Physiological age-grading and ovarian physiology of Prostephanus truncatus

Abstract. The reproductive tracts of male and female Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) were described for beetles between emergence and 30 days old in order to determine age-grading criteria. Seminal vesicles were bigger among non-mated males than among mated males due to accumulation of sperm; no age-specific differences were found for male P. truncatus. Ovaries (germarium size, number of follicles and follicle size) were similarly developed for females between 5 and 30 days old and did not differ between mated and non-mated females. Starved females were found to resorb follicles. Yellow body formation was strongly dependent on age, and was used as an age-grading criterion for female P. truncatus. Females flying off maize cobs and caught with pheromone traps were of varying physiological age and mated, and their ovarian development was suspended. All migrating females were mated, indicating that lone females may act as colonizers, independently of males. The applicability of migration theories to P. truncatus and adaptive inter-reproductive dispersal as part of its life history strategy are discussed.     

Prostephanus truncatus mate choice on contact: does pheromone signalling by males affect their mating success?

Prostephanus truncatus is an economically important beetle pest of stored maize and cassava in the tropics. Male beetles signal using an aggregation pheromone that attracts both female and male beetles over large distances. Females preferentially orientate towards the pheromone signals of particular males when given a choice. The influence of pheromone signalling on courtship and mating success was investigated using pheromone biossays and mating trials in both of which a female made a choice between two males. Signalling was manipulated by exposing males to a Female Factor that inhibits pheromone production. The relative attractiveness of males to females based on pheromone bioassays was found not to influence short-range courtship behaviour or mating success.     

Outdoor flight activity and immigration of Rhyzopertha dominica into seed wheat warehouses

The flight activity of lesser grain borer, Rhyzopertha dominica F. (Coleoptera: Bostrichidae), was monitored at two Foundation seed wheat warehouses during the 2003 and 2004 field seasons, using pheromone‐baited Lindgren funnel traps positioned indoors and outdoors. General stored‐product insect activity was also monitored using unbaited sticky traps positioned inside the warehouses around overhead doors. Pheromone‐baited traps were useful for monitoring R. dominica activity, however insect captures decreased when lures were not changed weekly. Flight peaks were documented in early May and again from September through October, and insect captures inside warehouses correlated with timing of outdoor captures. Multiple regression analyses showed that slightly more than half of the variability in R. dominica captures could be explained by mean ambient air temperature and wind speed during the 2 h preceding sunset. Stored‐product Coleoptera captured on unbaited glue boards around overhead doors included Ahasverus advena, Cryptolestes ferrugineus, R. dominica, Sitophilus oryzae, Tribolium castaneum, Trogoderma variabile, and Typhaea stercorea. Door gaskets significantly reduced the number of insect captures on glue boards placed around the overhead doors, and generally restricted their entry to ground level. These studies demonstrated that outdoor pheromone‐baited traps are effective monitoring tools for determining when grain‐handling facilities are most susceptible to infestation and that exclusion may be an effective component of a pest management program.     

Infestation of maize by Prostephanus truncatus initiated by male-produced pheromone

Delta traps baited with maize cobs, which were infested each with one male Prostephanus truncatus (Horn) (Col.: Bostrichidae), were distributed in southern Benin and collected after one, two, three and four weeks. The numbers of P. truncatus caught during the different trapping periods were not significantly different. Sixty-four percent of the trapped P. truncatus were females. Females attracted during the one-week trapping period produced a mean of 6.9 progeny during the seven days. The sex ratio of the progeny was 1:1. Trap catches with the infested cobs were on average 13 times lower than catches with 2 mg of the artificial pheromone. Estimation of P. truncatus densities in a maize store at the beginning of the storage period (based on laboratory data) revealed that small initial numbers of P. truncatus, possibly attracted by a single male, sufficed to initiate high infestation rates later in the storage season.     

Allozyme variation among Brazilian and U.S. populations ofRhyzopertha dominicaresistant to insecticides

The lesser grain borer (Rhyzopertha dominica (F.)) is an important pest of stored grain in many parts of the world (Paleartic, Ethiopian, Oriental, Australian, Neotropical, and Neartic regions) with the ability to fly long distances. These insects have been shown to be resistant to organophosphorus insecticides in several studies. Polyacrylamide gel electrophoresis was used to assess the genetic variability within and among eight Brazilian and seven United States populations of R. dominica and to determine how insecticide resistance may be spreading within both countries. Significant variation in allele frequency among populations was observed at all six polymorphic enzyme loci that were examined. The Brazilian and U.S. populations were genetically differentiated from one another; populations within the U.S. and those within Brazil were also differentiated from one another. The mean genetic similarity among the seven U.S. populations collected in a small region in northeast Kansas was smaller than that among eight Brazilian populations collected in a relatively large geographical area. These results are consistent with the resistance ratios to chlorpyriphos-methyl in R. dominica populations from Brazil and the U.S. and the information available concerning patterns of flight activity in this insect.     

