Biology of an egg parasite of Callosobruchus maculatus (Fab.) (Coleoptera: Bruchidae)

Uscana mukerjii (Mani) (Chalcidoidea, Trichogrammatidae) parasitizes eggs of Callosobruchus maculatus. Mated adult U. mukerjii lived for 5.0 ± 0.8 and 4.7 ± 0.9 days (males and females, respectively) at 27 °C. The female copulated only once, whereas males did so up to 4 times. The maximum parasitization of host eggs took place within the first 24 hours of egg laying and declined thereafter. The parasite completed its development inside the host egg in 7.2 days at 27 °C and 60–63% r.h. and emerged after cutting a circular hole in the chorion of the host egg. Mated and unmated females laid 35.4 ± 1.4 and 36.0 ± 2.2 eggs in their life time of which 27.3 ± 1.8 and 23.2 ± 2.8, hatched respectively. Parasitized host eggs did not hatch and were ultimately destroyed. The degree of parasitization varied with the pulses on which the host eggs were laid. This egg parasite may be useful in controlling the populations of C. maculatus and thus help in reducing the damage caused.     

Adult longevity and oviposition of Trogoderma parabile Beal (Coleoptera, Dermestidae) at different temperatures

Adult longevity and egg production of Trogoderma parabile Beal were determined at 14 temperatures from 4·4 to 40°C and 70±5 per cent r.h. In the range 12·8 to 32·5°C male and female longevity decreased with increasing temperature, particularly above 17·5°C. At temperatures below 12·8°C longevity decreased rapidly. From 22·5 to 37·5°C females had a shorter life span than males; but at all other temperatures females outlived males. The lengths of the preoviposition and oviposition periods were inversely related to temperature. Eggs of normal appearance were laid at temperatures from 17·5 to 37·5°C, a few deformed, non-viable eggs were laid at 15·6°C, and none beyond this range. Most eggs were laid at temperatures of 27·5 and 30°C. The number of fecund females rose as the temperature increased from 17·5 to 35°C and declined beyond 37·5°C. As the temperature increased above 17·5°C there was generally an inverse relationship between oviposition period and temperature. Females alternately exposed for 24-hr periods at 32·5 and 15·6°C during their adult life produced about the same total number of eggs as those held continuously at 32·5°C. The number of laying females and egg production per female on individual days was directly related to temperature. The finite rate of increase (λ) of T. parabile at 32·2±0·3°C and 70 per cent r.h. was 1·7 per 8 days. The results suggest that in Canada T. parabile is unlikely to become a serious pest of stored grain because of low winter temperatures and relatively short summers in the primary grain-growing regions.     

Infestation of maize cobs by Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae)—Aspects of biology and control

The initial attack and subsequent development of Prostephanus truncatus on maize cobs, with husk intact, was investigated at 27°C and 40, 50 and 70% r.h. The beetles showed a strong tendency to attempt infestation by first boring into the maize cob cores although they eventually gained access to the grain via the apex of the cob by walking between the grain and husk. At 50 and 70% r.h., the rate of oviposition over the first 2 wk was particularly high, while at 40% r.h. the rate was more or less constant. Some F₁ generation completed their development within 32–39 days at 50 and 70% r.h. and within 39–46 days at 40% r.h. Under all three moisture conditions, adult dispersal from the cobs was first detected at the end of the sixth week.

Estimates were made of the rate of increase of P. truncatus under each of the three moisture conditions. The population increased most rapidly at 70% r.h. and was at its peak between the eighth and twelfth weeks during which time grain damage and weight loss had effectively reached 100%. At 50% r.h., this stage was reached between the twelfth and sixteenth weeks while by this time at 40% r.h. the grain weight loss was only 40%.

Two novel techniques were tested for protecting maize cobs from infestation by P. truncatus. The exposed ends of maize cob cores were dipped into permethrin, 0.1% w/v aqueous dispersion or 0.5% w/w dilute dust, or untreated cobs were kept with permethrin-treated expanded-polystyrene blocks which acted as alternative refuges. Such treatments were examined at two beetle population densities. Dipping of the maize core was particularly effective in the prevention of infestation at low population density. This technique should be the subject of a field trial and if successful will offer important advantages over currently recommended control procedures.     

