Effect of artificial wetting and rainfall on the larval diapause of a stem borer, Busseola fusca in Western Kenya

Clarification of factors enabling diapause termination was carried out in a stem borer, Busseola fusca. Diapausing larvae very rarely pupated under dry conditions. Water apparently played a significant role in the termination of late diapause. During the late diapause period, larvae in the field were exposed to rains of the short rainy season. This precipitation, however, terminated diapause in only a few larvae, which indicate that termination requires sustained exposure to wet conditions that are not usually met during the short rains.

---

Résumé Les causes de la fin de la diapause ont été précisées sur B. fusca. Les chenilles diapausantes se nymphosent très rarement en conditions sèches. L'eau joue apparement un rôle important dans la fin de la dernière phase de la diapause. Dans la nature, les chenilles sont exposées pendant cette période aux plues de la brève saison de pluies. Cependant, ces précipitations n'interrompent la diapause que d'un nombre limité de chenilles, ce qui montre que la fin de la diapause exige une exposition prolongée à des conditions humides que l'on ne rencontre pas généralement pendant la brève saison des pluies.

     

Dissemination of entomopathogenic fungi using Busseola fusca male as vector

The stem borer, Busseola fusca (Fuller), is an important pest of maize Zea mays L. and sorghum Sorghum bicolor (L.) in eastern and southern Africa. To control this pest, biological control methods including the use of entomopathogenic fungi are being considered. The pathogenicity of one isolate of Metarhizium anisopliae (Metsch.) Sorok. and one isolate of Beauveria bassiana Bals. (Vuill.) were first tested on different developmental stages of B. fusca including eggs, neonate, 2nd and 3rd-instar larvae. Both fungal isolates were pathogenic to all the stages tested. However, differences in mortality were observed among larvae that hatched from treated egg masses. Experiments were conducted thereafter to test whether B. fusca males could serve as a vector for fungal conidia to contaminate B. fusca females and subsequently eggs and larvae. Results demonstrated that B. fusca males successfully transferred inoculum to females during copulation, which in turn transmitted it to the eggs they laid on maize plants, resulting in the decrease of leaf damages.     

Duration of diapause in the stem borers, Busseola fusca and Chilo partellus

The duration of diapause in the stem borers Busseola fusca (Fuller) and Chilo partellus (Swinhoe) was studied in South Africa by collecting diapausing larvae from the field throughout winter (April–August). B. fusca larvae emerged as moth around the middle of October regardless of the date of collection and the length of time they were kept in the laboratory under constant 21 °C. C. partellus larvae collected in April–June emerged in November, those collected in July emerged in October, and those collected in August emerged in September. Regardless of the collection date C. partellus started to emerge from diapause earlier and moth emergence lasted up to twice as long as in B. fusca. Under laboratory conditions at 60% RH both borer larvae lost about 50% of their body mass during diapause. When provided with water B. fusca larvae lost about 30% of their body mass and adults emerged 20 days earlier than when kept dry. C. partellus, on the other hand, lost only 13% of their body weight and emerged 34 days earlier. The differences between the two species are discussed in light of different types of diapause; i.e., obligatory diapause in B. fusca and facultative diapause in C. partellus.     

Variation in encapsulation sensitivity of Cotesia sesamiae biotypes to Busseola fusca

Many braconid wasp species inject polydnaviruses to overcome their host's immune system. In the species Cotesia sesamiae, two biotypes exist that differ in their ability to develop in the host Busseola fusca. The biotype from coastal Kenya is infected with Wolbachia and is not able to develop in larvae of B. fusca, whereas the uninfected inland biotype of this wasp can develop in B. fusca. The genetic transmission of the developmental ability was studied through a series of genetic crosses and superparasitization experiments. The Wolbachia infection of the coastal type did not play a role in the encapsulation response of the host. Experiments show that the polydnaviruses of the wasps could not prevent the encapsulation of the coastal parasitoid eggs. Most likely, larval characteristics such as surface proteins played a more important role in the encapsulation response of the host even in the presence of a functional polydnavirus.     

