The differential mortality at various life stages of the greenhouse whitefly,Trialeurodes vaporariorum (Homoptera: Aleyrodidae), by infection with the fungus Aschersonia aleyrodis (Deuteromycotina: Coelomycetes)

The parasitoid Encarsia formosa is commonly applied to control the greenhouse whitefly Trialeurodes vaporariorum in glasshouse tomatoes and cucumbers. Nevertheless, in some cases the control capacity of this natural enemy is insufficient and an additional selective pest-suppressing agent is desirable. The entomopathogenic fungus Aschersonia aleyrodis was applied to cucumber plants carrying whiteflies in different developmental stages. After spraying each leaf with 2 ml of spore suspension (4 × 10⁶ spores/ml) the plants were kept at 100% RH for 24 hr; thereafter the humidity was lowered to 70% RH at 20°C and the photoperiod was 16 hr. Treated eggs did not become infected, but larvae that hatched from these eggs and settled on the treated abaxial leaf surface were infected at the same rate and to the same degree as treated first instar larvae. This suggests that the spores persist for at least 7 days. The final percentages of infection over all instars when treated as young eggs, old eggs, and first larval instars were 94, 93, and 90%, respectively. The final percentages of infection when treated as third and fourth larval instars and prepupae were 76, 28, and 12%, respectively. The older instars were less susceptible and adults were seldom infected by the fungus. Several applications of A. aleyrodis as a microbial insecticide are needed to achieve sufficient control of whitefly populations in glasshouses.     

Effects of host instar and size on parasitization efficiency and life history parameters ofOpius dissitus

The braconid parasitoidOpius dissitus Muesebeck (Hymenoptera, Braconidae) produced 1.7 to 3 times more offspring when provided second and third instar leafminers (Liriomyza sativae Blanchard) as compared to first instars. Females arising from parasitization of different instars did not differ significantly in numbers of chorionated eggs in their ovaries at adult eclosion. Development time was prolonged by about two days when parasitoid oviposition occurred in first, as compared to third instar hosts. Parasitoid length was positively correlated with host weight (r²=0.75). Because only 7% of variation in host weight could be explained by host density, parasitoid length varied considerably among hosts reared at the same density. Longevity and lifetime fecundity of parasitoids were inversely related to the weight of their hosts.     

Performance of Microplitis tuberculifer (Hymenoptera: Braconidae) parasitizing Mythimna separata (Lepidoptera: Noctuidae) in different larval instars

The solitary parasitoid Microplitis tuberculifer (Wesmael) is an important biological control agent of various lepidopteran pests in Asia. We examined the preference of M. tuberculifer for different instars of its common host, Mythimna separata (Walker), host instar effects on parasitoid development, and the consequences of parasitism in different stages for growth and consumption of host larvae. The wasp successfully parasitized the first four larval instars of M. separata, but not the fifth, which appeared to be behaviorally resistant. First and second instars were parasitized at higher rates compared to thirds and fourths in no-choice situations, ostensibly due to longer handling times for the latter, but second instars were most preferred in a choice test that presented all stages simultaneously. Although later instar hosts yielded heavier cocoons, the fastest parasitoid development was obtained in second instars. Lower sex ratios were obtained from first instars as females appeared to lay a smaller proportion of fertilized eggs in small hosts. Both weight gain and food consumption of parasitized larvae were reduced significantly within 24 h of parasitism, regardless of the stage parasitized, and final body weights were less than 10% those of unparasitized larvae. Thus, M. tuberculifer has good potential as a biological control agent of M. separata, successfully parasitizing the first four larval instars and dramatically reducing plant consumption by the host in all cases.     

