[Odonata-l] RFI - Bti and Bsph larvicides - indirect effects on non-targets (including Odonata)

[Ethan Bright]

> Jones, Colin (MNR) wrote:
>>
>> Does anyone know of any studies and resulting literature looking at 
>> the effects on non-target organisms (e.g. Odonata) due to the use of 
>> Bti and Bsph to control mosquitoes?
>>
>> I know that quite a bit of work has been done on direct effects to 
>> non-targets (largely concluding the effects to be minimal) but I 
>> don’t know of any work that has examined the indirect effects (i.e., 
>> ecological effects related to reduced prey availability, for 
>> example). Is anyone aware of any work that has, or is currently being 
>> done, in this field? If so, are you able to point me to published or 
>> unpublished literature or preliminary findings?
>>
Painter MK, Tennessen KJ, Richardson TD. 1996. Effects of repeated 
applications of Bacillus thuringiensis israelensis on the mosquito 
predator /Erythemis simplicicollis/ (Odonata: Libellulidae) from 
hatching to final instar. Environmental entomology 25(1):184-191.

Nymphs of a common dragonfly, Erythemis simplicicollis (Say), were 
exposed to Bacillus thuringiensis israelensis de Barjac at 1.2 ppm once 
a week for an entire life cycle in a controlled laboratory environment. 
Eight weekly applications were administered to 2 treatment groups : 
external contact only, and external + internal contact using prey 
(mostly anopheline larvae) that had fed on B. thuringiensis. Each B. 
thuringiensis-treated group and a control group consisted of 15 nymphs. 
Mortality was not affected by B. thuringiensis applications. Repeated B. 
thuringiensis applications did not affect development to the adult 
stage, morphology, or maiden flight capability. Nymph size of the 
external contact group, measured by hind femur length and head width, 
was substantially smaller compared with the control group in most 
instars from 4-12. However, adult size, based on head width and hind 
wing length comparisons, did not differ among the 3 groups. Prey 
consumption and instar duration, which were highly correlated, did not 
account for the differences in size. Sex ratio (lower proportion of 
large females in the external group) and initial size (slightly smaller 
in instar 2 in the external group) appeared to be the major factors 
contributing to the size differences in the external group. However, 
these variables were not responsible for the external + internal contact 
group being smaller in instar 10 compared with the controls, as sex 
ratios and initial size were equal. If repeated B. thuringiensis 
applications affect size in E. simplicicollis, the effect may be 
insignificant in terms of reproductive success, as published studies do 
not show a positive relationship between size and reproductive success 
in dragonflies.