Fecundity and egg hatchability of Dastarcus helophoroides adults fed on different types of artificial diets
Xiao-juan Li?Guang-ping Dong?Li Yang?Wan-lin Guo
Both fecundities and egg hatchabilities were compared among three populations of Dastarcus helophoroides Fairmaire adults(Coleoptera:Bothrideridae)fed on three types of artificial diets(Diet of formula 1 composed of silkworm pupa powder,dried yeast powder, sucrose,peptone,egg yolk powder and poplar branch powder.Diet of formula 2 composed of silkworm pupa powder,dried yeast powder,sucrose,egg yolk powder, poplar branch powder,cricket powder,benzoic acid and distilled water.Diet of formula 3 composed of pine bark powder and Monochamus alternatus larva powder).for 90 days.The three diets showed no significant difference regarding the average number of eggs deposited by all D.helophoroides females(16622.3–23874.7);the average number of eggs per female(1278.6–1836.5);and the average number of eggs per female per day(14.2–20.4). The number of eggs one cluster contained mainly (82.06–82.66%)lied in 1–100 eggs,and the average number of eggs per cluster ranged from 61.7 to 63.1.In the first 10-day period,the number of eggs deposited by all females fed on formula 1 was significantly larger than that on formula 3.The eggs deposited in the last four 10-day periods were more than in the former five 10-day periods,on formula 3.There were no significant differences in hatchability of total eggs among the three artificial diets, and the average corrected egg hatchability ranged from 82.85 to 84.78%.No significant differences in the adult mortality and mean weightgain of D.helophoroides were found after feeding on three artificial diets.Our results suggest that D.helophoroides adults were not specialized on the diet,and the diet types might have little effect on fecundity and egg hatchability in D.helophoroides,as long as sufficient nutrition was supplied.
Dastarcus helophoroides Fairmaire(Coleoptera:Bothrideridae)is a major natural parasitoid of wood borers such as cerambycid beetles and buprestid beetles.It is mainly distributed within 30–40N and 105–135E.It is now known as unique to China and Japan(Wang etal.1996).
This parasitoid is a prominent biological control agent against Monochamus alternatus Hope(Coleoptera:Cerambycidae),the primary vector of the pine wood nematode,Bursaphelenchus xylophilus(Steiner and Buhrer) Nickle,which causes serious damage to several pine species in China and Japan.The release of both D.helophoroides adults and eggs has fataleffects on M.alternatus (Miura et al.2003;Urano 2003,2006;Wang et al.2010; Qin etal.2012).The mortality of M.alternatus was about 57–76%in trees treated with D.helophoroides adults, which was significantly higher than in untreated trees (5–27%)(Urano 2003).The total percent parasitism of D.helophoroides against M.alternatus was up to 87%,with an egg density of 40:1(egg:entrance hole)(Qin etal. 2012).
D.helophoroides larvae can be reared on a substitute host(pupae of carabid beetles,the species are patented) (Yang 2004),live M.alternatus larvae or pupae,and artificial diet(full-grown larvae of Galleria mellonella Linnaeus are needed)(Ogura etal.1999;Urano 2010).Adults could be reared in the laboratory using different types of artificial diets(Wang and Ogura 1999;Ogura et al.1999; Yang 2004;Lei et al.2005).
D.helophoroides adults can live over 4 years in laboratory(Weietal.2009a).Each female has two ovaries,and the number of ovarioles per female varies from 36 to 154 depending on maternal body length(Togashi and Itabashi 2005).A female lays severaloreven hundreds ofeggs;the eggs are small,0.8–1.0 mm long and 0.2 mm wide(Gao and Qin 1992).Therefore,it is difficult to counta precise number of eggs with naked eyes,magnifier or microscope. The numberofeggs deposited by a female was estimated to be more than 2,000 per year(Ishii 2004).
D.helophoroides females depositegg clusters on gallery walls bored into tree stems by host larvae in natural conditions,and the hatched larvae willsearch forand paralyze the hosts(Qin and Gao 1988).Eggs laid in a laboratory were processed into an egg card and released to control M.alternatus in the field(Qin etal.2012).Thus,fecundity and egg hatchability have a maximum influence on the success of parasitism.Diet types greatly affect fecundity and egg hatchability in coleopteran beetles;significant differences were found in the average number of eggs per female per day and in egg hatchability for Rynchophorus ferrugineus(Coleoptera:Curculionidae)females reared on various diets(Kaakeh 2005).
Fecundity and egg hatchability are importantindexes for predicting orevaluating the biologicalcontrolpotentialofa parasitoid.The main objective of this study was to determine the fecundity and egg hatchability of D.helophoroides.Both fecundities and egg hatchabilities were compared with three populations of D.helophoroides adults fed on three types of artificial diets.