不同番茄材料对B型烟粉虱个体发育和繁殖能力的影响

以甘蓝寄主上连续繁殖多代后的B型烟粉虱为对象,对其在8种番茄材料(4个栽培番茄、3个多毛番茄和1个醋栗番茄)上的产卵量、体型大小、发育历期、存活率以及第2代成虫的产卵量和寿命等生物学参数进行观察.自然情况下(10:00-14:00)接虫,烟粉虱在多毛番茄LA2329上的平均产卵量显著低于栽培番茄9706上的产卵量(分别为11粒,164粒).羽化后,烟粉虱雌虫在多毛番茄LA1777上的寿命显著低于在栽培番茄Moneymaker上的存活寿命(分别为5d,22d);而羽化后雌虫在LA1777上的平均产卵量显著低于在栽培番茄早粉2号上的产卵量(分别为7粒/头,95粒/头).在其他参数,如体型大小、存活率、发育历期等,没有显著性的变化.结果显示,较多毛番茄而言,栽培番茄是烟粉虱的较好寄主.而且,在评价抗烟粉虱番茄材料时,平均产卵量、羽化后雌虫寿命及产卵量是3个有效的评价参数.     

Effects of the chitin synthesis inhibitor buprofezin on survival and development of immatures of Chrysoperla rufilabris (Neuroptera: Chrysopidae)

Effects of buprofezin (Applaud), a chitin synthesis inhibitor, on survival and development of eggs, three instars, and pupae of Chrysoperla rufilabris (Burmeister) were determined in the laboratory. Buprofezin at three tested concentrations (100, 500, and 1,000 mg [AI]/liter) did not affect the viability and development of eggs when the eggs were treated, or third instars and pupae when those stages were treated. Although the degree of effects by buprofezin on larvae varied with instar, buprofezin at the higher concentrations (500 and 1,000 mg [AI]/liter) reduced survival rates 17-47% and prolonged the overall development from first instars to adult emergence by 2 or 3 d when first instars were treated, indicating that the first instar is the most vulnerable stage. When second instars were treated, the survival of C. rufilabris from second instars to pupae was not significantly affected. However, the developmental time from second instar to adult emergence was longer in the treatments with the highest concentration (1,000 mg [AI]/liter) than that with the lowest concentration (100 mg [AI]/liter). The compatibility of buprofezin with natural enemies in integrated pest management programs is discussed.     

Does superparasitism improve host suitability for parasitoid development? A case study in the Microplitis rufiventris-Spodoptera littoralis system

Superparasitism refers to the oviposition behavior of parasitoid females who lay their eggs in an already parasitized host. Recent studies have shown that allocation of additional eggs to an already parasitized host may be beneficial under certain conditions. In the present work, mortality of Microplitis rufiventris wasps was significantly influenced by both host instar of Spodoptera littoralis larvae at parasitism and level of parasitism. In single parasitization, all host instars (first through sixth) were not equally suitable. Percentage of emergence success of wasp larvae was very high in parasitized first through third (highly suitable hosts), fell to 60% in the fourth instar (moderate suitable) and sharply decreased in the penultimate (5th) instars (marginally suitable). Singly parasitized sixth (last) instar hosts produced no wasp larvae (entirely unsuitable), pupated and eclosed to apparently normal adult moths. The scenario was different under superparasitism, whereas supernumerary individuals in the highly suitable hosts were almost always killed as first instars, superparasitization in unsuitable hosts (4th through 6th) had significant increase in number of emergence success of wasp larvae. Also, significantly greater number of parasitoid larvae successfully developed in unsuitable hosts containing three wasp eggs than counterparts containing two wasp eggs. Moreover, the development of surplus wasp larvae was siblicidal in earlier instars and nonsiblicidal gregarious one in the penultimate and last “sixth” instars. It is suggested that the optimal way for M. rufiventris to deal with high quality hosts (early instars) is to lay a single egg, while the optimal way to deal with low quality hosts (late instars) might be to superparasitize these hosts.     

Food consumption,utilization and ecological efficiency of Parthenium beetle,Zygogramma bicolorata pallister (Coleoptera: Chrysomelidae)

Food consumption, utilization and ecological efficiency of Zygogramma bicolorata were studied in larvae and adults up to 45 days old. The study revealed that sex had a significant influence on dry food consumption in adults but not in larvae. The other parameters of ecological efficiencies, viz. efficiency of conversion of ingested food (E.C.I.), tissue growth and dry biomass, were highest in the fourth instar and in adult females. The Consumption Index (C.I.) was higher in males than females in both larval and adult stages. Developmental and growth rates were relatively higher in the first and second instars. The fourth instar and adult females were the most efficient consumers and converters of food. Food intake by females was an important determinant of the number of eggs laid.     