Anin vitro rearing system for the propagation of the ectoparasitoidCatolaccus grandis

An experimental ‘closed’ rearing system, where egg and larval manipulations were eliminated, was developed for the in vitro rearing of Catolaccus grandis (Hymenoptera: Pteromalidae) Burks, an important ectoparasitoid of the cotton boll weevil, Anthonomus grandis Boheman. In this rearing model, n-hexane (a synthetic ovipositional stimulant for this parasitoid), was smeared on the Parafilm® cover of a modified rearing chamber (a Multiwell®) tissue culture plate) to induce the deposition of uncontaminated eggs, on the inner side of this waxy membrane, and on or around an agar retained diet that had been dispensed into the individual chamber wells. When the efficiency of the in vitro rearing system was compared to the current in vivo rearing method for this species, the duration of the life cycle was significantly shorter in parasitoids reared in vivo, but this difference was less than one day (17.8 vs 17.1 days, respectively). On the other hand, the number of eggs laid in the in vitro rearing chamber during a 4 h period was c. 2.5 times greater than in the conventional in vivo rearing apparatus, and adult yields were c. 25% greater when using the in vitro closed rearing method. Male to female ratios were c. 1:9 when reared in vitro as compared to 1.0:1.5 for those reared in vivo. There were no apparent adverse effects of this in vitro rearing system on the parasitoid's general behavior and reproduction after two consecutive generations.     

饲养五种夜蛾科昆虫的一种简易人工饲料

以黄豆粉、酵母粉及麦麸粉等为主要营养成分 ,研制和筛选出了一种既可工厂化饲养斜纹夜蛾幼虫 ,又可大量饲养甜菜夜蛾、银纹夜蛾、粉纹夜蛾和棉铃虫幼虫的简易人工半合成饲料。利用该饲料目前已实现了工厂化饲养斜纹夜蛾幼虫增殖斜纹夜蛾核多角体病毒     

甜菜夜蛾人工饲料及饲养技术研究

研究了人工继代繁殖甜菜夜蛾饲料配方及饲养方法 ,测定了各虫态发育历期、幼虫死亡率、化蛹率、羽化率、蛹畸形率及不同世代蛹重。采用改进的饲料配方饲养的深圳种群 ,第 2代幼虫死亡率、化蛹率、蛹畸形率、羽化率分别为 7 8% ,97 3 % ,2 7%和 93 8% ,第 2 ,5 ,9,1 2代平均单头蛹重分别为 1 1 9 7± 1 6 1 ,98 3± 1 1 4,94 3± 1 2 6和 82 4± 9 6mg,平均单雌产卵量分别为 1 1 3 7 2± 63 3 ,684 5± 5 3 7,45 6 9± 40 2和 3 91 7± 45 6粒。人工饲养的甜菜夜蛾 ,卵、幼虫、蛹、雌性成虫的发育历期分别为 2 5～3 5 ,1 0～ 1 2 5 ,7～ 8 5和 8～ 1 4天 ,完成一个世代需要 2 1～ 2 5天。     

大螟人工饲养技术的初步研究

利用大豆粉、玉米粉、麦胚和鲜茭白等成分配制了大螟Sesamia inferens(Walker)的半合成人工饲料,利用该饲料配方,发展了大螟的长期、继代饲养技术,即初孵-2日龄幼虫在茭白上饲养,3日龄-化蛹在人工饲料上饲养。利用该方法连续饲养大螟3代,幼虫的发育历期、蛹重、幼虫存活率、化蛹率、羽化率、卵孵化率和单雌产卵量等生活史参数与在天然饲料茭白上饲养的大螟相比,二者没有任何显著差异。而且利用该方法饲养,成本低、省工省力,能显著减少病原菌的感染。这说明该饲养技术适于大螟种群的长期、继代饲养。     

二化螟人工饲料研究初报

在温度为(29±1)℃,相对湿度为80%~90%的条件下,分别以3种人工饲料和天然饲料(新鲜水稻茎杆)对二化螟Chilo suppressalisWalker进行连续继代饲养。结果表明,3种人工饲料饲养的二化螟幼虫的生长历期、化蛹率、蛹重、蛹期及羽化率等均与天然饲料的基本接近,而且这3种人工饲料配制简便、成本较低,也不易霉变,是3种较为理想的人工饲料。通过第2代和第3代的继代繁殖表明,3种人工饲料和天然饲料饲养的二化螟的发育情况都稍有下降,但3种人工饲料与天然饲料间不存在显著差异。     

