Precocious Mexican fruit fly methoprene‐fed males inhibit female receptivity and perform sexually as mature males

The sterile insect technique (SIT) has been used successfully for the control of fruit flies. The efficiency of this technique can be significantly reduced when sterile released insects are exposed to adverse conditions and predators, as a great number of sterile insects die before reaching sexual maturity and thus fail to mate with wild females. Treatments with juvenile hormone (JH) analogues such as methoprene (M) significantly reduce the time to reach sexual maturity by sterile Anastrepha ludens (Loew) (Diptera: Tephritidae) males. In this study, we compared the sexual performance of non‐treated sexually mature males with young males that had been sexually accelerated with M. Furthermore, we compared the ability of M‐fed males in inhibiting female remating compared with sexually mature males. Results showed that at 5 days M‐fed males had lower mating success than mature males; however, 6‐day‐old (0.1%) M‐fed males had the same amount of matings as mature 13‐day‐old males. Young 5‐ to 10‐day‐old M‐fed males also had similar number of matings as mature non‐treated 12‐ to 17‐day‐old males. There were no differences in copula duration between treatments. Moreover, there were no differences between the fertility, fecundity or refractory period of females mated with either young male fed M or normal sexually mature males. These results indicated that young males that were sexually accelerated with M have the same sexual performance as non‐treated sexually mature males. Implications of using M as a pre‐release treatment for A. ludens controlled through SIT are discussed.     

Raspberry ketone-supplemented diet has no effect on fitness parameters or lure responsiveness in male melon flies,Zeugodacus cucurbitae (Diptera: Tephritidae)

The male annihilation technique (MAT) and sterile insect technique (SIT) are often used to control pestiferous tephritid fruit flies (Diptera: Tephritidae). MAT involves the deployment of traps containing a male attractant and insecticide with the goal of drastically reducing male abundance and ultimately eliminating the entire population. SIT, which involves the mass production, sterilization, and release of the target species, may also be implemented to achieve final extirpation. Generally, simultaneous implementation of MAT and SIT is counterproductive, because the presence of large numbers of male-specific traps in the environment (MAT) would greatly reduce the number of sterile males available for copulating with wild females (SIT). However, studies on the Queensland fruit fly, Bactrocera tryoni (Froggatt), indicate that concurrent use of MAT and SIT may be feasible. Sexually mature males of B. tryoni are attracted to the raspberry ketone and its synthetic analogue cue-lure. Males of B. tryoni fed raspberry-ketone-supplemented diet when newly emerged showed lower attraction to cue-lure baited traps than control males. In addition, newly emerged males provided this diet displayed accelerated sexual maturation, which would allow the early release of sterile males and reduce pre-release holding costs. Here, we examined whether the addition of raspberry ketone to the adult diet of male melon flies, Zeugodacus cucurbitae (Coquillett), produced effects similar to those observed for B. tryoni. Despite using similar methods, no significant effect of raspberry ketone-supplemented diet on time to sexual maturity, survival, mating competitiveness, or attraction to cue-lure baited traps in mass-reared Z. cucurbitae males.     

Sex ratios and sex-biased infection behaviour in the entomopathogenic nematode genus Steinernema

In experimentally infected insects, the sex ratio of first generation nematodes of five species of Steinernema was female-biased (male proportion 0.35-0.47). There was a similar female bias when the worms developed in vitro (0.37-0.44), indicating that the bias in these species is not due to a lower rate of infection by male infective juveniles (IJs). Experimental conditions influenced the proportion of males establishing in insects, indicating that male and female IJs differ in their behaviour. However, there was no evidence that males are the colonising sex in any species, contrary to what has previously been proposed. Time of emergence from the host in which the nematodes had developed influenced sex ratios in experimental infections. In three species (Steinernema longicaudum, Steinernema glaseri and Steinernema kraussei), early emerged nematodes had a higher proportion of males than those that emerged later, with the reverse trend for Steinernema carpocapsae and Steinernema feltiae. In a more detailed in vitro study of S. longicaudum, the proportion of males was similar whether or not the nematodes passed through the developmentally arrested IJ stage, indicating that the female bias is not due to failure of males to exit this stage. The sex ratio in vitro was independent of survival rate from juvenile to adult, and was female-biased even when all juveniles developed, indicating that the bias is not explained by failure of males to develop to adults. The female-biased sex ratio characteristic of Steinernema populations appears to be present from at least the early juvenile stage. We hypothesise that the observed female bias is the population optimal sex ratio, a response to cycles of local mate competition experienced by nematodes reproducing within insect hosts interspersed with periods of outbreeding with less closely related worms following dispersal.     

Times for recovery from cold-torpor in the Queensland fruit fly Dacus tryoni: the relation to temperature during and after chilling

Recovery time after experience of a given minimum temperature below torpor threshold is related to the value of that minimum, the length of time spent at that minimum, and the temperature prevailing during the recovery period above torpor threshold. A model can predict recovery time for flies experiencing a given temperature fluctuation if the length of time spent at the minimum is expressed as a proportion of LE₅₀ at that minimum.The model has applications in defining the optimal protocol for chilling insects for use in the Sterile Insect Release Method. The model was confirmed by experiments showing that it is likely that flies will recover from non-lethal frosts before ant predators become active.