Studies on some aspects of the biology of Corcyra cephalonica (Stainton) (Lepidoptera: Galleriidae)

The biology of Corcyra cephalonica (Stainton) was studied under controlled conditions in the laboratory. At a constant temperature of 30°C, oviposition was influenced by relative humidity, an average of 148.9 eggs per female being laid at 70% r.h., compared with 131.8 eggs at 50% r.h. More eggs were retained in the ovaries of dead females at the lower r.h. Maize, rice and groundnuts were preferred to cowpea and cocoa for egg deposition. The incubation period was about 4 days at both humidities. Larval development was fastest at 70% r.h. (34.1 days) and slowest at 50% r.h. (43.3 days). Pupal duration was not affected by relative humidity. Development on different forms of a range of food commodities was studied. The larval period was generally shortest on brokens and meal, particularly of maize. Adult moths appeared weakly negatively phototactic and most locomotory activities were observed to take place at dusk.     

Environmental factors influencing the development and rate of increase of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) on stored maize

Temperature, relative humidity (r.h.), food density, and maize (corn) cultivar (CV) influenced oviposition, development and intrinsic rate of increase of Prostephanus truncatus (Horn). The lower and upper limits for complete development were 25 and 32°C at 40% r.h.; 18 and 37°C, at 70% r.h.; and 20 and 32°C at 90% r.h. The shortest developmental periods were 25.4 ± 0.2 days in ground maize, CV Golden Beauty, at 32°C, 70% r.h., and 24.1 ± 0.2 days in whole kernel maize, CV Pride 1108, at 32°C, 80% r.h. Ground maize at a density of 750 mg/cc promoted rapid development of larvae accompanied by lower mortality and fewer malformed adults than ground maize at a density of 450 mg/cc. P. truncatus laid 430 eggs per female in blocks of maize consisting of 6-cemented kernels during 22 weeks compared with 205 eggs per female in ground maize during 15 weeks, and 36 eggs in loose maize kernels during 4 weeks. Viable eggs were laid at 18°C, 70% r.h., and 32°C, 70–80% r.h. The rate of self-multiplication and the intrinsic rate of increase per week, were: 1.94–2.24 and 0.665–0.806, respectively, at 30–32°C, 70–80% r.h. The highest rate was on field maize, CV Pioneer 3993, at 30°C, 70% r.h. The wide range of temperatures and relative humidities at which P. truncatus can develop in maize favor its establishment in tropical and subtropical regions where maize is grown and stored.     

Variation in life history parameters of Oryzaephilus surinamensis (L). (Coleoptera: Silvanidae)

Rates of survival and development of immature stages, and survival and fertility of adults of four field populations and two laboratory strains of Oryzaephilus surinamensis (L.) were compared. Population parameters of the field populations were generally similar, although one had a lower fertility rate. A strain which had undergone about 70 laboratory generations differed from the field populations in most characteristics; it had higher immature mortality, was slower to develop with more larval instars and shorter adult survival. A strain with 6 laboratory generations differed from the field populations in having more larval instars and prolonged development of females as larvae.

Population parameters and statistics for the three similar field strains and the long-term laboratory strain were respectively: immature survival, 77–86% and 61.5% larval instars, 4 and 5: immature development time 22–24 days and 30 days; net reproductive rate (Ro), 212 217 and 176; innate capacity for increase (r_m), 0.82–0.85 and 0.68 per week; and mean length of a generation (T) 6.3 6.5 and 7.6 weeks.     

Distribution of and association between the larger grain borer Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) and the maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) in maize stores

Interspecific interactions between the larger grain borer Prostephanus truncatus and the maize weevil Sitophilus zeamais were studied during two storage seasons in maize stores, in Bénin. Maize ears, randomly sampled from farmers’ grain stores, were ‘reared out’, i.e., kept for 4 weeks under controlled conditions for F₁ to emerge, and periodically sampled, in order to examine colonisation patterns of P. truncatus and S. zeamais. For both storage seasons, P. truncatus and S. zeamais populations were sparsely aggregated and not associated with each other. The degree and strength of association increased with each monthly sampling occasion with the Ochiai, Jaccard and Dice indices of association. By the fourth sampling occasion, P. truncatus was found on most ears and on some ears in very high numbers (>300 insects). Almost all ears with P. truncatus contained at least a few S. zeamais individuals, but many ears with S. zeamais contained no P. truncatus.     