Materials and methods
Insects
D.helophoroides adults were the laboratory-reared offspring of the mother adults provided by the Research Institute of Forest Ecology,Environment and Protection, Chinese Academy of Forestry(CAF),Beijing,China.The ancestors were collected from dead Pinus massoniana Lamb in 2003 atGuangzhou City(23800N,113170E and altitude 120 m),Guangdong Province,China.Experiments were conducted at Institute of Forest Protection,Anhui Provincial Academy of Forestry,Hefei,China.
Rearing methods
Alive D.helophoroides adults(withoutoviposition experience)were distinguished between female and male by the end angle ofanalplate and the length and width ofanalplate under a 109 magnification according to Tang etal.(2007). Adults of the same size were chosen and individually weighed on a microbalance(0.032 g±0.0005 for females; 0.028 g±0.0004 for males).A total of 26 adults(13 females and 13 males)were reared in a 6.5 9 11 9 17 cm transparentplastic box(with four smallholes drilled in its lid)containing an induced spawning block (2.5 9 3.5 9 8.5 cm)of p.massoniana.Fourpiecesofkraft paper(3.5 9 8.5,4.5 9 9.0,3.5 9 8.5,3.0 9 7.5 cm)were tied on the block undera piece ofglassslide(2.6 9 7.6 cm), as the oviposition site.Two plastic centrifugaltubes(10 mm in diameter,50 mm long)contained tap water plugged by sponge balls.A piece of artificial diet(0.3 g)was provided once every 5 days in a small dish.The adults were maintained at 25C and 50%RH.The egg-containing kraft papers were collected once 5 days.The experiments were conducted from March 19,2012 to June 17,2012.The remaining live adults were counted,distinguished between female and male,and weighed.Each type of artificial diet was conducted in triplicate.
The adults for our experiments emerged in June 2012, and were stored at 15C and 50%RH for sexual maturation after the emergence,in a 6.5 9 11 9 17 cm transparent plastic box containing a block of p.massoniana (external dimensions:4.0 9 5.5 9 8.5 cm;inside dimensions:3.5 9 4.0 9 6.5 cm),as a resting place.Two plastic centrifugal tubes(10 mm in diameter,50 mm long)contained tap water plugged by sponge balls.The diet was replenished once a week.
Artificial diets
Three types of artificialdietformulas for D.helophoroides adults were chosen.Formula 1 contained:silkworm pupa powder(Hubei Longwanghen Fishing Bait Co.Ltd);dried yeast powder(Angel Yeast Co.Ltd);sucrose and peptone (both from Sinopharm Chemical Reagent Co.Ltd);selfmade egg yolk powder;and self-made poplar branch powder.The ingredients were weighed and mixed fully in accordance with the weight ratio of 6:6:2:2:2:1,and then stored under dry conditions(Wang and Ogura 1999;Ogura et al.1999).Formula 2 contained:3.3 g of agar powder (Tianjin Hengxing ChemicalReagentCo.Ltd)dissolved in 100 mlofhotwater,to which was added 10 g ofsilkworm pupa powder,10 g of dried yeastpowder,3.3 g of sucrose,2.5 g of self-made poplar branch powder,and 2 g of selfmade cricket powder.The mixture was sterilized under 121C for 20 min,and after it cooled down,0.02 g of benzoic acid(Shanghai Suyi Chemical Reagent Co.Ltd) and 14 g of self-made egg yolk powder were added,followed by drying at 80C for 6 h(Lei et al.2005).Formula 3,provided by Beijing Vocational College of Agriculture,mainly consisted of pine bark powder and M.alternatus larva powder.
Number of eggs
D.helophoroides usually laid egg masses or loose eggs on the kraft paper and the induced spawning block.The eggs were photographed using a digital camera and its microspur function.The photos were opened with MS painttool in Microsoft Windows,and the eggs were counted accurately with a red marking pencil.The totalnumber of eggs deposited from the females and the number of eggs per female per day were determined.
Egg hatchability
The egg-containing kraft papers were collected.After counting the eggs,one piece of egg-containing kraftpaper was placed in a transparent plastic box.The eggs were maintained in an artificial climatic chamber at 25C and 50%RH under a 10-hour light(L):14-hour dark (D)photoperiod.The eggs were observed every day,and the newly hatched larvae were counted and taken outusing a small brush.Egg hatchability was calculated from the total number of hatched larvae and the number of eggs. There were ten replications for each artificial diet.
Statisticalanalysis
Parameters relevantto fecundity and egg hatchability were compared among D.helophoroides adults fed on different artificial diets.Differences in each parameter were evaluated by a one-way analysis of variance(ANOVA).When F values were significant(p