Interactions between the Parasitoid Rhopus nigroclavatus (Ashmead) (Hymenoptera: Encyrtidae) and its Mealybug Hosts Tridiscus sporoboli (Cockerell) and Trionymus sp. (Homoptera: Pseudococcidae)

This research investigated age-class-specific parasitism rates of the buffalograss mealybugs Tridiscus sporoboli (Cockerell) and Trionymus sp. by Rhopus nigroclavatus (Ashmead) (Hymenoptera; Encyrtidae), size class preference of this parasitoid, and mealybug–parasitoid interactions through choice and no-choice studies. In the no-choice studies, the mean rates of parasitism by R. nigroclavatus were 45, 20, 0, and 0%, respectively, for mealybugs adult female, third and fourth instars, first and second instars, and eggs. Choice studies indicated that rate of parasitism increased with host size. The mean rates of parasitism on mealybugs in the choice studies were 100% for adult females, 24% for third and fourth instars, 0% for first and second instars, and 0% for eggs. A second set of choice studies investigating mealybug/parasitoid behavior revealed that R. nigroclavatus oviposits in all post-egg mealybug age classes, but first and second instars were less often parasitized than older mealybugs.     

Phenology, population trend and natural enemies ofAleurothrixus floccosus (Hom.: Aleyrodidae) at a newly invaded area in Athens, Greece

Aleurothrixus floccosus (Homoptera: Aleyrodidae) first invaded eastern urban areas of Athens, Greece, in May 1991. At Zographou, Athens, in 1992–1994, most overwinteringA. floccosus nymphs were of the 3rd and 4th instars, and pupae; during other periods of the year, all developmental instars were found, at fluctuating rates. In 1993, peaks in the numbers of eggs laid coinciding with sharp increases in percentage of 1st instar nymphs found permitted the distinction of 6 overlapping generations. High densities ofA. floccosus infesting citrus in autumn 1992, in the range of 9.1–10.9 nymphs/cm² leaf surface, were brought under control by autumn 1993, with maximum densities of 1.1–1.7 nymphs/cm². This reduction is attributed mostly to the action of the introduced parasitoidCales noacki (Hymenoptera: Aphelinidae), released 3 km from Zographou in 1992 and at Zographou itself in 1993. No indigenous parasitoid was ever found parasitizingA. floccosus. The first record ofClitostethus arcuatus (Coleoptera: Coccinellidae) in Greece is reported. In summer 1992, eggs larvae and adults ofC. arcuatus were noticed on citrus leaves infested withA. floccosus at Zographou. From 1992 to 1994, the adults were often detected in field samplings and on yellow sticky traps. C. arcuatus adults and larvae were successfully reared, under optimal laboratory conditions, on eggs and early-instar nymphs ofA. floccosus and on eggs ofAnagasta kuehniella (Lepidoptera: Pyralidae), but the adults did not reproduce.     

Life Cycle of the Mulberry Longicorn Beetle,Apriona germari Hope on an Artificial Diet

Mulberry longicorn beetle, Apriona germari, was reared on an artificial diet to investigate its life cycle. Average egg period was 17.95 days. Most larvae pupated at the 8th (33.3%) or 9th (33.3%) instars, but others emerged from the 7th to the 11th instars. The total duration of larval stage from the 1st to the end of the 9th and the 11th instars were 176.2 and 251.5 days, respectively. For terminatiopn of diapause and acceleration of pupation, low temperature treatment at 5°C for 60 days was highly effective. Average pupal period for female and male was 19.3 and 18.4 days, respectively. Average longevity of adults was similar with 40.5 days for female and 44.3 days for male. Mating had occurred from about 10 days after the adult emergence, and then a female adult laid one or two eggs per day. Average number of eggs oviposited by a female was approximately 47.7. Total life span of A. germari, when reared on an artificial diet in the laboratory, ranged broadly from 197.5 days to 331.5 days mainly depending on the larval period.     

