Host Deprivation Research Articles

Lifetime allocation of juvenile and adult nutritional resources to egg production in a holometabolous insect.

In holometabolous insects reproductive success is strongly determined by the nutritional resources available to the females. In addition to nutrients derived from adult feeding, resources for egg production may come from the limited reserves accumulated during the larval stages. The pattern of allocation of these larval reserves to egg production is expected to be strongly linked to the nutritional ecology of the adult. We investigate the temporal pattern of allocation of larval reserves to reproduction in a host-feeding parasitoid wasp. As predicted by the dynamics of allocation of an adult meal, larval reserves are the main source of nutrients for four or five days after emergence. However, despite the high frequency of host feeding and the high nutrient content of a haemolymph meal, which we predicted would lead to larval reserves being conserved in the event of host deprivation, larval reserves contribute to egg production throughout the lifetime of the female. We propose several mechanistic and adaptive explanations for our results, including the possible existence of a limiting or key nutrient for egg production of exclusively larval origin. We make further predictions concerning the pattern of allocation of larval resources in parasitoids with different adult nutritional requirements.

Pattern of Egg Management by Trichogramma cacoeciae and T. dendrolimi (Hymenoptera: Trichogrammatidae)

The effect of temporary host deprivation on parasitization rates of Trichogramma cacoeciae Marchal and T. dendrolimi Matsumura was investigated. The study was conducted with females that we allowed to engage in 3 days of oviposition after various periods of host deprivation. It seems that the production and management of eggs by the two species is completely different. During the first day of oviposition, parasitization by T. cacoeciae was almost unaffected after 1 to 5 days of host deprivation. As deprivation time increased, however, the number of parasitized hosts decreased from an average of 28.6 - 2.0 hosts provided at emergence to an average of 12.5 - 2.3 hosts when the waiting time was 10 days. The number of hosts parasitized on the first day of parasitization by T. dendrolimi were not affected whatever the waiting test period. During the second or third days of oviposition, the lack of suitable hosts for T. cacoeciae did not depress egg-laying potentiality, whereas a strong reduction in parasitization rates by T. dendrolimi occurred in the next 2 days of oviposition whatever was the waiting period. This leads to ca. 50% reduction in total activity of 3 days of oviposition. Only in T. cacoeciae was it possible to distinguish between ageing and host deprivation. The data suggest that T. dendrolimi is a typical proovigenic species, while T. cacoeciae is neither definitely proovigenic nor synovigenic. A slight decrease in rate of emergence of offspring of T. cacoeciae females that had waited 8 to 10 days for their hosts was observed. As far as biological control is concerned, the efficiency of T. dendrolimi females may be more sensitive to host deprivation than T. cacoeciae.

Long‐term egg retention and parasitization in Trichogramma principum (Hym., Trichogrammatidae)

Laboratory experiments with Trichogramma principium Sug. et Sor. females that were offered Sitotroga cerealella Oliv. eggs demonstrated that less than half of the ovipositing females started oviposition during the first 2 days of the experiment, whereas the rest of the ovipositing females showed a delay in parasitization ranging from 2 to 10 days after contact with the host. Almost 10% of the wasps refused to parasitize the grain moth eggs over 12 days. The delay in parasitization may be as long as 6–8 days without any significant decrease in the number of mature ovarial eggs, in the number of eggs laid during the first 48 h of oviposition, and in the total lifetime fecundity. This egg retention is responsible for the fact that in spite of a relatively short mean duration of the oviposition period in each individual female (approximately 4 days), host parasitization by a group of simultaneously emerged wasps was almost uniformly distributed over 8–10 days. When induced, the parasitization state (i.e. the tendency to parasitize sequentially offered portions of host eggs) was stable both in the presence of a host and under host deprivation extended up to 8 days. These data provide further evidence for our hypotheses that the stability of the parasitization state in Trichogramma is based on endocrine mechanisms.

