Effects of crop type on Bacillus thuringiensis toxicity and residual activity against Trichoplusia ni in greenhouses

We assessed the efficacy and persistence of a Bacillus thuringiensiskurstaki (Btk) formulation (Dipel) against Trichoplusia ni (Hubner) (Lep., Noctuidae), the cabbage looper, on three greenhouse vegetable crops (tomato, bell pepper and cucumber). First, T. ni larvae were fed leaf discs treated with Btk to assess how Btk toxicity varies with host plant. Secondly, T. ni larvae were fed leaf discs harvested from plants that had been sprayed with Btk 1, 5 and 9 days previously to assess the residual activity of Btk toxicity in greenhouse environments. Mortality of T. ni larvae fed tomato leaf discs was significantly higher than T. ni fed cucumber or pepper leaf discs. The toxicity of Btk had declined by less than 50% after 9 days, which suggests that Btk persistence is lengthy in greenhouse environments. No crop effects on the residual activity of Btk were found. These results demonstrate that the greenhouse environment and the crop should be considered when using Btk for insect management on greenhouse crops.     

Effect of host plant species of cotton whitefly Bemisia tabaci Middle East‐Asia Minor 1 (Hemiptera: Aleyrodidae) on the development,survival and reproduction of its predaceous ladybeetle Serangium japonicum (Coleoptera: Coccinellidae)

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Factors affecting oral regurgitation by larval spruce budworm

This study evaluated factors that influence the regurgitation behaviour of sixth instar spruce budworm, Choristoneura fumiferana Clemens (Lepidoptera: Tortricidae), reared on balsam fir, Abies balsamea (L.) Mill. (Pinaceae), under various experimental conditions in the laboratory. Upon physical disturbance, larvae discharged a median volume of regurgitant of 0.4 μl when fed and 1.6 μl when food‐deprived. Larvae deprived of food for 24 or 48 h disgorged more regurgitant than larvae feeding on balsam fir foliage, and the effect was consistent for laboratory‐reared and field‐collected larvae. The water content of the foliage fed upon by larvae had no immediate impact on the volume of regurgitant; following a 24‐h period of food deprivation, however, larvae that previously fed on fresh foliage discharged >2.5 times more regurgitant than larvae that previously fed on dry foliage. Self‐regulated regurgitation by larvae, measured using the number of regurgitant stains on filter paper, was >10 times higher when larvae had access to balsam fir foliage than when they were starved. The number of larvae confined inside the Petri dish (one or four individuals) had a relatively small effect on regurgitation. Larvae were deterred from feeding when balsam fir needles were entirely covered with regurgitant, but not when only a portion of the foliage was treated. These results suggest that the regurgitant does not serve as resource marking or spacing pheromone. The high level of regurgitation by larvae after contact with ants suggests that the regurgitant has evolved in part as a defence mechanism against natural enemies.     

Efficacy of Spodoptera exigua multiple nucleopolyhedrovirus as a biological insecticide for beet armyworm control in greenhouses of southern Spain

Chemical control measures targeted at Spodoptera exigua in greenhouse sweet pepper crops in Spain have resulted in pest resistance to virtually all commercially available insecticidal products. A multicapsid nucleopolyhedrovirus (SeMNPV), isolated from diseased S. exigua in Spain, was produced in laboratory reared larvae, tested for insecticidal activity in a laboratory bioassay, and was then applied in eleven commercial greenhouses planted with sweet pepper. Virus occlusion bodies (OBs) were applied on two occasions, at an interval of ～7 days, at a rate of 5×10⁸ OBs/L of spray in a volume of ～600 L/ha, depending on crop phenology and greenhouse area. The percentage of plants showing recent (<48 h old) feeding damage fell dramatically in greenhouses with high infestations of S. exigua; the same pattern was observed, although less dramatically, in greenhouses with low infestations. Average mortality of larvae collected from treated plants at 4 days after each application, and reared in the laboratory until death, was high (70–89%) and was not significantly affected by the degree of crop infestation. In a separate trial, the rate of acquisition of infection was examined in larvae that fed on plants treated with 1×10⁸ or 5×10⁸ OBs/L of spray. Of the 27 and 60% of larvae, respectively, that acquired infection in the 48 h period after spraying, about half became infected in the first 6 h post-application, irrespective of application rate. Acquisition of infection proceeded more slowly during the night-time compared to the daytime period, underlining the advantages of early morning applications of the virus. We conclude that the Spanish SeMNPV isolate merits registration as a biological insecticide for use in greenhouse crops in this region.     

