Functional response,host stage preference and interference of two whitefly parasitoids

The functional responses of two parasitoids, Eretmocerus hayati Zolnerowich & Rose and Encarsia sophia Girault & Dodd, of whitefly Bemisia tabaci Gennadius Middle East‐Asia Minor 1 were studied under laboratory conditions. In addition, the influence of host density and host stage on the competitive interactions between the two parasitoids, and biological control effect on whitefly were evaluated. In the functional response study, adult parasitoids were tested individually, with a conspecific or heterospecific competitor. Both Er. hayati and En. sophia exhibited a type II response to increasing host density, whether a conspecific or heterospecific competitor was present or not. Difference of searching rates and handling times between treatments suggested interference interactions existed between two parasitoid species. In the host stage preference study, two parasitoid species were jointly tested. Er. hayati had a competitive advantage over En. sophia when provided young host instars (first and second instar), whereas no advantage was found on old host instars (third and fourth instar). The biological control effect of Er. hayati and En. sophia in different introductions varied with host density. However, the effect of host instar on host mortality was not significant. These findings provide information for the practice of biological control and give better insight into how parasitoid species may coexist in diverse environments.     

Comparative life history and parasitism of a new colour morph of the walnut aphid in California

1 The walnut aphid Chromaphis juglandicola is a yellow aphid. In 2003, however, a white colour morph was discovered in the Sacramento Valley of California. The colour dimorphism occurs between clone lines and, when white morphs are present, they occur in mixed colour morph colonies on the underside of walnut leaves. 2 Laboratory experiments were undertaken to evaluate the thermal requirements for development, adult longevity and progeny production of the two colour morphs. Host instar preference of Trioxys pallidus, a parasitoid responsible for the successful biological control of the walnut aphid in California, was examined separately for each colour morph, and host colour preference was investigated for the preferred instar. 3 No differences in thermal requirements for development, adult size or mean longevity were detected between yellow and white colour morphs. A small difference in early reproduction was detected: white colour morphs produced more progeny on each of the two first days of adult reproduction than yellow colour morphs. 4 Trioxys pallidus showed a slight preference for the fourth instar of the yellow morph over the second‐ and third‐, but equal preference for second, third and fourth instars of the white morph. When offered equal numbers of fourth instars of the two colour morphs, T. pallidus did not show any colour preference. 5 The differences in early aphid reproduction and host instar preference by T. pallidus were combined in a stage‐structured matrix model. Model analysis showed a greater potential for population growth of the white morph over the yellow morph, with early reproduction having a greater influence than host instar preference.     

Host stage preference, functional response and mutual interference of Aphidius matricariae (Hym.: Braconidae: Aphidiinae) on Aphis fabae (Hom.: Aphididae)

Host stage preference, functional response and mutual interference of Aphidius matricariae (Haliday) (Hym.: Braconidae: Aphidiinae), parasitoid of the black bean aphid, Aphis fabae Scopoli (Hom.: Aphididae) were investigated in a growth chamber at a temperature of 25°C, 65% relative humidity and a photoperiod of 16 h light : 8 h dark on the PP8 variety of sugar beet. Nicholson's model and linear regression were used to determine per capita searching efficiency and interference coefficient, respectively. The highest parasitism percentage was observed on the third instar nymphs of A. fabae in both choice and no‐choice preference tests. There was significant difference between rates of parasitism on different stages of A. fabae (P < 0.01). Using logistic regression, a type II functional response was determined for A. matricariae. The Holling and Rogers models were used for estimating searching efficiency (a) and handling time (T_h). The data was fitted by the Rogers equation better than by the Holling disc equation based on the R² values. The estimated values of searching efficiency and handling time were 0.040 ± 0.013/h and 3.439 ± 0.383 h, respectively. The per capita searching efficiency decreased significantly from 0.272 to 0.139 as parasitoid densities increased from one to five. Therefore, different host‐parasitoid ratios could affect the efficacy of A. matricariae.     