Factors Affecting the Biology of Telenomus isis (Polaszek) (Hymenoptera: Scelionidae), an Egg Parasitoid of Cereal Stem Borers in West Africa

This study aimed at an assessment of the potential of the egg parasitoid Telenomus isis (Polaszek) as a biological control agent of cereal stem borers. Therefore, the effects of temperature, host species, host age, and time of host deprivation on the development and the reproductive potential of T. isis were studied in the laboratory. By use of linear regression and a modified Logan model and with eggs of the noctuid Sesamia calamistis Hampson as hosts, the lower and upper thresholds for development were estimated at 13.1 and 36°C, respectively, and the optimal temperature for development was 31°C. Female T. isis had no measurable preoviposition period, and the oviposition period ranged from 3 to 5 days. Approximately 66% of the total lifetime complement of eggs of T. isis were produced within 6 h after emergence. Average total lifetime fecundity was 61.1 and 82.1 eggs per female at 21 and 28°C, respectively. Longevity of adult females was 17.1 days at 21°C and 5.2 days at 30°C. Host acceptance and suitability were tested, using nine lepidopteran borer species. Only the noctuids S. calamistis, Sesamia poephaga (Tam & Bowden), Sesamia botanephaga (Tam & Bowden), and Busseola fusca (Fuller) were successfully attacked by T. isis. Parasitism and emergence did not differ among those species, but the sex ratio (expressed as proportion of female progeny) was significantly lower on S. calamistis. An increase of the host age from 1 to 4 days significantly reduced mean parasitism from 56.7 to 23.5%. Parasitoid emergence rates and sex ratio did not vary among 1-, 2-, or 3-day-old host eggs, but both parameters were significantly lower on 4-day-old eggs. With increasing duration of host deprivation from 0 to 17 days, longevity increased from 8.5 to 18.5 days, whereas average lifetime fecundity decreased from 81.2 to 40.5 eggs per female, respectively, indicating resorption of eggs. The results are discussed and compared with life table parameters of the ubiquitous egg parasitoid Telenomus busseolae (Gahan).

Responses of Ovipositing Moths (Lepidoptera: Geometridae) to Host Plant Deprivation: Life-History Aspects and Implications for Population Dynamics

For three species of geometrid moths with noneruptive population dynamics, physiological and behavioral responses of ovipositing females to larval host deprivation were recorded. Single substrate trials were used. Availability of adult food was also varied to manipulate physiological condition of the moths. Egg production rate decreased only weakly in the absence of host plant, whereas it was strongly influenced by adult feeding. The time from the beginning of the experiment to initiation of oviposition was largely determined by presence of suitable host. This variable, oviposition latency, was only weakly affected by nutritional status of the females. Oviposition rates also remained lower on unsuitable hosts after oviposition was initiated. This indicates that the effect of inferior oviposition substrate was not limited to postponing oviposition. Host deprivation and adult feeding both lead to accumulation of chorionated eggs in abdomens. However, high egg loads of the fed females did not alter their behavior in the direction predicted by optimality models. We conclude that oviposition latency was the only variable in which female responses to unsuitable hosts were sufficiently strong to have potential significance for population dynamics. Latency presumably corresponds to dispersing behavior in nature. Such a response, not having been observed in an outbreaking geometrid studied earlier, may reflect a behavioral mechanism capable of stabilizing local population dynamics. The results are discussed in the light of the gradation from capital to income breeding. In herbivorous insects, oviposition latency may serve as an index of overall sensitivity of ovipositing females to adverse environmental conditions.

Biology and field performance ofGryon clavigrallae(Hymenoptera: Scelionidae), an egg parasitoid ofClavigrallaspp. (Hemiptera: Coreidae) in India

The biology and impact of Gryon clavigrallae Mineo, an egg parasitoid of Clavigralla scutellaris Spinola and C. gibbosa (Westwood), was investigated. The calculated developmental threshold temperatures for females and males were 15.6 degrees C and 15.8 degrees C, respectively. Emergence exceeded 94% at temperatures between 22 and 30 degrees C. Adult females lived on average 28-96 days when fed with honey. Without food, adults lived < 6 days. Mean fecundity was 56.4 eggs per female. A significant trend of lower fecundity after longer periods of host deprivation was observed. Gryon clavigrallae females successfully oviposited in host eggs of all ages though eggs < 4 days old were preferred. Total host handling times were significantly longer on C. gibbosa eggs (23.5 min) than on C. scutellaris eggs (12.0 min). Females readily distinguished parasitized from non-parasitized host eggs. Superparasitism was observed when few or no unparasitized eggs were available. Eggs of the two Clavigralla species can be separated by surface structure and condition after eclosion. Clavigralla scutellaris laid significantly larger egg clusters than C. gibbosa (19.9 versus 10.5 eggs per cluster). Gryon clavigrallae was present as soon as the first Clavigralla spp. egg clusters were found on pigeonpea. The percentage of egg clusters parasitized increased early in the season with egg cluster density and remained high (up to 83%) despite fluctuations in host density. Overall, G. clavigrallae parasitized 40 and 58% of C. gibbosa and C. scutellaris eggs. The percentage of egg clusters parasitized and the number of eggs parasitized per cluster increased significantly with egg cluster size. The overall parasitoid sex ratio was highly female biased but varied with the number of eggs parasitized per cluster.