Ability of naturally occurring parasitoids to suppress the introduced pest Prostephanus truncatus (Horn) (Coleoptera, Bostrichidae) in traditional maize stores in Togo

Beneficial parasitoids associated with traditional maize stores in southern Togo were collected during three storage seasons (1988–1990) at different sites to investigate their relationship to the introduced pest, Prostephanus truncatus. Two parasitoids, Anisopteromalus calandrae and Theocolax elegans were observed regularly and in higher numbers in the samples and were therefore studied for their relationship with P. truncatus. Correlation analysis of population densities observed in stores showed that correlation coefficients for numbers of both parasitoids and P. truncatus were mainly negative and very close to zero, but positive and greater in value for the parasitoids and Sitophilus zeamais. Glass jar trials were carried out with A. calandrae and T. elegans on loose maize. A. calandrae reduced numbers of P. truncatus by 70.1% in the single species culture after 8 weeks, whereas T. elegans had no impact. In double species culture A. calandrae had an effect on both populations; P. truncatus was reduced by 61.3% and S. zeamais by 22.5%. T. elegans only had an influence on S. zeamais.     

Development of Ephestia kuehniella (Zeller), Plodia interpunctella (Hübner) and Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae) on kernels and wholemeal flours of Fagopyrum esculentum (Moench) and Triticum aestivum L.

Three stored product moth pests, Ephestia kuehniella, Plodia interpunctella and Corcyra cephalonica were reared on the following five foods: whole buckwheat with pericarp, decorticated buckwheat, wheat var. “Centauro” (kernels), wholemeal wheat flour and whole buckwheat flour. Results showed that achenes of buckwheat with pericarp are a poor food for the development of these species. A low rate of survival to adulthood for E. kuehniella and P. interpunctella was recorded, with a considerable extension of post-embryonic development. Although the mandibles of larvae are strong, they have trouble in breaking the fibrous buckwheat pericarp. It was observed that when the seed was decorticated there was a higher percentage of adults emerged. The emergence of E. kuehniella began, according to the food given, 34–42 days after the eggs were laid. The susceptibility index (s.i.) of achenes without pericarp (s.i. 9.7) was higher than that observed on wheat (s.i. 8.6). The first P. interpunctella adults were found after 29 days on wheat and after 56 days on buckwheat with pericarp. The shortest mean period of development occurred on wheat (34 days) while the longest was on buckwheat with pericarp at 81 days. The highest susceptibility index was on kernels (s.i. 12.8), the lowest one was on buckwheat with pericarp (s.i. 2.3). C. cephalonica began to emerge, according to the food given, after 40–55 days. In this case, fewer adults were recorded from buckwheat with pericarp, but no significant differences among the means of emerged adults on wheat, wholemeal wheat flour and whole buckwheat flour were observed. The longest mean period of development was recorded on wholemeal wheat flour (72 days) while the shortest was on wheat kernels (58 days). The highest value for the susceptibility index was obtained for wheat kernels (s.i. 7.4) and the lowest one for buckwheat with pericarp (s.i. 4.5).     

Feeding behaviour of the predatory mite Acaropsis docta (Berlese)

The behaviour of Acaropsis docta as a predator on the eggs of Trogoderma granarium was studied. The mite approached the beetle egg with her chelicerae and rostrum extended and both were inserted into the egg for feeding. The structure of the feeding apparatus is described. The average number of eggs per day consumed by different stages of the mite were: larva 0·74, protonymph 0·90 and deutonymph 1·06. During development from larva to adult in 8·3 days, an individual consumed 9·3 eggs. The female consumed an average of 19·2 eggs in 10 days of her feeding life, compared with 10·2 eggs by the male during a similar feeding period. There was a positive correlation between the number of Trogoderma eggs consumed and the number of eggs laid by a female.     

Laboratory studies on predation by Teretriosoma nigrescens Lewis (Col.: Histeridae) on Prostephanus truncatus (Horn) (Col.: Bostrichidae) infesting maize cobs in the presence of other maize pests

Over 14 weeks at 27°C, 70% r.h., the mean rate of increase of three pairs of Prostephanus truncatus (Horn) was reduced by a factor of ten or four by the addition, after 3 or 6 weeks respectively, of four adult Teretriosoma nigrescens Lewis. The effect of the predator on Tribolium castaneum (Herbst) and Sitophilus zeamais Motschulsky populations was not as great: the mean rate of increase ofT. castaneum was approximately halved; and S. zeamais was not affected by the presence of the predator. T. castaneum had no significant effect on the numbers of P. truncatus or the numbers and predatory ability of T. nigrescens. Selective predation of P. truncatus by T. nigrescens did not encourage significant increases in populations of S. zeamais or T. castaneum.     