Reciprocal influences and costs of parasitism on the development of Corcyra cephalonica and its endoparasitoid Venturia canescens

Many endoparasitoids develop successfully within a range of host instars. Parasitoid survival is highest when parasitism is initiated in earlier host instars, due to age-related changes in internal (physiological) host defences. Most studies examining fitness-related costs associated with differences in host instar have concentrated on the parasitoid, ignoring the effects of parasitism on the development of surviving hosts that have encapsulated parasitoid eggs. A laboratory experiment was undertaken examining fitness-related costs associated with encapsulation of Venturia canescens (Hymenoptera: Ichneumonidae) eggs by fifth (L5) instar larvae of Corcyra cephalonica (Lepidoptera: Pyralidae). Growth and development of both host and parasitoid were monitored in C. cephalonica larvae containing 0, 1, 2, or 4 parasitoid eggs. Adult size and fecundity of C. cephalonica did not vary with the number of eggs per host. However, there was a distinct increase in host mortality with egg number, although most parasitoids emerged from hosts containing a single egg. The most dramatic effect on the host was a highly significant increase in development time from parasitism to adult eclosion, with hosts containing 4 parasitoid eggs taking over 2.5 days longer to complete development than unparasitized larvae. The egg-to-adult development time and size of adult V. canescens did not vary with egg number per host, as demonstrated in a previous experiment using a different host (Plodia interpunctella). The results described here show that there are fitness-related costs to the host associated with resistance to parasitism.     

Effects of lufenuron on Lobesia botrana (Lepidoptera: Tortricidae) egg, larval, and adult stages

The effect of the chitin synthesis inhibitor lufenuron was evaluated against different developmental stages of Lobesia botrana Den. & Schiff. (Lepidoptera: Tortricidae). Lufenuron fed to adults at 10 ppm reduced their fecundity and fertility, but it did not affect adult longevity. High activity was observed against L. botrana eggs with greater effect on 1-d-old eggs than on the other age classes and on eggs treated by direct contact rather than those laid on a previously treated surface. Eggs laid by treated adults showed the same effects during development as eggs treated by contact or those laid on a treated surface. Larvae that emerged from treated eggs could not perforate grape berries. Administered into the diet, lufenuron had a larvicidal effect, resulting in similar LC50 values for different instars: 0.07 ppm for first instars, 0.08 ppm for third instars, and 0.11 ppm for fifth instars. None of the larvae treated with sublethal concentrations throughout their life emerged as adults at the highest concentration (0.08 ppm), and only 70% emerged at the lowest concentration (0.0025 ppm).     

Inducibility of life history changes by fish kairomone in various developmental stages of Daphnia

Life history changes in Daphnia galeata as a response to part-timeexposure to fish-exuded chemical (FEC) were studied in laboratoryexperiments. Exposure to FEC during one of the juvenile instarsdid not induce significant changes in life history parametersin D.galeata primiparae. Exposure in the first two instars injuvenile development induced earlier maturation, smaller primiparaeand the production of smaller eggs. Exposure in the third andfourth juvenile instars resulted in smaller primiparae withsmaller eggs. The adult daphnids, when exposed to FEC, reducedsomatic growth and produced more and smaller offspring. Resultsof other experiments presented here indicate that the perceptionof fish chemical signal by daphnids is not mediated by the ingestionof a chemically modified diet.     

Life history parameters of the microtype parasitoid fly Pales pavida (Diptera: Tachinidae), and effects of host age and number of eggs ingested by host on parasitism success