The effect of egg load and host deprivation on oviposition behaviour in aphidophagous hoverflies

Summary1. Two species of aphidophagous hoverfly, Episyrphus balteatus and Syrphus ribesii, were tested for the effects of egg load and host deprivation on oviposition choices.2. Egg load affected the total number of eggs laid in E. balteatus but not in S. ribesii, however it did not affect the proportion laid on any one aphid in E. balteatus but did affect the proportion laid on any one aphid in S. ribesii. The rank order of preferences remained unchanged by age or host deprivation.3. The dominant effects on host choices were aphid species (in both syrphids) and presentation order (in E. balteatus).4. Being deprived of hosts increased egg load substantially in E. balteatus, and increasing time of deprivation also had an effect on discrimination; there was no effect of host deprivation in S. ribesii.5. Reasons for these patterns are discussed.

Egg retention in the presence of a host in Trichogramma females

Abstract: Laboratory experiments with Trichogramma principium suggest that Trichogramma females may be in one of two alternative states: the parasitization state or the egg retention state. Dissections show that T. principium females at emergence have ≅ 20 mature ovarian eggs. Females in egg retention state have practically the same mean number of mature ovarian eggs, while the distribution is different, suggesting that both oosorption and oogenesis may occur during egg retention. In parasitizing females, additional maturation starts simultaneously with the oviposition. However, ovipositing females tend to lay eggs with maturation, which is why they mostly carry few (&lt; 5) mature ovarian eggs. The mean number of eggs laid during the first 48 h of the oviposition does not depend on whether the parasitization is delayed or not, suggesting that egg retention is connected just with oviposition behaviour rather than with the intensity of oogenesis. We conclude that ‘voluntary’ egg retention in the presence of a host does not differ with the state of ovaria from ‘forced’ egg retention under host deprivation. Supposedly, egg retention with the availability of a suitable host may be considered as a sort of short‐term adult diapause‐like state when not oogenesis, but oviposition is subject to hormonal regulation.

The dynamics of egg production, oviposition and resorption in a parasitoid wasp

1. The extent to which parasitoid wasps are limited by their egg supply is very important in understanding their reproductive strategies. Egg reserves are dynamic, with most wasps maturing new eggs throughout their life (synovigeny) and many species resorbing eggs that are not used in oviposition. We investigated the extent to which a parasitoid modulates its egg reserves in the light of its experience in finding hosts. 2. The egg dynamics of the Encyrtid Wasp Leptomastix dactylopii, a solitary parasitoid of mealybugs, were studied in the laboratory. This species is synovigenic and practises egg resorption. 3. We allowed newly emerged wasps to experience one of four environments of increasing value in terms of reproductive opportunities. We proposed that wasps that experienced good quality environments would maintain more mature eggs ready for oviposition. Dissection of wasps subject to different periods of host deprivation after the experimental treatment failed to confirm the hypothesis: egg load was independent of experience. 4. We also proposed that any adjustment of egg supply to make up for eggs oviposited would be effected through a reduction in egg resorption. Instead, we found that the wasp quickly made up for eggs oviposited by increased egg production.

Factors Influencing the Developmental Rates and Reproductive Potentials ofTelenomus busseolae(Gahan) [Hym.: Scelionidae], an Egg Parasitoid ofSesamia calamistisHampson (Lep.: Noctuidae)

The effect of seven constant temperatures on the development of Telenomus busseolae was determined, using Sesamia calamistis eggs as the host. The developmental threshold calculated was 13.7°C, the optimum temperature was 31°C, and the maximum temperature at which no parasitoid emergence occurred was 34°C. Female T. busseolae began ovipositing immediately after emergence. They produced more offspring during the first 24 h of adult life than during any subsequent period. At 20°C, adult females lived twice as long as those at 30°C (21.7 and 11.0 days, respectively). Total progeny of T. busseolae was significantly highest at 27°C. Mean fecundity ranged from 61 to 182 offspring per female. The effect of host age and host deprivation on the host parasitism rate, egg viability, and sex ratio of T. busseolae was also investigated. Only parasitism and emergence rates were affected by host age. The numbers of total progeny were the same between 0 and 10 days of host deprivation, whereas longevity tended to increase from 12.8 to 23.4 days from 0 to 14 days of withholding hosts. The percentage parasitoid emergence and the sex ratio were not affected by withholding hosts. T. busseolae is adapted to an ecosystem with strong environmental fluctuations that cause temporary scarcity of hosts and food.

