Influence of Seed Size on Exploitation by the Rice Weevil, Sitophilus oryzae

Oviposition decisions and their fitness consequences for the seed parasite Sitophilus oryzae (L.) (Coleoptera: Curculionidae) were investigated. Female S. oryzae lay eggs inside seeds such as wheat [Triticum aestivum (L.)]. Because larvae develop to adult within a single seed, the resources available are determined by the behavior of the female parent and characteristics of the seed in which the egg was deposited. Females were demonstrated to lay more eggs in kernels 20 mg. Females initiated the chewing of oviposition holes in shriveled kernels but were less likely to oviposit in them. Progeny size increased with increasing seed size, but the probability of an adult emerging was not affected. Females accepted large kernels more quickly than small kernels and this contributed to increased oviposition in large kernels. The increase in the number of eggs per kernel appears to result from an increase in number of visits resulting in oviposition rather than an increase in the number of eggs laid during a visit.     

The effect of cold temperature exposure and long-day photoperiod on the termination of the reproductive diapause of newly emerged female Pissodes strobi (Coleoptera: Curculionidae)

Abstract

• 1 There is confusion in the literature concerning a possible reproductive diapause in the adult white pine weevil Pissodes strobi.
• 2 We evaluated the effects of temperature, photoperiod, feeding substrate and mating status on the sexual maturation and oviposition of female white pine weevils.
• 3 Less than 30% of female P. strobi became sexually mature and laid eggs without experiencing dormancy under a temperature regime of 2 °C for 4 weeks.
• 4 Among the females that experienced a cold temperature treatment after emergence, 80% laid eggs after dormancy when exposed to a long‐day (LD 16 : 8 h) photoperiod and 17.6% laid eggs when exposed to a short‐day (LD 8 : 16 h) photoperiod.
• 5 Significantly more eggs were laid by all the females (with and without a cold treatment) when subjected to a long‐day photoperiod compared with a short‐day photoperiod.
• 6 A period of cold temperature followed by exposure to a long‐day photoperiod with warmer temperatures is required to break reproductive diapause and to obtain a good oviposition response in female P. strobi.
• 7 This study reveals the existence of much intraspecific variation in the response of the white pine weevil to temperature and photoperiod with respect to the induction and termination of reproductive diapause.

     

Modus operandi of oviposition in Dermacentor reticulatus (Acari: Ixodidae)

The process of oviposition in D. reticulatus was observed and found to be a sequence of exactly coordinated, interlocking events independent of the phase of oviposition. The average period of oviposition in the investigated ticks was 31.6 days at 20 °C and 95% relative humidity. The number of eggs deposited on each day increased until reaching a maximum on the fifth day of oviposition and then decreased continuously. As a result, most of the eggs were deposited during the initial phase of oviposition. The total number of eggs was proportional to the ticks' weight replenishment. Egg-laying commenced with the lowering of the capitulum and the simultaneous spread of the pedipalps which were lowered to the body wall embracing the genital aperture on both sides. Immediately afterwards the cuticular sac of Gene's organ was pushed out and retracted several times. At the cuticular sac's maximum extension, the vestibulum vaginae prolapsed, forming the ovipositor as an extended tube which handed over an egg to the two horns of the cuticular sac after a brief, but intensive, contact with the cuticular sac. Then the vestibulum vaginae invaginated, the pedipalps closed, and the cuticular sac was retracted. Finally, the egg was transported onto the dorsal area of the tick by means of a vigorous rising of the capitulum. During the course of oviposition most of the events, especially the period of egg embracement by the cuticular sac, were prolonged, as was the total time for laying one egg. Similarly, the intervals between successive egg-laying processes increased continuously.The number of eggs deposited was not dependent on the functional ability of Gene's organ, as shown by similar numbers of deposited eggs from ticks with and without mechanical blocking of the cuticular sac. But the participation of the organ in the process of oviposition proved to be a prerequisite for the viability of the eggs. Larvae developed and hatched only from those eggs which were deposited from ticks with an undisturbed Gene's organ. In comparison, eggs without contact to the cuticular sac of Gene's organ dried up and shrivelled immediately after being deposited and did not hatch. Consequently, it strongly suggests, together with the results from other studies, that Gene's organ covers the eggs with a secretion that prevents the loss of water.     

