline data for behavioural analysis of locust locomotion in relation to phase polyphenism.     

Solitary and gregarious locusts differ in circadian rhythmicity of a visual output neuron

Locusts demonstrate remarkable phenotypic plasticity driven by changes in population density. This density dependent phase polyphenism is associated with many physiological, behavioral, and morphological changes, including observations that cryptic solitarious (solitary-reared) individuals start to fly at dusk, whereas gregarious (crowd-reared) individuals are day-active. We have recorded for 24-36 h, from an identified visual output neuron, the descending contralateral movement detector (DCMD) of Schistocerca gregaria in solitarious and gregarious animals. DCMD signals impending collision and participates in flight avoidance maneuvers. The strength of DCMD's response to looming stimuli, characterized by the number of evoked spikes and peak firing rate, varies approximately sinusoidally with a period close to 24 h under constant light in solitarious locusts. In gregarious individuals the 24-h pattern is more complex, being modified by secondary ultradian rhythms. DCMD's strongest responses occur around expected dusk in solitarious locusts but up to 6 h earlier in gregarious locusts, matching the times of day at which locusts of each type are most active. We thus demonstrate a neuronal correlate of a temporal shift in behavior that is observed in gregarious locusts. Our ability to alter the nature of a circadian rhythm by manipulating the rearing density of locusts under identical light-dark cycles may provide important tools to investigate further the mechanisms underlying diurnal rhythmicity.     

Maternal effects on progeny size, number and body color in the desert locust, Schistocerca gregaria: Density- and reproductive cycle-dependent variation

The effects of rearing density and maternal age on the progeny size, number and coloration of the desert locust, Schistocerca gregaria, were investigated. Isolated-reared females deposited smaller, but more eggs than crowd-reared females. The former produced smaller and more eggs with age, whereas the latter showed a tendency to produce larger and fewer eggs over time. A similar tendency was also observed with virgin females, indicating that mating or the presence of males was not important. The first egg pod produced by each mated crowd-reared female contained significantly smaller and more eggs than did the subsequent egg pods. The former often produced many green hatchlings (0-100%) characteristic of solitarious forms, whereas the egg pods deposited after the first pod produced predominantly black hatchlings typical of gregarious forms. Adults were highly sensitive to a shift in rearing density and quickly modified the quality and quantity of their progeny depending on the density encountered. The number of eggs per pod was influenced not only by the mother's rearing density but also by rearing density of the grandmother. The present results demonstrated that the characteristics of progeny are influenced not only by the crowding conditions experienced by the mother and grandmother but also by the mother's reproductive cycle.