Effects of delayed mating on reproductive performance of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae)

Virgin male and female Indianmeal moths, Plodia interpunctella (Hübner), were mated soon after emergence or delayed from mating for 1-5 d, to determine the effect of age at mating on the number of spermatophores transferred by males to females, number of eggs laid (fecundity), egg viability, and adult longevity. When male and female moths were mated without delay, all females mated successfully. On average, each mated female had 2.2 spermatophores and laid 161 eggs. About 99% of the eggs laid were viable. Fecundity and egg viability were significantly and positively correlated with the number of spermatophores/female. For each day that mating of virgin male or female P. interpunctella was delayed, fecundity decreased by about 25 eggs. Egg viability decreased by 22%/d only when females were delayed from mating. Males delayed from mating for 5 d were unable to inseminate females. However, about 23% of females had one spermatophore when females or both males and females were delayed from mating for 5 d. On average, 22-39 non-viable eggs were laid by a female in treatments where male or female moths were delayed from mating for 5 d. Similarly, unmated (virgin) females laid 33 non-viable eggs. These results suggest that methods that can delay and disrupt mating may be effective behavioral strategies for managing this important pest of stored commodities and processed foods.     

Effect of hydroprene on Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

The effect of the insect growth regulator, hydroprene, was observed on Callosobruchus maculatus (F.). Hydroprene was applied topically to the last 2–3 sternites of unmated males and females with a micropipette. No significant decrease in fecundity was observed even with the highest dose of 0.75 μg of hydroprene, whereas the fertility of the eggs laid by treated females was affected on the first day of the oviposition period even with the lowest dose of 0.1 μg, and the effect was diluted with time. Male fertility was also affected. The emerged F₁ adults showed morphological abnormalities and the developmental period was prolonged.     

The influence of age of female at mating and duration of male presence upon the length of the pre-oviposition period and productivity of Sitophilus granarius (L.) (Coleoptera: Curculionidae) at 20°C

The pre-oviposition period of S. granarius (L.) was investigated. Virgin females of known age were paired and their oviposition monitored by regularly removing and replacing the wheat on which they were kept and incubating this until any progeny emerged. Females, paired at 0–10 days old, started to lay viable eggs at about 15 days. Females paired when 15 days or older began oviposition on average 3–4 days after pairing. When males were left with females for only one day, the percentage of fertile females was lower than when males were left for 3 days or longer. Mean production of offspring was 1.29 per day and was not affected by age at mating or by the presence or absence of males.     

Susceptibility of Dermestes maculatus De Geer (Coleoptera: Dermestidae) to gamma radiation in a nitrogen atmosphere

The susceptibility of developmental stages of the hide beetle, Dermestes maculatus to γ-radiation in a nitrogen atmosphere was determined. Newly oviposited eggs were most susceptible and pupae most tolerant. Within each stage, maturity resulted in increased tolerance. Typical approximate LD_99.9 values were: eggs, 36 hr, 27 Gy; 84 hr, 420 Gy; larvae, 1 week, 26 Gy; 2–3 weeks, 65 Gy; pupae 2 days, 270 Gy; 5 days, 800 Gy; adults > 50 Gy. Adult sterility was complete in males at 50 Gy and in females at 40 Gy. These results indicate that a commercial irradiation treatment at an average minimum dose of 1 kGy should effectively disinfest hermetically packaged products such as dried fish against this pest.     

Life history studies of the yam moth, Dasyses rugosella Stainton (Lepidoptera: Tineidae)

A life history study of the yam moth, Dasyses rugosella Stainton, was carried out in the laboratory at an ambient temperature of 28±2 °C and 75±5% relative humidity. Freshly emerged male and female adults were paired in glass vials and average fecundity determined. Eggs were incubated in Petri dishes lined with filter paper underneath which was moistened cotton wool. Hatchability and incubation period were noted. Freshly emerged first instar larvae were then reared on small Dioscorea alata L. tubers in plastic containers until adult emergence.The average fecundity per female D. rugosella was 107.4±9.9 eggs at an average oviposition period of 3.8±0.2 days. Most of the eggs were laid on the second day of oviposition. The eggs, which were laid singly, in groups and in chains, were elliptical in shape and measured 0.80±0.01 mm long and 0.42±0.01 mm wide. Hatchability was 66.7%. The mean incubation period was 5.1±0.2 days. Dasyses rugosella passed through six larval instars. The mature larva was eruciform with a large uniformly sclerotised head. The pupa was obtect, adecticous and highly sclerotised with a stout profile. The mean larval and pupal developmental periods were 44.5±1.8 and 11.9±0.2 days, respectively. The mean total developmental time from egg to adult was 61.6±3.7 days (range 53-75 days). The females were always bigger than the males. The wing span measurement of the female ranged from 18.0-18.5 mm, while that of the male ranged from 13.0-14.0 mm. The body length of the female ranged from 7.8-8.5 mm while that of the male ranged from 5.3-6.8 mm. The unmated males lived longer (8.5 days) than unmated females (7.1 days), mated males (3.8 days) and mated females (4.1 days).The maximum daily mean progeny production was 25.7 on the 63rd day of pivotal age. The innate capacity for increased r_c was 0.06 per female per day. The cohort generation time T_c was 63.0 days and the finite rate of increase h_c was 1.06. The net reproductive rate R_o was 52.9.     