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Résumé Le temps de récupération après avoir subi une température minimal située au-dessous du seuil d'engourdissement dépend de la valeur de ce minimum, du temps passé à ce minimum, et de la température au-dessus du seuil d'engourdissement pendant la période de récupération. Un modèle mathématique permet d'estimer le temps de récupération après avoir subi une chute de température déterminée, en fonction du temps passé au minimum thermique exprimé comme une fraction du LE₅₀ (temps nécessaire pour tuer 50% des mouches) à ce minimum.Ce modèle s'est trouvé étayé par des observations montrant qu'il est probable que les mouches se remettent des gelées sublétales avant la reprise d'activité des fourmis prédatrices. Ce modèle peut être utilisé pour définir les conditions optimales de refroidissement des insectes utilisés lors de la libération d'individus stériles.

     

Sperm availability in naturally occurring bisexual-unisexual breeding complexes involvingPoecilia mexicana and the gynogenetic teleost,Poecilia formosa

Synopsis Testicular maturation indices (TMI) were determined for wild-caught males ofPoecilia mexicana by quantitative analysis of the frequency of ongoing stages of spermatogenesis and spermatid differentiation in sections of testes stained with the Feulgen reaction for DNA. In nature, males maintain essentially constant levels of sperm production throughout the year and show no significant variations in mean TMI values associated with season, microhabitat, standard body length, or rank in male dominance hierarchies. Winter males or males isolated from females in the laboratory show accumulation of mature spermatophores. These findings suggest that fluctuations in the microstructure of wild populations ofPoecilia from northeastern Mexico may be due primarily to differences in the temporal scheduling of female reproductive cycles and not to limitations imposed by sperm availability or male reproductive competence. The data are discussed in terms of competitive interactions within unisexual-bisexual breeding complexes involving the Amazon mollyP. formosa, its related triploid hybrids, and the bisexual species,P. mexicana.     

Methoprene modulates the effect of diet on male melon fly,Bactrocera cucurbitae,performance at mating aggregations

The effect of access to dietary protein (P) (hydrolyzed yeast) and/or treatment with a juvenile hormone analogue, methoprene (M), (in addition to sugar and water) on male aggregation (lekking) behaviour and mating success was studied in a laboratory strain of the melon fly, Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae). Six‐day‐old males were treated with (1) protein and methoprene (M+P+), (2) only protein (M?P+), or (3) only methoprene (M+P?), and compared with 14‐day‐old sexually mature untreated males (M?P?). The lekking behaviour of the four groups of males when competing for virgin sexually mature females (14 –16 days old) was observed in field cages. The following parameters were measured at male aggregations: lek initiation, lek participation, males calling, male–male interaction, female acceptance index, and mating success. For all these parameters, the M+P+ males significantly outperformed the other males. Moreover, for all parameters, there was a similar trend with M+P+ > M?P+ > M?P? > M+P?. More M+P+ males called and initiated and participated in lek activities than all other types of male, which resulted in higher mating success. They had also fewer unsuccessful copulation attempts than their counterparts. Whereas treatment with methoprene alone had a negative effect in young males with only access to sugar, access to dietary protein alone significantly improved young male sexual performance; moreover, the provision of methoprene together with protein had a synergistic effect, improving further male performance at leks. The results are of great relevance for enhancing the application of the sterile insect technique (SIT) against this pest species. The fact that access to dietary protein and treatment of sterile males with methoprene improves mating success means that SIT cost‐effectiveness is increased, as more released males survive to sexual maturity.     

A comparison of in vitro and in vivo estimates of the viability of Taenia pisiformis eggs aged under controlled conditions, and their ability to immunise against a challenge infection

Storing the eggs of T. pisiformis for periods of 0 to 9 days at a temperature of 36–38°C and relative humidity of 87–93 % revealed at least 4 stages in the ageing process. Firstly, a stage in which eggs hatched and activated in vitro and were also fully infective for rabbits. Secondly, a stage in which eggs hatched and activated in vitro but underwent only partial development in rabbits. Thirdly, a stage in which eggs hatched and activated in vitro, and presumably therefore in vivo, but no evidence of infection could be found when they were fed to rabbits. Fourthly, a stage in which eggs either did not hatch, or if they did hatch, the oncosphere was rapidly digested. In vitro techniques for assessing viability of T. pisiformis eggs were not a reliable guide to their infectivity for rabbits. ‘Senescent’ eggs, that is eggs which produced evidence of early infection in rabbits but did not complete their development to cysticerci, failed to produce immunity to challenge infection with T. pisiformis eggs.     

A variable selection index for the compensation of correlated genetic change

Summary A selection index for two traits has been constructed which allows partial restriction for one of the traits. The index is used in a situation where correlated response to selection in one sex is compenstated for by selection for other traits in the opposite sex. A numerical example is given.