Effect of delayed mating on reproductive performance and life-history parameters of dengue vector Aedes aegypti.

Dengue is a fast-spreading mosquito-borne viral disease in the world. The primary vector of the disease is Aedes aegypti of the family Culicidae. It is a container breeder. Since a vaccine or a drug has not been developed against dengue, vector control appears to be the best method so far to control dengue. The current study was conducted to determine the effect of delayed mating on fecundity, fertility, life-history parameters, and longevity of Ae. aegypti, because such information can help formulate integrated vector control strategies involving the release of sub-fertile males into the environment. During this study, mating was delayed by 0, 2, 5, and 8 days after emergence. Males and females were separated by hand at the pupal stage using the apparent size difference of the sexes. The separated pupae were kept in separate cages until emergence. When mating was delayed for 8 days, the number of eggs laid by the female declined by 38%, and the percentage number of eggs that hatched reduced by 24%. However, the percentage of larval mortality, duration of the larval and pupal periods, and adult longevity were not significantly affected. The current results indicate that delayed mating has a negative effect on the reproductive performance of vector mosquitoes.

Influence of Vertebrate Excreta on Attraction, Oviposition and Development of the Asian Tiger Mosquito, Aedes albopictus (Diptera: Culicidae).

Aedes albopictus is an important vector of dengue worldwide. Eliminating dengue in Sri Lanka depends entirely on controlling the vector and human-vector contact. Thus, studying the bionomics and behavior of Ae. albopictus is paramount. The objective of this study was to evaluate the effect of the excreta of cow, goat and pig on the attraction, oviposition and development of Ae. albopictus. Bioassay chambers determined the mosquito stimulatory response. Ovitraps determined Ae. albopictus oviposition preference to excreta singly, in combination and on fermentation. The excreta effect on larval development was also determined. The results revealed that Ae. albopictus gravid females were significantly attracted to goat excreta but were repelled by pig excreta. The oviposition preference was highest for cow excreta and lowest for pig excreta. For excreta combinations, the Cow+Goat combination increased the oviposition while the Pig+Goat combination reduced the oviposition. The oviposition preference of Ae. albopictus increased with the rate of fermentation. The pig excreta increased the Ae. albopictus larval mortality, larval and pupal duration and reduced adult fecundity, whereas the cow excreta positively affected all these aspects. Our findings additionally suggest that a high abundance of Ae. albopictus in rural areas of Sri Lanka may be due to its oviposition attraction and growth performance for vertebrate excreta.

The effect of chemical exudates of three larvivorous fish species on oviposition preference of Aedes aegypti and Aedes albopictus (Diptera: Culicidae).

Mosquito species Aedes aegypti and Aedes albopictus are vectors of dengue worldwide. Mosquito vector control through maintaining larvivorous fish in water bodies is generally suggested, however, its underlying role towards oviposition preference of these dengue vectors is unknown in the Sri Lankan context. The current study investigated the effect of chemical exudates from larvivorous fish species Poecilia reticulata, Rasbora daniconius and Applocheilus dayi on the oviposition preference of Aedes mosquitoes. The number of eggs laid by each mosquito species was determined using ovitraps that contained water conditioned by the fish species both separately and in combination. The ovitraps were placed inside insect cages containing engorged gravid Aedes females. Both the mosquito species had the least preference of oviposition in water conditioned by A. dayi followed by R. daniconius. The highest preference of oviposition was shown for water conditioned by P. reticulata. The current study indicated that oviposition site selection in Ae. aegypti and Ae. albopictus was reduced by A. dayi and R. daniconius, however, it was not influenced by the fish combinations used. Further studies are warranted to understand the chemical cues associated with larvivorous fish towards the oviposition preference in Aedes mosquitoes.

Development of an Alternative Low-Cost Larval Diet for Mass Rearing of Aedes aegypti Mosquitoes.