Host shifts in biological weed control: Real problems, semantic difficulties or poor science?

Abstract Many biologists perceive organisms as constantly evolving and therefore consider the host plant ranges of biological control agents as labile. Host plant ranges are thus likely to undergo adaptive change should environmental conditions change, for example following successful biological control. As a consequence, the introduction of biological control agents against weeds is considered by many to be an inherently unsafe practice with non‐target plants at risk of attack. However, despite the introduction of over 600 insect species from one geographic region to another for biological weed control during this century, there are relatively few documented cases of changes in host plant range. Purported instances are discussed in relation to behavioural and genetic concepts. It is concluded that apparent additions to the host range can, in all of the cases examined, be explained in terms of established behavioural concepts of pre‐adaptation, threshold change resulting from host deprivation, and effects...

Biological Parameters for Mass Propagation of Catolaccus grandis (Hymenoptera: Pteromalidae)

We studied the influences of mating history, parental age, pupal weight of parasitoids, host deprivation, and host size on the reproductive potential and sex ratio of Catolaccus grandis (Burks), a parasitoid of the boll weevil Anthonomus grandis grandis (Boheman). Absence of hosts for 5 or 10 d reduced the fecundity of C. grandis females by 36.8 and 39.5%, respectively, compared with parasitoids continually exposed to host larvae. An acceptable sex ratio (65% females) in the propagation system was maintained if a ratio of 3 males per female parasitoid was used during the 1st h of mating, immediately after emergence. As female adults aged from 5 to 10 d, the percentage of female progeny increased from 64.0 to 77.2, respectively. However, a further increase in female age, from 20 to 25 d, resulted in a decline in percentage of female progeny from 54.0 to 48.5. The proportion of female progeny increased with the size of the host parasitized. A significant correlation was found between weight of female pupae of C. grandis and their fecundity during the first 30 d of oviposition. These data will be used to optimize mass rearing of C. grandis for inoculative and augmentative releases to suppress boIl weevil populations in cotton fields.

Effect of host deprivation on egg quality, egg load, and oviposition in a solitary parasitoid,Chetogena edwardsii (Diptera: Tachinidae)

Solitary parasitoids are limited to laying one egg per host because larvae compete within hosts. If host encounter rate is low, females should not increase the number of eggs/host in response. The tachinid fly, Chetogena edwardsii,was used to evaluate the effect of host deprivation on egg accumulation, oviposition behavior, and egg quality in a solitary parasitoid. Females deprived of hosts for 2– 7 days accumulate about 1 day's supply of eggs. Egg output of deprived females once hosts are restored does not differ from that of control females. Deprived females retain one egg in the uterus where it undergoes embryogenesis. Maggots emerging from retained eggs are more likely to survive in hosts molting in 40 h or less after receipt of an egg than are maggots emerging from eggs fertilized shortly before oviposition. Egg retention is a consequence of host deprivation that permits females to broaden the range of hosts they can exploit to include soon-to-molt hosts and possibly multiply parasitized hosts.

Effects of temporary host deprivation on the reproductive potential of Trichogramma brassicae

AbstractThe effect of host deprivation on the reproductive potential and parasitization behaviour of Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae) was investigated. Upon emergence, females were deprived of hosts for one to four days, and were subsequently provided with an unlimited number of hosts. Regardless of its duration, deprivation did not affect female longevity, overall rate of progeny emergence, or progeny sex‐ratio. As deprivation time increased, however, the total number of parasitized hosts decreased from an average of 81.2 when hosts were provided at emergence, to an average of 34.0 when the waiting time was 4 days. This reduction was mainly due to the reduction in the parasitizations following the first laying peak, which was not affected when deprivation lasted fewer than 4 days. Trichogramma females are able to store ripe eggs (about 35) for 3 days without damage, but resorption occurs after four days of deprivation. Our results suggest that imaginal vitellogenesis occurs in this proovigenic wasp but that it is affected by host deprivation. The behaviour of females, as measured by the average distance between all parasitized hosts, was also modified by host deprivation. When deprivation exceeded one day, parasitizations were more scattered over the host patch. Moreover, increased deprivation times also appeared to delay the initiation of parasitization by a few hours.Host shortage is likely to occur in nature, reducing the efficiency of Trichogramma as a biocontrol agent. The individual history of females must be taken into account in any study of the reproductive strategies of parasitoid females.