Host plant selection and development in Spodoptera exigua: do mother and offspring know best?

We examined the ovipositional preference and larval development of Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) on two common hosts in southern California, Chenopodium murale L. (Chenopodiaceae) and Apium graveolens L. (Umbelliferae) to determine if female oviposition preference is correlated with offspring performance. Greenhouse oviposition choice tests indicated that S. exigua oviposit more frequently on C. murale than on A. graveolens. However under laboratory conditions, larvae reared on C. murale had longer development times, lower relative growth rate, and lower survivorship than larvae reared on A. graveolens. larval and pupal masses were significantly greater on A. graveolens than on C. murale. Furthermore, pupal masses were significantly greater for individuals reared on A. graveolens than on C. murale. Because pupal masses and adult fecundity are positively correlated for Spodoptera spp., the fitness of S. exigua on A. graveolens is likely to be substantially higher than its fitness on C. murale. Despite better larval performance on A. graveolens, previous results from choice tests with whole plants and leaf discs indicate that the highly mobile S. exigua larvae strongly prefer C. murale over A. graveolens. Hypotheses attempting to explain this lack of correlation between larval and adult host preference versus development and survival in this system are discussed.     

Host selection behaviour of deathwatch beetle, Xestobium rufovillosum: Oviposition preference choice assays testing old vs new oak timber, Quercus sp.

In a choice bio-assay adult female deathwatch beetles were offered two dendrochronologically dated wood blocks from oak timber to study oviposition preference behaviour. There was a clear preference for ovipositing on old wood dating from the 13th to 19th centuries rather than new wood from the 20th century. Control, same-century choice, experiments showed that beetles will oviposit on young wood and that the age of the wood does not alter the overall oviposition potential. Oviposition frequency varied with insect age. Fecundity of insects collected from an infested building was similar to that of insects maintained in culture.     

Ovipositional enhancement through socially facilitated behavior in Rhagoletis pomonella flies

Apple maggot females, Rhagoletis pomonella (Walsh), were maintained (with males) singly or in groups of 5 in laboratory cages without fruit from eclosion until 15 days of age (when males were removed). When hawthorn, apple or artificial fruit were introduced on Day 16, females caged in groups laid significantly more eggs per female, irrespective of fruit type, than females caged singly. A follow-up laboratory experiment revealed that the oviposition-enhancing effect of grouping was due largely or exclusively to caging regime on day of access to fruit and not to prior caging regime. Subsequent laboratory-cage tests indicated that none of the following factors contributed significantly to the oviposition-enhancing effect of grouping under laboratory cage conditions: odor of fruit punctures, odor of eggs, odor of marking pheromone, or presence of other females on fruit, all as potential stimuli eliciting female attraction to fruit; or presence of fruit punctures, eggs, or marking pheromone, all as potential oviposition-enhancing stimuli following alighting on a fruit. The only contributing factor of significance uncovered here was the enhanced propensity of an arriving female to bore into a fruit shortly after encounter with an occupying female engaged in ovipositional behavior. We consider such enhancement as suggestive of socially facilitated egglaying behavior, which we discuss.     