The ability of powders and slurries from ten plant species to protect stored grain from attack by Prostephanus truncatus horn (Coleoptera: Bostrichidae) and Sitophilus oryzae L. (Coleoptera: Curculionidae)

Powders and slurries prepared from parts of 10 different plant species indigenous to Ghana were tested under laboratory conditions for their ability to protect stored grain from damage by Sitophilus oryzae L. and Prostephanus truncatus Horn on wheat and maize, respectively. Two concentration levels 10% and 1% (wt/wt) were used. Powders and slurries of all plant species of 10% (wt/wt) significantly (P < 0.001) reduced insect damage by the grains and caused mortality of both insect species. Powders of four species; Cissampelos owariensis, Azadirachta indica, Ricinus communis and Solanum nigrum, gave a significant (P < 0.001) reduction in grain damage by the insect species as well as high mortality, even at the lower concentration level of 1% (wt/wt). The slurry preparations were generally better protectants than the powders especially against S. oryzae where complete control was achieved except with Chromolaena odorata and Sida acuta, which permitted some survival. The pattern of action of the slurries against P. truncatus was similar to that of S. oryzae, except that P. truncatus was relatively more tolerant.     

Growth and development of Ectomyelois ceratoniae (Lepidoptera: Pyralidae) under laboratory mass-rearing conditions

A simple and inexpensive rearing procedure for Ectomyelois ceratoniae (Zeller) yielded mature, 45 mg female larvae 16 days after the eggs hatched. The average period from egg to adult was 26.2 days and some 69% of viable eggs yielded adults. The rate of increase was 20.7.     

Intraspecific and interspecific competition in Callosobruchus maculatus (F.) and Callosobruchus subinnotatus (Pic) on stored bambara groundnut, Vigna subterranea (L.) Verdcourt

Intraspecific competition was studied in Callosobruchus maculatus and Callosobruchus subinnotatus. Interspecific competition between the two bruchids was also studied to determine which of these species is likely to cause more damage to stored bambara groundnuts, Vigna subterranea in cases of joint infestation. Results showed that increasing the adult density up to 8 females per 10 g of bambara groundnut seeds did not significantly reduce the mean number of eggs laid per female, the number of eggs developing to the adult stage, or the weight of emerged adults of either species. The developmental period of the two species was also not significantly affected. The adult emergence curve of C. maculatus was similar to that of C. subinnotatus and was of the scramble type. C. maculatus performed better than C. subinnotatus in interspecific competition and it achieved this through a higher egg-laying ability and a higher rate of progeny production coupled with a shorter life-cycle. The implications of these findings with respect to damage and possible loss of stored bambara groundnut are discussed.     

Some factors affecting egg-laying of the granary weevil (Sitophilus granarius L.)

The effect of some factors affecting egg laying of the granary weevil Sitophilus granarius was studied. In choice-tests, females laid less eggs in grains previously infested, but in no-choice tests, there was no statistical difference between the number of eggs in sound grain (59 per female) and previously infested grain (66 per female). There was a negative correlation between the number of egg plugs deposited previously and the additional number of plugs: the greater the number of plugs initially, the fewer were added. Chemical analyses of plugs and female abdomens showed a compound appearing in both extracts. It was tentatively identified as a glycosidic derivative of hexose. The kernels from which cuticular waxes had been washed with n-hexane were less attractive for egg-laying females than the sound ones. Chemical analyses of grain cuticular lipids revealed alkanes, wax esters, triacylglycerols, free fatty acids, alcohols, sterols and unknown compounds. Grain fungal volatile metabolites such as 1-octanol and 2-methyl-1-butanol added to sterilized kernels increased egg laying.