Biology and performance of two indigenous larval parasitoids on Tuta absoluta (Lepidoptera: Gelechiidae) in Sudan

Tuta absoluta is an alien invasive pest in Sudan. Since it was detected in the country, the pest continues to cause major tomato losses. Alarmed by its devastating nature and the speed of spread, tomato growers resorted to the indiscriminate use of broad-spectrum insecticides. Promising indigenous parasitoid(s) may contribute to suppression of this pest. The biology and performance of the native parasitoids, Bracon nigricans Szépligeti (Braconidae) and Dolichogenidea appellator (Telenga) (Braconidae), was therefore evaluated against different immature stages of T. absoluta under laboratory conditions. A significantly higher number of fourth instar larvae was accepted for oviposition by B. nigricans. Similarly, fourth instar larvae yielded a considerably higher number of parasitoid offspring compared to third instar larvae. The male ratio of B. nigricans offspring which emerged from both larval instars was high, 0.96 and 0.66 for third and fourth instar larvae of T. absoluta, respectively. There was, however, no significant difference in the number of males and females that emerged from fourth instar larvae. Conversely, the number of hosts killed by stinging behaviour or host feeding was significantly higher on third instar larvae. B. nigricans potential fecundity varied with the age of the wasp with the lowest fecundity on the day of eclosion. The performance of D. appellator in terms of the total number of offspring produced and female progeny was similar for second and third instar larvae of T. absoluta. The preimaginal developmental time for both parasitoid species did not vary with either host stage or sex of the parasitoid. B. nigricans adult longevity was similar for both sexes, while that of D. appellator significantly varied with females living longer than males. Prospects for conservative biological control of T. absoluta are discussed in the light of the results of this study.     

Oviposition behaviour, influence of experience on host size selection, and niche overlap of the solitary Leptomastix epona and the gregarious Pseudaphycus flavidulus, two endoparasitoids of the mealybug Pseudococcus viburni

Oviposition behaviour and host size selection of the solitary parasitoid Leptomastix epona(Walker) and the gregarious Pseudaphycus flavidulus(Brèthes) [both Hymenoptera: Encyrtidae] were examined on five size classes of the mealybug Pseudococcus viburni(Signoret) [Hemiptera: Pseudococcidae]. The host size classes mostly consisted of one stage (first, second, third instar nymph, young adult and preovipositing adult) and were presented together to wasps of either parasitoid species. Both parasitoid species locate the host by drumming the surface of the patch with the antennae. Leptomastix eponaseems to use mainly the antennae to examine the host but P. flavidulusmay accept or reject a host for oviposition after antennation or insertion of the ovipositor. Leptomastix eponaattempts oviposition in all the host stages from second instar nymphs but P. flavidulusincludes first instar. Both parasitoid species select mainly larger hosts (>1 mm, third instar nymphs) to oviposit but P. flavidulusis able to parasitize more second instar nymphs compared to L. epona. Female wasps of L. eponamay host feed on small mealybugs (second and third instar nymphs) that they do not use for oviposition. Oviposition experience of either parasitoid species for 24 hours does not influence host size selection on patches with hosts of similar mixed sizes. Oviposition decisions are independent of the host sizes of the preceding ovipositions. Implications about stability of a single parasitoid – host system and the success of biological control of the mealybug were discussed in respect of the developmental refugia of the two parasitoid species. Niche overlap of the two parasitoid species was discussed with a view to giving an insight into a single or multiple introduction.     