Mass rearingCeratitis capitata: reuse of the finisher larval diet

The standard finisher larval diet used at Seibersdorf for rearing the Mediterranean fruit fly,Ceratitis capitata (Wiedemann), was reused following autoclave heat-treatment to kill larvae or pupae remaining from its first use. Only when the spent diet was mixed with water (about 40% of final diet, w/w) to reconstitute fresh-diet texture, and combined with fresh starter, a similar, but still inferior in respect to larval duration and pupal recovery and size, to the fresh finisher diet production of flies was achieved. Enrichment of the autoclaved spent finisher with small quantities of nutrients gave inconclusive results. Although spent-diet pupae were significantly smaller than fresh-diet control pupae, their adults survived significantly longer than control adults.

---

Zur massenaufzucht vonCeratitis capitata: die wiesderverwendung der endkomponente der larvendiät

Zusammenfassung Die in Seibersdorf zur Aufzucht der Mittelmeerfruchtfliege,Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), verwendete Standardendkomponente der Larvendiät konnte nach Abtötung der von der Erstverwendung verbliebenen Larven oder Puppen mittels Autoklavensterilisation wiederverwendet werden. Eine zur frischen Kontrolldiät vergleichbare, jedoch bezüglich der Länge des Larvenstadiums, der Entwicklung der Puppen nach dem Schlüpfen sowie der Größe der Puppen noch immer schlechtere Fliegenproduktion wurde erreicht, wenn die wiederverwendete, autoklavierte Diät mit Wasser (ca. 40% der Enddiät, w/w) zwecks Rekonstitution zur frischen Diättexture gemischt und mit frischem Starter kombiniert wurde. Eine Anreicherung der wiederverwendeten Diätendkomponente mit geringen Mengen von Nährstoffen ergab keine schlüssigen Resultate. Obwohl Puppen der wiederverwendeten Diät signifikant kleiner als Puppen der Frischdiät-Kontrolle waren, überlebten deren Erwachsene signifikant länger als die Erwachsenen der Kontrolle.

     

In vitro rearing ofExorista larvarum on tissue culture-based diets

Exorista (=Tachina) larvarum (L.) (Diptera, Tachinidae), a polyphagous parasitoid that attacksLymantria dispar L. andHyphantria cunea (Drury), was rearedin vitro from egg to adult on four tissue culture media-based diets (TMM-FH, SCHNEIDER'S, EX-CELL 400, and SF-900). The kind of tissue culture media in the diets did not influence the adult yield (34 to 55%) and puparium weight (26–27 mg). Adult yield and the puparium weight ofE. larvarum developed on TNM-FH and SCHNEIDER'S-based diets containing different amounts ofGalleria mellonella pupal extract (PE) (0, 1.25, 2.5 and 5%), were lower on diets without PE. In diets without PE development times from oviposition to adult emergence, were shorter on TNM-FH (19 days) than on SCHNEIDER'S-based diet (25–26 days). The adults that developed on artificial diets were able to parasitize the factitious hostG. mellonella and produce viable progeny. The results demonstrate thatE. larvarum is the most promising parasitoid ever studied forin vitro mass production.     

二化螟人工饲养技术

二化螟Chilo suppressalis(Walker)是我国水稻上的重要害虫,为促进其防控技术研究,迫切需要建立二化螟标准化饲养技术。根据二化螟对关键营养成分的需求,研制了一种适合其生长发育、存活和繁殖的人工饲料配方,并发展了其长期、继代、规模化饲养的标准饲养技术。已用该饲料配方和饲养技术连续饲养二化螟69代,其适合度指标仍保持较高水平。该饲料配方和饲养技术适合二化螟的周年继代和规模化饲养,同时也为其它寡食性昆虫人工饲料的研制与开发提供借鉴和参考。     

Increase in cereal stem borer populations through partial elimination of natural enemies