The Influence of Host Deprivation and Host Source on the Reproductive Biology and Longevity of the Squash Bug Egg Parasitoid Gryon pennsylvanicum (Ashmead) (Hymenoptera: Scelionidae)

Laboratory experiments were conducted to determine whether the reproductive biology and longevity of the squash bug egg parasitoid Gryon pennsylvanicum (Ashmead) were affected by (1) host deprivation and (2) host source, i.e., eggs from squash bugs reared on either a susceptible summer squash (Early Prolific Straightneck), or a resistant winter squash (Waltham Butternut), cultivar. Neither the duration nor the schedule of parasitoid oviposition was affected by host availability when G. pennsylvanicum females were deprived of squash bug eggs for intervals of 3 days throughout their adult lives. However, a significantly longer postreproductive period (i.e., the number of days until death after oviposition is completed) occurred in host-deprived parasitoids, but only in those females that emerged from eggs of squash bugs reared on the susceptible cultivar. When reared from squash bug eggs from the resistant cultivar, G. pennsylvanicum had a shorter postreproductive period which did not differ significantly between host-deprived and non-host-deprived females. Fecundity was significantly lower in host-deprived wasps associated with both cultivars than in non-host-deprived female wasps. Dissections revealed no oocyte resorption over the lifetime of 3-day host-deprived females across all treatments. However, when deprived of hosts for 5, 7, or 9 days, morphological changes appeared in the oocytes, suggesting possible resorption.

Plasticity in the egg-spacing behavior of a seed beetle: Effects of host deprivation and seed patchiness (Coleoptera: Bruchidae)

Egg-laying females of the seed beetle Callosobruchus maculatusdiscriminate between egg-free and egg-laden seeds and produce a nearly uniform distribution of eggs among seeds. We examined plasticity in this trait in response to both an internal factor (level of host deprivation) and an environmental one (the spatial configuration of available seeds). Responses to each factor were measured in genetically divergent strains that show a relatively strong (S strain) or weak (B strain) tendency to spread eggs evenly among seeds. Following a modest (10-h) period of host deprivation, S-strain females distributed their eggs less uniformly among seeds; the proportion of females committing at least one oviposition “mistake” increased from 20 to 50%. Similarly, S-strain females distributed their eggs less uniformly if seeds were presented in multiple, discrete patches instead of in a single, large patch. The higher frequency of oviposition mistakes in the multiple-patch arena was caused in part by females maintaining a uniform distribution of eggs within patches but not among patches. In contrast, females from the “sloppier” B strain were unaffected by either host deprivation or resource dispersion. Responses to seed patchiness are discussed in relation to the role of learning in the egg-spacing behavior of C. maculatus.

Influence of host deprivation on egg load and oviposition behaviour of Brachymeria intermedia, a parasitoid of gypsy moth

Abstract. Mated female Brachymeria intermedia (Hymenoptera: Chalcididae) deprived, since emergence, from pupae of their host Lymantria dispar (Lepidoptera: Lymantriidae), accumulated eggs but had a very low rate of hostacceptance. Parasitoids that were host‐deprived after encountering pupae early in life also accumulated eggs, but maintained a high acceptance rate. Thus early exposure to hosts promoted active reproductive behaviour. Total egg production depended on the total number of pupae encountered, indicating that B.intermedia adjust their egg production to host availability. Hence, in B. intermedia both the physiological state of the parasitoid (age and egg load) and the informational state (in this case host‐availability and experience) interact to shape oviposition behaviour.