BACKGROUND: Aedes aegypti is a major vector of arboviruses that may be controlled on an area-wide basis, using novel approaches such as Sterile Insect Technique (SIT) and Incompatible Insect Technique (IIT). Larval diet is a critical factor to be considered in mass rearing of Aedes mosquitoes for SIT and IIT programs. Therefore, the current study is aimed at evaluating the effects of two novel diets developed from dry fish powder on the growth and development of immature stages and adult fitness-related characteristics of Ae. aegypti in Sri Lanka. METHOD: Three batches of the first instar Ae. aegypti larva, each containing 250 larvae, were exposed to three different larval diets as standard dry fish powder (D1), dry fish powder meal and brewer's yeast (D2), and International Atomic Energy Agency- (IAEA-) recommended diet (D3), separately. Morphometric and developmental parameters of the 4th instar larvae, pupae, and adult mosquitoes reared under different dietary treatments were measured. The entire experimental setup was replicated thrice. A General Linear Model (GLM) in the form of two-way ANOVA was used for the statistical analysis. RESULTS: Significant diet-based variations were observed in the head length, head width, thoracic length, thoracic width, abdominal length, abdominal width, and total length (F 2,87 > 4.811; P < 0.05) of Ae. aegypti larvae. The highest pupation success and the larval size were observed from the larvae fed the D2 diet, while the lowest was reported from D1. All adult morphometric parameters of adult male and female Ae. aegypti mosquitoes also denoted significant dietary variations, reporting the best-sized adults from the D2 diet (F 2,87 > 3.54; P < 0.05). Further, significantly higher fecundity and male longevity were also shown by the adult Ae. aegypti (F 2,6 > 7.897; P < 0.01) mosquitoes reared under diet D2. CONCLUSION: Based on all the growth and developmental parameters, the D2 diet tends to perform similar to the IAEA-recommended diet in mass rearing of Ae. aegypti mosquitoes, while being more inexpensive. Therefore, larval diet D2 could be suggested as the ideal diet for mass rearing of Ae. aegypti for IIT and SIT-based vector control in Sri Lanka.

Why oviposit there? Fitness consequences of a gall midge choosing the plant's youngest leaf.

For animals that lay eggs, a longstanding question is, why do females choose particular oviposition sites? For insects that lay eggs on plants there are three hypotheses: maximizing suitable habitat for juveniles, maximizing female lifespan, and maximizing egg survival. We investigated the function of the oviposition-site choice behavior of a gall midge, the Hessian fly, Mayetiola destructor (Say). In spite of living less than a day and having hundreds of eggs, the ovipositing female is choosy about the placement of eggs. Choosiness makes sense. The tiny gall-making neonate larva has limited movement and strict requirements for colonization. We examined whether offspring benefit from the Hessian fly female's preference for the plant's youngest leaf. To do this we restricted the female's access to the first, second, or third leaf of a seedling (wheat Triticum aestivum L.) plant. Being placed on older leaves did not impact egg survival or larval survival during migration to attack sites at the base of the plant, but did have negative impacts on egg-to-adult survival (reduced by 48%) and reproductive potential (reduced by 30-45%). These negative impacts appear to come from larvae having to search harder to find the limited number of reactive plant cells that can be reprogrammed to form the gall nutritive tissue. We propose that the ability of larvae to find these reactive cells in spite of being placed on an older leaf is important because it creates leeway for female behavior to evolve in the face of other selection pressures, e.g., attack by egg parasitoids.

Impact of planting dates on a seed maggot, Neotephritis finalis (Diptera: Tephritidae), and sunflower bud moth (Lepidoptera: Tortricidae) damage in cultivated sunflower.

Neotephritisfinalis (Loew) (Diptera: Tephritidae), and sunflower bud moth, Suleima helianthana (Riley) (Lepidoptera: Tortricidae) are major head-infesting insect pests of cultivated sunflower (Helianthus annuus L.). Planting date was evaluated as a cultural pest management strategy for control of N. finalis and S. helianthana in several production regions of North Dakota during 2009 and 2010. Results of the nine site-year study revealed that late planting date (early to mid-June) reduced damage ratings and percentage of damaged heads for N. finalis compared with early planting dates (mid- to late May). Visual observations of adult N. finalis found that the majority of flies were found in the early planted sunflower (78.2%) compared with the late planted sunflower (21.8%). Late planting date also reduced the percentage of S. helianthana damaged heads compared with early planting dates. Yield losses were reduced with late planting date when populations of N. finalis and S. helianthana were high enough to cause damage. Results of this study showed that delayed planting is an effective integrated pest management strategy that can reduce head damage caused by N. finalis and S. helianthana and mitigate yield losses.