不同食料植物对棉铃虫生长发育和繁殖的影响

报道了棉花、烟草、番茄和辣椒4种植物对棉铃虫Helicoverpa armigera生长发育和繁殖的影响。棉铃虫成虫喜欢在番茄上产卵,在辣椒上的着卵量最少。初孵幼虫喜选食嫩棉叶,选食辣椒嫩叶的虫数最少。4组幼虫取食嫩叶时的平均相对生长速率都有显著差异,顺序为棉叶组>烟叶组>番茄叶组>辣椒叶组。幼虫存活率以取食棉花时最高,取食番茄时最低。棉花组成虫的产卵量最高,烟草组的产卵量最低。取食棉花的棉铃虫种群增长的速度约为取食番茄时的14倍。6龄幼虫能有效利用和转化棉铃、烟草蒴果、辣椒果实,而对番茄果实的利用和转化效率较低。棉铃虫可分别以这4种植物的不同器官为食完成世代循环。其中,棉花是最适宜的寄主,辣椒和番茄是较不适宜的寄主。     

Experimental tests of the mechanism for ant-enhanced growth in an ant-tended lycaenid butterfly

In a previous laboratory study, larvae of the ant-tended lycaenid butterfly Hemiargus isola developed into larger adults when reared with the ant Formica perpilosa than when reared without ants. Ants neither fed butterfly larvae nor significantly delayed developmental duration. We investigated two non-exclusive hypotheses for the mechanism of this effect: larvae tended by F. perpilosa (1) consume more food, and (2) digest the food they consume more efficiently, than those reared without ants. Larvae reared in the laboratory with F. perpilosa ants became significantly heavier adults but produced a significantly lighter fecal mass than their untended counterparts, suggesting that greater food consumption was not the primary mechanism for the higher growth rates of ant-tended larvae. Tended and untended larvae were equally proficient at digesting the contents of pollen (a major natural food source) throughout the tended portion of the life cycle. Taken together, the results suggest that neither greater consumption nor higher assimilation accounts for the larger size of F. perpilosa-tended larvae. We propose that tended larvae may expend less energy than their untended counterparts. Received: 3 January 1997 / Accepted: 18 June 1997     

Nitrogen fertilization rate affects feeding, larval performance, and oviposition preference of the beet armyworm, Spodoptera exigua, on cotton

Nitrogen (N) is one of the most critical chemical elements for plant and animal growth, exerting a variety of bottom‐up effects. Development and oviposition of the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), were studied in relation to varying N fertilization levels (42, 112, 196, and 280 p.p.m.) in cotton [Gossypium hirsutum L. (Malvaceae)]. Low N fertilization of cotton plants led to reduced plant biomass and a lower percentage of N in leaf blades and in leaf petioles. Development of S. exigua larvae fed with plants with reduced N applications (42 and 112 p.p.m.) was prolonged relative to treatments receiving higher N fertilization. Almost all larvae reared on artificial diets underwent only five instars before pupation. However, most larvae reared on cotton plants, irrespective of N levels, experienced a supernumerary sixth larval instar. Furthermore, significantly more larvae reared on lower N cotton plants underwent supernumerary development compared to larvae reared on higher N cotton plants. Life‐time feeding damage per larva ranged from 55 to 65 cm², depending on the nutritional quality of the food plant, although the differences were not statistically significant. Larvae distinguished between cotton plants with various nutritional qualities and fed preferentially on higher N plants. Female moth oviposition choice was also affected by host plant nutritional quality: cotton plants with higher N levels were preferentially chosen by S. exigua females for oviposition. The mechanisms of these effects are unclear, but they can have important implications for population dynamics and pest status of beet armyworms in the field.     

Effect of dietary selenium supplementation on resistance to baculovirus infection

We have examined the effects of dietary selenium (Se) supplementation on larval growth and immunocompetence of the lepidopteran pest, the cabbage looper, Trichoplusia ni. Supplementation of the diet of T. ni larvae with 10–20 ppm Se resulted in a 1 day delay in pupation. The effects of the addition and/or removal of dietary Se on total Se bioaccumulation and sequestration were determined by neutron activation analysis of pupae. Early penultimate instar larvae moved from selenium containing diet to basal diet lost total pupal Se content down to the level of those fed basal diet. Conversely, larvae moved from basal diet to diet containing additional Se rapidly attained pupal Se levels comparable to larvae fed Se throughout larval development. Therefore, dietary Se is rapidly accumulated or lost during larval development, but significant amounts are sequestered from diet into pupae. Larvae were reared on diet supplemented with 5 or 10 ppm Se until the onset of the penultimate instar then infected per os with increasing concentrations of the fatal baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV). Larvae fed Se in the penultimate and ultimate instars were more resistant to viral infection than larvae not fed Se in the final instars. This study indicates that dietary Se levels rapidly impact Se assimilation and sequestration and that tissue Se levels are an important factor in resistance to AcMNPV infection in larval T. ni.     