An insecticide exclusion method was used to evaluate the effect of parasitoids on level of infestation by the stem borers, Busseola fusca (Fuller) and Chilo partellus (Swinhoe), in grain sorghum. In field trials conducted at Brits and at Delmas, South Africa, a selective organophosphate insecticide, dimethoate, was applied twice weekly at each site to three subplots whereas three other identical subplots served as controls. Twelve plants were randomly selected from each subplot at weekly intervals and removed from the field. In the laboratory all plants were dissected to record borer infestation. In order to determine parasitism levels egg batches were kept in Petri dishes and all borer larvae and pupae were kept individually in vials until either parasitoids or moths emerged. At Brits ca. 97% of borers were C. partellus and 3% B. fusca, whereas at Delmas 37.5% were C. partellus and 62.5% B. fusca. The most abundant parasitoids of B. fusca were Cotesia sesamiae (Cameron) and Bracon sesamiae Cameron. The dominant parasitoids of C. partellus at both sites were C. sesamiae, Stenobracon spec., Dentichasmias busseolae Henrich and Pediobius furvus (Gahan). No egg parasitoids were found. At both sites, infestation levels in the sprayed plots were significantly higher than in the untreated plots. On the other hand, parasitism levels of borers in the unsprayed plots were significantly higher than in the treated plots. It was concluded that the higher infestation level of sorghum by stem borers in the sprayed plots was because of partial elimination of parasitoids and possibly other natural enemies by the pesticide.     

In vitro culture of Trichogramma pretiosum on an artificial medium

The composition of an artificial medium and environmental conditions are described for the in vitro rearing of the egg parasite Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae). The medium was composed of defined amounts of protein, carbohydrates, lipid, salts, and vitamins, but also contained up to 40% insect hemolymph. The hemolymph was necessary to induce pupation. T. pretiosum eggs were obtained by dissection of Heliothis virescens (F.) (Lepidoptera: Noctuidae) eggs. In vitro reared T. pretiosum were similar in size to H. virescens reared T. pretiosum, and females were fecund.

---

Résumé Les oeufs de Trichogramma pretiosum ont été obtenus par dissection d'oeufs d'Heliothis virescens. T. pretiosum Riley (Hymenoptère, Trichogrammatidae) a été élevé avec succès sur un substrat synthétique. Outre des quantités définies de protéines, glucides, lipides, éléments minéraux et vitamines, la ration contenait aussi jusqu'à 40% d'hémolymphe de Manduca sexta. L'hémolymphe était nécessaire pour induire la nymphose. En plus de la nourriture, les conditions d'environnement sont apparues extrêmement importantes pour élever T. pretiosum dans des conditions satisfaisantes. Le contrôle de l'humidité relative, en particulier, était le facteur le plus important. Les adultes produits au cours de cette étude étaient d'apparence normale; ils se sont accouplés sans problèmes, les femelles étaient fécondes et leur taille ne différait pas de celle d'individus élevés sur H. virescens.

     

Rearing the American bollworm Heliothis armigera on a grass-meal diet

The American bollworm Heliothis armigera (Hübner), Lepidoptera: Noctuidae, was shown to be capable of growing and developing on a simple diet that was based principally on star-grass (Cynodon dactylon) — meal. Neonatal H. armigera larvae introduced into the diet developed, pupated, and emerged successfully. There was no significant difference in the growth rate of larvae reared on the natural diet and grass meal-based diet at p=0.1. Pupae from the grass meal-based diet had a higher emergence rate, but female fecundity was not significantly different.

---

Résumé Heliothis armigera est capable de croître et de se développer sur un aliment artificiel simple constitué principalement de Cynodon dactylon. Les chenilles introduites dans le substrat alimentaire comme larves néonates du ler stade, se développent, se nymphosent et émergent. Il n'y a pas de différence significative — même à p=0,1 — avec le taux de croissance des chenilles élevées sur aliment naturel. Les chrysalides obtenues sur aliment artificiel émergent mieux, mais la fécondité des femelles n'est pas significativement différente.