Flight initiation byProstephanus truncatus in relation to time of day, temperature, relative humidity and starvation

Studies were carried out in the laboratory on the influences of time of day, temperature, relative humidity and starvation on flight initiation byProstephanus truncatus (Horn) (Coleoptera: Bostrichidae). Flight occurred throughout the 12 h photophase and at the beginning of the scotophase but peaked at 2–0 h before darkness. Temperature exerted a significant effect on flight. The frequency of flight take-off increased with temperature over the range 20–30°C but declined sharply at 35°C. Flight activity increased with starvation up to a maximum at 2 days after which it began to decline.     

Flight initiation in Prostephanus truncatus: influence of population density and aggregation pheromone

The influence of population density and aggregation pheromone were investigated as possible flight initiating factors for Prostephanus truncatus (Horn) (Col.: Bostrichidae). Maize grains (175 g in glass jars) were infested with 20, 50, 150 or 300 beetles, all of which were removed after 2 weeks. Flight initiation of the progeny was observed over a period of 4 weeks, with and without the synthetic aggregation pheromone of P. truncatus. Addition of the synthetic pheromone had no influence on the number of beetles taking off. The number of beetles dispersing increased with growing initial and progeny densities. Dispersal rates (% of total progeny dispersing) rose with declining rate till they reached a maximum at ca. 33%. Of the beetles dispersing, 74% left the cultures between 18.00 and 20.00 hours. Surviving progeny per female decreased with increasing initial density. Sex ratios in the initial cultures and in the F₁ were ca. 1:1, whereas a higher proportion of females (67%) was found among the dispersing beetles.     

Stable isotopes as markers to investigate host use by Rhyzopertha dominica

Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) is a serious worldwide pest of stored cereal grains that also has the ability to breed in non‐agricultural host plant material. Stable isotope signatures (concentrations of isotopes) were used as internal tissue markers to determine dietary differences among adult R. dominica and to make inferences about source habitats of field‐trapped insects. Adult R. dominica collected near granaries or from non‐agricultural forested sites near Stillwater, OK, USA, and insects reared on selected hosts under laboratory conditions were studied to determine the carbon and nitrogen isotope signatures. Laboratory‐reared R. dominica showed δ¹³C (stable isotope ratio of carbon) values similar to the host on which they developed with an enrichment of about 1 in the insect body. Insects reared on seeds of wheat and oak, which have C₃ photosynthetic pathways, showed much depleted δ¹³C values (–23.7 and –26.2, respectively) in comparison to insects reared on seeds of corn, a C₄ photosynthetic plant (–11.3). A majority of the field‐collected R. dominica showed δ¹³C values similar to expectations for a C₃ host. However, a few field‐collected insects had δ¹³C signatures similar to the C₄ plant‐reared insects in the laboratory experiment. Stored grain of C₄ crops were lacking at many of the sample field sites. These results suggest that R. dominica occurs on either C₃‐ or C₄‐based hosts in the field, and point to utilization of non‐grain C₄ plants as hosts. Our studies indicated that ¹³C isotope is a reliable marker to infer types of hosts used in the feeding history of R. dominica.     

进口竹藤中竹长蠹五近似种的鉴别(鞘翅目:长蠹科)

介绍了近年从进口竹藤检疫中多次截获的5种竹长蠹:双窝竹长蠹 Dinoderus bifoveolatus (Wollaston)、小竹长蠹D. brevis Horn、日本竹长蠹D. japonicus Lesne、竹长蠹D. minutus Fabricius及小点竹长蠹D. ocellari Stephens,分别介绍了头、前胸背板、鞘翅、腹面及足的主要鉴别特征,并编制了这5个近似种的检索表.     

我国首次截获有害生物小楔双棘长蠹

江门海关从冈比亚进境的刺猬紫檀木原木中检出活体长蠹科昆虫。通过显微形态特征的观察和测量,对该虫进行了物种鉴定。经形态特征鉴定,该虫为小楔双棘长蠹。该虫的形态特征与近似种的主要区别:斜面毛被稀疏、不太明显,近缝角处竖立短直;缝侧齿基部不粗糙;斜面侧上缘有3对胝状的痕迹显现。该虫在我国尚无分布记录,为国内口岸首次截获。该虫一般随着原木、木制品及木质包装进行远距离传播,一旦传入我国,将对我国的农林安全造成巨大威胁,各口岸须加强对进境原木、木制品及木质包装的检验检疫。