Host stage selection of the mealybug parasitoid Anagyrus spec. nov near sinope

The mealybug parasitoid Anagyrus spec. nov near sinope (Hymenoptera: Encyrtidae) is an undescribed parasitoid of the Madeira mealybug, Phenacoccus madeirensis Green (Homoptera: Pseudococcidae). We investigated the preference of Anagyrus spec. nov near sinope for six developmental stadia (first‐ and second‐instar nymphs, third‐instar immature females, third‐ or fourth‐instar immature males, pre‐reproductive adult females, and ovipositing adult females) of P. madeirensis and the fitness consequences of the host stage selection behavior. In the no‐choice test, Anagyrus spec. nov near sinope parasitized and completed development in all host stadia except third‐instar immature males. When all host stadia were offered simultaneously, the parasitoids preferred third‐instar immature and pre‐reproductive adult females. Dissection of the stung mealybugs revealed that the clutch size (number of eggs per host) was approximately four and three in the third‐instar and pre‐reproductive females, respectively, and one egg per first‐instar nymph. Parasitoids emerged from P. madeirensis parasitized at third‐instar or pre‐reproductive adult female completed development in the shortest duration, achieved a higher progeny survival rate, larger brood and body size, and the lowest proportion of males. We showed that the continued development of mealybugs had significant influence on the fitness of the parasitoids. Although deposited as eggs in first‐ or second‐instar nymphs, parasitoids emerged from mummies that had attained third‐instar or adult development achieved similar progeny survival rate, brood size, body size, and sex ratio as those parasitoids deposited and developed in third‐instar or adult mealybugs. By delaying larval development in young mealybugs, Anagyrus spec. nov near sinope achieved higher fitness by allowing the parasitized mealybugs to grow and accumulate body size and resources. We suggest that the fitness consequence of host stage selection of a koinobiont parasitoid should be evaluated on both the time of parasitism and the time of mummification.     

Dose-dependent influence of Microplitis rufiventris factors on developmental rate and growth of last-instar Spodoptera littoralis larvae

The solitary endoparasitoid, Microplitis rufiventris, attacks and can develop in earlier instars of Spodoptera littoralis larvae with preference to third‐instar larvae. We used the last stadium (sixth instar), a stage which is not naturally parasitized. The newly moulted larvae (0–3 h old) of this stadium were more acceptable for parasitization by the wasp females than the older ones (24 h old). Parasitization by M. rufiventris wasp of last instar S. littoralis larvae leads to dose (no. of eggs + parasitoid factors)‐dependent effects which were more pronounced at 20°C than at 27°C. A single oviposition into a sixth instar host larva resulted in normal development of the host. However, superparasitization increased the proportions of developmentally arrested hosts and number of live wasp larvae. Development of supernumerary individuals of the parasitoid in the host larva leads to dose‐related adverse effects on host growth and development. The present study may provide interesting opportunities for studying the physiological bases of host–parasitoid interactions and parasitoid intra‐specific competition in the biological system considered.     

Gregarious development of the solitary endo-parasitoid, Microplitis rufiventris in its habitual host, Spodoptera littoralis

Abstract:  Earlier research has shown that the koinobiont parasitoid, Microplitis rufiventris , attacks and can develop on early instars of Spodoptera littoralis larvae with preference to third instars. However, the present study was carried out using the newly moulted sixth instar larvae at two different temperatures (20 ± 1 and 27 ± 1°C) to study the developmental interaction between the parasitoid and the last instar host larvae. Parasitoid eggs laid in singly parasitized host larvae invariably died. As the number of parasitoid eggs/host larvae increased, the proportion of eggs that hatched and number of viable parasitoid larvae successfully reached to their final instar increased. The effect of superparasitization seems to be dose (no. of eggs + parasitoid factors)-temperature-dependent. The results demonstrate a kind of 'Allee effect' suggesting that superparasitized last instar S. littoralis larvae provide a better host environment than singly parasitized hosts for the parasitoid, M. rufiventris . This may be due to host's hormone and/or low dose of factors injected with parasitoid eggs. The supernumerary individuals of wasp larvae developed normally to the point of emergence but most did not successfully emerge from the host. The improvement of both hatchability and post-embryonic development of parasitoid wasp was significantly (P < 0.01) greater at 20°C than at 27°C. The results of the present study are useful in understanding the evolution of life-history strategies and host range in parasitic hymenoptera.     