     

Refinement of a cell line based artificial diet for rearing the parasitoid wasp, Trichogramma pretiosum

An artificial diet incorporating insect cells originally developed for Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae) was successfully used to rear Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae). To refine the diet, individual components were removed. Chicken egg yolk and the insect cells were identified as the most important components for T. pretiosum development. Their removal resulted in few pupae and no adults. Removal of Grace’s insect medium, a common component of artificial diets, was found to markedly improve the development of T. pretiosum, producing 60% larva to pupa transition and 19% pupa to adult transition. There was no significant difference in T. pretiosum development on diets in which milk powder, malt powder or infant formula were interchanged, despite differences in nutrient composition. The use of yeast extract resulted in significantly higher survival to the adult stage when compared with yeast hydrolysate enzymatic and a combination of yeast extract and yeast hydrolysate enzymatic. Comparison of four antimicrobial agents showed the antibacterial agent Gentamycin and the antifungal agent Nystatin had the least detrimental effect on T. pretiosum development. The use of insect cell line diets has the potential to simplify artificial diet production and significantly reduce T. pretiosum production costs in Australia compared to diets using insect hemolymph or the use of natural or factitious hosts.     

豆野螟在人工饲料上的发育和繁殖情况

以天然寄主豇豆的花和荚作为对照,考查一种改进后的人工饲料对豆野螟Maruca testulalis Geyer生长发育的影响。结果表明:人工饲料饲养的豆野螟幼虫总历期与对照组之间不存在显著差异,说明人工饲料可以满足豆野螟幼虫正常生长发育的需要。取食工人饲料的豆野螟1龄和2龄幼虫存活率低于对照组,3龄后的存活率则高于对照组。人工饲料饲养豆野螟1代和3代羽化率分别为96.72%和96.47%,对照组的羽化率为94.41%,二者之间存在显著差异。不同产卵条件对产卵量没有显著影响,但豇豆叶上卵的历期比滤纸和绒布短,且孵化率也较后两者高。     

Suitability ofBusseola fuscaandSesamia calamistis(Lepidoptera: Noctuidae) for the Development of Two Populations ofCotesia sesamiae(Hymenoptera: Braconidae) in Kenya

The suitability ofSesamia calamistisHampson andBusseola fusca(Fuller) for the development of two geographical populations ofCotesia sesamiae(Cameron) was examined in the laboratory. One population of the parasitoid was collected from the coast of Kenya and the other from the inland. Both populations of the parasitoid could develop onS. calamistis.OnB. fusca,the inland population ofC. sesamiaewas able to develop, while the population from the coastal area of Kenya was encapsulated. Mating studies revealed that the two parasitoid populations were partially reproductively isolated. Unidirectional incompatibility, possibly caused by theWolbachiainfection, was observed when males from the infected coastal population were mated with females from the uninfected inland population.     

Production ofNosema marucae for biological control of cereal stem borers

In a study covering 3 years, experiments were carried out in order to determine the feasibility of producing a microsporidian pathogenNosema marucae in the spotted stalkborerChilo partellus. A maximum yield of 4.9×10⁸ spores/larva (equivalent to 3.1×10¹⁰ spores/g fresh larval body weight) was obtained in 3rd instar larvae. It is considered that the production is inexpensive and can be readily adapted for small scale pathogen propagation systems in the tropics.     

Significance of water contact as a factor terminating larval diapause in a stem borer, Busseola fusca

Previous studies revealed that diapause larvae of Busseola fusca (Lepidoptera: Noctuidae) began to respond to water and pupated in artificial wet conditions only in late diapause. Experiments are designed to clarify how water is involved in the termination of larval diapause. Neither feeding the larvae on fresh sorghum stems (6 weeks old) nor allowing them to drink water stimulated a break in the larval diapause. Diapause larvae transferred to artificial wet conditions pupated without increase in fresh weight. It is thus concluded that water contact is more significant as a factor terminating diapause in B. fusca than water uptake.

---

Résumé Des études antérieures avaient montré que la diapause des chenilles de B. fusca (Lep., Noctuidae) commence par une réaction à l'eau et qu'elles ne se nymphosent dans des conditions artificiellement humides qu'en fin de diapause. Des expériences ont été conçues pour préciser l'intervention de l'eau dans la terminaison de la diapause. Ni l'alimentation des chenilles sur des tiges fraiches de jeune sorgho (de 6 semaines), ni la possibilité de boire de l'eau n'ont stimulé une rupture de la diapause larvaire. Des chenilles en diapause transférées dans des conditions artificiellement humides se sont nymphosées sans augmentation du poids frais. On en a conclu que le contact avec de l'eau était plus important que l'absorption d'eau comme facteur de fin de diapause chez B. fusca.