Vergara - 1976 - Physiological and morphological adaptability of ri

EXPERIMENTAL APPROACH ro iNsEirT-uuitiars RELNFIUNSHIPS 359
natural enemies for biological control fail for one reason or another, perhaps
because of mal-adaptiveness to the local climate. Bioclimatic studies of these
species. particularly in relation to the bioclimatic characteristics of their hosts,
may well improve the rate of successful introductions of these biological control
agents.
One of the early studies of the relative effects of temperature on an insect
parasitoid was that of Headlec (1914). who measured the rate of development
and survival of Lynriphlebus lestaceipets (Cresson). an aphidiid endoparasite of the
grain aphid. S. graminus. Both of these species are native to North America,
the aphid being one of the main pests of wheat, barley, and sorghum. Headlee
found that both species could complete development in constant temperatures
as low as 10°C, but that the parasitoid was inhibited at higher temperatures, 25°C
and above. while the aphid continued to develop up to 32°C. Shelford (1926), in
revievi-‘ing Headlees work, concluded that the parasitoid was limited more by
climate than its host was, and that the latter could not be exterminated (controlled?)
by the enemy because of this differential response to climate.
When the dipterous parasitoid, Winthenria qnadfipilstufura F. and its host,
the tomato hornvvorm. ilfaridzlca qufnquimacillatus (l-laworth). were exposed to
various constant relative humidities and a common constant temperature,
Hefley (1928) found that parasitoid survival was much reduced at low humidities,
whereas host survival was maximal. The exact opposite relation occurred at
high relative humidities, and parasitoid emergence was complete at 73% Rll
and above.
The hymcnopterous ectoparasitoid, Bracon heberor Say. has a wide host
range, including larvae of the Mediterranean flour moth, A. kfihniella. ln a
detailed study of the effects of constant temperatures and relative humidities on
development, reproduction. and survival of these two species, Payne (1933)
found that the parasitoid always developed more rapidly than the host. but did
not live as long (adult stage) nor produce as many progenyn However. when
gross reproductive rate was corrected for sex ratio, the parasitoid exhibited a
higher reproductive potential (mean number of female progeny per female
parent) at all temperatures above 20°C. Further, the braconid was able to
reproduce at 36°C while the host encountered its own upper thermal limit for
reproduction at 33°C. The host. Cttlllffllll)". held the advantage at temperatures
below 15°C, The developmental threshold for the parasitoid was 145°C‘, for the
host. 8°C. Payne also found that low relative humidities favored the host.
Bracon heberor- was also observed to pass through at least seven generations to
one of the host at 32°C, but only five generations to one at 15°C.
Burnett (1948, 1949, 1951a) explored the differential temperature relations of
the greenhouse whiteflv Trialeurades vaporariorum (Westwood) and its parasitoid
Encarsiaforniosa Gahan, by observing temperature preferences of both
species, and their rates of development, reproduction, oviposition rates, longevity.
and survival at different constant temperatures. The host and parasitoid
increased at similar rates above 24°C. but below this the host increased at a