Suitability of Bemisia tabaci (Hemiptera: Aleyrodidae) instars for the parasitization by Encarsia bimaculata and Eretmocerus sp. nr. furuhashii (Hymenoptera: Aphelinidae) on glabrous and hirsute host plants

The host instar preferences of Encarsia bimaculata and Eretmocerus sp. nr. furuhashii parasitizing Bemisia tabaci and their development on four host plants, collard, eggplant, cucumber and tomato, were studied in the laboratory. Both of the parasitoids accepted all nymphal stages of B. tabaci, but E. bimaculata preferred third and fourth instars while Er. sp. nr. furuhashii preferred second and third instars under both choice and no choice conditions. Regardless of host stage parasitized, adults of parasitoids emerged only from fourth instars. When given the simultaneous choice of all instars, E. bimaculata reduced parasitization of first and second instars (3.73 and 4.76%, respectively) while increasing parasitization of third and fourth instars (5.44 and 6.93%, respectively), in contrast Er. sp. nr. furuhashii increased its parasitization of second and third instar nymphs (1.27 and 3.17%, respectively) and decreased that of first and fourth instars (7.0 and 3.06%, respectively). Host plants did not significantly influence instar preference for either parasitoid. Developmental periods of both the parasitoids from egg to adult emergence were longest when first instars were parasitized and shortest when fourth instars were selected. Parasitoid developmental time was generally shorter on glabrous plants than on hirsute plants.     

Host-stage preference and functional response of aphid parasitoid Diaeretiella rapae (McIntosh) (Hym.: Braconidae) on greenbug,Schizaphis graminum (Rondani) (Hem: Aphididae)

Searching capacity is of great importance in the efficiency of natural enemies. In this research, the host-stage preference and functional response of Diaeretiella rapae (McIntosh) to different densities of greenbug, Schizaphis graminum (Rondani) were determined on Pishtaz wheat leaves at 25 ± 1°C, 60–70% relative humidity, and a photoperiod of 16:8 h (L:D). The host-stage preference was investigated by exposing 60 number of all nymphal instars and adults of greenbug to individual parasitoid females at eight replicates. Results indicated significant preference of D. rapae to second instar nymphs of S. graminum to perform functional response experiment. Densities of 2, 4, 8, 16, 32, 50, 64, 90 and 130 second instar nymphs of greenbugs were exposed to individual mated female wasps at 10 replicates for 24 h. Type of functional response was determined by logistic regression and its parameters, searching efficiency (a) and handling time (T _h), were estimated by non linear regression. The results indicated that the functional response of D. rapae was type III and values of searching efficiency, handling time and maximum rate of parasitism were calculated by two models as 0.1364 ± 0.084, 0.5761 ± 0.0179, 41.6594; 0.06489 ± 0.00652 (h^?1), 0.5628 ± 0.0173 (h) and 42.6439 (aphids/parasitoid/day), respectively.     

Bemisia tabaci (Homoptera: Aleyrodidae) instar effects on rate of parasitism by Eretmocerus mundus and Encarsia pergandiella (Hymenoptera: Aphelinidae)

Studies were conducted to compare preference among Bemisia tabaci Gennadius, biotype B instars for parasitization by Eretmocerus mundus Mercet and Encarsia pergandiella Howard when provided one instar only, two different instars, and four different instars simultaneously. In the single‐instar no choice treatment, Er. mundus was more successful in parasitizing the younger host instars, while En. pergandiella parasitized a greater proportion of the older instars. Similar results were observed when parasitoids were provided a choice of two instars in six different pair combinations. When all four instars were provided simultaneously, the numbers of first, second, and third instars parasitized by Er. mundus were not significantly different from each other (range 10.3–16.4%), but all were significantly higher than parasitism of fourth instar nymphs (2.1%). The highest percentage parasitization by En. pergandiella was in third instar (17.2%), and the lowest in first instar (2.8%).     