Divergence in larval responses to food plants between temperate and tropical populations of the black swallowtail butterfly

ABSTRACT.

• 1 Larvae of the black swallowtail butterfly, Papilio polyxenes Fabr., from New York and Costa Rica were reared under the same environmental conditions on Daucus carota L. and Spananthe paniculata Jacq. (Umbelliferae), which are the host plants most commonly used by the two populations, respectively. Feeding rates, growth rates and feeding efficiencies of the fifth instar larvae were measured by standard techniques.
• 2 Larvae from each population grew faster on the host-plant species from their region of origin than did larvae from the other population, though differences on S.paniculata were not significant. On D.carota the faster growth by New York larvae was attributable to greater efficiency. On S.paniculata, by contrast, the somewhat faster growth by Costa Rican larvae seemed to have resulted chiefly from faster feeding. The two populations have thus come to differ in metabolic and, probably, behavioural responses to host plants.
• 3 S.paniculata was a superior host plant for larvae of both populations, even though the total energy, nitrogen and water content of its foliage was similar to that of D.carota.
• 4 These results are consistent with the hypothesis that insects in the two populations have diverged in adaptation to their host plants following curtailment of gene flow between them as the species colonized Central America from the north.

     

Pine sawfly defence and variation in host plant resin acids: a trade-off with growth

Abstract.

• 1 The defence capability of pine sawfly larvae reared on Scots pines with low or high concentrations of resin acids was determined in a field experiment, where larvae were exposed to predatory ants, and in a laboratory experiment in which the rate of defence droplet replenishment was measured.
• 2 Larvae on low resin-acid shoots disappeared faster than larvae on high resin-acid shoots when exposed to predatory ants.
• 3 Larvae fed high resin-acid needles produced 50% larger defence droplets than larvae fed low resin-acid needles.
• 4 In an additional experiment high predation pressure was simulated by repeatedly removing defence droplets. Larvae responded by feeding more on tissue rich in resin acids, but at the cost of a reduction in growth rate.
• 5 Based on these data and earlier findings that survival and development of sawfly larvae are negatively affected by high resin-acid concentrations, we conclude that pine sawflies face a dilemma of conflicting demands, i.e. although high needle resin-acid concentrations enhance defence capability, they also reduce growth and survival. Our data also suggest that it is not necessarily the ovipositing female that has to balance this trade-off: plasticity in larval feeding behaviour provides larvae with a means to at least partly solve the dilemma.

     

Leaf age and larval performance of the leaf beetle Paropsis atomaria

ABSTRACT.

• 1 Larval performance of the leaf beetle Paropsis atomaria Oliver was determined for larvae raised on both new and mature leaves of Eucalyptus blakelyi Maiden. Larvae were transferred to mature leaves at different ages; control larvae stayed on new leaves through all instars.
• 2 Only larvae reared on new leaves through the third instar survived to pupate on mature leaves; developmental time was prolonged by 20% and pupal weight was reduced by 50% in these larvae compared with larvae reared entirely on new leaves. Almost all larvae died when transferred to mature leaves as first, second or third instars.
• 3 Low survival and slow development on mature leaves was mainly due to failure by larvae to feed. Larvae palpated leaves and could discriminate among leaf ages immediately, without biting into the leaf tissue.
• 4 New leaves had higher concentrations of oil and tannins than old leaves, while there were no significant differences in nitrogen concentrations in the two types of leaves. Mature leaves were more than 3 times tougher than new leaves, in terms of g mm^?2 of penetrometer force.
• 5 In drought years E. blakelyi may not produce sufficient new leaves to supply specialist herbivores with their preferred food resource. We infer that drought years reduce P. atomaria larval performance significantly, and influence the population dynamics of the insect.