With the aim of developing better procedures for rearing the microtype tachinid fly Pales pavida (Meigen), we performed ecological studies in the laboratory using the natural host Mythimna separata (Walker), investigating larval development, mating behaviour, individual oviposition patterns and relationships between parasitisation and number of eggs ingested (NEI) per host. The host instar at the time of parasitoid egg ingestion significantly affected the development time of the immature parasitoid: development took longer when the hosts ingested eggs when at the fifth instar than at the sixth (last) instar. There was no difficulty obtaining mated females in the laboratory when day 0–1 female flies were kept with day 2–4 males. Mean lifetime fecundity was 5805?±?568 eggs per female. Daily rates of oviposition by individual females varied widely; the greatest number of eggs laid in a day was exactly 1700. When the NEI by day 1 fifth instars or day 0 or 3 last instars was 1, 3, 6 or 10, the parasitisation percentage tended to increase with increasing NEI, although it did not differ significantly between NEI 6 and 10. Therefore, the percentage adult emergence per egg ingested decreased from NEI 6 to 10, particularly in the case of last instars. Using day 0 last instars, with six eggs ingested per host, should increase parasitisation rates and shorten the development time of the parasitoid for rearing.     

Trade-offs between developmental parameters of two endoparasitoids developing in different instars of the same host species

Trade-offs amongst life history traits is a major theme in evolutionary biology. Parasitoid wasps are important biological control agents and make excellent organisms to examine trade-offs in fitness related traits such as size, development rate and survival. Here, we examined trait-related trade-offs in 2 solitary endoparasitoids developing in different stages (or instars) of the same caterpillar host, the cabbage moth Mamestra brassicae. Microplitis mediator is a small specialist parasitoid that attacks first (L1) to third (L3) instars of M. brassicae; Meteorus pulchricornis is a larger highly generalized parasitoid that attacks L1–L4 instars of the same host species. When developing in early host instars (e.g. L1–L2), both parasitoids differently traded-off size against development time. In M. mediator, adult body mass was smaller in wasps developing in L1 than in L2 and L3 hosts, whereas development time was unaffected by instar. By contrast, adult body mass in M. pulchricornis was smaller and development time longer when developing in L1 and L2 than in L3 and L4 instars. Periodic starvation of M. brassicae caterpillars parasitized by M. pulchricornis further reduced adult mass and extended development time of wasps in L2 (but not L4) hosts. Maximum egg load in M. pulchricornis (but not M. mediator) was correlated with adult female body size. Our results imply that rapid development time is more important than body size for fitness in both species, although in M. pulchricornis both development time and adult size are traded off in determining the optimal phenotype. Developing a better understanding of association-specific patterns of development in parasitoids can assist in the optimization of mass rearing of these insects for biological control.     

Macrolophus caliginosus: Functional response to whiteflies and preference and switching capacity between whiteflies and spider mites

Laboratory experiments were performed with adult female Macrolophus caliginosus Wagner (Heteroptera: Miridae) at 22ºC on bean plants to determine the functional response towards whiteflies, as well as the preference and switching capacity between the two prey species: whiteflies and spider mites. Predation of females presented with first instars of Trialeurodes vaporariorum Westwood (Homoptera: Aleyrodidae) was of a Type III functional response. The observed maximum predation was approximately 75 first instars at high prey densities within a 24-h period. The preference of M. caliginosus females between eggs of T. vaporariorum and Tetranychus urticaeKoch (Acarina: Tetranychidae) changed with the ratio of offered prey. The preference for T. vaporariorum eggs increased non-linearly with increasing proportions of this prey type. The average maximum predation of whitefly and spider mite eggs were approximately 166 and 111 eggs per day, respectively, at the highest ratio of the two preys. The proportion of M. caliginosus females found on the test plants at the end of the experiment increased with prey density suggesting that this mirid spends more time in areas with high prey density. Macrolophus caliginosus females are voracious predators of eggs and first instars of T. vaporariorum as well as of spider mite eggs and may thus be a valuable addition to existing methods of biological control of T. vaporariorum and T. urticae.     

Life cycle of a new species of Amblyospora (Microspora: Amblyosporidae) in the mosquito Aedes taeniorhynchus

A new species of Microspora, Amblyospora polykarya, is described from the mosquito Aedes taeniorhynchus. The parasite is transovarially transmitted for one generation only. Spores in adult females extrude binucleate sporoplasms which infect developing eggs. Merogony occurs in larval oenocytes with diplokaryotic stages in early instars giving rise to plasmodia with many diplokarya. Plasmodia undergo cytokinesis to form diplokaryotic sporonts. In fat body cells, these sporonts secrete pansporoblastic membranes and undergo two nuclear divisions to form octonucleate sporonts. Cytokinesis and differentiation result in uninucleate spores in packets of eight. These spores are not transmissible per os and are of different morphotype from those in adult females. Infected larvae die in the fourth stadium.     