Nutritional indices in the gypsy moth (Lymantria dispar (L.)) under field conditions and host switching situations

A large proportion of gypsy moths (Lymantria dispar (L.)) are likely to experience multiple species diets in the field due to natural wandering and host switching which occurs with these insects. Nutritional indices in fourth and fifth instar gypsy moth larvae were studied in the field for insects that were switched to a second host species when they were fourth instars. The tree species used as hosts were northern pin oak (Quercus ellipsoidalis E. J. Hill), white oak (Q. alba L.), big-tooth aspen (Populus grandidentata Michx.), and trembling aspen (P. tremuloides Michx.). Conclusions of this study include: 1) Insects which fed before the host switch on northern pin oak performed better after the host switch than did insects with other types of early dietary experience. While the northern pin oak-started insects had very low relative food consumption rates on their second host species immediately after the switch, one instar later they had the highest ranked consumption rates. During both instars they had the second highest efficiencies of converting ingested and digested food to body mass. High food consumption rates and relatively high efficiency of food conversion helped these insects to obtain the highest ranked mean relative growth rates in the fifth instar compared to the relative growth rates obtained by insects from any of the other first host species. 2) Among the four host species examined, a second host of trembling aspen was most advantageous for the insects. Feeding on this species after the switch led to higher larval weights and higher relative growth rates for insects than did any of the other second host species. The insects on trembling aspen attained excellent growth despite only mediocre to low food conversion efficiencies. The low efficiencies were offset by high relative food consumption rates. 3) Low food consumption rates often tend to be paired with high efficiency of conversion and vice versa. 4) There is no discernable tendency for the first plant species eaten to cause long-term inductions which affect the ability of gypsy moths to utilize subsequent host plants. Insects did not tend to consume more, grow faster, or be more efficient if their second host plant was either the same as their rearing plant or congeneric to it. Methods are delineated which allow values of nutritional indices to be obtained for insects on intact host plants under field conditions. These methods are useful for the purpose of answering questions about the relative effects that different diet treatments have on insect response.     

BIONOMICS OF MICROPLITIS MEDIATOR (HYM: BRACONIDAE) PARASITIZING PSEUDALETIA SEPARATA (LEP: NOCTUIDAE)*

Abstract This paper deals with the bionomics of Microplitis mediator parasitizing Pseudaletia separata. There were some stings (ca. 3. 1%) in which female wasps oviposited more than one eggs and about 4. 6% stings that there was no egg laid into a host. A negative correlation existed between the host age and percentage of parasitization. When the host suffered more stings by the parasitoid wasps, the percentage of parasitization was higher. But there was no correlation between the parasitoid sex ratio and the host age or the frequency of stings by the parasitoids. The host age is not the major factor affecting the offspring sex ratio of the parasitoid. Some putative sex determinant factors in the parasitoid are discussed and the 2nd instar of the host is recommended as a suitable host age in which parasitization could be performed for the purpose of the parasitoid mass culture.     

Feeding preferences and their modification in early and late instar larvae of the bagworm,Thyridopteryx ephemeraeformis (Lepidoptera: Psychidae)

Feeding preferences in naive first instar and penultimate-final instar bagworm (Thyridopteryx ephemeraeformis)larvae were investigated using two choice tests. Naive first instar larvae showed a general (though not exclusive) preference for black willow (Salix nigra)over other hosts tested, regardless of the host of origin. Penultimate-final instar larvae showed strong preferences for the previous rearing host, suggesting induction of host preference; there was no evidence of host origin effects. The ability to discriminate among hosts is important if it is actually used to make host choices based on host quality. In bagworms, where host choices (if any) must be made by larvae in habitats where several hosts are often present, host discriminatory ability is likely important.     