     

Effects of Tomato chlorosis virus on the performance of its key vector,Bemisia tabaci,in China

Tomato chlorosis virus (ToCV), which is a newly emerged and rapidly spreading plant virus in China, has seriously reduced tomato production and quality over the past several years. In this study, the effect of ToCV on the demography of the whitefly, Bemisia tabaci biotype Q (Hemiptera: Aleyrodidae), fed on infected and healthy tomato plants was evaluated using the age‐stage, two‐sex life table. When reared on ToCV‐infected tomato plants, the fecundity, length of oviposition period and female adult longevity of B. tabaci biotype Q decreased significantly, while the pre‐adult duration significantly increased compared to controls reared on healthy tomatoes. Consequently, the intrinsic rate of increase (r) and finite of increase (λ) of B. tabaci biotype Q on ToCV‐infected tomato plants significantly decreased compared to those on healthy tomatoes. Population projection predicted that a population of B. tabaci biotype Q fed on ToCV‐infected tomatoes increases slower than on healthy plants. These findings demonstrated that ToCV infection decreased the performance of B. tabaci biotype Q on tomato plants.     

甜菜夜蛾对不同寄主植物的产卵和取食选择

为了探讨甜菜夜蛾Spodoptera exigua对不同寄主植物的产卵选择及成虫产卵选择与幼虫取食选择间的关联度, 本研究选取玉米、豇豆、甘蓝、黄瓜、棉花、辣椒和番茄7种植物进行了选择性和非选择性实验研究, 并采用Y型嗅觉仪测定了成虫对其中3种寄主植物及其挥发物抽提物的趋性。结果表明：在田间非选择性实验中, 甜菜夜蛾在不同寄主植物上的落卵量依次为：玉米>辣椒>棉花>黄瓜、豇豆、番茄>甘蓝。Y型嗅觉仪的行为测定表明, 雌成虫对玉米及其挥发物抽提物的趋性最强, 黄瓜次之, 对甘蓝的趋性最弱, 这与雌虫的产卵选择性一致。不同龄期甜菜夜蛾幼虫对寄主植物的取食选择性有所不同, 且随观测时间的延长有所改变;低龄幼虫对豇豆、玉米和黄瓜的选择性较强, 对甘蓝、番茄、辣椒和棉花的取食选择性则较弱, 高龄幼虫对辣椒也具有较强的选择性;5龄幼虫对寄主植物的选择性不如低龄幼虫明显。结果显示, 甜菜夜蛾对不同寄主植物的产卵选择性显著不同, 植物抽提物在雌成虫的产卵选择中具有重要作用, 甜菜夜蛾对寄主植物的产卵选择性和幼虫取食选择性并不一致。     

Host plant influences pathogenicity of Beauveria bassiana to Bemisia tabaci and its sporulation on cadavers

Laboratory bioassays were conducted to determine host plant effect on pathogenicity of the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuill. (Ascomycota: Hypocreales) to the sweetpotato whitefly, Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae). Fourth instar B. tabaci reared on cucumber, tomato, melon, green pepper, potato, eggplant, marrow, cabbage, bean or cotton, were treated with 1 × 10⁷ conidia/ml B. bassiana EABb 93/14-Tp isolate. Mortality caused by B. bassiana significantly increased with time and it was significantly affected by the host plant on which the nymphs were reared. Mean mortality of nymphs 8 days after inoculation ranged between 52.3±7.3 for nymphs reared on cotton and 91.8±5.8 for nymphs reared on cucumber. Average survival times of nymphs treated with the fungal suspensions were also significantly influenced by the host plant, with a mean of 4.7±0.1 days for nymphs reared on cucumber, 6.6±0.2 days for cotton and 6.9±0.1 days for green pepper. The production of newly formed conidia was also affected by host plant and varied from 111000±8600 conidia/cadaver for nymphs reared on cotton to 597000±28000 conidia/cadaver for those reared on melon.     

Biology and life table studies of the oriental tobacco budworm,Helicoverpa assulta (Lepidoptera: Noctuidae), influenced by different larval diets