温室白粉虱取食行为的刺探电位(EPG)研究

该文揭示了温室白粉虱Trialeurodes vaporariorum Westwood成虫及幼虫的刺探电位波形与其刺探、取食、产卵行为之间的对应关系,并讨论了这项技术在研究植物抗虫机理方面的应用价值。在成虫,A波、C波分别代表刺探的开始和进行过程;F波代表刺探过程中遇到机械障碍;G波表示吸食木质部导管汁液;E(pd)的(1)和(2)分别表示与取食韧皮部筛管汁液有关的两种行为;粉虱的产卵波形分为两种亚波,分别由Ovi-I和Ovi-II表示,各自代表产卵时的两种行为：产卵器接触并划破叶表皮及卵柄插入叶组织。在幼虫,H波代表吸食筛管液,而L波则表示在筛管细胞内的一种非吸食行为。幼虫蜕皮时先拔出口针,新龄期的幼虫将其口针重新刺入叶组织。     

Differential Postalightment Oviposition Behavior of Monarch Butterflies on Asclepias Species

The monarch butterfly, Danaus plexippus L., oviposits mainly on plants in the Asclepiadaceae, particularly within the genus Asclepias. We studied postalightment oviposition behavior of monarch females on three host species—Asclepias curassavica, A. incarnata , and A. tuberosa. After landing on the host, they used their forelegs, midlegs, and antennae to assess plant suitability. When these appendages were examined by scanning electron microscopy, contact chemoreceptor sensilla were found. In choice tests, A. incarnata was most preferred, while A. tuberosa was least preferred. However, the use of appendages varied for the different host species. Antennae were most frequently used during post-alightment behavior on A. curassavica, whereas forelegs were used more often on A. incarnata, and all three appendages were used extensively on A. tuberosa. Use of the midlegs was generally followed by use of the antennae. Tasting with either forelegs or antennae apparently may lead to egg laying on some host species. Rupture of the plant surface by midleg spines was also observed. The behavior and host preference of individual females varied significantly and may reflect differences in receptor sensitivity.     

Diamondback moth females oviposit more on plants infested by non‐parasitised than by parasitised conspecifics

Abstract 1. When offered a choice, female diamondback moths (Plutella xylostella) oviposited more eggs on plants with non‐parasitised conspecific larvae than on plants with parasitised larvae. 2. The leaf area consumed by parasitised larvae was significantly lower than that by non‐parasitised larvae. However, this quantitative difference in larval damage did not explain the female’s ability to discriminate between plants with parasitised and non‐parasitised larvae, as females showed an equal oviposition preference for plants infested by higher or lower densities of non‐parasitised larvae. 3. Pupal weight and duration of the larval stage of P. xylostella were independent of whether larvae were reared on plants that were previously infested by either non‐parasitised or parasitised larvae. 4. The larval parasitoid Cotesia vestalis did not distinguish between plants infested by non‐parasitised larvae and plants infested by larvae that had already been parasitised by conspecific wasps. 5. Based on these data, it can be concluded that the moth oviposition preference for plants infested by non‐parasitised conspecifics relative to plants infested by parasitised conspecifics was not explained by plant quality or by the attractiveness of plants towards wasps. It is hypothesised that one of the reasons for this preference is avoidance of plants where a relatively high risk of parasitism is expected due to the emergence of parasitoids from the parasitised host larvae.     

Differential responses to artificial selection on oviposition site preferences in Drosophila melanogaster and D. simulans

The preference–performance relationship in plant–insect interactions is a central theme in evolutionary ecology. Among many insects, eggs are vulnerable and larvae have limited mobility, making the choice of an appropriate oviposition site one of the most important decisions for a female. We investigated the evolution of oviposition preferences in Drosophila melanogaster Meigen and Drosophila simulans Sturtevant by artificially selecting for the preference for 2 natural resources, grape and quince. The main finding of our study is the differential responses of D. melanogaster and D. simulans. Although preferences evolved in the experimental populations of D. melanogaster, responses were not consistent with the selection regimes applied. In contrast, responses in D. simulans were consistent with expectations, demonstrating that this species has selectable genetic variation for the trait. Furthermore, crosses between D. simulans divergent lines showed that the genetic factors involved in grape preference appear to be largely recessive. In summary, our artificial selection study suggests that D. melanogaster and D. simulans possess different genetic architectures for this trait.