Influence of maternal age and host deprivation on egg production and parasitization byMicroplitis croceipes [Hym.: Braconidae

The effect of maternal age and hostHeliothis virescens (F.) deprivation on egg production and allocation byMicroplitis croceipes (Cresson) was determined in the laboratory on 0.5, 1.0, 3.0, 6.0, 9.0, and 12.0 days old parasitoids. In host-deprived parasitoids, newly-emerged (0.5-day old) females produced significantly fewer eggs than older ones; egg production peaked 3 to 6 days after emergence and declined thereafter. However, the number of eggs found in undeprived parasitoids at various ages suggested a cyclical pattern of egg production. The rate of parasitization by host-deprivedM. croceipes was higher in 1.0 to 6.0 days old than in newly-emerged or older females and was correlated strongly with egg production (r=0.93). The first observation on premature larval hatching inM. croceipes was documented.

Host Acceptance Behavior of Pear Psylla (Homoptera: Psyllidae) Affected by Plant Species, Host Deprivation, Habituation, and Eggload

The interactive effects of plant species, host deprivation (amount of time deprived of the host), and mature egg complement (eggload) on host acceptance activities of pear psylla, Cacopsylla pyricola Foerster, were monitored in laboratory bioassays. Plant species included a natural host, ‘Bartlett’ pear, Pyrus communis; an Asian pear, P. calleryana, currently of use in breeding programs; and the nonhost apple, Malus domestica. Plan species differed primarily in their effects on oviposition-related activities; settling-probing activity was similar among species. Increased duration of host deprivation resulted in increased time spent in oviposition activities, egg-laying rates, and eggload; fraction of oviposition-related activities that failed to result in an egg being deposited decreased with increasing deprivation. Largest differences among plant species in their effects on oviposition activities occurred at the longest deprivation level. On ‘Bartlett’ pear, oviposition activity and probability of oviposition increased with increasing eggload, whereas settling-probing activity decreased. On the Asian pear, significant relationships between eggload and activity were noted only at one deprivation level; the patterns were similar to those on ‘Bartlett’ pear. On apple, settling-probing activity decreased with increasing eggload at a single deprivation level. On all plant species, oviposition activities increased with time spent in contact with the leaf; for nonhosts, this result suggests that psylla habituated to novel species. First-order transitions between pairs of behaviors were quantified. Psylla rarely initiated oviposition activities immediately upon leaf contact. Rather, oviposition activities tended to be preceded by settling-probing activity. We interpret these results as evidence that plant cues received on initial contact were insufficient to release oviposition activity but that plant cues received during settling-probing activity released oviposition activities. Oviposition activity on P. calleryana and apple was ended before egg deposition with higher frequency than on ‘Bartlett’ pear. This result suggests that plant cues received during oviposition activities affected ultimately whether the egg was deposited.

GEOGRAPHIC VARIATION IN MATERNAL-AGE EFFECTS ON DIAPAUSE IN A CRICKET.

Maternal effects are developmental influences extended across life cycle stages, whereby genetic or environmental differences in the maternal generation are expressed as phenotypic differences in the offspring. Thus natural selection acts upon phenotypic variation that results in part from events in the previous generation. The evolutionary consequences of such transgenerational interactions can be numerous and complex. For example, Kirkpatrick and Lande (1989) found that because of lags in evolutionary response to selection on maternal traits, and the fact that the rate and direction of evolution depend upon the inheritance of traits not directly under selection, populations could evolve for an indefinite number of generations after selection has ceased; more importantly, the response can be larger or smaller than expected for direct genetic effects, and even in the opposite direction, thus allowing maternal selection to result in maladaptive evolution. Many maternal effects in insects may have evolved as a mechanism for adaptive phenotypic plasticity (Mousseau and Dingle, 199 1 a, 1 991 b; Janssen et al., 1988). These effects often involve developmental switches associated with predictable changes in the environment. Environmental cues associated with maternal effects include photoperiod, temperature, crowding, quality of diet, and host deprivation. Affected characters in offspring include diapause, sex ratio, body size, development time, coloration, dispersal behavior, and fecundity (Mousseau and Dingle, 199 la, 199 lb). Maternal effects on diapause have been particularly well studied (for reviews see Danks, 1987; Mousseau and Dingle, 1991a, 1991b; Saunders, 1982). In most cases, exposure of the maternal generation to short photoperiods and/or cool temperatures, cues related to approaching inclement winter weather, result in an increased incidence of diapause in offspring, whereas long photoperiods and/or hot temperatures can inhibit diapause. Support for the adaptive significance of such environmentally mediated maternal effects comes from comparative studies of intraspecific variation. Mousseau and Dingle (199 1 a) found that in 17 insect species, the strength of the maternal effect, or maternal sensitivity to environmental cues, varied among popula-