Development, survivorship, pupal weight, oviposition, and life table parameters of the oriental tobacco budworm, Helicoverpa assulta Guenée, were evaluated in the laboratory on an artificial diet, pepper (Capsicum frutescens L.), and tobacco (Nicotiana tobacum L.). We found that the average developmental time of immature stages was longest on tobacco (36.2 d), intermediate on pepper (34.4 d), and shortest on artificial diet (33.5 d). Immature survival from egg to pupa varied from 31% on tobacco, 43% on pepper, and 74% on artificial diet. Pupal weight ranged from 197.4 mg/pupa on tobacco, 233.1 mg/pupa on pepper and 253.4 mg/pupa on artificial diet. The average numbers of eggs laid by adults reared as larvae on the artificial diet, pepper, or tobacco were 614, 421 and 334 eggs/female, respectively. Numbers of remaining eggs in ovaries of the adult females reared as larvae on the artificial diet, pepper, or tobacco were 16, 26, and 42 eggs/female, respectively. The longevity of adult females developed from larvae reared on the three diets was not significantly different, whereas the longevity of male adults from the larvae reared on artificial diet was longer (16.8 d) than that for males reared on tobacco (13.8 d) and pepper (13.3 d). The intrinsic, finite, gross, and net rates of increase were highest for females reared as larvae on artificial diet, lowest for females emerging from larvae reared on tobacco, and intermediate for females emerging from larvae reared on pepper. Generation times and doubling time of H. assulta were shortest for larvae fed artificial diet, intermediate from larvae reared on pepper, and longest from larvae reared on tobacco. We concluded that the artificial diet was the most suitable larval diet of H. assulta followed by pepper, and tobacco.     

Assimilation of carbon and nitrogen from pollen and nectar by a predaceous larva and its effects on growth and development

Abstract. 1. Predaceous insects may benefit from feeding on non‐prey foods, such as pollen, nectar, and honeydew, because they can provide nutrients that help maintain metabolism and enhance overall nutrient intake. Yet, the extent to which predaceous insects can assimilate non‐prey food and the importance of diet mixing during particular life history stages is poorly understood. In this study the relative contribution of an omnivorous diet to the growth and survivorship of a predaceous larva was tested in a hypothetical situation in which nutritionally optimal prey was not available. The study system comprised a predaceous larva (second‐ and third‐instar larvae of the green lacewing Chrysoperla carnea), nutritionally poor prey (larvae of Drosophila melanogaster), and non‐prey food (pollen suspension, a mixture of bee pollen and artificial nectar (1 M sucrose solution)). Chrysoperla carnea larvae in the mixed diet treatment were provided with both Drosophila larvae and pollen suspension, while those reared on the prey and non‐prey diet treatments received only Drosophila larvae or pollen suspension respectively. 2. The inclusion of pollen and sucrose in their diet enhanced the growth of C. carnea larvae. Second instars reared on the mixed diet developed significantly faster than their cohorts reared on the prey diet, however third instars reared on the mixed diet did not develop faster than their cohorts reared on the prey diet. Larvae reared on the mixed diet became larger adults than did those reared on either the prey or non‐prey diets. Third instars reared on the non‐prey diet completed their development while second instars in the non‐prey diet treatment failed to pupate. 3. Stable isotope analysis indicated that the larvae obtained most of their carbon (55–73%) and nitrogen (71–73%) from Drosophila but acquired only a minor amount of carbon (2–5%) and nitrogen (3–11%) from pollen. Larvae reared on the mixed and non‐prey diets acquired a relatively significant amount of carbon (23–51%) from sucrose. 4. A model, which included a novel fractionation factor to account for the isotopic effect of metamorphosis, was developed to explain the proportion of larval growth attributable to each diet item. It explained the adult δ¹³C values to within 0.2‰ and adult δ¹⁵N values to within 0.7‰ in all treatments. 5. Adults fed ¹⁵N‐labelled pollen as larvae retained the ¹⁵N signal of the pollen as adults. 6. The collective results of this study support the view that, despite their dependence on prey arthropods to obtain most of their dietary nitrogen, omnivorous lacewing larvae can enhance their growth and development by supplementing their diets with alternative non‐prey food resources. This finding is consistent with the notion that omnivory has evolved as a feeding strategy to acquire both additional nitrogen as well as trace nutrients.     

Effects of two artificial diets on the development and reproduction of Tirathaba rufivena (Walker) (Lepidoptera: Pyralidae)

Growth, survival, fecundity, and nutrition of Tirathaba rufivena (Walker) fed on two artificial and one natural diet were studied at 29±1°C and 75±5% relative humidity. Larvae reared on the two artificial diets showed faster growth and development, higher pupal survival and weight, and higher adult fecundity than those reared on a natural diet of young coconuts, Cocos nucifera L. The relative growth rate, efficiency of ingested food conversion, and efficiency of digested food conversion in larvae fed on artificial diets were significantly higher than those of larvae fed on young coconuts. The relative consumption rate of larvae fed on artificial diets was significantly lower than that of larvae fed on young coconuts. T. rufivena showed no significant degradation in ability to propagate after being reared on the artificial diet for five successive generations. These results indicated that two artificial diets are suitable for mass rearing of T. rufivena.     