The parasitoidCotesia glomerata (Hymenoptera: Braconidae) discriminates between first and fifth larval instars of its hostPieris brassicae,on the basis of contact cues from frass,silk, and herbivore-damaged leaf tissue

Adult females of the larval parasitoidCotesia glomerata (L.) respond to chemical cues associated with feeding damage inflicted on cabbage plants by its host,Pieris brassicae (L.). The use of these infochemicals by the parasitoid during selection of the most suitable host instar was investigated. The parasitoid can successfully parasitize first-instar host larvae, while contacts with fifth-instar larvae are very risky since these caterpillars react to parasitization attempts by biting, spitting, and hitting, resulting in a high probability of the parasitoid being seriously injured or killed. Observations of the locomotor behavior of individual wasps on leaves with feeding damage inflicted by the first and the fifth larval instars and on host silk and frass showed that several cues affect the duration of searching by the parasitoids after reaching a leaf: cues on the margin of the feeding damage and cues in the host frass and silk. Whole frass, silk, and hexane extracts of frass obtained from first-instar elicited parasitoid's searching behavior significantly longer than frass, silk, and hexane extract of frass from the fifth instar. The results demonstrate thatC. glomerata can discriminate between first instars, which are more suitable hosts, and fifth instars ofP. brassicae without contacting the caterpillars, by exploiting instar-related cues.     

Effects of the parasitization of a braconid, Apanteles, on the blood of its host, Pieris

Parasitization of a braconid wasp, Apanteles glomeratus, of larvae of a common cabbage butterfly, Pieris rapae crucivora, caused changes in differential haemocyte count (DHC), total haemocyte count (THC), and encapsulative capacity against dead eggs of Apanteles in the fourth and fifth instar host larvae.However, no correlation could be found between the number of Apanteles eggs deposited and THC of the middle fourth instar host larvae or between the number of parasitoid larvae and specific gravity of the haemolymph from the late fifth instar host larvae.From the changes in DHC and in THC of both non-parasitized and parasitized Pieris larvae, an increase in the number of plasmatocytes of non-parasitized Pieris larvae in the early fourth instar period was supposed to be due to transformation of prohaemocytes into plasmatocytes, and a low population of plasmatocytes of parasitized larvae in the comparable period was assumed to be due to a suppression of transformation of prohaemocytes by some factor released from the parasitoid eggs.Failure of the parasitized fourth instar Pieris larvae to encapsulate injected dead eggs of Apanteles indicated that the parasitoid embryos were, in some way, actively inhibiting the encapsulation reactions of the host.The increase in THC of the parasitized fifth instar larvae could not be ascribed to a decrease in the volume of host haemolymph. Rather it could be interpreted by a suppression of adhesive capacity of haemocytes in the host haemocoel to tissue surfaces.Reduced encapsulative capacity of the parasitized fifth instar larvae might be attributed either to a depression of the adhesive activity of plasmatocytes resulting from a depletion of energy source for haemocytes in the host haemolymph by parasitization, or from an active suppression of adhesiveness of the plasmatocytes by secretions from ‘giant cells’ (teratocytes) originated from the parasitoid.     

Seasonal phenology and stage-specific parasitism of the apple ermine moth, Yponomeuta malinellus Zeller, in Korea

The apple ermine moth, Yponomeuta malinellus Zeller (Lepidoptera: Yponomeutidae), is a tent caterpillar that feeds on Malus spp. in Korea. Populations of the moth in native areas appeared to be regulated by the assemblage of parasitoids. Phenological associations between host stages and parasitoids, susceptible stage(s) of the host for each parasitoid, and stage‐specific parasitism were studied. The egg larval parasitoid Ageniaspis fuscicollis (Dalman) had highest parasitism of first instar larvae (24%), with 14% parasitism of other larval stages. Dolichogenidea delecta (Haliday) was recovered from all larval instars with the highest parasitism rate of second instar larvae (20.1%), followed by 19.9% parasitism of mid‐larval hosts. Herpestomus brunicornis Gravenhorst was reared from second instar larvae through to pupal collection, and had the highest parasitism rate (29.9%) at the pupal stage. The larval pupal parasitoid Zenillia dolosa (Meigen) was recovered from mid‐larval to pupal stages with the highest parasitism rate (5.5%) occurring in third to fourth instar larvae. The host stages for developing A. fuscicollis completely overlap with those of D. delecta, and with those of H. brunicornis to some degree. A statistically significant negative correlation exists between A. fuscicollis and these dominant parasitoids, indicating competitive interaction within the host.     