Eat or be eaten: prevalence and impact of egg cannibalism on two-spot ladybirds, Adalia bipunctata

Ladybirds commonly engage in cannibalistic behaviour. Egg cannibalism by first instars is considered advantageous to the cannibal, because it not only results in direct metabolic gain but also a reduction in potential competitors. In this study, we quantified the effect of cannibalism on the development rate and survival of Adalia bipunctata (L.) (Coleoptera: Coccinellidae) larvae through development to the adult stage. We also assessed the synchrony of egg‐hatching in relation to laying order and compared the proportion of eggs cannibalized in egg batches laid as clusters or linearly. Larvae that had consumed a conspecific egg after hatching reached the adult stage 1.65 days earlier than those larvae that had not. Larval and pupal mortality was lower for cannibals compared to non‐cannibals; only 46% of non‐cannibalistic individuals reached the adult stage whereas 81% of cannibals pupated successfully. Egg cannibalism is undoubtedly advantageous to A. bipunctata larvae both in terms of faster development and increased survival. There is a positive correlation between laying and hatching order for eggs laid linearly or in a cluster. There was no significant difference in the proportion of eggs hatching in clusters or in a line (80 and 77%, respectively). The remaining eggs were either cannibalized or did not hatch. The ecological implications of these results are discussed with particular reference to trophic egg plasticity.     

The effect of gypsy moth metamorphosis on the development of nuclear polyhedrosis virus infection

The development of nuclear polyhedrosis virus (NPV) infection in gypsy moth (Lymantria dispar) was studied before, during, and after host metamorphosis, and in larvae and pupae in the subsequent generation, to determine whether NPV ingested by late instars can replicate in host tissues through metamorphosis and whether it can be vertically transmitted to progeny. Individuals that survived sublethal dosages of NPV did not differ from undosed insects in pupal weight, fecundity, larval and pupal weight of progeny, or response of progeny to NPV challenge. No evidence of NPV infection or of abnormal histology was found in adult tissues examined by light microscopy and no virus was detected on the surface of eggs produced by NPV-treated moths. No NPV-caused mortality was recorded among undosed progeny of dosed or undosed parents. The progeny of dosed parents were neither more resistant nor more susceptible to LdMNPV than were progeny of undosed parents and lethal times did not differ between groups. Examination of larval, pupal, and adult tissues by DNA hybridization revealed that insects in which NPV DNA was detected died prior to adult eclosion. NPV was not detected in any hosts surviving to the adult stage. These results suggest that survivors of sublethal dosages of NPV avoid infection and are therefore incapable of vertically transmitting infectious virus to progeny.     

Life history,diagnosis, and biological aspects of Engytatus varians (Hemiptera: Miridae), a predator of Bactericera cockerelli (Hemiptera: Triozidae)

The life cycle and several life parameters of the zoophytophagous predator Engytatus varians (Distant) (Heteroptera: Miridae), including nymphal growth according to Dyar’s rule, were examined in the laboratory. The egg, nymph (five instars), and adult stages were 9.20, 17.36, and 19.02?d in length, respectively. The growth ratio for nymphs was consistent with Dyar’s rule based on the lengths of the femora of the forelegs, the tibiae and femora of the middle legs, and the antennae. Some biological characteristics of E. varians were also evaluated when the mirid was fed three different diets (B. cockerelli third instars, Sitotroga cerealella Olivier [Lepidoptera: Gelechiidae] eggs, and a mixture of both instars and eggs). The length of the nymphal stage was three days longer on a diet of only S. cerealella eggs than when the mirids were fed the third instars of B. cockerelli only or a mixture of both. The sex ratio was not affected by the type of diet. Nymphs of E. varians consumed B. cockerelli nymphs (80–85) when fed third instars only and third instars?+?S. cerealella eggs, respectively. The potential use of this predator as a biological control agent of B. cockerelli is discussed.