Toxicity of the aphid Aulacorthum magnoliae to the predator Harmonia axyridis (Coleoptera: Coccinellidae) and genetic variance in the assimilation of the toxic aphids in H. axyridis larvae

Larvae of the ladybird Harmonia axyridis are reported to suffer high mortality when they are fed with the aphid Aulacorthum magnoliae associated with the elder Sambucus sieboldiana. In the present study we first examined whether aphid toxicity to H. axyridis was altered when the aphids were reared on different host plants, and second whether some ladybird families could adapt specially to the toxic aphids. Ladybird larvae from each egg batch were divided into two groups; one group was fed with A. magnoliae reared on potato, and the other group was fed with A. magnoliae reared on elder. The ladybird larvae fed with elder aphids suffered significantly higher mortality and grew more slowly than did larvae fed with potato aphids. This result indicates that A. magnoliae aphids absorbed toxic substances or their precursors from S. sieboldiana. We suggest that host association of A. magnoliae with the primary host plant S. sieboldiana has been maintained because of the advantage of deterring predation. Significant and positive correlation was detected across H. axyridis sib families between the mean weight of larvae fed with elder aphids and the mean weight of larvae fed with potato aphids. The hypothesis that some ladybird families adapt specially to the toxic aphids was not supported. However, the available evidence showed that a large amount of genetic variance in performance is maintained in a wild population of the ladybird H. axyridis.     

Biotypes of the seed beetle Callosobruchus maculatus have differing effects on the germination and growth of their legume hosts

• 1 Populations of the seed beetle Callosobruchus maculatus (F.) exhibit considerable differences in body size and larval behaviour. We examined whether such variation modifies the relationship between beetle infestation and host plant performance.
• 2 Larvae from African and Asian biotypes were reared in seeds of four hosts that represented an almost four‐fold variation in seed mass. We estimated mass lost to larval consumption, and compared germination rates and seedling growth between infested and control seeds.
• 3 In seeds bearing a single larva, the larger‐bodied, contest‐competing larvae of the Asian biotype caused a 38–47% greater reduction in seed mass compared with the smaller‐bodied, scramble‐competing larvae of the African biotype. The amount of seed mass lost per larva remained similar in seeds with one or two scramble‐competing larvae but decreased significantly in seeds bearing two contest‐competing Asian larvae.
• 4 Differences in larval consumption and behaviour produced striking differences in the frequency of germination. Germination of singly‐infested mung bean (i.e. the smallest host) was 71% for African‐infested seeds versus 11% for Asian‐infested seeds. In cowpea (i.e. the largest host), 76% of Asian‐infested seeds germinated, whereas the germination rate of African‐infested cowpeas (92%) was similar to that of uninfested seeds.
• 5 Effects of beetle origin persisted after germination. Seedlings derived from Asian‐infested seeds had greater cotyledon damage 7 days after germination, and displayed lower height and less biomass 15 days after germination. Cotyledon damage was a good predictor of seedling performance (i.e. better than seed mass consumed) 15 days after germination.
• 6 Previous studies have suggested that population differences in larval size and burrowing behaviour (‘centripetal tendency’) reflect adaptation to different‐sized seeds. The present study demonstrates that these differences in turn influence the impact of larval feeding on host viability. Strong biotypic variation makes it difficult to generalize about pest impacts at the level of pest species.

     

Biological control of the leafminer,Liriomyza trifolii by introduction,releasing, evaluation of the parasitoids Diglyphus isaea and Dacnusa sibirica on vegetables crops in greenhouses in Egypt

Abstract

The serpentine leafminer, Liriomyza trifolii (Burgess) (Diptera: Agromyzidae), is one of the most serious pests of various floricultural and vegetable crops. The European strains of the parasitoids Diglyphus isaea (Walker) (Hymenoptera: Eulophidae) and Dacnusa sibirica Telenga (Hymenoptera: Braconidae) were imported from The Netherlands. A total of 90,000 of these parasitoids were reared and released on cucumber and tomato in greenhouses. The parasitism rates of D. sibirica reached maximum 11.6% and 7.2% in the 11th week from the releasing date, on cucumber and tomato, respectively. Also the parasitism rates of the European strain of D. isaea increased until it reached a maximum 2.1% and 1.4%, in the tenth week from the releasing date on cucumber and tomato, respectively. It is concluded that the parasitoids D. sibirica and the European strain of D. isaea can be established in Egypt.