蚜茧蜂产卵对寄主龄期的选择与其对蚜虫种群影响大小的计算机模拟研究

利用苦苣菜蚜-苦苣菜蚜茧蜂混合种群系统模拟模型,通过改变种群参数、初始虫量和温度条件,探讨了蚜茧蜂产卵选择寄主龄期特性对整个种群系统行为的影响,并比较了这一特性与蜂产卵量两者的相对重要性。结果表明,蜂产卵对寄主龄期选择特性的改变可明显改变其对蚜虫种群增长影响的程度,当产卵选择特性改变,产卵量在多数情况下必须要大幅度直至成倍的增减,才能补偿其对蚜虫种群的控制作用。不过,当蜂产卵嗜好三龄、二龄、四龄若蚜时(这在蚜茧蜂中较普遍),其作用和产卵无选择性时基本相似。     

Growth and development of Cardiochiles nigriceps viereck (hymenoptera,braconidae) larvae and their synchronization with some changes of the hemolymph composition of their host,Heliothis virescens (F.) (Lepidoptera,Noctuidae)

Larval development of the parasitoid Cardiochiles nigriceps Viereck occurs in the last instar larva of its host, Heliothis virescens (F.). This allows the parasitoid to exploit the nutritional increase in the biosynthetic activity occurring in the host in preparation for metamorphosis. To understand the biochemical basis of this host parasitoid developmental synchrony, we undertook host ligation studies and analyzed host hemolymph for proteins and glycerol esters. Parasitization affected the biochemical profile of the host. The hemolymph protein concentration of parasitized last instar H. virescens larvae increased through time, whereas unparasitized (control) larvae were characterized by a decrease in the protein titer when they reached the prepupal stage. The effect of parasitism on glyceride titers of host hemolymph was not as pronounced as the effect on proteins. Ligation conducted on 5th instar hosts, which were parasitized as 4th instars, affected parasitoid development in a time-dependent way. The percentage of successfully developing C. nigriceps larvae increased with the increase of the time interval between parasitization and ligation. Ligation performed before day 2 of the 5th larval instar of H. virescens completely inhibited parasitoid development. Ligations that disrupted parasitoid developmentwere associated with a low host hernolymph protein concentration. Parasitoid development was successful when hernolymph protein titer was high, as occurred when ligations were performed after day 3 of the 5th host instar in both control and parasitized larvae. Ligations in both situations resulted in a slight increase in glyceride titers. The results suggest that host proteins and/or some factor(s) associated with them may play a role in parasitoid growth and development. © 1993 Wiley-Liss, Inc.     

Host stage preference and parasitism behaviour of Aenasius bambawalei an encyrtid parasitoid of Phenacoccus solenopsis

In Pakistan, the cotton mealybug, Phenacoccus solenopsis Tinsley (Sternorrhyncha (Homoptera): Pseudococcidae), is a serious pest of many cultivated plants. A parasitoid, Aenasius bambawalei Hayat (Hymenoptera: Encyrtidae), is associated with P. solenopsis. In order to mass rear A. bambawalei for a biological control programme, it is important to investigate the parasitoid’s host stage preference and its parasitism behaviour for P. solenopsis in order to optimise production. The present study showed that under both choice and no-choice conditions, the parasitoid preferred third instar and pre-reproductive host stage mealybugs for parasitism. Parasitoid larva developing inside the host exhibited a greater longevity, shorter developmental period and longer body size in these preferred host stages. Our study also confirmed that A. bambawalei showed no attraction to male mealybugs and no host feeding on any host stage was recorded. The ability of the parasitoid to effectively discriminate between suitable and non-suitable stages means that it is feasible to rear it on a mixed population.